SUPERSTRIPES 2017
edited by Antonio Bianconi
superstripes press
S u p e r s t r i p e s P r e ss science series SUPERSTRIPES 2017
Quantum in Complex Matter:
Superconductivity, Magnetism & Ferroelectricity
edited by Antonio Bianconi
superstripes press
S u p e r s t r i p e s P r e ss science series Science Series No.11
Title: Superstripes 2017
Published on June 2017 by Superstripes Press, Rome, Italy http://www.superstripes.net/science/science.htm
© 2017 Superstripes Press © 2017 Multiple authors
ISBN 978 88 6683 069 6 ISBN A 10.978.886683/0696
This work is licensed under the Creative Commons Attribution ShareAlike 4.0 International License. To view a copy of this license, visit http://creativecommons.org/licenses/by sa/4.0/ or send a letter to Creative Commons, PO Box 1866, Mountain View, CA 94042, USA.
Authors :
Abbamonte P., Aeppli G., Alarco J.A., Albertini R., Aoki D., Attanasio C., Avigo I., Babaev E., Bachar N., Badoux S., Balakirev F.F., Balicas L., Bao W., Barbiellini B., Berciu M., Berthod C., Bianconi A., Billinge S.J.L., Bonca J., Boris A., Borisenko S., Borzenets I., Bozin E.S., Brazovskii S., Brun C., Bussmann Holder A., Capone M., Carlström J., Chang J., Chávez I., Chu P.C.W., Conradson S.D., Coslovich G., Crisan A., Daghero D., de Llano M., de’ Medici L., Dean M. P. M., Degiorgi L., Destraz D., Deutscher G., Di Gioacchino M., Di Giorgio C., Dobrosavljevic V., Drechsler S.L., Efremov D., Egami T., Einaga M., Eremets M.I., Eremin I., Eremin M., Fanfarillo L., Farina D., Feng S., Fine B.V., Fink J., Flammia L., Frésard R., Fujimori A., Fujita M., Galda A., Giannetti C., Glatz A., Goncharov A.F., Goto H., Goto Y., Gray A.X., Grilli M., Grochala W., Guguchia Z., Guidi T., Guo H., Guzman Verri G.G., Hanaguri T., Hayden S., Hess C., Huecker M., Iavarone M., Ideue T., Imada M., Irizawa A., Ivanov A.A., Jackeli G., Joon E., Jurkutat M., Kanazawa I., Kapcia K.J., Kataev V., Kato R., Khaliullin G., Khomski D.I., Kimura A., Kimura T., Kirova N., Knebel G., Kokalj J., Kolodziej J.J., Komarek A.C., Kontani H., Kresin V., Kruger F., Krzton Maziopa A., Ksenofontov V., Kubozono Y., Langerome B., Larkin T.I., Leridon B., Littlewood P., Liu C., Lorenzana J., Louca D., Luo J., Lychkovskiy O., Madan I., Maeno Y., Marcelli A., Markiewicz R.S., Marsiglio F., Massarotti D., Mazziotti M.V., Mazzoli C., McNally D.E., Mertelj T., Mesaros A., Miletto Granozio F., Mironov A. Yu., Miyasaka S., Mizuguchi Y., Mizukami Y., Moewes A., Momono N., Monney C., Moreo A., Moroni M., Moskvin A.S., Mukhin S.I., Mustre de León J., Nattermann T., Neilson D., Nissinen J., Oda M., Oles A.M., Orgad D., Orth P.P., Ovchinnikov S.G., Pelliciari J., Peng Y., Perali A., Perring T., Pomarico E., Ponomarenko L.A., Popović D., Prassides K., Ptok A., Pudalov V., Purans J., Puzniak R., Quader K., Raimondi R., Rajasekaran S., Renner Ch., Reznik D., Robinson I.K., Roy P., Sanna S., Sato M., Schmitt T., Schneider W. D., Seibold G., Semenov A.G., Shen D., Shengelaya A., Shi M., Shimizu K., Shimojima T., Silaev M., Silhanek A.V., Soh Y. Ah, Soldatov A.V., Spera M., Spivak B., Steppke A., Stornaiuolo D., Strinati Calvanese G., Sumida K., Sunko V., Sushkov O.P., Tafuri F., Tallon J., Tanatar B., Tanner D.B., Teitel’baum G., Terao T., Timusk T., Toda Y., Tortello M., Tripathi V., Truccato M., Tsuchiizu M., Uemura Y.J., van der Marel D., van Wezel J., Vanacore G.M., Vargas Paredes A.A., Vinokur V.M., von Rohr F., Wahl P., Wall S., Wirth S., Wohlfeld K., Wysokiński K.I., Wysokinski M.M., Yanagisawa T., Yoshida Y., Zaanen J., Zaikin A.D., Zhigadlo N.D., Zhuang J., Zwicknagl G.
*These authors presented the scientific reports collected in this book at the Superstripes 2017 conference held in Ischia (It) on June 4 10, 2017
Papers presented at the international conference
Superstripes 2017
Ischia Italy June 4 10, 2017
Organized by Non profit organization for scientific research Superstripes onlus Rome International Center for Materials Science Superstripes RICMASS
Chairman Prof. Antonio Bianconi, RICMASS, Rome, I
Organizing Committee Gabriel Aeppli, Paul Scherrer Institute, CH Bernd Büchner, IFW Dresden, D Takeshi Egami, University of Tennessee, USA Vladimir Kresin, University of California, USA P.B. Littlewood, Argonne National Laboratory, UK Despina Louca, University of Virginia, Charlottesville, USA Andrea Perali, University of Camerino, I Kosmas Prassides, Durham University, UK Valerii Vinokur, Argonne National Laboratory, USA Jan Zaanen, University of Leiden, NL Superstripes 2017, Ischia June 4 10, 2017
Superstripes 2017
Book of Abstracts
Superstripes 2017, Ischia June 4 10, 2017
Table of Contents
Guy Deutscher: Multi level Kondo effect and enhanced critical temperature in nanoscale granular Al...... 12 Steven Conradson: The Fröhlich type, non equilibrium, polaronic condensate in the Mott system UO2(+x) ...... 13 Leonardo Degiorgi: Investigation of the optical anisotropy in the nematic phase of FeSe ...... 14 Kosmas Prassides: New candidate quantum spin liquids in ionic polyaromatic hydrocarbons ...... 16 Dmitry Reznik: Dynamic charge stripe spectrum in nickelate perovskites ...... 17 Yoshiteru Maeno: Mott transition and strong diamagnetism in Ca2RuO4 tuned by electric field/current ...... 18 Annette Bussmann Holder: The road map toward room temperature superconductivity ...... 20 Takeshi Egami: d9 Nickelates under Pressure ...... 22
Yasutomo Uemura: Three novel features in the correlations between Tc and the superfluid density: local phase coherence below the Bose gas temperature TB and multiple ratios of Tc/TF ...... 24 Vladimir Kresin: Electron lattice and electron electron interactions in novel systems: paths to room temperature superconductivity...... 27 Hiroshi Kontani: Strong interplay between high Tc superconductivity, nematicity, and magnetism in Fe based Superconductors...... 28 Daniel Khomskii: Strong covalency and ligand holes, or how to make magnetic gold?...... 29 Stephen Hayden: Spin and charge density wave fluctuations in cuprates ...... 30 Johan Chang: Electronics of high temperature cuprate superconductors ...... 32 Naoki Momono: 1/8 Anomaly and Charge Order in Dy doped Bi2212 ...... 33 Masaki Fujita: Neutron Scattering Study of Magnetic Excitations in Electron Doped Cuprate ...... 35 Dirk van der Marel: Superconductivity and electronic structure of SrTiO3 ...... 37 Yoshihiro Kubozono: Pressure driven high Tc superconductivity in carbon based and inorganic materials ...... 39 Akio Kimura: Non equilibrium Surface Dirac Fermion Dynamics of Topological Insulators Probed By Time Resolved ARPES ...... 41 Dragana Popović: Charge dynamics near the onset of charge density wave order in La 214 cuprates ...... 43 Dror Orgad: Dimensional Crossover of Charge Density Wave Correlations in the Cuprates ...... 45 Superstripes 2017, Ischia June 4 10, 2017
Marco Truccato: Modifications induced by synchrotron radiation in Bi2Sr2CaCu2O8+delta and YBa2Cu3O7 x: a novel non destructive patterning method ...... 46 Michael Jurkutat: Local charges and charge order in the cuprates revealed by NMR ...... 48 Nikolai Zhigadlo: Crystal Growth and Advanced Synthesis of Contemporary Functional and Superconducting Materials: From Simplicity to Complexity ...... 49 Alexander Shengelaia: Rapid Synthesis of Superconducting and Magnetic oxides by Light Irradiation ...... 51 Jose Alarco: A complete and accurate description of superconductivity of AlB2 – type structures from phonon dispersion calculations ...... 52 Wolf Dieter Schneider: Atomic structure of supported ultrathin Germania films.... 54 Mauro Tortello: Nanoscale Characterization of the Thermal Conductivity of Supported Graphite Nanoplates, Graphene and Few layer Graphene ...... 55 Yoshikazu Mizuguchi: Material design strategies for BiCh2 based layered superconductors ...... 56
Yosuke Goto: Enhanced thermoelectric performance in BiS2 based layered compound LaOBiS2 xSex ...... 57 Wojciech Grochala: Ag/F vs. Cu/O: powerful analogy with far reaching implications ...... 59 Timofei Larkin: Exciton phonon complexes and giant exciton Fano resonances in Ta2NiSe5...... 61 Jianlin Luo: Pressure induced superconductivity in Cr and Mn based materials ... 62 Yeong Ah Soh: Crystal structure and epitaxy of topological insulator films grown on Si and SrTiO3 ...... 63
Despina Louca: Elastic and Electronic Tuning of Magnetoresistance in MoTe2 ..... 65 Robert S. Markiewicz: Entropia cupratesque cano… [A new model of the cuprate pseudogap] ...... 67 Dario Daghero: Effects of a pressure induced topological Fermi surface transition on the order parameter of CaFe2As2 ...... 69 Brigitte Leridon: Ionic ...... 70 Wei Bao: Simultaneous occurrence of multiferroism and short range magnetic order in DyFeO3 ...... 72 Gian Giacomo Guzman Verri: Random Electric Field Instabilities of Relaxor Ferroelectrics ...... 73 Tsuyoshi Kimura: Multiple order parameters and their domain control in magnetoelectric multiferroics ...... 74 Benjamin Langerome: High Pressure – Low Temperature Set up for Infrared Spectroscopy of H3S at the AILES Beamline ...... 75 Superstripes 2017, Ischia June 4 10, 2017
Takahito Terao: Preparation of new metal intercalated FeSe superconductors and their pressure dependence ...... 77 Jonathan Pelliciari: Resonant Inelastic X ray Scattering on Iron Pnictides ...... 79 Luca de’ Medici: Hund’s correlated metals ...... 81 Boris Spivak: Macroscopic character of composite high temperature superconducting wires...... 82 Jacek Kolodziej: Effect of a skin deep surface zone on the formation of a two dimensional electron gas at a semiconductor surface ...... 83 Masahisa Tsuchiizu: Functional Renormalization Group Analysis on Electron Nematic State and Charge Density Wave State in Cuprate Superconductors...... 84 Johan Carlström: Spontaneous breakdown of time reversal symmetry induced by thermal fluctuations ...... 85 Stefan Ludwig Drechsler: Constraints on the total coupling strength to low energy bosons in iron based superconductors ...... 86 Dmitri Efremov: Multiband Eliashberg approach – a way to the realistic description of iron based superconductors ...... 89 Takashi Yanagisawa: Crossover induced spin fluctuation and electron pairing in strongly correlated electrons...... 90 Bilal Tanatar: Drag Effect in Bilayer Systems of Dipolar Bosons and Fermions .... 92 Donato Farina: Raman of YBCO out of equilibrium ...... 93
Paul C. W. Chu: A Possible Paradigm Shift in the Search for Higher Tc ...... 94 Atsushi Fujimori: Multiple component Fermi surfaces of high Tc cuprates revealed by ARPES ...... 95 Gregory Teitel’baum: On the phenomenological two component physics for cuprates ...... 97 Masatoshi Imada: Frontiers of high Tc studies and spin liquids ...... 99 Simon Billinge: Orbital degeneracy lifting, broken local symmetries and properties in correlated electron materials ...... 100 Claudio Mazzoli: On the time correlation of long range ordered CDW state in LBCO ...... 101 Ian Robinson: Stripe Pinning in LBCO...... 102 Mark P. M. Dean: Precursor Charge Density Wave in La2 xBaxCuO4 ...... 104 David Tanner: Optical spectroscopy of La2 xBaxCuO4 single crystals: influence of stripe order...... 106 Markus Huecker: High Pressure 3D to 2D Tuning of Magnetism in Cuprates ...... 107 Andrej Mesaros: Building blocks of cuprate charge density modulations ...... 108 Superstripes 2017, Ischia June 4 10, 2017
Shiping Feng: Pseudogap generated a coexistence of Fermi arcs and Fermi pockets in cuprate superconductors ...... 109 Toby Perring: Magnetic field induced magnon decay in the spin ½ square lattice Heisenberg antiferromagnet ...... 110 Vladimir Dobrosavljevic: Disorder Driven Metal Insulator Transitions in Deformable Lattices ...... 111 Oleg Sushkov: Multiple universalities in order disorder magnetic phase transitions ...... 112 Jaakko Nissinen: Three dimensional quantum liquid crystals and dislocation worldsheet condensation ...... 113 Alexander Boris: Proximity of superconductivity and magnetism in δ doped La2CuO4 heterostructures ...... 114 Alexander Gray: Emerging X ray Techniques for Probing Matter with Depth and Time Resolution ...... 115 Götz Seibold: The inverse Edelstein effect at oxide interfaces ...... 116 Yasuo Yoshida: Emergence of surface orbital ordering in the heavy fermion superconductor CeCoIn5 ...... 117 Tetsuo Hanaguri: STM studies of superconductivity and nematicity in Fe(Se,S) .. 118 Shigeki Miyasaka: Change of phase diagram of 1111 type iron pnictide by varying of rare earth element, solid solution of pnictogens and electron doping...... 119 Mona Berciu: One hole and two holes low energy states in a cuprate layer ...... 121 Sven Badoux: Signature of the pseudogap critical point in cuprate superconductors ...... 122 Peter P. Orth: Enhanced nematic fluctuations near the Mott insulating phase of high Tc cuprates ...... 124 Zurab Guguchia: Cooperative coupling of static magnetism and bulk superconductivity in the stripe phase of La2 xBaxCuO4: Pressure and doping dependent studies ...... 126 Adrian Crisan: Non centrosymmetric vortices in multi component superconductors ...... 128 Roman Puzniak: Anisotropy, phase separation, and superconductivity in iron based superconductors ...... 130 Maria Iavarone: Low temperature STM/STS of FeSe ...... 132
Migaku Oda: STM/STS studies on the spatial dependence of energy gap in high Tc cuprate Bi2Sr2CaCu2O8+δ ...... 133 Isabella Avigo: Ultrafast doublon dynamics in photo excited 1T Tas2 ...... 135 Natasha Kirova: Dynamical phase transition to a charge transfer state ...... 136 Claudio Giannetti: Ultrafast orbital manipulation in copper oxides ...... 138 Superstripes 2017, Ischia June 4 10, 2017
Tomaz Mertelj: Collective electronic orders under strong optical drive studied by means of time resolved multipulse optical spectroscopy ...... 139 Giovanni Maria Vanacore: Unraveling the ultrafast dynamics of spatially confined phonons and plasmons in low dimensional nanosystems ...... 140 Yasunori Toda: Nonequilibrium quasiparticle dynamics in Bi based superconductors measured by modulation photoexcitation spectroscopy ...... 141 Janez Bonca: Delocalized charge carriers in strongly disordered t–J model ...... 143 Matteo Moroni: Superconductivity emerging from an electronic phase separation in the charge ordered phase of RbFe2As2 ...... 144 Mikhail Eremets: High temperature superconductivity in hydrides at high pressures ...... 146 Alexander Goncharov: Stable high pressure phases in the H S system determined by chemically reacting hydrogen and sulfur up to 140 GPa ...... 147 Katsuya Shimizu: Search for Pressure Induced Superconductivity in Other Hydrides ...... 148
Thomas Timusk: Optical Spectroscopy of H3S: Evidence of a new Energy Scale for superconductivity ...... 149 Antonio Bianconi: Fano Resonances at Lifshitz transitions driving high Tc superconductivity: from iron based superconductors to the case of H3S and p Terphenyl ...... 151
Jeff Tallon: Compressed H2S, superfluid density and the quest for room temperature superconductivity ...... 153 Frank Marsiglio: High Temperature Superconductivity in H3S why so high? . 155
Mari Einaga: Formation Process of High Tc Phase of Sulfur Hydride ...... 156 Luis Balicas: Impurity dependent superconductivity, Berry phase and bulk Fermi surface of the Weyl type II semi metal candidate MoTe2 ...... 157 Jose Mustre de León: Resonant X ray Inelastic Scattering and nanoscale inhomogeneity in FeSe1 xTex ...... 159 Serguei Brazovskii: Phenomenological theory of switching of electronic phases by optical, current, voltage and STM pulses in TaS2...... 161 Jasper van Wezel: Collective modes of the excitonic condensate in 1T TiSe2...... 162 Marco Grilli: Intrinsic inhomogeneity of 2D crystalline superconductors ...... 163 Massimo Capone: Exploiting multiorbital physics to achieve high temperature superconductivity: Fullerene and beyond...... 165 Sergei Mukhin: Eliashberg equations with antiferromagnetic ‘hidden order’ induced pairing boson in cuprates...... 167 Alexander Moskvin: Topological structures in a model cuprate ...... 169 Enno Joon: Spin Peierls dimerization caused by Jahn Teller effect in NaTiSi2O6 171 Superstripes 2017, Ischia June 4 10, 2017
Reizo Kato: Quantum spin liquid in a molecular Mott system based on Pd(dmit)2 173 Jure Kokalj: Half filled anizotropic triangular Hubbard model and organic charge transfer salts based on BEDT TTF ...... 175 Takahiro Shimojima: Nematic electronic structure of the iron based superconductor FeSe ...... 176 Sergey Borisenko: ARPES of iron based superconductors ...... 177 Jörg Fink: Non Fermi liquid behavior, Lifshitz transitions, and Hund’s metal behavior of iron based superconductors and related compounds from ARPES ..... 178 Ming Shi: Electron electron correlation in iron Pnictides, revealed by ARPES .... 179 Francesco Tafuri: The new frontiers of the Josephson effect in novel unconventional nano scale and magnetic systems ...... 180 Alejandro Silhanek: Superconducting weak links created by electromigration ..... 181 Andrei Zaikin: Quantum decay of supercurrent in transparent nanojunctions ...... 183 Claude Monney: Resonant inelastic x ray scattering to measure short range magnetic order ...... 184 Alexander Moewes: Studying Silicene mono and multilayers with soft X ray spectroscopy and DFT ...... 185 Hidenori Goto: Doping effects on electronic properties of bilayer graphene ...... 186 Canhua Liu: Superconductivity of K doped FeSe ultra thin films on SrTiO3(001) substrate ...... 187 David Neilson: Multicomponent electron hole superfluidity and the BCS BEC crossover in double bilayer graphene ...... 188 Leonid Ponomarenko: High temperature quantum oscillations in graphene superlattices ...... 190 Ivan Borzenets: Governing energies of graphene Josephson junctions from dirty to ultra clean regimes ...... 191 Daniel Destraz: Superconducting fluctuations in a thin NbN film probed by the Hall effect ...... 193 Fabian von Rohr: Electron count and chemical complexity in high entropy alloy superconductors ...... 194 Samuele Sanna: Extensive study of the superfluid density of oxypnictides...... 195 Yuta Mizukami: Quantum critical points in iron based superconductors ...... 197 Krzysztof Wohlfeld: How different are the iridates from the cuprates? Insights from the RIXS and ARPES spectroscopies ...... 199 Jan Zaanen: Principles of holographic duality in the laboratory ...... 200 Valerii Vinokur: Gauge theory of the BKT transition in disordered systems ...... 201 Adriana Moreo: Multi orbital Hamiltonian for Iron Chalcogenides ...... 202 Superstripes 2017, Ischia June 4 10, 2017
Gabriel Aeppli: Non destructive high resolution three dimensional imaging of intelligent matter ...... 204 Peter Littlewood: Elastic Effects at the Mott Transition ...... 205 Sergei Ovchinnikov: Effect of electron phonon interaction on the doping and temperature dependent spectral function in cuprates ...... 206 Ilya Eremin: Robust determination of the superconducting gap sign structure via quasiparticle interference ...... 207 Fedor Balakirev: Magnetotransport Signatures of Competing Ground States and Critical Scaling in Strongly Correlated Superconductors ...... 208 Christoph Renner: Conventional vortices in the high temperature superconductor YBa2Cu3O7 δ ...... 209 Roberto Raimondi: SU(2) Gauge Theory Description of the Current Induced Spin Polarizations in an Electron Gas ...... 210 Vladislav Kataev: Insights into the spin orbital entanglement in complex iridium oxides from high field ESR spectroscopy ...... 211 Khandker Quader: Electronic Structure Study of Filled Skutterudites ...... 212 Vladimir Pudalov: Spin susceptibility of the correlated 2D electron system ...... 214 Tatiana Guidi: INS study of single and entangled rings ...... 215 Enrico Pomarico: Enhancement of electron phonon interaction in bilayer graphene with optically driven lattice ...... 216 Nimrod Bachar: Detailed optical spectroscopy of hybridization gap and hidden order transition in high quality URu2Si2 single crystals ...... 218 Davide Massarotti: Phase dynamics and macroscopic quantum phenomena in unconventional Josephson junctions ...... 220 Andrew Semenov: Voltage noise in short superconducting bridges...... 221 Carmine Attanasio: Small NbN superconducting nanonetwork fabricated using porous silicon templates ...... 222 Raymond Frésard: On superconducting stripes of the two dimensional Hubbard model ...... 223 Hanjie Guo: Magnetic ground state of the pyrochlore iridate Nd2Ir2O7...... 224 George Jackeli: Spin orbital frustration in Mott insulators ...... 225 Giacomo Coslovich: Observing Interactions As They Happen: Ultrafast X ray and THz Studies of Charge Ordered Materials ...... 226 Marcin Wysokinski: Topological Kondo semi metals ...... 227 Konrad J. Kapcia: Magnetic Lifshitz transition in iron based superconductors ..... 229 Andrzej Ptok: The ab initio study of unconventional superconductivity in CeCoIn5 and FeSe ...... 231 Superstripes 2017, Ischia June 4 10, 2017
Boris Fine: Modeling low energy electronic excitations in the background of spin vortex checkerboard ...... 232 Peter Wahl: Local probing of magnetic order and excitations in iron based superconductors ...... 234 Christophe Berthod: Local spectroscopy of vortices in the presence of disorder: application to YBCO ...... 236 Yingying Peng: RIXS study on charge order and magnetic excitations in superconductor Bi2201 ...... 237 José Lorenzana: Berezinskii–Kosterlitz–Thouless in curved space ...... 239 Alexey Mironov: Effect of Nanoperforation on critically disordered NbTiN films 240 Thomas Nattermann: BKT phases in disordered systems, past and present ...... 241 Vikram Tripathi: Disordered BKT criticality and superinsulation ...... 242 Manuel de Llano: BCS Bose Crossover Extended with Hole Cooper Pairs ...... 244 Israel Chávez: Dimensionless Coupling Constants in Superconductivity...... 245 Luca Flammia: Quantum size effects in superconducting nanostripes with step edge ...... 246 Alfredo Vargas Paredes: Competition between Intraband Pairing and Crosspairing ...... 247 Masatoshi Sato: Topological Crystalline Materials ...... 249 Egor Babaev: Dirty multi band superconductors: time reversal symmetry breaking, multiple coherence lengths, type 1.5 superconductivity and vortex matter ...... 251 Karol Izydor Wysokiński: Low temperature thermoelectric power of strongly correlated quantum dot ...... 252 Andrea Perali: Enhancement of Superconductivity by Shape Resonances: from Nano films to Nano stripes ...... 253 Andrzej M. Oles: Topological phases emerging from spin orbital physics ...... 255 Thorsten Schmitt: Ground state oxygen holes and the metal–insulator transition in the negative charge transfer rare earth nickelates ...... 256 Juris Purans: In situ EXAFS studies of metal to insulator transition in ReO3 WO3 and related electrochromic materials ...... 257 Pascale Roy: Room temperature ferroelectricity in SrTiO3 ultrathin films on silicon: Infrared and ab initio study ...... 259 Peter Abbamonte: Bose condensation of excitons in a transition metal dichalcogenide ...... 261 Dai Aoki: Unconventional superconductivity in uranium compounds ...... 262 Christophe Brun: Two dimensional topological superconductivity in Pb/Co/Si(111) ...... 263 Superstripes 2017, Ischia June 4 10, 2017
Kazuki Sumida: Ultrafast Surface Dirac Fermion Dynamics of Sb2Te3 based Topological Insulators...... 265 Steffen Wirth: STS studies on correlated f electron systems: Kondo lattice, quantum criticality and topological Kondo insulator ...... 267 Georg Knebel: Field induced Lifshitz transitions in heavy fermion systems ...... 268 Gertrud Zwicknagl: Transport spectroscopy and Electronic Topological Transitions in heavy fermion materials ...... 269 Alexander Komarek: Physical properties of LaNiO3 single crystals...... 270
Emil Bozin: Orbital Degeneracy Lifting and Short Range Orbital Order in CuIr2S4 ...... 271 Veronika Sunko: Spin split surface states of transition metal delafossite oxides .. 273 Anna Krzton Maziopa: Electrochemical intercalation of alkali metal ions into the layered structure of iron chalcogenides ...... 275 Mikhail Silaev: Structure and dynamics of composite vortex states in multiband superconductors ...... 276 Ikuzo Kanazawa: Quantized Massive Gauge Fields and Anomalous Angle resoluved Photoemission Spectra in HIgh Tc Cuprates ...... 278 Mikhail Eremin: Asymmetry of critical temperatures in e and h doped cuprates 279 Andreas Glatz: Detailed Simulation of Vortex Crossing ...... 281 Fabio Miletto Granozio: Engineering the functional properties of 2 dimensional electron gases at oxide interfaces...... 283 Daniela Stornaiuolo: Josephson junctions based on LAO/STO 2DEG...... 285 Laura Fanfarillo: Orbital selectivity and Hund's physics in Iron based superconductors ...... 286 Christian Hess: Temperature dependent quasiparticle interference of LiFeAs ...... 287 Toshiya Ideue: Superconductivity in noncentrosymmteric low dimensional materials ...... 288
Alexander Steppke: Strong peak in Tc of Sr2RuO4 under uniaxial pressure...... 290 Frank Kruger: Topological Excitations and Bound States in a Quantum Dimer Antiferromagnet ...... 292 Simon Wall: Imaging the insulator metal phase transition with resonant soft X ray holography ...... 294 Daniel McNally: Thickness and Temperature Driven Metal Insulator Transitions in CaVO3: A Resonant Inelastic X ray Scattering Study ...... 296 Alexey Galda: Spin transfer torque induces parity time symmetry breaking ...... 297 Ivan Madan: Optical control of skyrmions in helimagnetic FeGe...... 298 Superstripes 2017, Ischia June 4 10, 2017
Srivats Rajasekaran: Nonlinear Terahertz Spectroscopy of Cuprates – A Probe of the ...... 299 Marcello Spera: Remarkable energy dependent domain formation in the CDW of 1T CuxTiSe2 ...... 300 Andrey Ivanov: X ray magnetic circular dichroism at the K edge of Cu in Bi2Sr2CaCu2O8+x ...... 302 Alexander Soldatov: Picometer scale determination of 3D local atomic structure parameters in nanostructured materials ...... 304
Augusto Marcelli: Nanoscale phase separation and lattice complexity in VO2, a complex multiphase correlated electron systems ...... 305 Akinori Irizawa: Metal Insulator transitions in calcium ferrite compounds ...... 308 Bernardo Barbiellini: Metal Insulator Transitions in Complex Oxides Probed by x ray inelastic scattering ...... 309 Giancarlo Strinati Calvanese: Non local equation for the superconducting gap parameter ...... 311 Giniyat Khaliullin: Soft spins and Higgs mode in ruthenates ...... 312 Vadim Ksenofontov: Interplay of superconductivity and magnetism in Fe based superconductors under high pressure ...... 313 Jincheng Zhuang: STM study of germanene ...... 314
Ruben Albertini: Micro XAS measures of the local structure changes in BaPb1 xBixO3 as a function of temperature ...... 315 Michael Di Gioacchino: Levy flight distribution of fluctuation supramolecular structure of myelin ...... 317 Cinzia Di Giorgio: Low temperature scanning probe microscopy investigation of FeSe single crystals ...... 319 Oleg Lychkovskiy: Spin excitations in cuprates from spin cluster calculations..... 320 Maria Vittoria Mazziotti: High Tc in the organic superconductor Kx p Terphenyl by Fano resonances in superconducting gaps at the Lifshitz transition ...... 321
Superstripes 2017, Ischia June 4 10, 2017
1.1
Multi level Kondo effect and enhanced critical temperature in nanoscale granular Al.
Aviv Moshe1, Nimrod Bachar1,2, Y. Lereah3 and G. Deutscher1 1 School of Physics and Astronomy, 2 Faculty of Engineering, Tel Aviv University, Israel 3 Department of Physics, University of Geneva, Switzerland
The normal state conductance of high resistivity granular Al films, having an enhanced critical temperature above 3K, shows a non monotonous temperature dependence. Upon cooling the conductance first increases, reaches a broad maximum, then decreases, and finally increases sharply again at low temperatures. This behavior bears a striking resemblance to that predicted for the conductance of quantum dots in a regime where the broadening of discrete energy levels, due to coupling of the dot to the leads reservoirs, is larger than the level separation. In this regime a multi level Kondo temperature can be larger than the effective Coulomb charging energy, leading to a metallic like behavior at high temperatures. This is followed by a Coulomb dominated regime, while at yet lower temperatures the single level Kondo behavior can be recovered (1). We believe that this multi level Kondo resonance model for single dots may apply to our 3D network of nanoscale grains. The multi level resonance prevents the insulating state from setting in already at high temperatures, which is favorable for superconductivity. This interpretation of the experimental conductance data is in line with the previously reported presence of magnetic moments in these films (2). High Resolution Electron Microscopy shows that intergrain coupling can take place through atomic size Sharvin contacts, which is consistent with the typical values of the intergrain resistance of the films as the Metal to Insulator transition is approached.
N. Bachar and G. Deutscher are indebted to Antoine Georges for illuminating discussions on the multi level Kondo resonance effect.
References 1. S. Florens et al., Phys. Rev. B68, 245311 (2003). 2. N. Bachar et al., Phys. Rev. B91, 041123 (2015).
12 Superstripes 2017, Ischia June 4 10, 2017
1.2
The Fröhlich type, non equilibrium, polaronic condensate in the Mott system UO2(+x)
Steven D. Conradson Institut Jozef Stefan, Washington State University, NEqCST Corporation
Email: [email protected] Keywords: condensation, non equilibrium condensate, Fano Feshbach resonance
Results from a large number of experiments on O and photo doped UO2(+x), a 5f Mott insulator, are best and perhaps only interpreted as demonstrating that the polarons aggregate and self organize into a Bose Einstein condensate. The basis for this is Fröhlich's prediction of a non equilibrium condensate composed of specific phonons that become coherent because of dipole interactions that are enhanced by anharmonicity. The charge transfer that we have observed in UO2 would be an extreme case of that. An evaluation of the electronic density of states also shows that the polaronic quantum phase meets the conditions for stabilization by a Fano Feshbach resonance. Evidence will be presented for typical condensate properties as well as several that have not been predicted.
References 1. H. Frohlich, Phys. Lett. A A 26, 402 (1968). 2. A. Bianconi, Nature Phys. 9, 536 (2013). 3. S. D. Conradson, et al., Phys. Rev. B 88, 115135 (2013). 4. S. D. Conradson, et al., Sci. Rep. 5, 15278 (2015). 5. S. D. Conradson, et al. Phys. Rev. B, (2017) submitted.
13 Superstripes 2017, Ischia June 4 10, 2017
1.3
Investigation of the optical anisotropy in the nematic phase of FeSe
L. Degiorgi ETH Zurich
Email: [email protected] Keywords: optical properties, iron pnictide superconductors
The iron pnictide superconductors provide the most recent playground in which to address the competition between structural, magnetic and superconducting phases. In the well known 122 materials, the non superconducting parent compounds undergo an antiferromagnetic transition into a broken symmetry spin density wave (SDW) ground state at TN, which is always preceded by or coincident with a tetragonal to orthorhombic structural distortion at Ts ≥TN. Their relevant resistivity anisotropy at Tce due to the SDW collective state in the orthorhombic state. Understanding the effects of the structural transition on the charge dynamics and the electronic bands by studying the optical properties of the system is an important step in order to develop a comprehensive description of these materials. We use our technique [1] that allows in situ variation of uniaxial stress to probe the polarization dependence of the optical reflectivity of FeSe through the tetragonal to orthorhombic structural transition and with respect to the electronic nematic phase (Fig. 1). We will compare our newest results with our early data on the representative Co underdoped 122 iron arsenide [1]. These measurements reveal a different hysteretic behavior of the anisotropic optical response to uniaxial stress (i.e., degree of sample detwinning) in the orthorhombic state for the two classes of materials, which may reveal important peculiarities of their own electronic structure and their sensitivity to the nematic phase.
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(a) Optical reflectivity of FeSe at 10 K in the fully detwinned orthorhombic phase and along both axes. The main panel emphasizes the mid infrared spectral range, while the inset shows the full measurement from the far infrared up to the UV. (b) Reflectivity ratio between data along both axes at 10 K with increasing uniaxial stress (p) after a zero pressure cooling protocol [1].
References 1. C. Mirri et al., Phys. Rev. B 93, 085114 (2016) and references therein.
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2.2
New candidate quantum spin liquids in ionic polyaromatic hydrocarbons
Kosmas Prassides WPI AIMR, Tohoku University
Email: k.prassides@wpi aimr.tohoku.ac.jp Keywords: ionic polyaromatic hydrocarbons; Mott localization; frustrated topology; quantum magnetism
Molecular solids whose cooperative electronic properties are based purely on pi electrons from carbon atoms offer a fertile ground in the search for exotic states of matter, including unconventional superconductivity and quantum magnetism. The field was ignited by reports of high temperature superconductivity in materials obtained by reaction of alkali metals with polyaromatic hydrocarbons (PAHs) such as phenanthrene and picene. However, the results have not been reproduced and the compound identities have remained unknown. Recently we have been successful in devising new reproducible synthetic routes of ionic salts of PAHs under mild conditions; crystalline single phase materials of ionic PAHs (phenanthrene, pentacene, picene) are available for structural and electronic characterization for the first time [1,2]. The binary phenanthrene salts, CsPhen and Cs2Phen are multi orbital strongly correlated Mott insulators. Cs2Phen is diamagnetic due to orbital polarisation while CsPhen is a Heisenberg antiferromagnet with a gapped spin liquid ground state. The absence of long range magnetic order renders the compound an excellent candidate of a spin ½ quantum spin liquid arising purely from carbon pi electrons.
References 1. Y. Takabayashi, M. Menelaou, H. Tamura, N. Takemori, T. Koretsune, A. Štefančič, G. Klupp, A. J. C. Buurma, Y. Nomura, R. Arita, D. Arčon, M. J. Rosseinsky, and K. Prassides, Nature Chem. 9, in press (2017). 2. F. D. Romero, M. J. Pitcher, C. I. Hiley, G. F. S. Whitehead, S. Kar, A. Y. Ganin, D. Antypov, C. Collins, M. S. Dyer, G. Klupp, R. H. Colman, K. Prassides, and M. J. Rosseinsky, Nature Chem. 9, in press (2017).
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2.3
Dynamic charge stripe spectrum in nickelate perovskites
Dmitry Reznik University of Colorado Boulder
Email: [email protected] Keywords: Dynamic charge stripes, nickelates
The insulator to metal transition continues to be a challenging subject, especially when electronic correlations are strong. In layered compounds, such as La2–xSrxNiO4 and La2–xBaxCuO4, the doped charge carriers can segregate into periodically spaced charge stripes separating narrow domains of antiferromagnetic order. Although there have been theoretical proposals of dynamically fluctuating stripes, direct spectroscopic evidence of charge stripe fluctuations has been lacking until recently. I will discuss our measurements of critical lattice fluctuations, driven by charge stripe correlations, in La2–xSrxNiO4 using inelastic neutron scattering. This scattering is detected at large momentum transfers where the magnetic form factor suppresses the spin fluctuation signal. The lattice fluctuations associated with the dynamic charge stripes are narrow in q and broad in energy. They are strongest near the charge stripe melting temperature. Recent work established that the stripe dispersion is anisotropic and strongly depends on temperature between the charge and magnetic ordering transitions. Our results open the way towards the quantitative theory of dynamic stripes and for directly detecting dynamical charge stripes in other strongly correlated systems, including high temperature superconductors such as La2–xSrxCuO4.
References 1. R. Zhong, B.L. Winn, G. Gu, D. Reznik, J.M. Tranquada, arXiv:1608.04799 (2016). 2. S. Anissimova, D. Parshall, G. D. Gu, K. Marty, M. D. Lumsden, Songxue Chi, J. A. Fernandez Baca, D.L. Abernathy, D. Lamago, J.M. Tranquada, D. Reznik, Nature Communications 5, 3467 (2014).
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2.4
Mott transition and strong diamagnetism in Ca2RuO4 tuned by electric field/current
Yoshiteru Maeno Department of Physics, Kyoto University, Kyoto 606 8502, Japan.
Email: [email protected] u.ac.jp Keywords: Mott transition; diamagnetism; non equilibrium; Ca2RuO4.
The Mott insulator is considered as an electron “solid” frozen due to strong electron correlations. It has a potential to become a good metal if the electron solid melts by suitable stimuli. In this talk, we will describe novel phenomena we found in the layered ruthenium oxide Ca2RuO4, for which non equilibrium conditions introduced by DC electric field and current trigger and maintain the charge “liquid” state down to low temperatures [1]. When the electric current is not very strong, the Mott gap can be tuned to disappear gradually. In such a condition, Ca2RuO4 exhibits a semi metallic conduction and giant diamagnetism [2]. We will discuss how the partial Mott gap closing leads to such diamagnetic behavior. The important implication of this study is that simple DC current may be used as a useful control parameter to induce new states from some Mott insulators.
Figure 1: Schematic crystal structure of undistorted Ca2RuO4. In reality, the ground state Mott insulating phase has strong distortions with RuO6 octahedra flattening, as well as tilting and rotation.
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This work is done mainly in collaboration with F. Nakamura, C. Sow, S. Yonezawa, T. Oka, S. Kitamura, and K. Kuroki. This work was supported by JSPS KAKENHI Nos. JP26247060 and JP15H05852 (Topological Materials Science).
References 1. “Electric field induced metal maintained by current of the Mott insulator Ca2RuO4”, F. Nakamura, M. Sakaki, Y. Yamanaka, S. Tamaru, T. Suzuki, and Y. Maeno, Sci. Rep. 3, 2536 (2013). 2. “Current induced giant diamagnetism in the Mott insulator Ca2RuO4”, C. Sow, S. Yonezawa, S. Kitamura, T. Oka, K. Kuroki, F. Nakamura, and Y. Maeno, arXiv. 1610.02222.
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2.5
The road map toward room temperature superconductivity
Annette Bussmann Holder MPI FKF
Email: a.busmann [email protected] Keywords: multiband Superconductivity, isotope effects
Combining real space and momentum pairing corresponds to the coexistence of BEC and BCS physics. While typically the crossover between both is discussed and analyzed, we consider here their coexistence within a weak coupling approximation. The most profound results for this scenario are: a substantial increase in the superconducting transition temperature which easily reaches values of 300K (Figure 1a). The isotope exponent α deviates substantially from the BCS value to decrease to vanishingly small numbers with increasing Tc (Figure 1b). Further consequences related to the gap to Tc ratio and the variation of the gaps with the parameters are discussed and brought into relation with real materials.
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a) The superconducting transition temperature Tc as a function of the polaronic coupling λ1 for three different parameter sets as indicated in the figure. b) The isotope exponent α as a function of Tc where the color code is identical to figure 1a).
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3.1 d9 Nickelates under Pressure
T. Egami1,2,3 D.C. Mitchell1,2 and K.A. Lokshin1,3 1Shull Wollan Center – Joint Institute for Neutron Sciences, University of Tennessee and Oak Ridge National Laboratory, Oak Ridge, TN 37831, USA 2Department of Physics and Astronomy, University of Tennessee, Knoxville, TN 37996, USA. 3Department of Materials Science and Engineering, University of Tennessee, Knoxville, TN 37996, USA.
Email: [email protected] Keywords: nickelates; pressure; cuprate analog; metallic conductivity.
Nickel ions are commonly seen in Ni3+ (d7) or Ni2+ (d8) state. However, by strong reduction it is possible to produce nickelates in the Ni+ (d9) state in the square planar structure as in the cuprates. Because of the charge transfer gap larger than that in the cuprates d9 nickelates are insulating in the ambient condition, but it can be made metallic under pressure. Various interesting properties have been observed for La4Ni3O8 [1] and related compounds. Here we discuss the physical properties of 8.67 8.5 Nd4Ni3O8 (d ) and Nd3Ni2O6 (d ) under pressure. The insulator to metal transition was observed, but so far superconductivity has not been observed. We discuss why superconductivity does not occur in this system. The measurements were made by home made pressure apparatus compatible with the PPMS. The contacts were deposited on the sample by micro fabrication technique. We also discuss the possibility of superconductivity in undoped cuprates. In Fe pnictides isoelectronic doping, such as As to P, suppresses AFM order and induces superconductivity. Thus the role of AFM order is simply to compete and suppress superconductivity, and superconductivity can occur without spin fluctuations. Recent results [2,3] suggest that the phase diagram of the cuprates is more similar to that of the pnictides than considered earlier. We argue that a similar logic applies also to the cuprates to some extent.
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107 Nd4Ni3O8 ZFC 106
5 10 4GPa 15GPa 4 ) 10 28GPa
37GPa-1 3 37GPa-2
R ( R 10 51GPa 60GPa 102
101
100 10 100
T (K)
Figure 1: Resistivity of Nd4Ni3O8 as a function of temperature and pressure.
References 1. V.V. Poltavets, K.A. Lokshin, A.H. Nevidomskyy, M. Croft, T.A. Tyson, J. Hadermann, G.V. Tendeloo, T. Egami, G. Kotliar, N. ApRoberts Warren, A.P. Dioguardi, N.J. Curro and M. Greenblatt, Phys. Rev. Lett. 104, 206403 (2010). 2. M. Brinkmann, T. Rex, H. Bach and K. Westerholt, Phys. Rev. Lett. 74, 4927 (1995). 3. M. Horio, T. Adachi, Y. Mori, A. Takahashi, T. Yoshida, H. Suzuki, L.C.C. Ambolode II, K. Okazaki, K. Ono, H. Kumigashira, H. Anzai, M. Arita, H. Namatame, M. Taniguchi, D. Ootsuki, K. Sawada, M. Takahashi, T. Mizokawa, Y. Koike and A. Fujimori, Nature Commun. 7, 10567 (2015).
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3.2
Three novel features in the correlations between Tc and the superfluid density: local phase coherence below the Bose gas temperature TB and multiple ratios of Tc/TF
Yasutomo J. Uemura1 1 Department of Physics, Columbia University, New York, NY 10027, USA
Email:[email protected] Key words: superfluid density, Nernst effect, photo induced transient response, Bose Einstein condensation
Since 1988, the present author performed muon spin relaxation (MuSR) measurements of the magnetic field penetration depth, and reported nearly linear relationship between Tc and the superfluid density in high Tc cuprate, Fe based, A3C60, organic BEDT and heavy fermion superconductors [1 3]. These results have been shown in a plot of Tc versus effective charge energy scale TF derived from the superfluid density, as shown in Fig. 1. The strong correlations between Tc and the carrier density cannot be expected in BCS theory, while Bose Einstein Condensation (BEC) of preformed pairs give the linear relationship, yet with significantly higher transition temperature TB if one calculates the condensation temperature of corresponding number (ns/2) and mass (2m*) of tightly bound bosons forming a non interacting Bose gas. In this talk, I would like to point out three new features by including new results from Nernst effect, transient optical responses and additional MuSR measurements.
(1) Signatures of dynamic or transient superconductivity have been seen in Nernst effect and diamagnetic susceptibility above Tc, pioneered by Ong [4], and optical responses to photo excited state reported in recent measurements of Cavalleri et al. [5]. When we plot the onset temperature of Nernst effect TNER:on of LSCO, URu2Si2 and CeCoIn5 against the equilibrium value of TF, the points come very close to the TB line, as demonstrated in Fig. 1 for an underdoped LSCO. Furthermore, the onset point of the photo excited transient response may also come close to the TB line, for the cases of LBCO, YBCO, and K3C60. These features can be understood as representing the formation of local phase coherence of pre formed pairs below TB, yet the actual equilibrium condensation temperature Tc is significantly (factor of 4 or more) lowered due to the competition with the antiferromagnetic spin/charge order. In the photo excited states, this competition may not play a destructive role for the gapped transient optical responses.
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(2) The lowering of actual Tc from the hypothetical Bose gas temperature TB can be explained by the existence of inelastic resonance mode originating from the spin and charge correlations of the competing state, analogous to rotons in superfluid He [2,3]. Indeed we find the resonance mode features in YBCO, LSCO, URu2Si2 and CeCoIn5, which has the mode energy proportional to Tc with the same proportionality constant as that of roton energy versus Lambda temperature in superfluid 4He. (3) Recently, MuSR results on the superfluid density have been added for (a) Fe(Se,Te), single layer FeSe, (b) electron doped cuprates, and (c) MoTe2 under pressure and NbSe2 [6]. The ratio of Tc/TF in (a) is similar to those of hole doped cuprates, while about 4 times reduced in (b) and about 16 times reduced in (c), as shown in Fig. 2. This demonstrates that even for systems with a rather small Tc/TF, linear correlations between Tc and the superfluid density (reminiscent of BEC) survive within a given family, presenting a new challenge in interpreting these features with BEC BCS crossover phenomenology.
(left) Figure 1. Plot of the transition temperature Tc versus effective Fermi temperature TF derived from the superfluid density ns/m* [1 3]. N:on denotes the Nernst onset temperature in an underdoped LSCO. TB denotes the Bose condensation temperature of an ideal non interacting gas of tightly bound bosons with the density ns/2 and mass 2m*. The onset temperature of the gapped response measured by Cavalleri et al. [5] in the transient photo induced state in K3C60 comes close to the TB line. (right) Figure 2. Plot of the transition temperature Tc versus the superfluid density ns/m* proportional to the inverse square of the magnetic field penetration depth λ, in various superconductors. Linear relationship can be found with three proportionality constants for three different groups of materials: (a) hole doped cuprates, Fe(Se,Te). 1111 FeAs, 122 FeAs with the largest ratios of Tc/TF; (b) electron doped cuprates with the ratio about 4 times smaller than that of the group (a); and (c) transition metal dichalcogenides (TMDC) MoTe2 under pressure and NbSe2 in ambient pressure with the ratio 16 times reduced from that of the group (a). From Guguchia et al. [6].
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References 1. Y.J. Uemura et al., Phys. Rev. Lett. 62 (1989) 2317; 66 (1991) 2665; Nature 352 (1991) 605. 2. Y.J. Uemura, J. Phys. Condens. Matter 16 (2004) S4515; Physica B404 (2009) 3195. 3. Y.J. Uemura, Nature Materials 8 (2009) 253. 4. Y. Wang, N.P. Ong et al., Phys. Rev. B73 (2006) 024510; Phys. Rev. Lett. 95 (2005) 247002. 5. M. Mitrano, A. Cavalleri et al., Nature 530 (2016) 461, and references therein. 6. Z. Guguchia, Y.J. Uemura et al., arXiv:1704.05185
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3.3
Electron lattice and electron electron interactions in novel systems: paths to room temperature superconductivity
Vladimir Kresin* and Lev Gor’kov** *Lawrence Berkeley Laboratory, University of California, Berkeley, CA 94720, USA **NHMFL, Florida State University, Tallahassee, Florida, 32310, USA
Email: [email protected] Keywords: strong coupling; nano; carbon
According to microscopic theory, the room temperature superconductivity is a perfectly realistic phenomenon. Recent progress in the area of high Tc has attracted a lot of interest. The record value of Tc observed recently in sulfur hydrides is provided by strong electron lattice coupling with high frequency optical modes. However, one should go beyond the usual approach to describe such a state. This is caused by complex nature of the phonon spectrum, which is broad and contains various branches. The proposed two coupling constants model and the coupling re distribution concept can be used to describe the non trivial phase diagram, that is the pressure dependence of T¬c. The future tunneling spectroscopy will allow one to observe the two gap picture for the highest Tc phase. The strengthening of the interaction caused by polaronic effects and by drastic increase in the density of states for nano systems (nano clusters and quantum dots) will be also discussed. High Tc superconducting state can be caused by electron electron interaction between two electronic groups, for example, between two specially arranged carbon nanotubes. Superconducting state of biologically active systems and organic molecules is caused by the electron lattice interaction and merit a more detailed study.
References 1. A. Drozdov, M. Eremets, et al., Nature 525,73 (2015). 2. A. Bianconi, T. Jarlborg, Novel Supercond. Mater. 1,15(2015). 3. L. Gor’kov and V. Kresin, Nature, Sci. Rep. 6, 25608 (2016). 4. A. Hamo et al., Nature 535,395 (2016). 5. M. Rosseinsky and K. Prassides, Nature,464,39 (2010). 6. V. Kresin et al., Superconducting State, Sec.14.6, Oxford Univ. Press (2014).
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3.4
Strong interplay between high Tc superconductivity, nematicity, and magnetism in Fe based Superconductors
Hiroshi Kontani Nagoya Univerisity
Email: [email protected] u.ac.jp Keywords: Fe based superconductors, electronic nematic state, pairing mechanism
The interplay between the nematicity, magnetism and high Tc superconductivity in Fe based superconductors is one of the key unsolved problems [1,2]. To understand this issue, the plane s wave superconducting state in heavily electron doped FeSe, in which the Fermi surfaces are composed of only two electron pockets, attracts great attention. We attacked this issue by focusing on the higher order many body effect called the vertex correction (VC) that has been neglected in conventional Migdal Eliashberg (ME) formalism [3]. Due to the VC, the dressed effective Coulomb interaction possesses nontrivial spin and orbital dependences. We find in FeSe that (i) the orbital fluctuation mediated pairing interaction is strongly magnified by the Aslamazov Larkin type VC due to the strong modification of the electron boson coupling constants. In addition, (ii) sizable pairing glue is caused by the multi fluctuation exchange processes. Due to both important beyond ME effects, which are caused by the interplay between orbital and spin fluctuations, the anisotropic plane s wave state in heavily electron doped FeSe is satisfactorily explained. The proposed hole pocket less pairing mechanism would be important for various Fe based superconductors. We also study the rich electronic phase diagram in FeSe under pressure [4]. Based on the first principles calculations, we find that the pressure induced xy orbital Fermi pocket appears. Then, the spin fluctuations on the xy orbital are enhanced, whereas those on other orbitals are reduced. For this reason, the orbital order , which is caused by the spin fluctuations on xz and yz orbitals via the Aslamazov Larkin VC, is suppressed and replaced with the magnetism of xy electrons. The nodal s wave state at ambient pressure in the nematic state and the enhancement of Tc under pressure are driven by the cooperation between spin and orbital fluctuations.
References 1. Y. Yamakawa, S. Onari, and H. Kontani, Phys. Rev. X 6, 021032 (2016). 2. S. Onari, Y. Yamakawa, and H. Kontani, Phys. Rev. Lett. 116, 227001 (2016). 3. Y. Yamakawa and H. Kontani, arXiv:1611.05375. 4. Y. Yamakawa and H. Kontani, arXiv:1609.09618.
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3.5
Strong covalency and ligand holes, or how to make magnetic gold?
D.I. Khomskii II.Physikalisches Institut, Universitaet zu Koeln, Germany
Email: [email protected] koeln.de Keywords: negative charge transfer gaps, self doping, gold telluride AuTe2.
In this talk I will discuss some effects occurring in transition metal compounds with small or negative charge transfer gap and with large contribution of ligand (e.g. oxygen) holes. Special attention will be paid to the compounds of 4d and 5d elements. The apparent inversion of crystal field levels, as well as the tendency to spontaneous charge disproportionation will be discussed. Specifically, some systems containing gold, such as Cs2Au2Cl6 and AuTe2 will be discussed, and the question formulated in the title will be addressed.
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4.1
Spin and charge density wave fluctuations in cuprates
Stephen Hayden1 1H. H. Wills Physics Laboratory, University of Bristol, Tyndall Ave., Bristol, BS8 1TL, UK
Email: [email protected] Keywords: high temperature superconductivity, spin fluctuations, charge and spin order.
We discuss recent investigations of spin fluctuations and charge density wave correlations (CDW) in La2 xSrxCuO4 (LSCO) and YBa2Cu3O6+x (YBCO) [1 5]. YBCO shows CDW order near p=1/8. Here we present our recent determination of the atomic displacements associated with the CDW [4]. Specifically, we find that the mirror symmetry of the CuO2 is broken by the CDW. LSCO is a canonical layered cuprate system which may be continuously doped from parent antiferromagnet, through high temperature superconductor to an over doped metal. We have recently shown that near p=1/8 the system shows charge density wave order [2] together with the well known incommensurate spin freezing. In theories of magnetically mediated superconductivity, it is
Fig. 1 Atomic displacements of the important to know the evolution of the CDW in YBa2Cu3O6+x [4]. spin fluctuations with doping across the phase diagram. Thus here we report a systematic neutron scattering and x ray studies of the evolution of the magnetic excitations and low energy spin freezing with doping. Specifically, we have measured the magnetic excitations for the charge ordered composition p~1/8. We find that pseudogap and optimally doped compositions show a strong commensurate (π,π) excitation which forms at high temperature and
30 Superstripes 2017, Ischia June 4 10, 2017 persists over an energy range 40 100 meV. The similar features are present in other cuprate systems. At lower energies near p=1/8 we show how the charge and spin order are coupled.
References 1. J. Chang, E. Blackburn, A. T. Holmes, N. B. Christensen, J. Larsen, J. Mesot, R. Liang, D. A. Bonn, W. N. Hardy, A. Watenphul, M. v. Zimmermann, E. M. Forgan, and S. M. Hayden, Nat Phys 8, 871 (2012). 2. T. P. Croft, C. Lester, M. S. Senn, A. Bombardi, and S. M. Hayden, Phys. Rev. B 89, 224513 (2014). 3. M. Hücker, N. B. Christensen, A. T. Holmes, E. Blackburn, E. M. Forgan, R. Liang, D. A. Bonn, W. N. Hardy, O. Gutowski, M. v. Zimmermann, S. M. Hayden, and J. Chang, Phys. Rev. B 90, 054514 (2014). 4. E. M. Forgan, E. Blackburn, A. T. Holmes, A. K. R. Briffa, J. Chang, L. Bouchenoire, S. D. Brown, R. Liang, D. Bonn, W. N. Hardy, N. B. Christensen, M. V. Zimmermann, M. Hucker, and S. M. Hayden, Nat Commun 6, 10064 (2015). 5. J. Chang, E. Blackburn, O. Ivashko, A. T. Holmes, N. B. Christensen, M. Hucker, R. Liang, D. A. Bonn, W. N. Hardy, U. Rutt, M. v. Zimmermann, E. M. Forgan, and S. M. Hayden, Nat Commun 7, 11494 (2016).
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4.2
Electronics of high temperature cuprate superconductors
C. E. Matt1, D. Sutter1, Y. Sassa2, A. Cook1, L. Das1, N.C. Plumb3, M. Shi3, M. Månsson4, S. M. Hayden5, T. Neupert, Johan Chang1 1 Physik Institut, Universität Zürich, Winterthurerstr 190, CH 8057 Zürich, Switzerland 2 Department of Physics and Astronomy, Uppsala University, S 75121 Uppsala, Sweden 3 Swiss Light Source, Paul Scherrer Institut, CH 5232 Villigen PSI, Switzerland 4 KTH Royal Institute of Technology, Materials Physics, S 164 40 Kista, Sweden 5 H. H. Wills Physics Laboratory, University of Bristol, Bristol BS8 1TL, United Kingdom
Email: [email protected] Keywords: Cuprates, Superconductivity, Electronic structure
The minimal ingredients to explain the rich phenomenology of cuprate superconductors are still heavily debated. In this talk, recent photoemission experiments aiming to address the electronic structure of these materials will be presented. It will be discussed how these new results (C.E. Matt et al. In preparation) impact superconductivity and the pseudogap phase.
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4.3
1/8 Anomaly and Charge Order in Dy doped Bi2212
N. Momono1, K. Kawamura1, C. Kobashi1, N. Kaimai1, S. Takahashi1, Y. Kawai1, T. Kurosawa2, M. Oda2, M. Ido2 1 Applied Physics Course, Muroran Institute of Technology, Mizumoto cho 27 1, Muroran 050 8585, Japan 2 Department of Physics, Hokkaido University, Sapporo 060 0810, Japan
Email: [email protected] it.ac.jp Keywords: 1/8 anomaly, checker board charge order, STM/STS
In high Tc cuprate superconductors, it is considered that the superconductivity and various competing orders coexist in the underdoped region. It is important to clarify the anomalous electronic states in the underdoped region. In Bi2Sr2Ca1 xDyxCu2O8+d (Dy Bi2212), we found an anomalous "dip" feature near the hole concentration p~1/8 on the Tc p curve, which is not seen in the Tc p curve of pure Bi2212. In STM/STS experiments on Dy Bi2212 with p~1/8, the so called ‘checkerboard charge order’ with a wave vector q~0.3 r.l.u. is observed. The STS spectra for the sample with p~1/8 exihibit no well defined coherent peaks, which is similar to the results reported in ARPES experimens on Dy Bi2212 [1]. The dip of the Tc p curve induced by the substitution of Dy in Bi2212 was similar to that observed in Zn doped Bi2212 [2], suggesting that the suppression of Tc near p~1/8 in Dy Bi2212 is related to the pinning of the charge order.
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Figure 1: Doping dependence of Tc for Bi2Sr2Ca1 xDyxCu2O8+d (Dy Bi2212).
References 1. J. Zhao et al., PNAS 110, 17774 (2013). 2. M. Akoshima et al., Phys. Rev. B 57, 7491 (1998).
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5.1
Neutron Scattering Study of Magnetic Excitations in Electron Doped Cuprate
Masaki Fujita1 , Shun Asano2 , Kensuke Suzuki1 1 Institute for Materials Research, Tohoku Univsersity Sendai 980 8577, Japan 2 Department of Physics, Tohoku University, Sendai 980 8578, Japan
Email: fujita @imr.tohoku.ac.jp Keywords: electron doped cuprate, magnetic excitations, neutron scattering
The doping evolution of spin and charge dynamics in a doped Mott insulator is an important issue in the research field of strongly correlated electron system. The entire excitation spectra have been intensively and continuously studied with the development of spectroscopic techniques after the discovery of high transition temperature (high TC) superconductivity in a lamellar cuprate oxide. The recent state of the art spectrometers at large research facilities such as J PARC enables us to study the details of composite dynamics in the energy momentum space arising from the interacting degrees of freedom [1, 2]. Although the comprehensive study on both hole and electron doped systems are indispensable to extract the universal mechanism of high TC superconductivity, the majority of spectroscopic measurements was done on the hole doped system. Here, we introduce the results of systematic inelastic neutron scattering measurements done on the electron doped copper oxide to explore the entire spin excitations. First, we confirmed that the spin excitation in Pr1.4La0.6CuO4, which is the parent compound of electron doped superconductor, is consistent with the spin wave excitation expected from the s=1/2 two dimensional Heisenberg model. The evaluated nearest neighbor exchange coupling is 140±5 meV, comparable to the value for the parent compound of hole doped superconductor, La2CuO4. It was found that the spin excitation tends to elongate toward the higher energy region upon electron doping in Pr1.4 xLa0.6CexCuO4 and the zone boundary energy exceeds 300 meV in the sample with x ≥ 0.08, suggesting the steeper dispersion in the highly doped samples [3]. This doping evolution is in stark contrast with a negligible doping effect on the high energy spin excitation in the hole doped La2 xSrxCuO4, Therefore, the electron hole asymmetry exists in the observed spin excitation against the doping. We furthremore studied the annealing effect and the thermal effect on the spin excitations of Pr1.4La0.6CuO4. The results will be discussed in connection with the possibility of “undoped superconductivity” in T’ structured system.
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References 1. M. Matsuura, S. Kawamura, M. Fujita, R. Kajimoto, and K. Yamada, “Development of spin wave like dispersive excitations below the pseudogap temperature in the high temperature superconductor La2 xSrxCuO4” Phys. Rev. B 95, 024504 (2017). DOI: https://doi.org/10.1103/PhysRevB.95.024504 2. K. Sato, M. Matsuura, M. Fujita, R. Kajimoto, S. Ji, K. Ikeuchi, M. Nakamura, Y. Inamura, M. Arai, M. Enoki, and K. Yamada, ”Temperature Dependence of Spin Fluctuations in Underdoped La1.90Sr0.10CuO4”, Proc. Int. Conf. Strongly Correlated Electron Systems (SCES2013), JPS Conf. Proc. 3, 017010 (2014), DOI: http://dx.doi.org/10.7566/JPSCP.3.017010 3. K. Ishii, M. Fujita, T. Sasaki, M. Minola, G. Dellea, C. Mazzoli, K. Kummer, G. Ghiringhelli, L. Braicovich, T. Tohyama, K. Tsutsumi, K. Sato, R. Kajimoto, K. Ikeuchi, K. Yamada, M. Yoshida, M. Kurooka, and J. Mizuki, ”High Energy Spin and Charge Excitations in Electron Doped Copper Oxide Superconductors”, Nature Communications 5, 4714 (2014). DOI:10.1038/ncomms4714
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5.2
Superconductivity and electronic structure of SrTiO3
Dirk van der Marel A. Stucky, G. Scheerer, Z. Ren, D. Jaccard, J. M. Poumirol, C. Barreteau, E. Giannini University of Geneva
Email: [email protected] Keywords: superconductivity, electron phonon interaction, ferro electricity, quantum criticality, isotope effect, polaron, SrTiO3
Doped SrTiO3 is a very intriguing superconductor. In principle it is a garden variety semiconductor, but the pristine material can be made ferroelectric by substition of 18O on the oxygen sites. The RPA electronic structure calculations predict that, depending on the level of doping, one, two or three bands get occupied, at critical doping levels that have been confirmed by quantum oscillation experiments. Doping with less than 1 electron per 10'000 formula units makes the materials superconducting. Moreover, the maximum value of Tc is of the order 0.5 Kelvin regardless whether obtained in 2D interfaces or in bulk SrTiO3. The doped electrons are coupled to the lattice parameters, and from a wealth of optical and ARPES experiments it is known that this causes a factor of two mass enhancement, corresponding to the limit of large and highly mobile polarons. With regards to superconductivity there exists universal agreement that it pairing is mediated by electron phonon coupling, but it is not clear which phonons are the most important ones. Recently it has been suggested that the optical phonons that soften at the para ferro electric transition are the main culprits, on the other hand optics and ARPES data suggest strong coupling to the highest energy branch of optical phonons. Our isotope studies demonstrates a factor 1.5 enhancement of Tc, with a sign opposite to standard BCS. The effect can be due to polaronic band narrowing, coupling to ferro electric fluctuations or a combination of these two.
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Polarons in SrTiO3 as demonstrated by optical conductivity data (J.L.M. van Mechelen et al.; PRL 100, 226403 (2008); T. Devreese et al.; PRB 81, 125119 (2010)).
References 1. K.A. Mueller, and H. Burkard, Phys. Rev. B, 19, 3593 3602 (1979). 2. S. E. Rowley, L. J. Spalek, R. P. Smith, M. P. M. Dean, M. Itoh, J. F. Scott, G. G. Lonzarich, and S. S. Saxena, Nat. Phys. 10, 367 372 (2014). 3. A. S. Alexandrov, Phys. Rev. B 46, 14932 (1992). 4. J. M. Edge, Y. Kedem, U. Aschauer, N. A. Spaldin, and A.V. Balatsky, Phys. Rev. Lett. 115, 247002 (2016). 5. D. van der Marel, J.L.M. van Mechelen, and I.I. Mazin, Phys. Rev. B 84, 25111 (2011). 6. A. Stucky, G. Scheerer, Z. Ren, D. Jaccard, J. M. Poumirol, C. Barreteau, E. Giannini, and D. van der Marel; Scientific Reports 6, 37582 (2016).
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5.3
Pressure driven high Tc superconductivity in carbon based and inorganic materials
Yoshihiro Kubozono1, Saki Nishiyama1, Xiao Miao1, Takahiro Terao1, Xiao Fang Yang1, Hidenori Fujita2, Masatoshi Hoshi2, Hidenori Goto1, Takafumi Miyazaki3, Tomoko Kagayama2, Katsuya Shimizu2, Hitoshi Yamaoka4, Hirofumi Ishii5, Yen Fa Liao5 1 Research Institute for Interdisiplinary Science, Okayama Univertsity, Okayama 700 8530, Japan; 2 Center for Science and Technology under Extreme Conditions, Osaka University, Osaka 560 8531, Japan; 3 Research Laboratory for Surface Science, Okayama University, Okayama 700 8530, Japan; 4 Riken Harima Branch, Hyogo 679 5198, Japan; 5 National Synchrotron Radiation Research Center, Hsinchu 30076, Taiwan
Email: [email protected] u.ac.jp Keywords: pressure, high Tc, superconductivity, carbon based materials, transition metal dichalcogenides, Fe based superconductors, topological materials
Pressure dependence of superconductivity in diverse two dimensional (2D) materials, is investigated in a wide pressure range from their temperature dependence of magnetic susceptibility (M / H) and resistance (R). All superconducting materials were prepared by doping of 2D layered materials (graphite, MoSe2, FeSe1 zTez and Bi2Se3). The preparation of superconductors was achieved using a liquid metal alloy for metal intercalated graphite (graphite intercalation compound (GIC)), and a liquid NH3 (or ND3) and liquid organic solvents for other inorganic compounds. Superconducting transition temperature, Tc, of Ca0.5(2)Sr0.5(2)C6, which takes a SrC6 type structure (hexagonal, space group No. 194, P63/mmc), was 3.2 K at ambient pressure (0 GPa). The Tc increased rapidly with increasing pressure up to 8.3 GPa; the maximum Tc was 5.4 K. With further increasing pressure, the Tc suddenly dropped. This behavior is similar to those of CaC6 and Ca0.6K0.4C8 (KC8 type structure) [1,2]. The increase in Tc against pressure for CaC6 was assigned to the softening of Ca Ca phonon (hardening of Ca – C phonon), and the decrease in Tc attributed to the order disorder transition originating from random off center displacement of Ca atoms in the plane which accompanies the lattice softening. The same transition may take place in Ca0.5(2)Sr0.5(2)C6. In Ca0.5(2)Sr0.5(2)C6 (SrC6 type structure), the lattice shrank monotonically up to 20 GPa, but 112 Bragg peak disappeared at around 10 GPa. Here, it should be noticed that the graphene graphene distance, dGG (= c / 2), of Ca0.5(2)Sr0.5(2)C6 at around 10 GPa is close to that (dGG = c / 3) of CaC6 (CaC6 type structure). In the case of Ca0.6K0.4C8 (KC8 type structure), the graphite – non graphite transition emerged
39 Superstripes 2017, Ischia June 4 10, 2017 when the dGG (= c /4) was close to that of CaC6 [2]. Therefore, the disappearance of 112 Bragg peak may be associated with graphite – non graphite transition. To sum up, the GIC superconductors show an exciting positive pressure dependence of Tc. Furthermore, we succeeded in preparation of metal doped FeSe1 zTez and MoSe2 using NH3 (ND3) and organic solvents such as ethylenediamine (EDA). The metal doped FeSe1 zTez compounds showed a pressure driven high Tc superconducting phase, Tc of which reached ~50 K. The (NH3)yNaxMoSe2 compound also provided two different superconducting phases above / below 2 GPa. In this conference, we will show new metal doped 2D layered superconductors and their exciting pressure dependence of superconductivity.
References 1. A. Gauzzi et al. Phys. Rev. Lett. 98, 067002 (2007). 2. T.L.H Nguyen et al. Carbon 100, 641 646 (2016).
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5.4
Non equilibrium Surface Dirac Fermion Dynamics of Topological Insulators Probed By Time Resolved ARPES
Akio Kimura Graduate School of Science, Hiroshima University, 1 3 1 Kagamiyama, Higashi hiroshima 739 8526, Japan
Email: akiok@hiroshima u.ac.jp Keywords: Topological insulators; Nonequilibrium surface Dirac fermion dynamics
Topological insulators (TIs) have attracted a great deal of attention in spin electronics field. Gapless and massless edge or surface states appear where the topological number changes, while their bulk is insulating. One of the most remarkable properties of the topological surface states (TSS) are their helical spin textures in momentum space where the backscattering is forbidden. It would lead to a dissipationless spin transport on the surface of TIs, which is very promising for spintronic applications. Here, the surface Dirac fermion dynamics in the “carrier tuned” topological insulator (Sb1 xBix)2Te3 have been explored by time and angle resolved photoelectron spectroscopy implementing pump probe method that enables us to observe not only occupied/unoccupied electronic states but also carrier dynamics. The experiment was carried out with linearly polarized pump (hν=1.48 eV) and probe (5.92 eV) pulses generated by Ti:sapphire laser system operating at a repetition rate of 250 kHz [1].
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Probe 5.9 eV Pump 1.5 eV
4 s +1.33 ps ∝ 1.33 ps
(a) n type (b)n type (c) n type
ΓΓ ΓΓ
Figure 1: Time resolved ARPES images recorded without pump (a), and with pump t= 1.33ps (=∼4 s) (b) and t =1.33ps(c). Pump probe configurations are also illustrated.
A prolonged duration of the excited surface carriers has been observed for the sample with its Fermi energy tuned at the Dirac point of the TSS [2]. We have also observed a downward (an upward) surface photovoltage shifts in n type (p type) sample of Bi2Te3 [Figure 1]. This finding paves a pathway to ambipolar optical control of spin current generation on the surface of TIs in the next generation opto spinelectronic devices [3].
References 1. Y. Ishida et al., Rev. Sci. Instrum. 85, 123904 (2014). 2. K. Sumida et al., submitted. 3. T. Yoshikawa et al., submitted.
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6.1
Charge dynamics near the onset of charge density wave order in La 214 cuprates
Dragana Popović* National High Magnetic Field Laboratory, Florida State University, 1800 E. Paul Dirac Drive, Tallahassee, FL 32310, USA
Email: [email protected] Keywords: cuprates; stripes; charge dynamics; phase transitions.
The dynamics of charge ordered states is one of the central unresolved issues in underdoped cuprate high temperature superconductors. Static short range charge density wave (CDW) domains have been detected in almost all cuprates. The key questions that arise are: (1) Do the observed static domain structures correspond to a ground state or a long lived metastable state? (2) What is the role of disorder? We introduce a new method for detecting and probing domain dynamics in cuprates. We focus first on the regime across the CDW (and structural) transition in La1.48Nd0.4Sr0.12CuO4. By employing two different nonequilibrium protocols, a response to a change in temperature T and magnetic field H, we find evidence for metastable states in the CDW ordered phase, including slow, nonexponential relaxations of resistance R, hysteresis and memory in the magnetoresistance (MR) (Fig. 1), and avalanches with a power law distribution of sizes.[1] A picture emerges of interacting domains that, although strongly pinned by disorder, are not static, but
Figure 1: Negative out of plane magnetoresistance in La1.48Nd0.4Sr0.12CuO4 just below the onset of CDW order.[1] The arrows and numbers show the direction and the order of field sweeps. Inset: subloops shifted vertically for comparison.
43 Superstripes 2017, Ischia June 4 10, 2017 trapped in long lived metastable states. Surprisingly, nonequilibrium effects are revealed only when the transition is approached from the charge ordered phase. In order to clarify precisely the interplay of charge and lattice degrees of freedom, we have performed similar measurements on La1.7Eu0.2Sr0.1CuO4, in which CDW ordering at T=TCO does not coincide with the structural transition at T=TLTT. We find that, for H||c axis, both materials exhibit a similar onset of negative magnetoresistance near TCO. In contrast, the MR is positive for all field orientations near TLTT in La1.7Eu0.2Sr0.1CuO4, indicating that H||c cannot drive the structural transition.[2] Therefore, these results show that our observations in La1.48Nd0.4Sr0.12CuO4 [1] are related to the onset of charge order, and not to the structural transition. Other similarities and differences in charge transport of the two materials will also be discussed. By unveiling the asymmetry of the transition to a CDW ordered phase [1], our work points a way to detecting fluctuating CDWs in the cuprates using also other experimental techniques. In addition, nonequilibrium protocols in charge transport can be extended to other correlated electron systems, such as iron pnictides, to probe charge domain dynamics.
This work was partially supported by NSF grant No. DMR 1307075 and the NHMFL via NSF Cooperative Agreement DMR 1157490 and the State of Florida.
References 1. P. G. Baity, T. Sasagawa, and D. Popović, (under review); arXiv:1609.02591v2 (2016). https://arxiv.org/abs/1609.02591 2. P. G. Baity, T. Sasagawa, and D. Popović (unpublished).
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6.2
Dimensional Crossover of Charge Density Wave Correlations in the Cuprates
Dror Orgad, Yosef Caplan The Hebrew University
Email: [email protected] Keywords: CDW correlations, underdoped cuprates, competing orders
Short range charge density wave correlations are ubiquitous in underdoped cuprates. They are largely confined to the copper oxygen planes and oscillate out of phase from one unit cell to the next in the c direction. Recently, it was found that a considerably longer range charge density wave order develops in YBCO above a critical magnetic field. This order is more three dimensional and is in phase along the c axis. Here, we show that such behavior is a consequence of the tension between the conflicting ordering tendencies induced by the disorder potential and the Coulomb interaction, where the magnetic field acts to tip the scales from the former to the latter. We base our conclusion on analytic large N analysis and Monte Carlo simulations of a non linear sigma model of competing superconducting and charge density wave orders. Our results are in agreement with the observed phenomenology in the cuprates, and we discuss their implications to other members of this family, which have not been measured yet at high magnetic fields.
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6.3
Modifications induced by synchrotron radiation in Bi2Sr2CaCu2O8+delta and YBa2Cu3O7 x: a novel non destructive patterning method
Marco Truccato1, Valentina Bonino1, Lorenzo Mino1, Angelo Agostino2, Carmelo Prestipino3, Elisa Borfecchia2, and Carlo Lamberti2,4 1 Department of Physics, Interdepartmental Centre NIS, University of Torino, via P.Giuria 1,I 10125Torino, Italy 2 Department of Chemistry, Interdepartmental Centre NIS, University of Torino, via P.Giuria 7,I 10125 Torino, Italy 3 Institut Sciences Chimiques de Rennes, UMR CNRS 6226, Campus de Beaulieu, Université de Rennes 1, 35042 Rennes Cedex, France 4 IRC “Smart Materials”, Southern Federal University, ul. Andreya Sladkova 178/24, 344090 ,Rostov on Don, Russia
Email: [email protected] Keywords: synchrotron X rays nano beam, direct write patterning, high temperature superconductors, Bi 2212, intrinsic Josephson junctions
Changes in the material properties induced by synchrotron nanobeams are typically neglected or considered as unwanted side effects implied by sample characterization. At the same time, conventional X rays nano lithography is based on the traditional approach of photoresist impression and development, which suffers from the difficulty of producing masks with sufficient contrast at the nanoscale. On the other hand, in our direct write approach we have successfully controlled material changes over selected areas and exploited them to produce Josephson devices out of high Tc superconducting crystals without the use of any photoresist or etching process. Here we report on the doping change of Bi2Sr2CaCu2O8+δ (Bi 2212) obtained by means of synchrotron radiation [1] and on the fabrication of devices based on the instrinsic Josephson junction structure of Bi 2212 and YBa2Cu3O7 x (Y 123) that achieve spatial resolution in the nanometric domain [2]. We have used highly focused synchrotron radiation with energy of about 13 or 17 keV, with minimum feature size of 50 nm and online monitoring of the device resistance during irradiation, which enabled us to tune the desired material condition into a non superconducting state. Although actual microscopic mechanisms have not been clarified yet and include both local heating and knock on interstitial oxygen atoms by photoelectrons as possible processes, X ray nano diffraction patterns show that the crystal structure has not been remarkably perturbed in the irradiated regions in spite of their electrical changes.
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These results prove that a conceptually new patterning method is actually possible for oxides, based on the local change of electrical properties, with remarkable potential in terms of heat dissipation, chemical contamination, miniaturization and high aspect ratio of the devices.
Figure 1: View of a Josephson device patterned by means of a synchrotron radiation nano beam. Violet boxes delimit the regions acting like trenches in the device.
References 1. A. Pagliero et al, Nano Lett. 14, 1583 1589 (2014). 2. M. Truccato et al, Nano Lett. 16, 1669 1674 (2016).
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6.4
Local charges and charge order in the cuprates revealed by NMR
Michael Jurkutat, Steven Reichardt, Jürgen Haase University of Leipzig, Faculty of Physics and Earth Sciences, Linnéstr. 5, 04103 Leipzig, Germany
Email: [email protected] leipzig.de Keywords: superconducting cuprates, charge order, high pressure NMR, phase diagram
Quantitative determination of the local charges in the ubiquitous CuO2 plane with NMR reveals unsuspected differences in terms of material chemistry between the various cuprate families. It turns out that the material specific charge distribution between Cu and O reflects depending on the model the charge transfer gap, the covalency of the bond, or orbital contributions to electronic bands, and has been found to set many electronic properties, e.g., the maximum Tc and superfluid density. Interestingly, substantial charge density variations within the CuO2 plane were found for most cuprate materials, although it has long been debated whether this reflects merely chemical inhomogeneity or actually interesting electronic features. Using high pressure NMR that only affects the electronic properties, but leaves the chemistry unchanged, optimally doped YBCO is found to exhibit charge order. The spectral changes observed for planar Cu and O NMR cannot be accounted for structurally, and combined with field and temperature dependent NMR linewidths, we can conclude on the universality of charge order in the YBCO family. This can likely even be extended to all cuprates if charge order is perturbed, differently aligned or pinned in some fashion by chemical inhomogeneities, magnetic field, or some other form of symmetry breaking in the CuO2 plane.
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7.1
Crystal Growth and Advanced Synthesis of Contemporary Functional and Superconducting Materials: From Simplicity to Complexity
Nikolai D. Zhigadlo1, Mitra Iranmanesh1, John R. Kirtley2, Wilfried Assenmacher3, Werner Mader3, Jürg Hulliger1 1 Department of Chemistry and Biochemistry, University of Bern, 3012 Bern, Switzerland 2 Geballe Laboratory for Advanced Materials, Stanford University, Palo Alto, California, 94305, USA 3 Institute of Inorganic Chemistry, University of Bonn, D 53117 Bonn, Germany
Email: [email protected] or [email protected] Keywords: superconductors; helical magnets; van der Waals; intermetallics; oxides.
In this talk we will provide new insights to the materials synthesis and characterization of contemporary functional and superconducting materials. Mainly, two different approaches such as the high pressure, high temperature method and ceramic combinatorial solid state chemistry will be presented with application to several typical compound classes. First, the high pressure phase diagram of the Mg B N system will be explored. Here, we discovered the simultaneous growth of completely different types of crystals: a rare two band superconductor MgB2 and a wide band semiconductor hBN [1]. Besides interesting physics, both of these materials hold great potential for practical applications. Then, we further emphasize the beneficial role of the high pressure, high temperature conditions in exploring the crystal growth of various intermetallic superconductors, such as MgCNi3 [2], Mo3Al2C, SrPt3P [3], pyrochlores, helical magnets MnP [4], CrAs [5], magnetocaloric MnAs compound, and 2D van der Waals semiconductors (hBN, black P, P1 xAsx). The underlying correlations and the general trends between composition, structure, magnetism and superconductivity in these materials will be discussed. Successively, we will highlight the key role of extreme conditions in the growth of Fe based superconductors, where a careful control of the composition structural relations is vital for understanding of the physical behavior [6]. The availability of sizable, high quality LnFeAsO (Ln: lanthanide) single crystals with substitution of O by F or H, Sm by Th, Fe by Co, and As by P, allowed us to measure intrinsic and direction dependent superconducting properties [6 12]. Finally, we will demonstrate that combinatorial ceramic solid state chemistry is an efficient way to search for new superconducting compounds, while the problem of determining which compositions are strongly diamagnetic in a mixed phase sample is challenging. A single sample synthesis concept based on multi element ceramic samples can produce a variety of local products. When applied to cuprate superconductors (SC), statistical modeling predicts the occurrence of possible compounds in a concentration in the order of 50 ppm. A sample with such a low
49 Superstripes 2017, Ischia June 4 10, 2017 concentration needs local probe analytical or separation techniques to identify compounds of interest. We will report the results obtained from random mixtures of Ca, Sr, Ba, La, Zr, Pb and Cu oxides reacted at different conditions under ambient pressure [13]. The bulk state displays superconductivity up to about 125 K. By magnetic separation technique many SC grains in the range of 50 to 300 m were collected for further analysis. Scanning SQUID microscopy applied to single grains has detected local m sized areas of SC up to 115 K. Transmission electron microscopy applied to some grains shows evidence for the formation of Sr Ca Ba Cu based phases, containing a small amount of La and Pb. According to the literature, in this phase system known superconducting phases were obtained so far only at high pressure. Here, we report a new synthetic approach for either known or unknown compounds attaining a high Tc without containing Bi, Tl, Hg or the need for a high pressure synthesis [13].
References 1. N. D. Zhigadlo, J. Cryst. Growth 402, 308 (2014). https://dx.doi.org/10.1016/j.jcrysgro.2014.06.038. 2. R. T. Gordon, N. D. Zhigadlo, S. Weyeneth, S. Katrych, R. Prozorov, Phys. Rev. B 87, 094520 (2013). https://doi.org/10.1103/PhysRevB.87.094520. 3. N. D. Zhigadlo, J. Cryst. Growth 455, 94 (2016). https://dx.doi.org/10.1016/j.jcrysgro.2016.10.003 4. R. Khasanov, et al., Phys. Rev. B 93, 180509 (2016) https://doi.org/10.1103/PhysRevB.93.180509 5. R. Khasanov, et al., Sci. Rep. 5, 13788 82015). https://doi:10.1038/srep13788 6. N. D. Zhigadlo, et al., Phys. Rev. B 86, 214509 (2012). https://doi.org/10.1103/PhysRevB.86.214509 7. N. D. Zhigadlo, et al., Phys. Rev. B 84, 134526 (2011). https://doi.org/10.1103/PhysRevB.84.134526 8. L. Fang, et al., Nature Communications 4, 2655 (2013). https://doi:10.1038/ncomms3655 9. T. Mertelj, et al., Phys. Rev. B 87, 174525 (2013). https://doi.org/10.1103/PhysRevB.87.174525 10. P. J. W. Moll, et al., Phys. Rev. Lett. 113, 186402 (2014). https://doi.org/10.1103/PhysRevLett.113.186402 11. A. Charnukha, et al., Sci. Rep. 5, 10392 (2015); ibid. 5, 18273 (2015). https://doi:10.1038/srep10392 ; https://doi:10.1038/srep18273 12. S. V. Borisenko, et al., Nature Physics 12, 311 (2016). https://doi:10.1038/nphys3594 13. N. D. Zhigadlo, et al., J. Supercond. Nov. Magn. 30, 79 (2017). https://doi:10.1007/s10948 016 3800 z
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7.2
Rapid Synthesis of Superconducting and Magnetic oxides by Light Irradiation
A. Shengelaya1, D. Daraselia1, D. Japaridze1, Z. Jibuti1, K. A. Müller2 1 Department of Physics, Tbilisi State University, GE 0179, Tbilisi, Georgia 2 Physik Institut der Universität Zürich, CH 8057, Zürich, Switzerland
Email: [email protected] Keywords: oxide materials, light effects
Most of the technologically important oxide materials are usually obtained through solid state reaction. This implies long term (for tens of hours) heating of reactants in powder form at high temperatures in furnace, which is a highly time and energy consuming process. Moreover, the long term high temperature synthesis may result in deviation from stoichiometry and other unwanted side effects. Therefore there is a significant worldwide effort to develop technologies to considerably reduce the solid state reaction temperature and time. We report a novel kind of synthesis of oxide materials, which involves the irradiation of the mixture of starting oxides by light in a broad spectral range from infrared to ultraviolet with intensity sufficient for starting the solid state reaction between the reagents contained in the powder mixture [1, 2]. We synthesized different superconducting and magnetic oxides using this method. It was demonstrated that light irradiation leads to a dramatic increase of the solid state reaction speed and a lowering of the reaction temperature. The rate of the resulting reaction exceeds the conventional thermal solid state reaction rate in furnace by about two three orders of magnitude. The photostimulated solid state reaction (PSSR) method demonstrated is quite general and opens up the possibility of fast synthesis of a wide range of technologically important bulk and thin film oxide materials.
References 1. D. Daraselia, D. Japaridze, Z. Jibuti, A. Shengelaya and K. A. Müller, Journal of Superconductivity and Novel Magnetism 26, 2987 (2013). 2. D. Daraselia, D. Japaridze, Z. Jibuti, A. Shengelaya, and K. A. Müller, “Rapid solid state reaction of oxides with ultraviolet radiation”, European Patent Application PCT/EP2013/050664.
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7.3
A complete and accurate description of superconductivity of AlB2 – type structures from phonon dispersion calculations
Jose A Alarco, Peter C Talbot and Ian D. R. Mackinnon Institute for Future Environments, and Science and Engineering Faculty, Queensland University of Technology
Email: [email protected] Keywords: phonon dispersions; anomalies; thermal energy; isotope; substitution, pressure and temperature effects
A predictive tool for the design of new, higher temperature superconductors requires a simple, first principles technique, based on well established axioms as embodied in Density Functional Theory without post calculation corrections or increased levels of complexity. We show that anomalies in the calculated phonon dispersions of compounds with AlB2 type structures are good descriptors of their superconducting transition temperatures. This ab initio methodology has proven robust for descriptions of: the superconductivity of MgB2 and other related AlB2 type structures [1], the different isotopic forms of MgB2 [2], a series of substituted MgB2 compositions with Al [3] and transition metals [4], the pressure dependence of the superconductivity of MgB2 [5] and various temperature effects. Calculated values are well correlated with experimentally determined values within experimental errors, when sufficiently fine k grids are used to resolve Fermi surface details [1 5]. This methodology provides invaluable insight on the mechanisms of superconductivity can be extended to other crystal systems and has been used to predict superconducting Tc for new compounds [3, 4].
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Figure 1: Comparison of calculated and experimentally measured superconducting transition temperatures (Tc) for Al substituted MgB2 compositions (left) and MgB2 under hydrostatic pressure (right).
References 1. J. A. Alarco, A. Chou, P. C. Talbot and I. D. R. Mackinnon, “Phonon modes of MgB2: super lattice structures and spectral response”, Physical Chemistry Chemical Physics 16 (2014) 24443 24456. 2. J. A. Alarco, P. C. Talbot and I. D. R. Mackinnon, “Coherent phonon decay and the boron isotope effect for MgB2”, Physical Chemistry Chemical Physics 16 (2014) 25386 25392. 3. J. A. Alarco, P. C. Talbot and I. D. R. Mackinnon, “Phonon anomalies predict superconducting Tc for AlB2 type structures”, Physical Chemistry Chemical Physics 17 (2015) 25090 25099. 4. I. D. R. Mackinnon, P. C. Talbot and J. A. Alarco “Phonon dispersion anomalies and superconductivity in metal substituted MgB2” Computational Material Science 130 (2017) 191 203. 5. J. A. Alarco, P. C. Talbot and I. D. R. Mackinnon, “Phonon dispersion models for MgB2 with application of pressure”, submittted to Physica C, 2017.
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8.1
Atomic structure of supported ultrathin Germania films
A. Lewandowski, P. Schlexer, K. Burson, C. Büchner, W. D. Schneider, M. Heyde, G. Pacchioni, H. J. Freund Fritz Haber Institute of the MPG, Berlin, Germany, Dipartimento di Scienza dei Materiali, Uni di Milano Bicocca
Email: wolf [email protected] Keywords: oxides, 2D ultrathin films, 2D network structures, glass formers,
The high refractive index of germanium dioxide makes it an important material for optical fibers, lenses and windows [1]. Such applications benefit from well defined surface structures, which illustrates the need for a fundamental understanding of germania surfaces. However, to our knowledge, no surface structure for GeO2 has been experimentally established up to now. This situation was the motivation for the present study. GeO2 thin films were grown epitaxially on Ru(0001) by physical vapor deposition and subsequent annealing in oxygen. They were characterized by low energy electron diffraction and scanning tunneling microscopy. Layer by layer growth of atomically flat films is observed and the coverage tuned by varying the deposition time. Atomic resolution images reveal a hexagonal lattice with a variety of line defects. Different imaging contrasts show either the oxygen or the germanium atoms in the network. Two layers of corner sharing GeO4 tetrahedral building blocks are connected by oxygen bridges to form a bilayer structure. Three in plane oxygen bridges and one out of plane bridge per tetrahedron result in a chemically saturated flat sheet that interacts weakly with the substrate. Density functional theory proposes a low energy structure in agreement with experimentally observed atomic arrangements. Moreover, a theoretical investigation of different building blocks sheds light on the most common defects found in germania films. These defect structures, similar to observations for SiO2 films [2 4], are analyzed and discussed as possible precursors for a glassy GeO2 phase.
References 1. F. Mitschke, Fiber Optics, Springer Berlin Heidelberg, Berlin, Heidelberg, 2010. 2. L. Lichtenstein, M. Heyde, H. J. Freund, Atomic Arrangement in Two Dimensional Silica: From Crystalline to Vitreous Structures, J. Phys. Chem. C. 116 (2012) 20426. 3. L. Lichtenstein, C. Büchner, B. Yang, S. Shaikhutdinov, M. Heyde, M. Sierka, et al., The Atomic Structure of a Metal Supported Vitreous Thin Silica Film, Angew. Chemie, Int. Ed. 51 (2012) 404. 4. L. Lichtenstein, M. Heyde, H. J. Freund, Crystalline Vitreous Interface in Two Dimensional Silica, Phys. Rev. Lett. 109 (2012) 106101.
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8.2
Nanoscale Characterization of the Thermal Conductivity of Supported Graphite Nanoplates, Graphene and Few layer Graphene
Mauro Tortello1, Samuele Colonna2, Julio Gomez3, Iwona Pasternak4, Wlodek Strupinski4, Fabrizio Giorgis1, Guido Saracco1, Renato S. Gonnelli1, Alberto Fina2 1. Dipartimento di Scienza Applicata e Tecnologia, Politecnico di Torino, 10129 Torino, Italy. 2. Dipartimento di Scienza Applicata e Tecnologia, Politecnico di Torino, 15121 Alessandria, Italy. 3. AVANZARE Innovacion Tecnologica S.L., 26370 Navarrete, Spain. 4. Institute of Electronic Materials Technology, 01 919 Warsaw, Poland.
Email: [email protected] Keywords: Graphene, Scanning Thermal Microscopy, SThM
Scanning Thermal Microscopy (SThM) [1,2] is a powerful technique for the thermal characterization and can reach a spatial resolution on the order of a few tens of nanometers while recording nanoscale topography at the same time. Here we show that [3] i) annealing in vacuum at 1700 °C for 1 h strongly reduces the amount of defects in reduced graphite oxide (RGO) nanoplates, as shown by Raman, XRD, XPS and TGA measurements. ii) As a consequence, their thermal conductivity considerably increases, as revealed by high resolution SThM results on individual RGO flakes supported by SiO2/Si. iii) This fact is more clearly observed when the RGO nanoplates are supported by a less conducting substrate (PET). iv) Lumped parameter models and finite element analysis are discussed in order to interpret the results and try to determine the thermal conductivity and the effect of the substrate. Moreover, SThM results are also presented for a case study of multilayer (1 to 4) CVD graphene [4] supported by different substrates, i.e. SiO2/Si, PET, Al2O3. We found that a) the thermal conduction of multilayer graphene supported by SiO2/Si improves with increasing number of layers. b) In the SThM maps, the thermal contrast observed between the supported graphene and the bare substrate changes depending on the thermal conductivity of the substrate itself.
References 1. A. Majumdar, Annu. Rev. Mater. Sci. 29, 505 (1999). 2. S. Gomes, A. Assy, P. O. Chapuis, Phys. Status Solidi A 212, 477 (2015). 3. M. Tortello et al., Carbon 109, 390 (2016). 4. I. Pasternak et al., AIP Advances 4, 097133 (2014).
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8.3
Material design strategies for BiCh2 based layered superconductors
Yoshikazu Mizuguchi Tokyo Metropolitan University
Email: [email protected] Keywords: new superconductor; BiCh2 based layered superconductor; local structure
In 2012, we have discovered new layered superconductors with BiS2 type conducting layers, such as Bi4O4S3 [1] and REO1 xFxBiS2 [2]. Since the layered crystal structure resembles to those of cuprates and Fe based superconductors, many researchers have explored new BiS2 based superconductors and the possibility of higher transition temperature (Tc) and unconventional nature of the superconductivity mechanisms in the system. To address the mechanisms of BiS2 based superconductivity, we have focused on the relationship between the crystal structure and superconducting properties. We revealed that, in the REOBiCh2 system (RE: rare earth; Ch: calcogen), the emergence of bulk superconductivity in BiS2 based compounds correlates with the in plane chemical pressure, which can be manipulated by systematic isovalent substitutions at the blocking and/or conducting layers [3,4]. In addition, the importance of the suppression of in plane local disorder has been proposed in the BiS2 xSex layers [5]. In this presentation, I will review the crystal structure and physical properties of the BiCh2 based compounds. Then, the material design strategies will be discussed on the basis of the latest results on local structure analysis and revealed intrinsic phase diagram.
References 1. Y. Mizuguchi et al., Phys. Rev. B 86, 220510(1 5) (2012). 2. Y. Mizuguchi et al., J. Phys. Soc. Jpn. 81, 114725(1 5) (2012). 3. Y. Mizuguchi et al., Sci. Rep. 5, 14968(1 8) (2015). 4. Y. Mizuguchi et al., Phys. Chem. Chem. Phys. 17, 22090 22096 (2015). 5. K. Nagasaka, Y. Mizuguchi et al., arXiv: 1701.07575.
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8.4
Enhanced thermoelectric performance in BiS2 based layered compound LaOBiS2 xSex
Yosuke Goto1, Atsuhiro Nishida1, Osuke Miura1, Chul Ho Lee2, Yoshikazu Mizuguchi1 1 Tokyo Metropolitan University, 1 1, Minami osawa, Hachioji, Japan. 2 National Institute of Advanced Industrial Science and Technology (AIST), 1 1 1, Umezono, Tsukuba, Ibaraki 305 8568 Japan
Email: [email protected] Keywords: new thermoelectric material; layered compound; BiS2 based compound
We have studied the thermoelectric properties of LaOBiS2 based compounds, which have drawn much attention as a new layered superconductor [1], because the layered structure and relatively narrow band gap are preferable for thermoelectric materials. With an aim to enhance dimensionless figure of merit (ZT), we have demonstrated systematic substitutions of S by Se, which should result in chemical pressure effects. We have investigated crystal structure and thermoelectric properties (electrical resistivity, Seebeck coefficient, and thermal conductivity) of LaOBiS2 xSex [2 4]. Crystal structure analysis clarified that the doped Se selectively occupy the in plane site. Then, with increasing Se concentration, the packing density of ions at the conducting plane is enhanced, which can be regarded as a positive in plane chemical pressure effect [3]. With increasing in plane chemical pressure, electrical resistivity largely decreased, while the absolute Seebeck coefficient exhibited large value [4]. From Hall measurements, we revealed that the low electrical conductivity was induced by the large enhancement of carrier mobility [4]. As a result, high ZT of 0.36 (at 650 K) was observed for x = 1 (LaOBiSSe) [5]. In this presentation, we discuss the origins of the enhancement of ZT in LaOBiS2 xSex in detail, and the recent advances on the exploration of new thermoelectric materials with BiS2 related structure.
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Figure 1: (a) Schematic image of the crystal structure of LaOBiS2. (b) Temperature dependences of dimensionless figure of merit ZT for LaOBiS2 xSex.
References 1. Y. Mizuguchi, J. Phys. Chem. Solids, 84, 34 48 (2015). 2. Y. Mizuguchi et al., J. Appl. Phys. 116, 163915 (2014). 3. Y. Mizuguchi, A. Nishida et al., J. Appl. Phys. 119, 155103 (2016). 4. A. Nishida et al., J. Phys. Soc. Jpn. 85, 074702 (2016). 5. A. Nishida et al., Appl. Phys. Express 8, 111801 (2015).
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9.1
Ag/F vs. Cu/O: powerful analogy with far reaching implications
Wojciech Grochala1*, Zoran Mazej2 1Centre of New Technologies, University of Warsaw, Zwirki i Wigury 93, 02089 Warsaw, Poland 2 Department of Inorganic Chemistry and Technology, Jožef Stefan Institute, Jamova 39, SI 1000 Ljubljana, Slovenia.
Email: [email protected] Keywords: electronic structure; hybridization; magnetic properties; superconductivity
The ongoing quest for quantum systems showing high temperature superconductivity and/or strong magnetic interactions seems nowadays to be largely serendipitous. Regretfully, physical theories describing these complex quantum phenomena do not offer a basis for steady rational material design or improvement of desired observables, since they introduce parameters which are difficult to be translated to language of synthetic chemists. Here I will briefly describe the 17 year lasting attempts to design a novel family of high TC superconductors using chemical intuition and the ramifications of the Molecular Orbital theory (Figure 1) translated from molecules to solids [1,2].
Figure 1: Ideographic comparison of Ag/F vs. Cu/O analogy within the framework of spin unpolarized MO theory applied for solids.
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The materials in focus are fluoride (F–) connections of Ag(2+) which are isoelectronic to undoped Cu(2+) oxides (i.e. both cation and anion have the same valence electron count). [3] Both families show many striking similarities, including but not limited to: structural features,[4] pronounced hybridization of metal/nonmetal valence states,[5] similar character of electronic bands, comparable energy scale for phonons,[2] as well as ultra strong magnetic superexchange, [6] – and all that despite the seemingly “ionic” character of chemical bonding in metal fluorides. The recent high level density functional theory calculations show that the magnetic superexchange constant, J, may reach over 300 meV in certain one dimensional silver(2+) fluorides at ambient (p,T) conditions, thus exceeding the corresponding record value of ~250 meV for analogous copper(2+) oxides.[7] The most recent experimental confirmation of giant superexchange constant will be presented.
References 1. W. Grochala, R. Hoffmann, J. Phys. Chem. A 104, 9740 (2000). DOI: 10.1021/jp0017745 2. W. Grochala, R. Hoffmann, Angew. Chem. Int. Ed. 40, 2742 (2001). DOI: 10.1002/1521 3773(20010803)40:15<2742::AID ANIE2742>3.0.CO;2 X 3. W. Grochala, Z. Mazej, Phil. Trans. A 373, 20140179 (2015). DOI: 10.1098/rsta.2014.0179 4. W. Grochala, Nature Mater. 5, 513 (2006). DOI: 10.1038/nmat1678 5. W. Grochala, R. G. Egdell, P. P. Edwards, Z. Mazej, B. Žemva, ChemPhysChem 4, 997 (2003). DOI: 10.1002/cphc.200300777 6. T. Jaroń, W. Grochala, Phys. Stat. Sol. RRL 2, 71 (2008). DOI: 10.1002/pssr.200701286 7. D. Kurzydłowski, W. Grochala, Angew. Chem. Int. Ed., submitted (2017).
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9.2
Exciton phonon complexes and giant exciton Fano resonances in Ta2NiSe5
T. I. Larkin 1, A. N. Yaresko 1, D. Pröpper 1, K. A. Kikoin 2, Y. F. Lu 3, T. Takayama 1, Y. L. Mathis 4, A. W. Rost 1,5, H. Takagi 1,3,5, B. Keimer 1 & A. V. Boris 1 1 Max Planck Institute for Solid State Research, Heisenbergstraße 1, 70569 Stuttgart, Germany 2 School of Physics and Astronomy, Tel Aviv University, 69978 Tel Aviv, Israel 3 Department of Physics, The University of Tokyo, Hongo, Tokyo 113 0033, Japan 4 Synchrotron Facility ANKA, Karlsruhe Institute of Technology, 76344 Eggenstein Leopoldshafen, Germany 5 Institute for Functional Materials and Quantum Technology, University of Stuttgart, Pfaffenwaldring 57, 70550 Stuttgart, Germany
Email: [email protected] Keywords: excitonic insulator, exciton phonon complexes, fano resonances
The excitonic insulator (EI) is a long conjectured electronic state of matter that may arise in narrow gap semiconductors or small overlap semimetals. Though several EI candidates have been studied by means of transport measurements or photoemission spectroscopy, unambiguous evidence of the EI state is so far lacking. Furthermore, excitons have not yet been directly observed in any EI candidate. In this study we employ spectroscopic ellipsometry to detect doublets of Fano resonances in the EI candidate Ta2NiSe5 [1] and the related Ta2NiS5. We develop a Green function based approach to model a coupling between discrete excitations of an excitonic nature and a broad continuum of single electron excitations, enabling us to extract the parameters of the Fano resonances. The spectral weight of the excitonic Fano resonances is found to be at a very large value of ~1 e /u.c. in Ta2NiSe5 and a more modest, but still appreciable 0.1 e /u.c. in Ta2NiS5. We interpret these large spectral weights in the framework of Rashba's theory for exciton phonon complexes [2]. This leads us to conclude that we are observing spatially extended complexes of excitons weakly bound to the self induced lattice distortions. The larger spectral weight of the excitonic resonances in Ta2NiSe5 suggests a weaker binding with larger spatial extent of the complex and corroborates the EI scenario in this material.
References 1. Phys. Rev. Lett. 103, 026402 (2009). 2. Soviet Physics Semiconductors 8, 807–816 (1975).
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9.3
Pressure induced superconductivity in Cr and Mn based materials
Jianlin Luo Institute of Physics, Chinese Academy of Sciences
Email: [email protected] Keywords: CrAs, MnP, new superconductors
Transition metal pnictides, CrAs and MnP, have been studied over fifty years ago due to the presence of interesting magnetic properties: CrAs forms a double helical magnetic structure below 270 K accompanied with a strong first order structural transition, while MnP first undergoes a ferromagnetic transition at 290 K and then adopts a similar double helical order below 50 K. Both compounds are correlated metals and exhibit distinct anomalies at these characteristic magnetic transitions. By application of high pressure, we recently observed superconductivity with a maximum superconducting transition temperature of Tc ~ 2 K and 1 K when their helimagnetic orders are suppressed under a critical pressure of Pc ~ 0.8 and 8 GPa for CrAs and MnP, respectively. Despite of a relatively low Tc, CrAs and MnP are respectively the first superconductor among the Cr and Mn based compounds in that the electronic density of states at Fermi energy are dominated by the Cr/Mn 3d electrons. In this talk, I will summarize the current progresses achieved about the superconductivity in CrAs and MnP. Work done in collaboration with Wei Wu, Jinguang Cheng, F. K. Lin and K. Matsubayashi, Y. Uwatoko.
References 1. W. Wu, J. G. Cheng, K. Matsubayashi, P. P. Kong, F. K. Lin, C. Q. Jin, N. L. Wang, Y. Uwatoko, and J. L. Luo, Nat. Comm. 5, 5508 (2014). 2. J. G. Cheng, K. Matsubayashi, W. Wu, J. P. Sun, F. K. Lin, J. L. Luo, and Y. Uwatoko, Phys. Rev. Lett. 114, 117001 (2015).
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9.4
Crystal structure and epitaxy of topological insulator films grown on Si and SrTiO3
Yeong Ah Soh1 1 Hanover, NH, USA
Email: * [email protected] Key words: topological insulator, crystal structure, epitaxy, capping.
New quantum materials called topological insulators have attracted considerable attention due to fascinating properties such as almost dissipationless surface transport and potential for “spintronic” applications. For electronic device research and applications it is required to fabricate low dimensional nanostructures. Therefore, growth of high quality thin films of topological insulators is essential and has been attempted using various methods. The surfaces of topological insulators are prone to oxidation and environmental doping by exposure to air resulting in degradation of the surface characteristics. One method used widely for the protection of the topological insulator surface is the deposition of a capping layer. Since not only the substrate, but also the capping layer determines the electrical properties of the films it is important to characterize the capping layer as well. It has been, in particular, reported that the capping layer hinders the occurrence of sensitive effects such as the quantum anomalous Hall effect [1]. In this talk, I will present comprehensive x ray diffraction studies of the crystal structure and epitaxy of thin films of the topological insulator Bi2Te3 grown on Si (1 1 1) [2] and the ferromagnetic topological insulator Crx(BiySb1 y)2 xTe3 grown on SrTiO3 (1 1 1) with and without a Te capping layer [3]. Our studies show that the films are single crystals with the crystal quality being substantially higher for the films grown on Si substrates than those grown on SrTiO3 substrates even though the most promising electrical transport data have been found for SrTiO3 substrates. Furthermore, we found that the Te capping layer grows epitaxially and the deposition of the capping layer does not degrade the crystallinity of the Crx(BiySb1 y)2 xTe3 thin film even though it hinders the observation of the anomalous quantum Hall effect.
References 1. “Experimental observation of the quantum anomalous Hall effect in a magnetic topological insulator”, Chang, C. Z. et al., Science 340, 167 170 (2013).
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2. “Crystal structure and epitaxy of Bi2Te3 films grown on Si”, Jihwey Park, Yeong Ah Soh, G. Aeppli, S. R. Bland, Xie Gang Zhu, Xi Chen, Qi Kun Xue, and Francois Grey, Applied Physics Letters 101, 221910 (2012) http://dx.doi.org/10.1063/1.4768259 3. “Crystallinity of tellurium capping and epitaxy of ferromagnetic topological insulator films on SrTiO3”, Jihwey Park, Yeong Ah Soh, Gabriel Aeppli, Xiao Feng, Yunbo Ou, Ke He, Qi Kun Xue, Scientific Reports 5,11595 (2015). http://dx.doi.org/10.1038/srep11595
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10.1
Elastic and Electronic Tuning of Magnetoresistance in MoTe2
Despina Louca1,*, J. Yang1, J. Liu1, G. W. Chern1 1University of Virginia, Department of Physics, 382 McCormick Road, Charlottesville, VA 22904, USA.
Email: [email protected] Keywords: tensile strain, electron cyclotron mass, anisotropy.
The transition metal dichalcogenide (TMD) semiconductors exhibit many versatile physical features and have become a new paradigm for optoelectronic applications [1 11], based on exfoliated single layer molecular structures [3 6]. Fueled by intense interest on new device concepts, TMDs provide a platform from which optoelectronic properties such as spin valley coupled physics and two dimensional valley excitons can be pursued [12]. They have a desirable optical band gap in the 1 2 eV energy range, important for visible and near infrared technologies. Manipulation of the band gap either by reducing the sample thickness down to a monolayer or applications of strain can lead to distinct changes in their physical characteristics. The observation of an extremely large magnetoresistance (MR) in the layered TMDs of WTe₂ and MoTe₂ has led to a surge of interest in this field [4]. The layered crystal structure consists of strong in plane covalent bonding and weaker van der Waals type interactions between planes [13]. MoTe₂ in particular [14] can exist in several crystal configurations that includes the high temperature 2H, the intermediate temperature 1T' and the low temperature Td structures. β MoTe₂ (1T') is metastable at room temperature and is metallic with a monoclinic (P2₁/m) structure [13 15]. Upon cooling from room temperature, an anomaly appears in the transport data around 240 K that has been linked to a first order structural transition from the 1T' of β MoTe₂ to the orthorhombic Td phase (Pmn2₁). The Td phase exhibits the extreme MR effect and the host of a Weyl semimetal state, a new state of matter in which collective excitations known as Weyl fermions may exist. It has been suggested that the band structure of MoTe₂ is highly sensitive even to small changes in the lattice constants either brought upon by strain or as a function of temperature. The anomalously large MR observed under high magnetic fields in MoTe₂ can be reversibly controlled under tensile strain. The MR is enhanced by as much as ∼ 30 % at low temperatures and high magnetic fields, when uniaxial strain is applied along the a crystallographic direction and reduced by the same amount when strain is applied along the b direction. The large in plane electronic anisotropy sets in at the transition from the 1T' monoclinic to the Td orthorhombic Weyl phase. Ab initio calculations of
65 Superstripes 2017, Ischia June 4 10, 2017 the electronic structure under strain show a comparable change in the electron cyclotron mass closely related to the MR under high magnetic field. The sensitivity of the cyclotron mass to tensile strain could have its origin to the presence of Weyl points between electron and hole pockets.
References 1. Q. H. Wang et al., Nat. Nanotechnol. 7, 699 (2012). 2. D. H. Keum et al., Nat. Phys. 11, 482 (2015). 3. M. Chhowalla et al., Nat. Chem. 5, 263 (2013). 4. B. Radisavljevic, A. Radenovic, J. Brivio, V. Giacometti, A. Kis, Nat. Nanotechnol. 6, 147 (2011). 5. M. N. Ali et al., Nature 514, 205 (2014). 6. S. Song et al., Nano Lett. 16, 188 (2016). 7. Y. Qi et al., Nat. Commun. 7, 11038 (2016). 8. X. Qian, J. Liu, L. Fu, J. Li, Science 80, 346 (2014). 9. M. Rifliková, R. Martoňák, E. Tosatti, Phys. Rev. B 90, 35108 (2014). 10. K. A. N. Duerloo et al., Nat. Commun. 5, 10451 (2014). 11. H. Zeng, J. Dai, W. Yao, D. Xiao, X. Cui, Nat. Nanotechnol. 7, 490 (2012). 12. K. S. Novoselov et al., Proc. Natl. Acad. Sci. U. S. A. 102, 10451 (2005). 13. B. E. Brown, Acta Cryst. 20, 268 (1966). 14. H. P. Hughes et al., J. Phys. C Solid State Phys. 11, L103 (1978). 15. R. Clarke, E. Marseglia. H. P. Hughes, Philos. Mag. B 38, 121 (1978).
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10.2
Entropia cupratesque cano… [A new model of the cuprate pseudogap]
R.S. Markiewicz, I.G. Buda, P. Mistark, C. Lane, and A. Bansil Northeastern University, 360 Huntington Ave., Boston MA 02459 USA.
Email: [email protected] Keywords: pseudogap, Mott Slater transition; bosonic entropy
We extend our earlier density functional theory + quasiparticle GW (DFT+QPGW) approach to correlated materials by incorporating vertex corrections via Moriya’s mode coupling theory[1]. We find[2] that the cuprate pseudogap can be understood as a regime of short range magnetic order caused by competition between many different density wave modes trying to soften at the same time. This ‘bosonic entropy’ effect is closely akin to McMillan’s phonon entropy effect in strongly coupled charge density wave systems[3], and similarly suppresses transition temperatures, leading to anomalously large values of 2 /kBTN, wher is the magnetic gap and TN the Neel temperature.
We find that the entropy can diverge at a crossover between commensurate and incommensurate magnetic order near (π,π) in the Brillouin zone, signaling a transition between Mott physics at (π,π) and Slater physics associated with Fermi surface nesting at an incommensurate wave vector. The driving force for (π,π) nesting is found to be Van Hove nesting, with a strong temperature dependence associated with Pauli unblocking. We find that cuprates differ in their degree of correlation, and by introducing a concept of reference families, we are able to tune between different band structures. While most cuprates fall on the Slater side of the transition, La2 xSrxCuO4 (LSCO) lies just on the Mott side. Remarkably, just at the transition there is an emergent spin liquid phase, which may play a role in the LSCO phase diagram.
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Figure 1: Left: At the commensurate incommensurate transition, the susceptibility has a very flat peak. Right: This corresponds to a very large entropy, measured by the susceptibility density of states, N , leading to anomalously small correlation lengths consistent with a spin liquid.
References 1. T. Moriya, Spin Fluctuations in Itinerant Electron Magnetism, (Springer, Berlin, 1985). 2. T. Das, R.S. Markiewicz, and A. Bansil, “Intermediate coupling model of the cuprates”, Advances in Physics 63, 151 266 (2014). 3. W.L. McMillan, “Microscopic model of charge density waves in 2H TaSe2”, Phys. Rev. B16, 643 (1977).
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10.3
Effects of a pressure induced topological Fermi surface transition on the order parameter of CaFe2As2
D. Daghero 1, R.S. Gonnelli 1, M. Tortello 1, G. A. Ummarino 1, Z. Bukowski 2, J. Karpinski 3, P. G. Reuvekamp 4, R. K. Kremer 4, G. Profeta 5, K. Suzuki 6, and K. Kuroki 6 1 Dipartimento di Scienza Applicata e Tecnologia, Politecnico di Torino, 10129 Italy 2 Polish Academy of Sciences, 50 950 Wrocław, Poland 3 Ecole Polytechnique Fédérale de Lausanne, CH 1015 Lausanne, Switzerland 4 Max Planck Institute for Solid State Research, Stuttgart, Germany 5 Dipartimento di Scienze Fisiche e Chimiche, Università dell’Aquila, L’Aquila, Italy 6 Department of Physics, Osaka University, Toyonaka, Osaka 560 0043, Japan
Email: [email protected] Keywords: Iron based superconductors, Lifshitz transition, poit cntact spectroscopy, order parameter symmetry
Iron based compounds (IBS) display a surprising variety of superconducting properties that seems to arise from the strong sensitivity of these systems to tiny details of the lattice structure. In this respect, systems that become superconducting under pressure, like CaFe2As2 [1,2,3] are of particular interest. Here we report on the first directional point contact Andreev reflection spectroscopy (PCARS) measurements on CaFe2As2 crystals under quasi hydrostatic pressure [4] and on the interpretation of the results using a 3D model for Andreev reflection combined with ab initio calculations of the Fermi surface (within the density functional theory) and of the order parameter symmetry (within a random phase approximation approach in a ten orbital model). This combined experimental/theoretical approach shows that, on the verge of the pressure induced structural transition between the orthorhombic and the collapsed tetragonal phase [4], that corresponds to a topological 2D 3D transition in the holelike Fermi surface sheet, i) a horizontal line node emerges in the relevant order parameter, ii) the critical temperature increases, iii) the amplitudes of the gaps increase even more, which suggests a considerable enhancement of the electron boson coupling.
References 1. M. S. Torikachvili, S. L. Bud’ko, N. Ni and P. Canfield, Phys Rev. Lett. 101, 057006 (2008). 2. T. Park, et al. J. Phys.: Condens. Matter 20, 322204 (2008). 3. K. Prokeš et al., Phys. Rev. B 81, 180506(R) (2010). 4. R.S. Gonnelli et al., Scientific Reports 6, 26394 (2016). 5. A. Sanna, G. Profeta, S. Massidda, and E. K. U. Gross, Phys. Rev. B 86, 014507 (2012).
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11.1
Ionic «ferroelectricity» and colossal dielectric constant: when a dielectric is not an insulator
Brigitte Leridon LPEM ESPCI Paris, PSL Research University, CNRS, Sorbonne Universités, UPMC, 10 rue Vauquelin, F 75005 Paris, France
Email: [email protected] Keywords: ferroelectricity; titanium oxide; colossal dielectric constant; superionic conductor.
Electrical conductivity and high dielectric constant are in principle self excluding, which makes the terms insulator and dielectric usually synonymous. This is certainly true when the electrical carriers are electrons, but not necessarily in a material where ions are extremely mobile, electronic conduction is negligible and the charge transfer at the interface is immaterial. In this case, although the material conducts charge internally, it may possess huge polarization and dielectric constant. The electrical properties of a newly synthetized two dimensional perovskite titanate are explored. This material is shown to exhibit ferroelectric like I V cycles together with extremely high (around 109, so well above state of the art) dielectric constant at low frequency. Detailed investigations of dielectric constant behavior allow to demonstrate that it is due to ion migration and accumulation that this material behaves like a giant dipole, exhibiting colossal ferroelectric like polarization (of the order of 0.1 C.cm 2). This material may therefore be considered as an «ionic ferroelectrics» or a strictly speaking a «ferro ionet» and is extremely promising in terms of applications.
Figure 1: Typical I V curves. Inset: polarization obtained from time integration of the current as function of voltage.
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References 1. B. Leridon, R. Federicci and S. Holé “Super condensateur à électrolyte perfectionné» FR 16 59322 patent (2016). 2. R. Federicci, et al., “Rb2Ti2O5−δ: A superionic conductor with colossal dielectric constant”, to be published.
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11.2
Simultaneous occurrence of multiferroism and short range magnetic order in DyFeO3
Wei Bao, Jinchen Wang, Juanjuan Liu, Jieming Sheng Renmin Univ. of China
Email: [email protected] Keywords: short range magnetic order, multiferroics
We report a combined neutron scattering and magnetization study on the multiferroic DyFeO3, which shows a very strong magnetoelectric effect [1]. Applying magnetic field along the c axis, the weak ferromagnetic order of the Fe ions is quickly recovered from a spin reorientation transition, and the long range antiferromagnetic order of Dy becomes a short range one. We found that the short range order concurs with the multiferroic phase and is responsible for its sizable hysteresis. OurH−Tphase diagram suggests that the strong magnetoelectric effect in DyFeO3 has to be understood with not only the weak ferromagnetism of Fe but also the short range antiferromagnetic order of Dy [2].
References 1. Y. Tokunaga, S. Iguchi, T. Arima, and Y. Tokura, Phys. Rev. Lett. 101, 097205 (2008). 2. Jinchen Wang et al., Phys. Rev. B 93, 140403(R) (2016).
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11.3
Random Electric Field Instabilities of Relaxor Ferroelectrics
G. G. Guzman Verri U of Costa Rica and Argonne Natl. Lab
Email: gguzman [email protected] Keywords: relaxor ferroelectrics; theory; random electric fields
Relaxor ferroelectrics are complex oxide materials which are rather unique to study the effects of random field disorder on phase transitions. Unlike the mostly studied random field magnets where the order parameter is uniaxial or isotropic, the polarization of typical relaxors lives in a cubic environment. Moreover, the exchange interaction that drives the magnetic transition is short ranged and isotropic, while the relevant interaction in ferroelectrics is the highly anisotropic and long ranged dipolar force. This puts relaxors in a different universality class from that of disordered magnets making the standard model of random field disorder inadequate to describe their unusual properties. Here, we study the effects of cubic random electric fields on the lattice instabilities that lead to the ferroelectric transition and show that, within a microscopic model and a statistical mechanical solution, even weak compositional disorder can prohibit the development of long range order and that a random field state with anisotropic and power law correlations of polarization emerges from the combined effect of dipole forces and their inherent charge disorder. We compare and reproduce several key experimental observations in the well studied relaxor PbMg1/3Nb2/3O3 PbTiO3. [1]
References 1. J. R Arce Gamboa and G. G. Guzman Verri, arXiv: 1612.07667
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11.4
Multiple order parameters and their domain control in magnetoelectric multiferroics
Tsuyoshi Kimura Osaka University
Email: [email protected] u.ac.jp Keywords: magnetoelectric, multiferroics, noncollinear magnetic order
One of the most important concepts in condensed matter physics is the spontaneous breakdown of symmetry in a solid, which bears the ordered phase and domains in its consequence. In magnetoelectric multiferroics, multiple order parameters coexist in a system, sometimes couple with each other, and exhibit nontrivial crossed phenomena. In this presentation, we deal with magnetoelectric multiferroics in which a symmetry breaking due to the orderings of various order parameters such as electric dipole, magnetic dipole, and magnetic quadrupole moments as well as chirality originating from these multipole moments. We show our recent research activity on exploration for new magnetoelectric multiferroics and manipulations of their multiple order parameters as well as domains.
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12.1
High Pressure – Low Temperature Set up for Infrared Spectroscopy of H3S at the AILES Beamline
B. Langerome1,*, F. Capitani1, J. B. Brubach1, A. Drozdov2, M.I. Eremets2, E. J. Nicol3, J. P. Carbotte4,5, T. Timusk4,5 and P. Roy1 1 Synchrotron SOLEIL, AILES Beamline, Saint Aubin, 91190, France 2 Biogeochemistry Department, Max Planck Institute for Chemistry, PO Box 3060, 55020 Mainz, Germany 3 Department of Physics, University of Guelph, Guelph, N1G 2W1 ON Canada 4 Department of Physics and Astronomy, McMaster University, Hamilton, ON L8S 4M1, Canada 5 The Canadian Institute for Advanced Research, Toronto, ON M5G 1Z8 Canada
Email: benjamin.langerome@synchrotron soleil.fr Keywords: high pressure – low temperature, infrared reflectance, synchrotron radiation, H3S
In solid state physics, it is important to explore the phase diagram of materials through a fine control of physical parameters such as pressure and temperature. Such control when combined with spectroscopic measurements provides rich information on the fundamental properties of a system. We described here an optical setup which has yielded the first spectroscopic data on the superconducting phase in sulfur hydride [1]. The discovery of superconductivity in H3S with a record transition temperature above 200K under pressure of 150GPa is a breakthrough for the physicist community. Although electric and magnetic measurements clearly demonstrate the presence of superconductivity, the mechanism at the origin still remains to be determined. This spectroscopic study, done at the AILES beamline of the synchrotron SOLEIL [2], demonstrates that superconductivity in H3S is driven by the electron–phonon interaction making this material a conventional BCS superconductor. Infrared measurements of the H3S system are challenging for the following reasons: • Size of the sample is 50 µm or less • Expected spectroscopic features represent less than 4% of total intensity • Measurements have to be performed in the reflectivity mode with a diamond anvil cell. • Temperature of the sample has to be controlled from RT down to 80K To overcome these technical problems, we exploited the high brilliance synchrotron radiation source, which allows measurements in a wide spectral range (60 – 600 meV), even on such tiny samples. The reflectance measurements were carried out with a setup specifically designed for infrared spectroscopy on samples at high pressure and low temperature [3].
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The samples (synthetized in high pressure laboratory in Mainz) were placed in a diamond anvil cell, which itself was in thermal contact with the cold tip of a helium flow cryostat. A camera was used to view the radiation beam spot on the sample and to maintain optimal alignment. The reproducibility of the signal from one measurement to another was better than 1%. In order to extract superconducting features, data are presented as ratio of the signal from the sample in superconducting state (~150K) to that of the normal metallic state (~220K). In addition, H3S phonons were observed at 300 K with the use of the NaCl gasket or the front surface of the diamond anvil as reference surface. This presentation will provide the experimental details complementing the talk about the optical properties of H3S given by Pr. Timusk in this conference.
Left panel: Schematic view of the optical HPLT setup. The right chamber is a part of the interferometer while the left chamber contains optics designed for reflectivity measurements. Right panel: Camera picture of the visible synchrotron radiation focused on and reflected from the sample (orange spot in the center). The dashed circles correspond approximately to the spot size in the mid infrared. A yellow light passing through the NaCl gasket allows to visualize the cell
References 1. A. Drozdov, M. Eremets, I. Troyan, V. Ksenofontov and S. Shylin. Nature 525, 73 76 (2015). 2. P. Roy, M. Rouzières, Z. Qi and O. Chubar. Infrared Physics and Technology 49, 139 146 (2006). 3. A. Voute, M. Deutsch, A. Kalinko, F. Alabarse, J. B. Brubach, F. Capitani, M. Chapuis, V. Ta Phuoc, R. Sopracase and P. Roy. Vibrational Spectroscopy 86, 17 23 (2016).
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12.2
Preparation of new metal intercalated FeSe superconductors and their pressure dependence
Takahiro Terao, Xiao Miao. Hidenori Goto, Takahumi Miyazaki and Yoshihiro kubozono
Email: [email protected] u.ac.jp Keywords: FeSe, pressure, superconductivity, structure, XRD
A pressure driven superconducting phase has recently attracted much attention from viewpoint of pursuing new materials with high superconducting transition temperature (Tc). Application of pressure higher than 10 GPa for (NH3)yCsxFeSe produced the high Tc superconducting phase, Tc of which reached ~50 K at 21 GPa [1]. Such pressure driven high Tc phases were also found in other metal intercalated FeSe compounds [2]. In this study, we investigated the superconducting properties of (NH3)yNaxFeSe under high pressure. This material provides two different superconducting phases (Tc = 46 K and Tc = 33 – 36 K at 0 GPa) depending on x; the 46 K or 33 36 K phase is independently realized at ≥ 0.8 or ≤ 0.4. These phases are termed ‘high Tc phase’ and ‘low Tc phase’. Figure 1 shows the pressure dependence of Tc in the low Tc phase (Tc = 36 K) of (NH3)yNaxFeSe, suggesting a presence of two distiguished superconducting phases (SC I and SC II). Contrary to the pressure dependence of Tc in (NH3)yCsxFeSe, the maximum Tc value achived in the high pressure range (≥ 10 GPa) was at most 12 K at 17.5 GPa (see Figure 1). The reason why the pressure driven high Tc phase did not emerge in the low Tc phase of (NH3)yNaxFeSe is still unclear. The study on pressure dependence of Tc in the high Tc phase of (NH3)yNaxFeSe is now in progress. The powder X ray diffraction (XRD) pattern was measured for both phases under pressure of 0 – 30 GPa, and the monotonical shrinkage of lattice was observed for both phases. In the conference, more detailed study on superconductivity and structure under high pressure will be reported.
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Figure 1: Pressure dependence of Tc in the low Tc phase.
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12.3
Resonant Inelastic X ray Scattering on Iron Pnictides
J. Pelliciari1,2*, Y. Huang1, 3, K. Ishii3, M. Dantz1, V. Strocov1, X. Wang3, L. Xing3, C. Q. Jin3, X. Lu1, D. McNally1, T. Watashige5, S. Kasahara5, H. S. Jeevan6, P. Gegenwart6, Y. Matsuda5, T. Shibauchi5,7, T. Das8, and T. Schmitt1 1 Swiss Light Source, Paul Scherrer Institut, Switzerland 2 Massachusetts Institute of Technology, Cambridge, USA 3 Beijing National Lab for Condensed Matter Physics, Institute of Physics, China 4 Spring 8, Japan Atomic Energy Agency, Japan 5 Department of Physics, Kyoto University, Japan 6 Center for Electronic Correlations and Magnetism, University of Augsburg, Germany 7 Department of Advanced Materials Science, Tokyo University, Japan 8 Department of Physics, Indian Institute of Science, India
Email: [email protected] Keywords: iron pnictides, magnetism, scattering, unconventional superconductivity
Superconductivity in iron pnictides was discovered in 2008 [1], and since then, a lot of effort has been devoted in order to explain their unconventionality. As in other high temperature superconductors (HTSCs), magnetism and superconductivity (SC) exhibit proximity, competition and / or coexistence along the phase diagram, indicating strong connections between them [2 4]. In this context, the experimental characterization of static and dynamic magnetism is of vital importance in constraining advanced theoretical models. I will describe Resonant Inelastic X Ray Scattering (RIXS) experiments on NaFe1 xCoxAs. RIXS has proven to be a powerful spectroscopic tool for probing high energy spin fluctuations in HTSCs [5 7]. The NaFe1 xCoxAs series of pnictide superconductors contrasts with the most studied BaFe2 xCoxAs2 because of their much lower magnetic moment (ca 0.1 µB for NaFeAs vs. ca 1.3 µB for BaFe2As2) even though TC of Co optimal doped materials is similar (21 K vs. 22 K) [2,4]. I will present a high resolution Fe L3 RIXS study of parent and doped NaFe1 xCoxAs spanning optimal and overdoped regimes. Spectral shape decomposition reveals the persistence of broad dispersive magnetic excitations for all doping levels. In contrast to previous RIXS experiments on hole doped BaFe2As2 compounds [6], the energy of such modes is not strongly affected by doping and the magnetic weight per iron atom of magnons / paramagnons remains constant. However, renormalized per formula unit the magnetic weight slightly decreases with doping. We argue that cobalt doping is mainly tuning the electronic correlations. In the second part of my talk, I will discuss the work carried out on the BaFe2(As1 xPx)2 series. The BaFe2(As1 xPx)2 series is an interesting case because SC appears
79 Superstripes 2017, Ischia June 4 10, 2017 with isovalent doping without changing the number of carriers [2,4]. I present a combined Fe L3 RIXS and Kβ X rays emission spectroscopy (XES) study of parent and doped BaFe2(As1 xPx)2 spanning a large portion of the phase diagram. RIXS measurements reveal the persistence of broad dispersive magnetic excitations for all doping levels. Remarkably, the energy of such modes is strongly hardened by doping contrasting with the case of hole doped BaFe2As2 [6]. Moreover their spectral weight is conserved along the phase diagram. XES experiments show a gradual quenching of the local magnetic moment, intriguing if compared to the behavior of spin correlations. Employing intermediate coupling calculations (DFT GW), we link the unconventional evolution of magnetism to the shift from 2 to 3 dimensional electronic structure of the system, hand in hand with the warping of the Fermi surface. This speaks for a picture where unconventional SC emerges from a balance of local and correlated magnetism, further demonstrating that magnetism is not detrimental for SC.
References 1. Y. Kamihara et al, J. Am. Chem. Soc. 130, 3296 (2008). 2. G. R. Stewart, Rev. Mod. Phy., 83, 1589 (2011). 3. D. J. Scalapino, Rev. Mod. Phy., 84, 1383 (2012). 4. D. C. Johnston, Advances in Physics Vol. 59, No. 6, 803 (2010). 5. L. J. P. Ament et al, Rev. Mod. Phys. 83, 705 (2011). 6. K. J. Zhou et al, Nat. Comm., 4, 1470 (2013). 7. M. P. M. Dean et al, Nat. Mat. 12, 1019 (2013).
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12.4
Hund’s correlated metals
Luca de’ Medici Ecole Supérieure de Physique et Chimie Industrielles de la Ville de Paris (ESPCI)
Email: [email protected]
Metallic phases with Hund’s correlations (“Hund’s metals”) are presently the focus of intensive research, in particular in relation to unconventional Fe based superconductors. Recent experiments validate this emerging theoretical picture of the normal phase with evidences of large local paramagnetic moments, large and orbital selective mass renormalizations and orbitally selective pairing in the superconducting state. Further theoretical insight shows that Hund’s coupling can also alter the quasiparticle interactions in some regimes, thus potentially renormalizing the pairing strength. This is shown to correlate with experimental high Tc superconductivity in Fe based pnictides and FeSe.
References 1. L. de’ Medici, Phys. Rev. Lett. 118, 167003 (2017) 2. P. Villar Arribi and L. de’ Medici, unpublished (2017)
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13.1
Macroscopic character of composite high temperature superconducting wires
Boris Spivak University of Washington
Email: [email protected]
“d wave” symmetry of the superconducting order in the cuprate high temperature superconductors is a well established fact, and one which identifies them as “unconventional.” However, in macroscopic contexts – including many potential applications (i.e. superconducting “wires”) – the material is a composite of randomly oriented superconducting grains in a metallic matrix, in which Josephson coupling between grains mediates the onset of long range phase coherence. Here, we analyze the physics at length scales large compared to the size of such grains, and in particular the macroscopic character of the long range order that emerges. While XY glass order and macroscopic d wave superconductivity may be possible, we show that under many circumstances – especially when the d wave superconducting grains are embedded in a metallic matrix – the most likely order has global s wave symmetry. We also show that magnetic field may enhance superfluid density in the wires, and more generally, in composite D wave superconductors.
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13.2
Effect of a skin deep surface zone on the formation of a two dimensional electron gas at a semiconductor surface
Jacek J. Kolodziej (1), Natalia Olszowska (1), Jakub Lis (1), Piotr Ciochon (1), Lukasz Walczak (2), Enrique G. Michel (2) (1) Faculty of Physics, Astronomy, and Applied Computer Science, Jagiellonian University. (2) Departmento de Fısica de la Materia Condensada and Condensed Matter Physics Center Universidad Autonoma de Madrid
Email: [email protected] Keywords: 2DEG, two dimensional electron gas, semiconductor surface, angle resolved photoemission
Two dimensional electron gases (2DEGs) at surfaces and interfaces of semiconductors are described straightforwardly with a one dimensional (1D) self consistent Poisson Schroedinger scheme. However, their band energies have not been modeled correctly in this way. Using angle resolved photoelectron spectroscopy we study the band structures of 2DEGs formed at sulfur passivated surfaces of InAs(001) as a model system. Electronic properties of these surfaces are tuned by changing the S coverage, while keeping a high quality interface, free of defects and with a constant doping density. In contrast to earlier studies we show that the Poisson Schroedinger scheme predicts the 2DEG band energies correctly but it is indispensable to take into account the existence of the physical surface. The surface substantially influences the band energies beyond simple electrostatics, by setting nontrivial boundary conditions for 2DEG wave functions.
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13.3
Functional Renormalization Group Analysis on Electron Nematic State and Charge Density Wave State in Cuprate Superconductors
Masahisa Tsuchiizu Department of Physics, Nagoya University
Email: [email protected] u.ac.jp Keywords: electron nematic state; charge density wave state; cuprate superconductors
The discovery of the charge density wave state in the cuprate superconductors has activated intensive theoretical studies for the pseudogap states. To elucidate charge instabilities in the cuprate superconductors, we analyze the charge susceptibilities theoretically by utilizing the improved functional renormalization group method [1,2] to the d p Hubbard model [3]. We reveal that the charge fluctuation of the uniform (q = 0) modulation on the px and py orbitals with antiphase (d symmetry) form factor develops owing to the strong spin fluctuations. The spontaneous symmetry breaking with respect to the occupation of px and py orbitals with the wavevector q = 0 accounts for the recently observed electronic nematic phase transition in cuprates. In addition, we find that the p orbital density wave instability at the wavevectors Q ~ (0.3 pi, 0) and (0, 0.3 pi) also develops in the strong spin fluctuation region, and is further enhanced when the q=0 nematic ordering is present. We predict that the main driving force of these charge fluctuations is the Aslamazov Larkin vertex correction that becomes singular near the magnetic quantum critical point.
This work has been done in collaboration with Dr. H. Kontani and Dr. Y. Yamakawa.
References 1. M. Tsuchiizu, Y. Ohno, S. Onari, and H. Kontani, Phys. Rev. Lett. 111, 057003 (2013). 2. M. Tsuchiizu, Y. Yamakawa, S. Onari, Y. Ohno, and H. Kontani, Phys. Rev. B 91, 155103 (2015). 3. M. Tsuchiizu, Y. Yamakawa, and H. Kontani, Phys. Rev. B 93, 155148 (2016).
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14.2
Spontaneous breakdown of time reversal symmetry induced by thermal fluctuations
Johan Carlström, Egor Babaev University of Massachusetts
Email: [email protected] Keywords: Frustrated superconductivity, broken time reversal symmetry
In systems with broken U(1) symmetry, such as superfluids, superconductors or magnets, the symmetry restoration is driven by proliferation of topological defects in the form of vortex loops. Here we discuss that in certain systems the proliferation of topological defects can, by contrast, lead to the breakdown of an additional symmetry. As a particular example we demonstrate that this effect should take place in s+is superconductors, which are widely discussed in connection with the Iron based materials. In these systems a vortex excitation can create a "bubble" of fluctuating Z2 order parameter. Thermal excitation of vortices then leads to breakdown of time reversal symmetry when the temperature is increased.
References Phys. Rev. B 91 140504(R) (Rapid Communication) (2015). Phys. Rev. B 84, 134518 (2011).
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14.3
Constraints on the total coupling strength to low energy bosons in iron based superconductors
Stefan Ludwig Drechsler1, S. Borisenko1, H. Rosner2, V. Grinenko 1,2, J. Tomczak4, and S. Johnston4 1 Leibniz Inst. f. Solid State and Materials Research IFW Dresden, D 01169 Dresden, Helmholtz. Str. 20, Germany 2 MPI for Chem. Phys. of Solids, Dresden, Germany 3 Dpmt. of Physics. TU Dresden, Dresden Germany 4 Vienna University of Technology, Wien, Austria 5 Dpmt. of Physics and Astron.omy, University of Tennesee, Knoxville 37996 USA
Email: s.l.drechsleri@ifw dresden.de Keywords: mass renormalization, band shifts, VAN HOVE singularities, pairing strength.
Although the Fe based superconductors (FeSC) were discovered ten years ago, there is still no consensus on the microscopic pairing mechanism(s) and main interactions involved. Also a consistent interpretation of their normal state pro perties is still lacking. Especially the strength of the el el interaction and correla tion effects are under debate. Here, we examine several materials and illustrate various problems and concepts that are generic for all FeSC. Based on empirical observations and qualitative insight from DFT, we show that the super conduc ting (SC) and normal state properties of the FeSC can be described semi quantitatively within multiband MIGDAL ELIASHBERG theory. We account for the large high energy mass renormalization (MR) phenomenologically and a mode rate low energy bosonic MR, in accord with constraints provided by thermodyna mic, optical, and ARPES data. Then, all FeSCs with Tc < 55~K, studied so far, are found to belong to an intermediate coupling regime at odds with strong coup ling suggested in the early period of the FeSC history. Support of SC by intraband el ph or el orbital fluctuations couplings [11 and phonon anomalies detected by point contact [2] and EXAFS [3] measurements are briefly addressed, too. We discuss band shifts [4] as counter parts of the MR measured conveniently by the positions of VAN HOVE singularities (VHS), and the nature of a suggested quantum critical point (QCP) [5] in the h overdoped systems AFe2As2 (A=K, Rb, Cs). Using high precision full relativistic GGA calculations for the total DOS at EF,, we arrive at a milder MR for Cs122 and the same MR for K122 and Rb122 at variance with other studies. The importance of spin orbit coupling is supported by GW calculations [4]. From the calculated mass anisotropies of all Fermi surface sheets, only the ε pocket near the corner of the BZ is compatible with the observed anisotropy of the upper critical field Hc2 [6],
86 Superstripes 2017, Ischia June 4 10, 2017 pointing to its dominant role in the SC of these three systems. At high fields only that band survives as evidenced by a single band elliptical angular mass anisotropy [7]. Finally, a general doping phase diagram shown in Fig. 1 is proposed. The QCP slightly be low 0.5 hole doping is ascribed to the vicinity of an orthorhombic stripe phase triggered by the dxz /dyz derived VAN HOVE singularity close to EF (at 14.5 meV for KFe2As2 (K122 ) according to ARPES) in qualitative accord with DMFT and GW calculations and 75As NMR data [7]. Its puzzling absence in a STT study for CsFe2As2 [8] is ascribed to critical stripe fluctuation causing a local splitting of the tetragonal symmetry and yielding an additional MR seen in the large SOMMERFELD constant γ, but being detrimental for dx2 y2 pairing in contrast to Sr2RuO4 where the VHS approaching EF strengthens also the SC pairing [9]. Here, it enhances the MR, only, detrimentally for SC and explains the lowest Tc.
Figure 1: Suggested Fe pnictides phase diagram. Blue (red): magnetic (SC) regions, resp.,. Phase I a combined charge, orbital, and spin ordered phase near the QCP responsible for the non Fermi liquid in Cs122 [7]. Yellow line: isovalent/no doping for such systems as Li(Na)FeAs, P doped Ba(Sr) 122 and bulk FeSe where the competing magnetic SDW magnetic stripe phase is absent or strongly suppressed. Phhase II observed but not yet characterized experimentally. The hypothetical SDW phase around Fe+ is our suggestion. Bright (dark red) regions: 122 and H doped La 1111 (under pressure) [10] FeSC , respectively.
References 1. S. Johnston, M. Abdel Hafiez, L. Harnagea, et al., PRB 89, 134507 (2014). 2. V. Ivanov, A. Ivanov, et al. J. Supercond. Nov. Mat. 29, 3035 (20016). 3. Y. Naidyuk, O. Kvitnitskaya, N. Gamayunova et al , PRB 90, 094505 (2014). 4. J. Tomczak, M. van Schilfgaarde, et al. Phys. Rev. Lett. 109, 237010 (2012).
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5. F. Eilers, K. Grube, D. Zocco, et al., Phys. Rev. Lett. 116, 237003 (2016). 6. F. Eilers, PhD, Thesis (2014): S. Khim, phys. stat. s.( b) 254, 1600214 (2016). 7. T. Terashima, M. Kimata, et al, J. Phys. Soc. Jpn. 78, 060504 (2009). 8. Z. T. Zhang, D. Dmytrieva, S. Molatta, et al., arXiv:1703.00780 (2017). 9. H. Yang, J. Xing, Z. Du, X.Yang, H. Lin, et al., PRB 93, 224516 (2016). 10. A. Stepke, L. Zhao, M.E. Barber et al., Science 355 (6321) eaaf9398 (2017). 11. N. Kawaguchi, Fujiwara, S. Iimura, et al. PRB 94, 161104 (2016)
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14.4
Multiband Eliashberg approach – a way to the realistic description of iron based superconductors
Dmitri Efremov1, Micha Benjamin Schilling2, Andreas Baumgartner2, Boris Gorshunov2,4,5, Elena Zhukova2,4,5, Valery Dravin6, Kiril Mitsen6, Kazumasa Iida1,3, Oleg Dolgov6,7, Martin Dressel2, Sina Zapf2 1 IFW Dresden, Institute for Solid State Research, D 01171 Dresden, Germany 2 Phylikashches Institut, Universität Stuttgart, Pfaffenwaldring 57, 70569 Stuttgart, Germany 3 Department of Crystalline Materials Science, Graduate School of Engineering, Nagoya University, Nagoya 464 8603, Japan 4 Moscow Institute of Physics and Technology (State University), 141700, Dolgoprudny, Moscow Region, Russia 5 P.N. Lebedev Physical Institute, Moscow, 119991 Russia
Email: d.efremov@ifw dresden.de Keywords: multiband superconductivity, iron based superconductors, Eliashberg theory
Since the discovery of the Fe based superconductors (FeSC) a lot of efforts has been applied to elucidate the microscopic mechanism behind cooper pairing and the symmetry of the order parameter. Here we propose an experimental approach to investigate the order parameter symmetry of unconventional multiband superconductors, which is based on a disorder induced change from sign reversed (s±) to sign preserved (s++) symmetry [1,2]. We present an investigation of a Ba(Fe0.9Co0.1)2As2 thin film by THz spectroscopy and stepwise proton irradiation [3]. With increase of the irradiation, the low energy superconducting gap first vanishes but recovers at higher irradiation doses. At the same time, the decrease of the superfluid density with disorder comes to a halt. The behavior is explained by the change from sign reversed (s±) to sign preserved (s++) symmetry and consequently by s± symmetry in the pristine sample.
References 1. Efremov, D.V.; Korshunov, M. M; Dolgov, O.V.; Golubov, A.A.; Hirschfeld, PJ, Phys Rev B, 84, 180512 (2011). 2. Efremov, D. V.; Golubov, A. A.; Dolgov, O. V., NJP, 15,013002 (2013). 3. M. B. Schilling, A. Baumgartner, B. Gorshunov, E. S. Zhukova, V. A. Dravin, K. V. Mitsen, D. V. Efremov, O. V. Dolgov, K. Iida, M. Dressel, and S. Zapf, Phys. Rev. B 93, 174515 (2016).
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15.1
Crossover induced spin fluctuation and electron pairing in strongly correlated electrons
Takashi Yanagisawa National Institute of Advanced Industrial Science and Technology
Email: t [email protected] Keywords: strong correlation; mechanism of superconductivity; crossover; spin fluctuation; Hubbard model; d p model
The mechanism of high temperature superconductivity has been studied intensively since the discovery of cuprate high temperature superconductors. The electron correlation plays an important role in cup rate superconductors because parent compounds without doped carriers are insulators. It is important to clarify the phase diagram of electronic states in the CuO2 plane. The ground state of the two dimensional single band Hubbard model and three band d p model is investigated by adopting improved wave functions that take into account intersite electron correlation beyond the Gutzwiller ansatz. The ground state energy is lowered considerably, which gives the best estimate of the ground state energy for the two dimensional Hubbard model. We argue that there is a crossover from weakly to strongly correlated regions as the on site Coulomb repulsion U increases when holes are doped. The antiferromagnetic (AF) correlation function increases as U increases in weakly correlated region, and has a peak at the intermediate value of U being of the order of the bandwidth. The large U, greater than the bandwidth, suppresses the AF correlation to lower the ground state energy, by increasing the kinetic energy gain. Large spin and charge correlations are induced in the strongly correlated region. This results in electron pairing and would lead to high temperature superconductivity. The conventional spin fluctuation in weakly correlated region should be distinguished from that in strongly correlated region. It is just the spin fluctuation in strongly correlated region that would induce high temperature superconductivity.
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Superconducting condensation energy as a function of the gap function for dp = εp−εd = 2, 4, 8 in units of tdp for the d p model. Numerical calculations were carried out on 8x8 lattice with 76 holes. The band parameters are tpp = 0.4, Ud = 10 and Up = 0.
References 1. T. Yanagisawa, J. Phys. Soc. Jpn. 85, 114707 (2016). 2. T. Yanagisawa, S. Koike and K. Yamaji, J. Phys. Soc. Jpn. 67, 3867 (1998). 3. T. Yanagisawa and M. Miyazaki, EPL 107, 27004 (2014). 4. T. Yanagisawa, New J. Phys. 15, 033012 (2013). 5. K. Yamaji, T. Yanagisawa, T. Nakanishi and S. Koike, Physica C304, 225 (1998). 6. T. Yanagisawa, S. Koike and K. Yamajji, Phys. Rev. B64, 184509 (2001).
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15.2
Drag Effect in Bilayer Systems of Dipolar Bosons and Fermions
Bilal Tanatar1,* 1 Department of Physics, Bilkent University, Bilkent, Ankara, 06800, Turkey.
Email: [email protected] Keywords: drag effect, dipolar gases.
We consider two parallel layers of two dimensional, ultracold spin polarized dipolar Fermi or dipolar Bose gases, without any tunneling between the layers. The effective interactions describing screening and correlation effects between the dipoles in a single layer (intra layer) and across the layers (inter layer) are modeled within the Hubbard approximation. We calculate the rate of momentum transfer between the layers when the gas in one layer has a steady flow. The momentum transfer induces a steady flow in the second layer which is assumed initially at rest. This is the drag effect familiar from double layer semiconductor and graphene structures. Our calculations show that the momentum relaxation time has temperature dependence similar to that in layers with charged particles and and it is enhanced by the contributions from the collective modes of the bilayer system.
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15.3
Raman of YBCO out of equilibrium
Donato Farina1, G. De Filippis2 and V. Cataudella2 1 Scuola Normale Superiore, Piazza dei Cavalieri 7, 56126, Pisa, Italy. 2 SPIN CNR and Dip. di Scienze Fisiche Università di Napoli Federico II I 80126 Napoli, Italy
Email: [email protected] Key words: Cuprates; Magnetism; Raman scattering; non equilibrium; electron phonon interaction.
It is widely accepted that the electronic correlations play an important role in mediating Cooper pairing in high critical temperature superconducting cuprates [1] . For this reason the accurate characterization of collective electronic excitations in these materials assumes crucial importance. We studied numerically electronic Raman scattering on insulating YBCO in B1g symmetry the most sensitive configuration to the electronic excitations showing a resonant peak at 2900 cm 1, originated by two magnon bound states [2]. Our analysis is based on the exact diagonalization of the Hubbard model of small lattices [3] both at thermal equilibrium [4,5] and out of equilibrium [6] to simulate a pump and probe experiment. The comparison with experimental data for half filled YBCO and predictions on the effect of hole doping will be discussed together with the effects of electron phonon interaction.
References 1. Keimer, B., et al. "From quantum matter to high temperature superconductivity in copper oxides." Nature 518.7538 (2015): 179 186. 2. Blumberg, G., et al. "Resonant two magnon Raman scattering in cuprate antiferromagnetic insulators." Physical Review B 53.18 (1996): R11930. 3. Dagotto, Elbio, "Strongly correlated electronic systems with one hole: Dynamical properties." Rev. Mod. Phys 66 (1994): 763. 4. Shastry, B. Sriram, and Boris I. Shraiman. "Theory of Raman scattering in Mott Hubbard systems." Phys. Rev. Lett. B 65 (1990): 1068. 5. Thomas P. Devereaux and Rudi Hackl, “Inelastic light scattering from correlated electrons”, Rev. Mod. Phys. 79 (2007):175. 6. G. De Filippis, et al., “Quantum Dynamics of the Hubbard Holstein Model in Equilibrium and Nonequilibrium: Application to Pump Probe Phenomena”, Phys. Rev. Lett. 109 (2012): 176402
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16.1
A Possible Paradigm Shift in the Search for Higher Tc
Paul C. W. Chu,1,2 1 Department of Physics and Texas Center for Superconductivity, University of Houston, Houston, Texas 77204 5002, USA 2 Lawrence Berkeley National Laboratory, 1 Cyclotron Road, Berkeley, California 94720, USA.
Email: [email protected] Keywords: cuprates, iron based superconductors, interfacial superconductivity.
In the last 30 years, great progress has been made in all areas of high temperature superconductivity (HTS) research and development from raising the transition temperature Tc, discovering new HTS compounds, and developing theoretical models of HTS, to fabricating HTS prototype devices. For example, the Tc has been increased to 134 K in the stable cuprate HgBa2Ca2Cu3Ox at ambient by the ETH group and 164 K at 30 GPa achieved by the Houston group in 1993 and to 203 K in the unstable H3S above 200 GPa by Eremets et al. in 2015; more than 200 cuprate compounds stable at ambient and four superconducting hydrides under ultrahigh pressures have been found; numerous theoretical models have been developed; and many HTS prototype devices have been tested to display superior performance to that of their non superconducting counterparts. However, several questions concerning the occurrence of HTS remain, for example: 1) Why do all Tcs above 77 K occur in cuprates until very recently? 2) Are the strong electron correlation and the two dimensional feature characteristic of HTS cuprates necessary and sufficient for high Tc as previously suggested by many? 3) What is the role of interfaces in the enhancement of Tc? 4) Will there be a paradigm shift needed for our understanding of high temperature superconductivity and for the search for higher Tc, especially in view of the recently reported Tc of 203 K? A brief review of recent experimental results relevant to the above questions will be presented and discussed.
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16.2
Multiple component Fermi surfaces of high Tc cuprates revealed by ARPES
Atsushi Fujimori Department of Physics, University of Tokyo
Email: [email protected] tokyo.ac.jp Keywords: fermi surface, multi layer cuprate, electron doped cuprate, charge order, antiferromagnetism
The physical properties of cuprate superconductors are often discussed based on a large single hole Fermi surface centered at the Brillouin zone corner. However, the large Fermi surface consists of Fermi arc and pseudogap regions (with a van Hove singularity) (Fig. 1(a), (b)), giving rise to two component behaviors [1]. Long range and short range magnetic or charge order induces band folding and creates small multiple Fermi surfaces in electron doped cuprates (Fig. 1(c)) [2]. Furthermore, more complex crystal structures such as the co existence of Cu O chains in YBCO [3] and the neighboring CuO2 layers in multi layer cuprates [4] indeed lead to multiple Fermi surfaces. In this talk, overview is given on ARPES studies of the complex Fermi surfaces in relation to quantum oscillation studies [5] and their implications for phase competition, enhancement of Tc, and other new phenomena.
I thank my collaborators M. Horio, S. Ideta, K. Okazaki, T. Mizokawa, T. Yoshida, K. Tanaka, A. Ino, H. Namatame, M. Taniguchi, S. Shin, K. Horiba, S. Minohara, H. Kumigashira, M. Hashimoto, D. Lu, Z. X. Shen, Y. Ando, H. Eisaki, K. Kojima, S. Uchida, Y. Krockenberger, H. Yamamoto, T. Adachi, and Y. Koike.
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Fig. 1: Fermi surfaces of single layer cuprates and band dispersion around the van Hove singularity (VHS) at k = (p,0). (a) Hole doped cuprates with VHS below the Fermi level (EF). (b) The same as (a) with VHS above EF. (c) Electron doped cuprates showing antiferromagnetic zone folding. q’s are nesting vectors for possible charge and/or spin ordering.
References 1. L. P. Gor’kov and G. B. Teitel’baum, Phys. Rev. Lett. 97, 247003 (2006) 2. M. Horio et al., Nat. Commun. 7, 10567 (2016). 3. Y. Sassa et al., Phys. Rev. B 83, 140511 (2011). 4. S. Ideta et al., Phys. Rev. Lett. 104, 227001 (2010). 5. S. E. Sebastian et al., Nature 511, 61 (2014).
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16.3
On the phenomenological two component physics for cuprates
Gregory Teitel’baum,1 1E.K. Zavoiskii Institute for Technical Physics of the Russian Academy of Sciences, Sibirskii trakt, 10/7, 420029 Kazan, Russia
Email: [email protected] Keywords: cuprates; pseudogap state, electronic propertiess.
At the very beginning of high Tc boom Gor’kov and Sokol suggested [1] that the strong lattice distortions induced by hole doping of the cuprates CuO2 planes give rise to microscopic phase separation into the metal and magnetic sub phases. Later it was shown [2] that the most favorable type of such separation, at least for LSCO is the creation of incommensurate stripes. The observation of stripe structures by EXAFS and diffraction [3], by neutron scattering [4] and elucidation of its local properties was followed by numerous papers on various aspects of coexistence of the localized and itinerant states in high Tc cuprates. Later it has been argued that the combined analysis of the ARPES and transport data together unequivocally gives evidence in favor of the two component physics for cuprates also in the momentum representation. We report an attempt to further comprehend these findings unifying them with the more recent data on the energy spectrum, quantum oscillations and charge ordering in cuprates into a self consistent phenomenological picture. We address details of the electronic spectrum in the pseudogap (PG) phase critical for understanding mechanisms of high temperature superconductivity (SC) in cuprates. The angle resolved photoemission spectroscopy finds coherent excitations only at so called “Fermi arcs” (FAs). Another branch small electronic pocket is seen in the quantum oscillations [5]. With tendency to a charge ordering (CO) revealed in few recent X rays experiments the view became popular that pockets emerge via reconstruction of the Fermi surface (FS) in vicinity of the nodal points in a CO transition. However the residual metallic contribution into the specific heat deep in the SC phase of YBCO observed in [6] contradicts the reconstruction scenario, as SC suppressing the CO would thereby destroy such pocket. Recently it was suggested [7] that at doped hole concentrations x>0.08 0.10 the experimental Hall coefficient identifies the pocket as a permanent feature, in contrast to the idea of FS reconstruction at the charge ordering phase transition. To reveal the origin of the electron pocket we analyze the impact of the lattice structural changes on the energy spectrum in cuprates. It is important that the quantum oscillation which may be considered as the manifestation of the electron pocket were observed in the doping range corresponding to the so called low temperature tetragonal
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(LTT) phase. In this respect it is necessary to take into account, that the well known LTO LTT structural transition influences not only the lattice degrees of freedom but also the charge ones. We suggest that the corresponding changes of the electronic dispersion may result in opening of the small electron pocket at the center of Brillouin zone.
References 1. L. P. Gor’kov and A. V. Sokol, JETP Lett. 46, 420 (1987). 2. J. Zaanen and O. Gunnarson, Phys. Rev. B 40, 7391(R)1989. 3. A. Bianconi, M. Missori, J. Phys.I (France) 4, 361 (1994); Solid State Commun. 91, 287 (1994). 4. J. M. Tranquada et al., Nature 375, 561 (1995). 5. N. Doiron Leyraud et al., Nature 447, 565 568 (2007). 6. S. C. Riggs, et al., Nature Phys. 7, 332 335 (2011). 7. L. P. Gor’kov & G. B. Teitel’baum, G.B., Sci. Rep. 5, 8524 (2015).
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16.4
Frontiers of high Tc studies and spin liquids
Masatoshi Imada University of Tokyo
Email: [email protected] tokyo.ac.jp Keywords: organic materials, Ir compounds
We focus on frontiers of high temperature superconductivity. The first subject is the mechanism for the bulk cuprates, which attracts renewed interest in the light of the possible existence of hidden fermions. The hidden fermions boost up the superconducting transition temperature high and is an electronic state that is bistable with quasiparticles. This bistability or fractionalization of electrons is a side of the same coin opposite to the charge inhomogeneity or phase separation ubiquitous in the cuprates and iron based superconductors. The high critical temperature of superconductivity requires strong effective attraction of electrons while it also induces the charge inhomogeneity such as charge ordering and electronic phase separation. The understanding of the bistability has inspired ideas for pioneering at frontiers of high Tc superconductivity beyond conventional bulk equilibrium. One is interfaces and thin films, which have unique functions of self optimizing strong coupling superconductivity. The second is to utilize the nonequilibrium state that is not possible in equilibrium because of the instability to charge inhomogeneity. We also discuss possibilities of realizing quantum spin liquids, driven by geometrical frustration effects.
References 1. S. Sakai, M. Civelli and M. Imada, Phys. Rev. Lett. 116 (2016) 057003. 2. T. Misawa and M. Imada, Phys. Rev. B 90 (2014) 115137. 3. T. Misawa and M. Imada, Nat. Commun. 5 (2014) 5738. 4. T. Misawa, Y. Nomura, S. Biermann and M. Imada, Sci. Adv. 2 (2016) e1600664. 5. R. Kaneko, S. Morita and M. Imada, J. Phys. Soc. Jpn. 5, 5738 (2014). 6. S. Morita, R. Kaneko and M. Imada, J. Phys. Soc. Jpn. 84, 024720 (2015).
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16.5
Orbital degeneracy lifting, broken local symmetries and properties in correlated electron materials Simon J. L. Billinge1,2 1 Department of Applied Mathematics and Applied Physics, Columbia University, New York, NY 10027, US. 2Condensed Matter Physics and Materials Science Department, Brookhaven National Laboratory, Upton, NY 11973
Email: [email protected] Keywords: orbital order, nematicity, local structure, PDF analysis, orbital degeneracy.
We now understand the broken symmetry states are widespread in strongly correlated electron materials, including charge, spin and orbital orders. All these involve arranging local objects in patterns that break the average structure, for example, antiferromagnetic arrangements of spins, and striped arrangements of charges and spins. In the case of orbital order, less focus has been placed on the exact nature of the local objects that arrange themselves and more on how they arrange; the order. However, when considering what happens when the order goes away, by melting for example, this distinction becomes important. Local probes such as atomic pair distribution function analysis (PDF) allow us to study disordered and short range ordered states of matter. To help understand our observations I will introduce language of orbital degeneracy lifting (ODL) as a general concept that can span all the way from disordered locally symmetry broken orbital states through short range ordered domain states all the way to long range orbital order. We are finding ODL states in a wide range of materials evident in the local structure, that plays an important role in understanding the properties of correlated electron materials.
Figure 1: Schematic of how orbital degeneracy lifting comes about
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17.1
On the time correlation of long range ordered CDW state in LBCO
X. M. Chen, V. Thampy, C. Mazzoli, A. M. Barbour, H. Miao, G. D. Gu, Y. Cao, J. M. Tranquada, I. Robinson, M. P. M. Dean and S. B. Wilkins Brookhaven National Lab, Upton, USA
Email: [email protected] Keywords: CDW, HTSC, time correlation
The occurrence of charge density wave (CDW) order in underdoped cuprates is now well established, although its nature and its relationship with superconductivity is not. Theoretical proposals include contrasting ideas such as that pairing may be driven by CDW fluctuations or that static CDWs may intertwine with a spatially modulated superconducting wave function. We report on the CDW order dynamics in LBCO by using x ray photon correlation spectroscopy at its wave vector, detected by resonant soft x ray diffraction at the Cu L3 edge. The long time stability of the measured CDW signal is discussed in the view of its varying correlation length with temperature.
References 1. Phys. Rev. Lett. 117, 167001 (2016) and references therein.
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17.2
Stripe Pinning in LBCO
I. K. Robinson, X. M. Chen, V. Thampy, H. Miao, Y. Cao, M. P. M. Dean, C. Mazzoli, A. M. Barbour, W. Hu, S. B. Wilkins, G. D. Gu, and J. M. Tranquada
Soft X ray coherent diffraction at NSLS II has been used to address the pinning of stripes in the cuprate HTSC material La1.825Ba0.125CuO4 (LBCO) [1]. LBCO’s relatively long stripe correlation length of 26nm [2], compared with only 5.5nm for the YBCO, meant that the resonant signal level at CSX 1 was sufficient to record coherent diffraction at the charge density wave (CDW) vector (0.24,0,1.5) on resonance at the Cu L3 edge. The CDW domains were found to be surprisingly static, with no evidence of significant fluctuations up to the 2.75 hour duration of the measurements from 15K up to 45K, approaching the stripe melting temperature [3]. To ensure consistent illumination of the same region, we introduced a fabricated pinhole array physically attached to the sample and attempted to depin the CDW domains using temperature excursions. We found that the observed pattern of stripe pinning is extremely robust and survives temperature sweeps as high as 220K, but not beyond. Since this temperature is close to the 235K “LTO HTT” structural transition, we postulate that the pinning sites are the orthorhombic grain boundaries which are rearranged by crossing it. A possibly related “return point memory” effect has been studied before in magnetic systems [4,5], but never for CDWs. We are presently attempting to image the pattern of domains by inversion of the Bragg coherent diffraction pattern [6].
Coherent X ray diffraction pattern of the cuprate La1.825Ba0.125CuO4 (LBCO) recorded at the charge density wave vector (0.24,0,1.5) on resonance at the Cu L3 edge, using the CSX 1 beamline of NSLS II.
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References 1. J. M. Tranquada, B. J. Sternlieb, J. D. Axe, Y. Nakamura, and S. Uchida, Nature 375 561 (1995). 2. V. Thampy, S. Blanco Canosa, M. Garcıa Fernandez, M. P. M. Dean, G. D. Gu, M. F ̈orst, T. Loew, B. Keimer, M. Le Tacon, S. B. Wilkins, and J. P. Hill, “Comparison of charge modulations in La1.875Ba0.125CuO4 and YBa2Cu3O6.6.”, Phys. Rev. B 88 024505 (2013). 3. X. M. Chen, V. Thampy, C. Mazzoli, A. M. Barbour, H. Miao, G. D. Gu, Y. Cao, J. M. Tranquada, M. P. M. Dean and S. B. Wilkins, “Remarkable Stability of Charge Density Wave Order in La1.875Ba0.125CuO4”, Phys. Rev. Letts. 117 167001 (2016). 4. M. S. Pierce, C. R. Buechler, L. B. Sorensen, J. J. Turner, S. D. Kevan, E. A. Jagla, J. M. Deutsch, T. Mai, O. Narayan, J. E. Davies, K. Liu, J. Hunter Dunn, K. M. Chesnel, J. B. Kortright, O. Hellwig, and E. E. Fullerton, “Disorder Induced Microscopic Magnetic Memory”, Phys. Rev. Letts. 94 017202 (2005). 5. K. A. Seu, R. Su, S. Roy, D. Parks, E. Shipton, E. E. Fullerton and S. D. Kevan, “Microscopic return point memory in Co/Pd multilayer films”, New Journal of Physics 12 035009 (2010). 6. Ian Robinson and Ross Harder, “Coherent Diffraction Imaging of Strains on the Nanoscale”, Nature Materials 8 291 298 (2009).
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17.3
Precursor Charge Density Wave in La2 xBaxCuO4
Mark P. M. Dean Brookhaven National Laboratory
Email: [email protected] Keywords: Cuprates, CDW, stripes, superconductivity, x rays
It has long been hypothesized that long range charge density wave (CDW) order is an intrinsic property of the cuprates that arises from the pinning of precursor high temperature CDW fluctuations. Many years after this initial discovery of CDW order in 214 cuprates, the idea of a universal tendency towards CDW order was bolstered by the observation of CDW correlations in various systems such as YBa2Cu3O6+x (YBCO). However, the CDW in YBCO has a very different wavevector (~0.3 rather than 0.24) and is seemingly unrelated to the low energy spin correlations (which are gapped in YBCO) impeding efforts to understand the cuprates within a universal framework. Much of the difficulty is that although precursor spin density wave (SDW) correlations have been studied in detail, the corresponding transition between long range ordered and precursor CDW correlations has never been observed. Here we report the discovery of precursor CDW correlations in La1.875Ba0.125CuO4 [1]. As shown in Fig 1., the precursor CDW has a correlation length of a few unit cells and exists at a different wavevector from the low temperature CDW decoupled from the SDW correlations. We find that the CDW and SDW correlations lock together at low temperature to form a phase with meandering partially ordered CDW correlations, reconciling the apparently different properties of the charge correlations in different cuprates.
Figure 1: Decoupling of the CDW and SDW in the precursor phase [1]. The results of fitting the quasi elastic intensity showing: a the full width at half maximum, b the incommensurability.
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The black dashed line at 54 K corresponds to the low temperature LTT LTO structural phase transition which is depicted in b, blue and yellow code temperatures below and above this threshold [2]. The behavior of the SDW, taken from inelastic neutron scattering results at 3 and 6 meV energy transfer from Ref. [3] are included on panels a and b. We see that the CDW and SDW incommensurabilities evolve in different directions above 54 K, which indicates a decoupling of the charge and spin degrees of freedom.
References 1. H. Miao, J. Lorenzana, G. Seibold, Y.Y. Peng, A. Amorese, F. Yakhou Harris, K. Kummer, N. B. Brookes, R. M. Konik, V. Thampy, G. D. Gu, G. Ghiringhelli, L. Braicovich, M. P. M. Dean, arXiv:1701.00022 (2017) 2. S. B. Wilkins, M. P. M. Dean, Jörg Fink, Markus Hücker, J. Geck, V. Soltwisch, E. Schierle, E. Weschke, G. Gu, S. Uchida, N. Ichikawa, J. M. Tranquada, and J. P. Hill, Phys. Rev. B 84, 195101 (2011) 3. M. Fujita, H. Goka, K. Yamada, J. M. Tranquada, L. P. Regnault, Phys. Rev. B 70, 104517 (2004)
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18.1
Optical spectroscopy of La2 xBaxCuO4 single crystals: influence of stripe order
D.B. Tanner, Luyi Yan, and Genda Gu University of Florida and Brookhaven National Laboratory
Email: [email protected] Keywords: high Tc, infrared, cuprate, stripes
The ab plane and c axis reflectance spectra of ten La2 xBaxCuO4 single crystals, with x ranging from undoped to optimally doped, have been measured over a wide frequency range and at temperatures from 10 to 300 K. The influence of stripe order around x=0.125 appears in the spectra below T = 50 K, observed both as a reduction in the free carrier (normal state) and superfluid (superconducting state) density and by the appearance of a relatively narrow conductivity band near 25 meV. The superfluid density is estimated from the real part of the dielectric function and the f sum rule. The c axis spectra are those of an insulator or very bad metal, with very little doping or temperature dependence. The Josephson plasma edge is not observed in any of these spectra.
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18.2
High Pressure 3D to 2D Tuning of Magnetism in Cuprates
Markus Huecker Department of Condensed Matter Physics, Weizmann Institute of Science, 234 Herzl St., Rehovot 76100, ISRAEL
Email: [email protected] Keywords: Cuprates, Magnetism, Stripes, Superconductivity
Broken lattice symmetries often play an integral part in the selection process of the electronic ground state. A prime example is found in the La 214 cuprates, where lattice distortions result in a complex relationship between superconductivity, charge and magnetic orders. In an attempt to dissect this problem into its various parts, here we highlight the impact of lattice distortions on the pristine magnetism of a cuprate parent compound.
Figure 1: High pressure phase diagram of magnetic order and crystal structure in a cuprate parent compound.
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18.3
Building blocks of cuprate charge density modulations
Andrej Mesaros, Kelvin Chang, Ehsan Khatami, Michael J. Lawler, J.C. Seamus Davis, Eun Ah Kim Cornell University, San Jose State University
Email: [email protected] Keywords: high Tc, cuprates, charge density wave, machine learning, STM
Charge modulations in cuprates have been described from opposing theoretical standpoints, predicting either commensurate or incommensurate charge order wave vectors. A recently introduced method for analyzing STM data on Bi2Sr2CaCu2O8+x has shown[1] that the underlying charge wave vector is commensurate, in contrast to conventional diffraction measurements on some other cuprates which find incommensurate wave vectors. To understand the universality of charge order in cuprates it is necessary to relate the conventionally averaged wave vector value to the underlying wave vector, which is challenging due to disorder at different lengthscales. To illuminate the nanoscale configuration and organization of the disordered charge modulations in cuprates, here we for the first time apply methods beyond Fourier analysis to the STM data on cuprates. I will describe the quantitative views which the methods of machine learning and wavelet analysis provide into the nanoscale patterns of charge modulations. I will also discuss how different types of randomness in the charge modulations relate the nanoscale to the larger scale averaged observables relevant for diffraction techniques.
References 1. A. Mesaros, K. Fujita, S.D. Edkins, M.H. Hamidian, H. Eisaki, S. i. Uchida, J.C. Seamus Davis, M.J. Lawler, E. A. Kim, Proc Natl Acad Sci USA 113, 12661 (2016).
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18.4
Pseudogap generated a coexistence of Fermi arcs and Fermi pockets in cuprate superconductors
Shiping Feng, Huaisong Zhao, and Deheng Gao Department of Physics, Beijing Normal University, Beijing 100875, China
Email: [email protected] Keywords: Pseudogap; Fermi arc; Fermi pocket; Electron spectrum; Cuprate superconductor
One of the most intriguing puzzle is why there is a coexistence of Fermi arcs and Fermi pockets in the pseudogap phase of cuprate superconductors? This puzzle is calling for an explanation. Based on the t J model in the fermion spin representation, the coexistence of the Fermi arcs and Fermi pockets in cuprate superconductors is studied by taking into account the pseudogap effect. It is shown that the pseudogap induces an energy band splitting, and then the poles of the electron Green's function at zero energy form two contours in momentum space, however, the electron spectral weight on these two contours around the antinodal region is gapped out by the pseudogap, leaving behind the low energy electron spectral weight only located at the disconnected segments around the nodal region. In particular, the tips of these disconnected segments converge on the hot spots to form the closed Fermi pockets, generating a coexistence of the Fermi arcs and Fermi pockets. Moreover, the single particle coherent weight is directly related to the pseudogap, and grows linearly with doping. The calculated result of the overall dispersion of the electron excitations is in qualitative agreement with the experimental data. The theory also predicts that the pseudogap induced peak dip hump structure in the electron spectrum is absent from the hot spot directions.
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19.1
Magnetic field induced magnon decay in the spin ½ square lattice Heisenberg antiferromagnet (5CAP)2CuCl4
Toby Perring1*, Paul Gosuly1,2, Martin Mourigal3, Niels Christensen4, Goran Nilsen1, Henrik Rønnow5, Des McMorrow2 1 ISIS Facility, STFC Rutherford Appleton Laboratory, Didcot, OX11 0QX, UK 2 London Centre for Nanotechnology, UCL, London WD1H 0AH, UK 3 School of PhysicsGeorgia Institute of Technology, Atlanta, GA 30332, USA 4 Department of Physics, Technical University of Denmark, DK 2800 Kgs. Lyngby, Denmark 5 Laboratory for Quantum Magnetism, École Plytechnique Fédérale de Lausanne (EPFL), CH 1015, Switzerland
Email: [email protected] Keywords: Quantum magnetism, magnon decay, cuprates
The concept of quasi particles is ubiquitous in condensed matter physics, as it offers a major simplification of the strongly interacting many body problem by which the low energy excited states can be characterised by weakly interacting long lived particles. Correspondingly, the circumstances when this picture breaks down are also important. In ordered magnetic systems in two or three dimensions the elementary excitations are magnons. Here we report the breakdown of magnons in the spin ½ quasi two dimensional (2D) square lattice Heisenberg antiferromagnet (5CAP)2CuCl4 in a magnetic field applied perpendicular to the plane of the ordered moments in zero field, using the results of high resolution time of flight inelastic neutron scattering experiments. Above a critical field HS the moments are fully aligned, and we obtained the magnetic exchange parameters in the Hamiltonian from the measured magnon dispersion relation. At H=0.85HS we observe marked damping of the magnons around (0.5,0.5) and (0.5,0) and the formation of a continuum of magnon scattering, as well as a small renormalisation of the magnon energies. We find a good quantitative agreement between the data and predictions of renormalised 1/S spin wave theory using the intra and inter plane exchange parameters extracted from the polarised phase. Our results provide the first experimental evidence for spontaneous magnon decay in the quantum limit of the Heisenberg antiferromagnet on a square lattice in applied magnetic field.
References 1. M. Mourigal et al, Phys Rev B 82 144402 (2010). 2. W.T. Fuhrman et al., Phys Rev B 85 184405 (2012).
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19.2
Disorder Driven Metal Insulator Transitions in Deformable Lattices
Vladimir Dobrosavljevic Florida State University and MagLab
Email: [email protected] Keywords: Anderson localization, polarons
We show that, in the presence of a deformable lattice potential, the nature of the disorder driven metal insulator transition is fundamentally changed with respect to the noninteracting (Anderson) scenario. For strong disorder, even a modest electron phonon interaction is found to dramatically renormalize the random potential, opening a mobility gap at the Fermi energy. This process, which reflects disorder enhanced polaron formation, is here given a microscopic basis by treating the lattice deformations and Anderson localization effects on the same footing. We identify an intermediate “bad insulator” transport regime which displays resistivity values exceeding the Mott Ioffe Regel limit and with a negative temperature coefficient, as often observed in strongly disordered metals. Our calculations reveal that this behavior originates from significant temperature induced rearrangements of electronic states due to enhanced interaction effects close to the disorder driven metal insulator transition.
References 1. Domenico Di Sante, Simone Fratini, Vladimir Dobrosavljević, and Sergio Ciuchi Phys. Rev. Lett. 118, 036602 (2017).
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19.3
Multiple universalities in order disorder magnetic phase transitions
H. D. Scammell, O. P. Sushkov University of New South Wales
Email: [email protected] Keywords: Quantum phase transition
Phase transitions in isotropic quantum antiferromagnets are associated with the condensation of bosonic triplet excitations. In three dimensional quantum antiferromagnets, such as TlCuCl3, condensation can be either pressure or magnetic field induced. The corresponding magnetic order obeys universal scaling with thermal critical exponent ∅. Employing a relativistic quantum field theory, the present work predicts the emergence of multiple (three) universalities under combined pressure and field tuning. Changes of universality are signalled by changes of the critical exponent ∅. Explicitly, we predict the existence of two new exponents ∅ = 1 and 1/2 as well as recovering the known exponent ∅ = 3/2. We also predict logarithmic corrections to the power law scaling.
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19.4
Three dimensional quantum liquid crystals and dislocation worldsheet condensation
Jaakko Nissinen, Aron J. Beekman, Kai Wu, Jan Zaanen Lorentz Institute for Theoretical Physics, the Netherlands and Low Temperature Laboratory, Aalto University, Finland; Keio University, Japan; Standford, USA; Leiden University, the Netherlands
Email: [email protected] Keywords: Liquid crystals, vortices, two form gauge fields, duality
A crystalline quantum solid can partially melt into a liquid crystal, where spontaneous rotational symmetry breaking is maintained while translational symmetry is (partially) restored. The melting can be understood via the unbinding of dislocations, the topological defects of translational order. Through a duality mapping, phonons turn into flavored dual gauge fields mediating interactions between dislocations. The phenomenological Landau Ginzburg theory for this dual gauge theory allows one to study liquid crystal phases in a unified fashion. Upon condensation of dislocations, the dual gauge fields undergo the Anderson Higgs mechanism and become gapped, signaling the loss of shear rigidity. We recently provided a comprehensive review of quantum dislocation mediated melting in 2D (arXiv:1603.04254, Phys. Rep. to be published). Here we extend this theory to three dimensions. Dislocations are now linelike objects, strings, tracing out worldsheets in imaginary time, while the dual gauge fields become two form (Kalb Ramond) fields. We obtain the Higgs phase of these two form gauge fields. Translational symmetry can be restored in three, two or one directions leading to nematic, smectic or columnar quantum liquid crystals. We derive the spectrum of low energy excitations and its linear response. Goldstone modes due to broken rotational symmetry as well as superconductivity emerge whenever translational symmetry is restored. The peculiar features of liquid crystalline order can be probed by finite momentum spectroscopy.
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19.5
Proximity of superconductivity and magnetism in δ doped La2CuO4 heterostructures
Alexander Boris Max Planck Institute for Solid State Research, Stuttgart, Germany
Email: [email protected] Keywords: superlattices; superconductivity; magnetism; proximity effects
Proximity and concomitant emergence of superconductivity (SC) and magnetism bear much fundamental interest and potential for applications. A striking manifestation of this phenomenon occurs in the (La,Sr)2CuO4+δ family, where SC and magnetism appear to have the same onset temperature [1 3]. To gain insight on the intimate connection between the SC and magnetic ground states, we follow a novel approach to dope La2CuO4. Instead of random La/Sr substitution, we replace single planes of LaO2 with SrO2 dopant planes by means of atomic layer by layer oxide MBE [4]. We investigate superlattices (SLs) with the composition [(LaO SrO CuO2) + N × (LaO LaO CuO2)] (δSr LCON), N = 3…12. These heterogeneously δ doped SLs have inherent broken inversion symmetry and substantially reduced Sr disorder, compared with homogeneously doped bulk La2CuO4. Utilizing the low energy muon spin rotation technique, we find up to 30 percent enhancement in the magnetic volume fraction in δSr LCON right below Tc, ranging from 18 K to 30 K. While resembling phase separated bulk (La,Sr)2CuO4+δ, the close proximity of the magnetic and SC ground states in δSr LCON is leading to a non trivial interplay between these two orders. Our THz spectroscopy study confirms that the SC state in this system is essentially two dimensional. The upper critical field is significantly reduced in the Faraday geometry the SC gap closes at HC2 ≈ 1.5 T, whereas an external magnetic field parallel to the SC layers is much less effective for the pair breaking. The experimental optical spectra reveal the thermally activated charge transfer between the SC and magnetic phases while effective at high temperatures it becomes no longer noticeable when approaching the SC and magnetic transition temperature.
References 1. Y. S. Lee et al., Phys Rev B 60, 3643 (1999). 2. L. Udby et al., Phys Rev Lett 111, 227001 (2013). 3. H. E. Mohottala et al., Nature Matt. 5, 377 (2006). 4. F. Baiutti et al., Nature Commun.6, 8586 (2015).
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20.1
Emerging X ray Techniques for Probing Matter with Depth and Time Resolution
Alexander X. Gray Department of Physics, Temple University, Philadelphia, Pennsylvania, PA 19122, USA
Email: [email protected] Keywords: hard x ray photoemission spectroscopy, standing wave photoemission spectroscopy, oxide interfaces, 2DEG
In this talk I will describe several new directions in the fields of x ray spectroscopy and imaging, made possible with the advent of third generation synchrotron light sources and free electron lasers, and enabling investigations of fundamental physical processes in novel complex materials and technologically relevant nanostructures and interfaces with depth and time resolution. I will present the first results of hard x ray angle resolved photoemission measurements (HARPES) at excitation energies of up to 6 keV [1,2]. Compared to the traditional ARPES, carried out in the UPS regime (6 120 eV), this new technique enables one to probe up to 40 times deeper below the surface, thus allowing for more bulk sensitive momentum resolved electronic structure determination. Furthermore, I will introduce a new x ray photoemission technique (SWARPES) which combines soft x ray ARPES with standing wave (SW) excited photoelectron spectroscopy, wherein the intensity profile of the exciting x ray radiation is tailored within the sample in order to provide a depth selective probe of the electronic structure of buried layers and interfaces [3,4]. Finally, I will discuss the latest applications of the above mentioned techniques to the studies of superconducting/magnetic heterostructures [5] and two dimensional electron gas at oxide interfaces [6].
References 1. A. X. Gray et al., Nature Materials 10, 759 (2011). 2. A. X. Gray et al., Nature Materials 11, 957 (2012). 3. A. X. Gray et al., Europhys. Lett. 104, 17004 (2013). 4. A. X. Gray et al., J. Electron Spectrosc. Relat. Phenom. 195, 399 (2014). 5. B. A. Gray et al., Scientific Reports 6, 33184 (2016). 6. S. Nemsak et al., Phys. Rev. B 93, 245103 (2016).
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20.2
The inverse Edelstein effect at oxide interfaces
G. Seibold(1), S. Caprara(2), M. Grilli(2), R. Raimondi(3) (1) Institut f. Physik, BTU Cottbus Senftenberg, PBox 101344, 03013 Cottbus, Germany; (2) Dipartimento di Fisica, Universita di Roma 'La Sapienza', piazzale Aldo Moro 5, 00185 Roma, Italy; (3) Dipartimento di Matematica e Fisica, Universita Roma Tre, Via della Vasca Navale 84, 00146 Roma, Italy
Email: seibold@b tu.de Keywords: oxide interfaces, spintronics, Edelstein effect
The manipulation of spin degrees of freedom in order to generate a charge current and the inverse process are at the heart of spintronics devices. One of the most prominent examples is the spin Hall effect (SHE) where a charge current induced by an electric field along the x direction produces a z polarized spin current flowing along the y direction. Another related phenomenon is the Edelstein effect where a charge current is converted into a non equilibrium spin polarization. Both, SHE and Edelstein effect occur in systems with strong spin orbit coupling, in particular two dimensional electron gases which lack inversion symmetry perpendicular to the gas plane and which are usually described with the so called Rashba hamiltonian. The situation is more complex in LaAlO3/SrTiO3 interfaces where the interplay between inversion asymmetry and atomic spin orbit coupling is at the heart of strong Rashba interactions. Recently, two experiments [1,2] have demonstrated a strong inverse Edelstein effect at such interfaces by generating a strong non equilibrium spin polarization at the interface and detecting the resulting charge current. The reported spin to charge efficiency is more than order of magnitude larger than in conventional metallic layers which suggests the LAO/STO interface as a promising system for spintronic devices. Within linear response theory we investigate the inverse Edelstein effect in oxide interfaces by generalizing the approach of Raimondi et al. [3] to a multiband model which involves the 3d t2g bands of the Ti ions. Consistently with experiment we find a gate tunable inverse Edelstein effect which changes sign depending on the occupation of and ⁄ orbitals.
References 1. E. Lesne et al., Nature Materials 15, 1261 (2016). 2. Q. Song et al., Nature Communications, 10.1038 (2016). 3. K. Shen, G. Vignale and R. Raimondi, Phys. Rev. Lett. 112, 096601 (2014).
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21.1
Emergence of surface orbital ordering in the heavy fermion superconductor CeCoIn5
Yasuo Yoshida University of Tokyo
Email: [email protected] tokyo.ac.jp Keywords: orbital order, STM, heavy fermion
The newfangled orbital mediated quantum phenomena have proved over the past decade to be far reaching and complex as exemplified in exotic orbital orders, nontrivial orbital fluctuation mediated superconductivity, orbital Kondo effect, and multipole moment ordering. To understand electronic, spin, and orbital correlations in these phenomena, it is crucial to have a direct access to real space orbital texture, but so far orbital sensitive probes have shown rather limited functionality. Recent progress of a scanning tunneling microscope (STM) has enabled orbital selective tunneling by fine tuning the tip sample distance (TSD). We exploit the orbital sensitivity of STM to unveil a surface assisted cobalt d orbital order in the heavy fermion compound CeCoIn5. We find that at a small TSD, cobalt atoms in STM topographies take on dumbbell shapes alternatingly aligned in the [100] and [010] directions on a cleaved (001) surface. A domain boundary of this ordered structure, which is localized within a terrace, denotes two dimensionality of the ordered structure. First principles calculations show that the structure is a consequence of a staggered dxz dyz orbital order assisted by surface termination. This novel surface assisted orbital ordering seems to be ubiquitous in transition metal oxides, heavy fermion superconductors and other materials, but has been overlooked until now.
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21.2
STM studies of superconductivity and nematicity in Fe(Se,S)
Tetsuo Hanaguri
Email: [email protected]
Spontaneous breaking of lattice rotational symmetry in the electronic state, which is known as electronic nematicity, has been observed in various materials including unconventional superconductors such as cuprates and iron based materials. In order to make clear the relationship between superconductivity and nematicity, we have performed spectroscopic imaging STM on FeSe1 xSx. The parent material FeSe undergoes tetragonal to orthorhombic transition at 90 K, which is a manifestation of electronic nematic order. Superconductivity sets in at lower temperature of 9 K. The electronic nematic order is suppressed with increasing sulfur content x and disappears above x ~ 0.17, whereas superconducting transition temperature remains intact1. We have investigated the evolution of the band structure as a function of x by analyzing the quasiparticle interference patterns. We have found that anisotropy of the in plane band structure diminishes with increasing x but there is little change in the band structure at x = 0.17. Superconducting gap is hardly affected by sulfur doping in the nematic phase but is suddenly smeared once the nematic phase diminishes. This result indicates that superconductivity and nematicity are strongly interrelated.
References 1. S. Hosoi et al., Proc. Natl. Acad. Sci. USA 113, 8139 (2016).
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21.3
Change of phase diagram of 1111 type iron pnictide by varying of rare earth element, solid solution of pnictogens and electron doping
S. Miyasaka, T. Yamamoto, M. Uekubo, H. Tsuji, K. T. Lai, A. Takemori, M. Nakajima, S. Tajima Dept. of Phys., Osaka Univ., Osaka 560 0043, Japan
Email: [email protected] u.ac.jp Keywords: Iron based superconductor, Fermi surface nesting.
In spite of many experimental and theoretical studies on iron based superconductors, their superconducting mechanism has not clarified yet. Just after the discovery of these superconductors [1], it has been reported that the system can be described within a moderated electron correlation regime where the band theory works well. Then, antiferromagnetic spin fluctuation due to Fermi surface nesting was considered as a strong candidate for the pairing interaction of superconductivity. [2,3] Recently, three different antiferromagnetic states were found in LaFeAsO system, which is called La1111 system. In this system, the first antiferromagnetic phase (AFM1) exists around LaFeAsO. By P substitution for As, AFM1 disappears and superconducting phase (SC1) appears around x=0.6 0.8 in LaFeP1 xAsxO. The further P substitution induces the appearance of another antiferromagnetic phase (AFM2) between x=0.3 and 0.6. Below x=0.3, the different superconducting phase (SC2) exists. [4,5] On the other hand, the heavily H doping induces third antiferromagnetic phase (AFM3) and superconducting one (SC3) in LaFeAsO. [6] In the present work, we have investigated the change of electronic phase diagram of 1111 type systems by varying of rare earth element (R), solid solution of pnictogens (Pn) and electron doping. The R change, Pn solid solution and electron doping induce the variety of Fermi surface topology, and resultantly the 1111 type systems show a complicated phase diagram. For example, RFeP1 xAsxO shows the systematic but complicated change of phase diagram, when R is changed from La to Nd. Figure 1 presents the electronic phase diagram of RFeP1 xAsxO with R=La, Pr and Nd. As described above, LaFeP1 xAsxO has two antiferromagnetic and superconducting phases (AFM1, AFM2, SC1 and SC2). The antiferromagnetic states of AFM1 and AFM2 are caused by the Fermi surface nesting in FeAs type and FeP type Fermi surface states, respectively. [7] With the change of R from La to Nd, the Pn height from Fe layer increases, and xy hole Fermi surface around zone corner are expanded. The Fermi surface nesting related with xy Fermi surface is enhanced and the AFM1 is stabilized. As shown in Fig. 1, the AFM1 survives in lower As concentration (x) regions in PrFeP1 xAsxO and NdFeP1 xAsxO. Another
119 Superstripes 2017, Ischia June 4 10, 2017 antiferromagnetic phase (AFM2) exists at x~0.4 in these systems. As a result, AFM1 and AFM2 merge, and the antiferromagnetic phase is observed in wider x region in PrFeP1 xAsxO and NdFeP1 xAsxO.
150 (a) LaFeP1 xAsxO T 100 N AFM2 SC1 50 SC2 AFM1 Tc TN Tc 0 150 (b) PrFeP1 xAsxO TN
(K) 100 c T , ,
N 50
T Tc Tc 0 (c) NdFeP As O 150 1 x x TN 100
50 Tc Tc 0 0.2 0.4 0.6 0.8 1 As content x
Figure 1: Electronic phase diagrams of (a) LaFeP1 xAsxO, (b) PrFeP1 xAsxO and (c) NdFeP1 xAsxO. Red and blue dots indicate superconducting transition temperature Tc and magnetic transition one TN.
References 1. Y. Kamihara et al., J. Am. Chem. Soc. 128, 10012 (2006). 2. K. Kuroki et al., Phys. Rev. B 79, 224511 (2009). 3. I. I. Mazin et al., Phys. Rev. Lett. 101, 057003 (2008). 4. K. T. Lai et al., Phys. Rev. B 90, 064504 (2014). 5. H. Mukuda et al., J. Phys. Soc. Jpn. 83, 083702 (2014). 6. M. Hiraishi et al., Nat. Phys. 10, 300 (2014). 7. H. Usui et al., Sci. Rep. 5, 11399 (2015).
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21.4
One hole and two holes low energy states in a cuprate layer
Mona Berciu, Clemens Adophs, Mirko Moeller, Hadi Ebrahimnejad, George Sawatzky University of British Columbia
Email: [email protected] Keywords: three band models, quasiparticle dispersion, spin polarons, effective magnon mediated interactions
We use a variational method to study the strongly correlated limit of the three band Emery model, which has spins at Cu sites and doped holes on the O sublattice. For an infinite layer with one doped hole, we find a quasiparticle with the correct dispersion for reasonable values of the Emery parameters. However, unlike in one band models, the quasiparticle dispersion is not controlled by the spin fluctuations of the antiferromagnetic background; this is due to the hierarchy of the energy scales. We also study two holes doped in an infinite layer, and characterize the effective magnon mediated interactions that arise between them.
References 1. "The dynamics of a doped hole in cuprates is not controlled by spin fluctuations", Hadi Ebrahimnejad, George A. Sawatzky and Mona Berciu, Nature Physics 10, 951 955 (2014). 2. "Differences in the quasiparticle dynamics for one band and three band cuprate models", Hadi Ebrahimnejad, George A. Sawatzky and Mona Berciu, J. Phys.: Cond. Mat. 28, 105603 (2016).
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22.1
Signature of the pseudogap critical point in cuprate superconductors
Sven Badoux Département de physique & RQMP, Université de Sherbrooke, Sherbrooke, Québec J1K 2R1, Canada
Email: [email protected] Keywords: superconductivity, pseudogap, cuprates
Understanding the mechanism of the superconductivity in cuprates will go through the understanding of the different phases that composed these materials and the link between them. One of the biggest mysteries of the cuprates remains the nature of the pseudogap phase. In order to study this phase at low temperature, high magnetic fields are required to suppress superconductivity. I will present measurements of the resistivity, Hall, Seebeck coefficients and thermal conductivity on three cuprate materials, YBCO [1] and LSCO [2,3] and Nd LSCO[4], performed in magnetic fields large enough to suppress superconductivity at low temperature. These measurements lead to two main findings. First, the pseudogap critical doping p* and the onset of the charge density wave order occur at different doping values. So the two phenomena are separate. Secondly, the carrier density n is observed to drop sharply at p*, going from n = 1+ p above p* to n = p below p* (fig. 1). This signature imposes strong constraints on the possible nature of the pseudogap phase.
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Doping dependence of the Hall number, nH = V / e RH. A sharp drop of nH is observed to occur at p*.
References 1. S. Badoux et al, Nature 531, 210–214 (2016). 2. S. Badoux et al, PRX 6, 021004 (2016). 3. F. Laliberté et al, arXiv:1606.04491 (2016). 4. C. Collignon et al, arXiv:1607.05693 (2016).
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22.2
Enhanced nematic fluctuations near the Mott insulating phase of high Tc cuprates
Peter P. Orth, Bhilahari Jeevanesan, Joerg Schmalian, Rafael M. Fernandes Iowa State University, Karlsruhe Institute of Technology, Karlsruhe Institute of Technology, University of Minnesota
Email: [email protected] Keywords: high Tc superconductors, cuprates, nematicity, strong coupling Mott physics
The complexity of the phase diagram of the cuprates goes well beyond its unique high Tc superconducting state, as it hosts a variety of dierent electronic phenomena, such as the pseudogap, nematic order, charge order, and strange metallic behavior. The parent compound, however, is well understood as a Mott insulator, displaying quenched charge degrees of freedom and low energy antiferromagnetic excitations described by the Heisenberg exchange coupling J. Here we show that doping holes in the oxygen orbitals inevitably generates another spin interaction a biquadratic coupling that must be included in the celebrated t ∇ J model. While this additional interaction does not modify the linear spin wave spectrum, it promotes an enhanced nematic susceptibility that is peaked at a temperature scale determined by J. Our results explain several puzzling features of underdoped YBCO, such as the proximity of nematic and antiferromagnetic order, the anisotropic magnetic incommensurability, and the in plane resistivity anisotropy. Furthermore, it naturally accounts for the absence of nematicity in electron doped cuprates, and supports the idea that the pseudogap temperature is related to strong local antiferromagnetism.
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Nematic uctuations induce a short ranged magnetic stripe ordered region (light red) within a Néel ordered background (green), as seen in our Monte Carlo simulations.
References 1. V. Hinkov et al., Science 319, 597 (2008). 2. D. Haug et al., New J. Phys. 12, 105006 (2010).
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22.3
Cooperative coupling of static magnetism and bulk superconductivity in the stripe phase of La2 xBaxCuO4: Pressure and doping dependent studies
Z. Guguchia,1,2, R. Khasanov,1 A. Shengelaya,3, 4 E. Pomjakushina,5 S.J.L. Billinge,6 Y.J. Uemura,2, A. Amato,1 E. Morenzoni,1 and H. Keller7 1 Laboratory for Muon Spin Spectroscopy, Paul Scherrer Institute, CH 5232 Villigen PSI, Switzerland 2 Department of Physics, Columbia University, New York, NY 10027, USA 3 Department of Physics, Tbilisi State University, Chavchavadze 3, GE 0128 Tbilisi, Georgia 4 Andronikashvili Institute of Physics of I.Javakhishvili Tbilisi State University, Tamarashvili str. 6, 0177 Tbilisi, Georgia 5 Laboratory for Developments and Methods, Paul Scherrer Institut, CH 5232 Villigen PSI, Switzerland 6 Condensed Matter Physics and Materials Science Department, Brookhaven National Laboratory, Upton, NY 11973, USA 7 Physik Institut der Universit at Zurich, Winterthurerstrasse 190, CH 8057 Zurich, Switzerland
Email: [email protected] Keywords: Pressure effects, Static stripe order, Cuprate superconductors
Static spin stripe order and superconductivity were systematically studied in La2−xBaxCuO4 (0.11 ≤ x ≤ 0.17) at ambient pressure by means of magnetization and µSR experiments [1,2]. We find that all the investigated La2−xBaxCuO4 samples exhibit static spin stripe order and that the quasi two dimensional superconducting (SC) transition temperature Tc1 and the static spin stripe order temperature Tso have very similar values throughout the phase diagram. Moreover, the magnetic and the SC properties of the x = 0.155 (LBCO 0.155) and x = 0.17 (LBCO 0.17) samples were studied under hydrostatic pressure. As a remarkable result, in these bulk cuprate superconductors the three dimensional SC transition temperature Tc and Tso nearly coincide [Tc(p) = Tso(p)] (Fig. 1) at all pressure investigated (0 ≤ p ≤ 2.3 GPa). We also observed a pressure induced transition from long range spin stripe order to a disordered magnetic state at p = 1.6 GPa in LBCO 0.155, coexisting with a SC state with substantial superfluid density. In LBCO 0.17 a disordered magnetic state is present at all p. The present results indicate that static magnetic order and SC pairing correlations develop in a cooperative fashion in La2−xBaxCuO4, and provide a new route of understanding the complex interplay between static magnetism and superconductivity in the stripe phase of cuprates.
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The superconducting transition temperature TC and the magnetic ordering temperature TSO of LBCO 0.155, obtained from DC susceptibility and muSR experiments, are plotted as a function of pressure. The magnetic volume fraction Vm is shown as a colormap.
References 1. R. Khasanov, Z. Guguchia et. al., High Pressure Research 36, 140 (2016). 2. Z. Guguchia et. al., Phys. Rev. B 94, 214511 (2016).
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22.4
Non centrosymmetric vortices in multi component superconductors
Adrian Crisan National Institute of Materials Physics Bucharest, 405A, Atomistilor Str., 077125 Magurele, Romania
Email: [email protected] Keywords: multicomponent superconductors; ac susceptibility; vortex dynamics; non centrosymmetric vortices
Multicomponent superconductivity is a novel quantum phenomenon in many different superconducting materials, such as multiband ones in which different superconducting gaps open in different Fermi surfaces, films engineered at the atomic scale to enter the quantum confined regime, multilayers, two dimensional electron gases at the oxide interfaces, and complex materials in which different electronic orbitals or different carriers participate in the formation of the superconducting condensate [1]. (Cu,C) , Tl and Hg based multilayer cuprate superconductors are outstanding multiband superconductors, where the interband interaction is very weak and they can be considered as multicomponent superconductors. One of the consequences of two gap superconductivity could be the presence, in certain conditions, of non Abrikosov (non centrosymmetric) vortices, which may be similar (or close) from the point of view of topology, to those proposed theoretically [2 4]. In a certain, but large range of applied DC field, the out of phase susceptibility of (Cu,C)Ba2Ca2Cu3Oy with aligned crystallites has two dissipation peaks [5]. Due to the characteristics of the sample, the shape of the second peak and its position’s field dependence, the possibility of inter grain dissipation was ruled out. The anomalous intra grain second peak was explained by a resonant rotational motion of a non centrosymmetric vortex molecule, composed of two fractional flux quanta from the two condensates, glued by a soliton [6]. At that time, this (and subsequent) work has attracted rather little interest due to the rather unconventional cuprates in discussion, the fact that they could be produced only by high pressure synthesis, and to the impossibility to obtain large single crystals. In the last few years, the discovery of MgB2 and of iron based superconductors ignited a huge interest in multi component superconductors. In this context, we have investigated the ac susceptibility of a high quality single crystal of isovalently substituted iron pnictide BaF2(As0.68P0.32)2 with Tc=28.8K. At the maximum frequency of 10 kHz provided by the PPMS equipment, we have clearly detected a second dissipation peak, which is absent at lower frequencies. An example is shown in
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Fig. 1. Further investigation on such single crystals are on the way. Taking into account that now we have investigated a single crystal, we are confident to claim that the ac susceptibility measurement are clearly an experimental evidence of non centrosymmetric vortices in multi component superconductors.
Figure 1: Temperature dependence of the out of phase susceptibility of the BaF2(As0.68P0.32)2 single crystal in a DC field of 5 T, ac field amplitude of 1 Oe, and frequencies of 6, 8 and 10 kHz
References 1. M.V. Milosevic and A. Perali, Supercond. Sci. Technol., 28 (2015) 060201. 2. V. Stanev and Z. Tesanovic, Phys. Rev. B 81 (2010) 134522. 3. R. Geurts, M.V. Milosevic, F.M. Petters, Phys. Rev. B 81 (2010) 214514. 4. J. Garaud, J. Carlstrom, E. Babaev, Phys. Rev. Lett. 107 (2011) 197001. 5. A. Crisan, Y. Tanaka, et al., Japn. J. Appl. Phys., 46, 19 (2007) L451 L453. 6. Y. Tanaka, A. Crisan, et al., Japn. J. Appl. Phys., 46, 1 (2007) 134 145.
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23.1
Anisotropy, phase separation, and superconductivity in iron based superconductors
Roman Puzniak Institute of Physics, Polish Academy of Sciences, PL 02 668 Warsaw, Poland
Email: [email protected] Keywords: high Tc superconductors, iron based superconductors, anisotropy, nanoscale phase separation
The iron chalcogenide superconductors attract a lot of attention due to flexible solid state chemistry and very high critical temperature, Tc, up 100 K for single layer of FeSe. The iron chalcogenides FeSe1−x superconductors are composed of two dimensional sheets held together by van der Waals interactions, which enables their intercalation with various species and interestingly leads to an enhancement of Tc. It was suggested that an inhomogeneous spatial distribution of ions and small inclusions of hexagonal phase chalcogenides with nanoscale phase separation seems to enhance the superconductivity [1]. The pnictides, with constituting layers held by stronger ionic forces, do not provide such a possibility of material modification through intercalation chemistry. Nevertheless, it seems that they are excellent material to introduce fine changes in the microstructure of the crystals. Furthermore, they exhibit strong anisotropy of superconducting state properties being a common ingredient for all high Tc superconductors. Comprehensive review of methods of synthesis and crystal growth, structural and superconducting properties of alkali metal intercalated iron selenides superconductors AxFe2−ySe2 (A = K, Rb, Cs, Tl) was published recently by Krzton Maziopa et al. [2]. It was concluded that magnetic order is mutually combined with defined iron vacancy order in the structure. It was shown that magnetic order does not hinder an appearance of superconductivity in these materials below ~ 30 K and both magnetism and superconductivity can coexist, as a phase separation occurs in apparently single crystals. The majority phase of the composition A2Fe4Se5 (245) is insulating, magnetic and shows ordered pattern of Fe vacancies in the structure. The second, minority 122 phase is conducting/semiconducting and becomes superconducting below Tc ~ 30 K. The minority phase, which fills about 10–15% of the crystal volume, is uniformly distributed within the volume of the crystal and it looks to be impossible to increase significantly the minority phase fraction by doping or annealing. The superconducting state is characterized by a very small lower critical field and a large
130 Superstripes 2017, Ischia June 4 10, 2017 superconducting penetration depth of the order of 1.8 m. Superconducting properties were found to strongly depend on exact stoichiometry and post synthesis annealing. Magnetic and transport measurements of RbxFe2−ySe2 single crystals showed that after annealing at the temperature of phase separation, Tp, a significant rise of Tc is observed and the transition to the superconducting state becomes narrower. The muon spin rotation and relaxation ( SR) and scanning transition electron microscopy (STEM) measurements showed that nonmagnetic regions of the crystal reorder after annealing at Tp = 488 K. It was found that regions size decreases, however, their number increases, hence, in consequence total volume remains the same. It was concluded that annealing of RbxFe2−ySe2 is an effective tool to vary the microstructure of the crystals resulting from mesoscopic phase separation and to improve their superconducting properties, in particular Tc. The aim of presented studies is to clarify the nature of Fe sites of RbxFe2−ySe2 and to determine the impact of annealing at phase separation temperature, leading to more homogenous phase distribution in mesoscopically phase separated superconductors. The mechanism leading to appearance of superconducting state is proposed.
This work was partially supported by the National Science Centre of Poland based on decision No. DEC 2013/08/M/ST3/00927.
References 1. A. Wittlin, P. Aleshkevych, H. Przybylinska, D. J. Gawryluk, P. Dluzewski, M. Berkowski, R. Puzniak, M. U. Gutowska, and A Wisniewski, “Microstructural magnetic phases in superconducting FeTe0.65Se0.35”, Supercond. Sci. Technol. 25, 065019 (2012) http://iopscience.iop.org/0953 2048/25/6/065019 2. A. Krzton Maziopa, V. Svitlyk, E. Pomjakushina, R. Puzniak, and K. Conder, “Superconductivity in alkali metal intercalated iron selenides”, J. Phys.: Condens. Matter 28, 293002 (2016) https://doi.org/10.1088/0953 8984/28/29/293002
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23.2
Low temperature STM/STS of FeSe
C. Di Giorgio 1, A. Putilov 1, D. Trainer 1, E. Lechner 1, A. Aladishkin2, A. Melnikov2, O.S. Volkova4,5A. N. Vasiliev, 4,5,6 D. A. Chareev, 7 G. Karapetrov, 2 and M. Iavarone1 1 Department of Physics, Temple University, Philadelphia, Pennsylvania 19122, USA 2 Institute for Physics of Microstructures, Russian Academy of Sciences, Nizhni Novgorod (Russia) 3 Department of Physics, Drexel University, Philadelphia, Pennsylvania 19104, USA 4 Physics Faculty, M.V. Lomonosov Moscow State University, Moscow 119991, Russia 5 Theoretical Physics and Applied Mathematics Department, Ural Federal University, 620002 Ekaterinburg, Russia 6 National University of Science and Technology “MISiS”, Moscow 119049, Russia 7 Institute of Experimental Mineralogy, Russian Academy of Sciences, 142432 Chernogolovka, Moscow District, Russia
Email: [email protected] Keywords: low temperature STM, Fe based superconductors, multigap superconductivity, vortex matter
FeSe superconductors and their related systems have attracted much attention in the study of iron based superconductors owing to their simple crystal structure and peculiar electronic and physical properties. The bulk FeSe superconductor has a superconducting transition temperature (Tc) of ~8 K and it can be dramatically enhanced both by applying pressure and by chemical substitution. We will present low temperature scanning tunneling microscopy and spectroscopy measurements of high quality FeSe single crystals. Our results show the multigap nature of superconductivity in this material from the vortex lattice and the change of tunneling spectra as a function of chemical substitution. The role of disorder and twin boundaries in this material will be discussed as well.
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23.3
STM/STS studies on the spatial dependence of energy gap in high Tc cuprate Bi2Sr2CaCu2O8+δδδ
M. Oda,1 Kurosawa,1 S. Mizuta,1 T. N. Momono,2 K. Takeyama,3 H. Yoshida1 and M. Ido1 1Department of Physics, Hokkaido Univ., Sapporo, Japan 2Department of Applied Science, Muroran Institute of Technology, Muroran, Japan 3Department of Physics, Asahikawa Medical Univ., Asahikawa, Japan
Email: [email protected] Keywords: STM/STS; 1d superlattices; superconducting gap; pseudogap; charge order.
One of the interesting features of Bi based high Tc cuprates such as Bi2Sr2CaCu2O8+δ (Bi2212) is the one dimensional (1D) superlattice structure along the b axis (forming a slant angle of 45° from the Cu Oinplane bond direction), modulating the bond length between the Cu and the apical O (Oapical) atoms of CuO5 pyramids [1]. This has been considered to cause a periodic modulation of the antiferromagnetic (AFM) coupling between Cu spins J(r) [2]. The period of the 1D superlattice, ~26 Å, is similar to the superconducting (SC) coherence length of this system; therefore, it may affect local properties of the superconductivity [2, 3]. In this study, to clarify the effect of such a superlattice structure on the high Tc superconductivity, we performed STM/STS experiments at 8 K on cleaved surfaces of underdoped (UD) and optimal (OP) Bi2212 crystals and examined the intrinsic spatial dependence of the SC gap (SCG). In many cases of STM/STS experiments on UD Bi2212 crystals, we observe STS spectra consistent with a two gap structure consisting of a d wave SCG and a spatially inhomogeneous pseudogap (PG), the so called “large PG,” whose size PG varies in nanometer scale over a wide range from an energy of the d wave SCG amplitude 0 to several times larger one [6,8]. In such UD crystals, images of the local density of states (LDOS) exhibit a nanostripe Cu O Cu bond centered modulation at higher energies around PG and a checkerboard modulation at lower energies around 0 [4~8]; therefore, it is unclear whether the overall SCG on the entire Fermi surface correlates with the 1D supperlattice. On some cleaved surfaces of OP Bi2212, however, no nanostripe and checkerboard modulations are observed, and the STS spectrum exhibits a single d wave like SCG structure within the areas examined; it is characterized by sharp peaks at bias voltages
Vs corresponding to the gap edges Vs = ± 0/e and a V shaped bottom at lower voltages around Vs=0. This enabled us to demonstrate the intrinsic spatial dependence of SCG in Bi2212. Thus, it has been demonstrated that the d wave like SCG changes along the b axis with an amplitude of ~5% of its average value and the same period as in the 1D superlattice or J(r). This finding probably suggests a correlation between the SCG and the AFM coupling of Cu spins.
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References 1. A. Bianconi et al., Phys. Rev. B 54, 4310 (1996). https://doi.org/10.1103/PhysRevB.54.4310 2. M. Mori et al., Phys. Rev. Lett. 101, 247003 (2008). https://doi.org/10.1103/PhysRevLett.101.247003 3. J. A. Slezak et al., PNAS 105, 3203 (2008). https://doi.org/10.1073/pnas.0706795105 4. Y. Kohsaka et al., Science 315, 1380 (2007). https://doi.org/10.1126/science.1138584 5. Y. Kohsaka et al., Nature 454, 1072 (2008). https://doi.org/10.1038/nature07243 6. T. Kurosawa et al., Phys. Rev. B 81, 094519 (2010). https://doi.org/10.1103/PhysRevB.81.094519 7. T. Machida et al., Nature Communications 7, 11747 (2016). http://doi.org/10.1038/ncomms11747 8. T. Kurosawa et al., J. Phys. Soc. Jpn. 85, 0447091 (2016). http://doi.org/10.7566/JPSJ.85.044709
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24.1
Ultrafast doublon dynamics in photo excited 1T Tas2
Isabella Avigo1, Manuel Ligges1, Denis Golež 2, Hugo U. R. Strand2, Ljupka Stoichevska1, Matthias Kalläne3, Kai Rossnagel3, Martin Eckstein4, Philipp Werner2, Uwe Bovensiepen1 1 Faculty of Physics, University of Duisburg Essen, 47048 Duisburg, Germany 2 Department of Physics, University of Fribourg, 1700 Fribourg, Switzerland 3 Institute of Experimental and Applied Phisics, University of Kiel, 24098 Kiel, Germany 4 Max Plank Research Departement of Structural Dynamics, University of Hamburg CFEL, 22761 Hamburg, Germany
Email: isabella.avigo@uni due.de Keywords: Ultrafast spectroscopy; Charge density wave; Mott physics; Metal insulator transition
Complex matter is characterized by a rich interplay among different microscopic degrees of freedom. This competition or coexistence often occurs on comparable energy scales and, thus, might be hard to disentangle in the spectral domain. Analyzing the dynamics of such systems, driven out of equilibrium, has the potential to shed new light on the underlying short and long range interactions because different coupling mechanisms can result in the time domain on experimentally distinguishable femto to picosecond time scales[1]. 1T TaS2 is a quasi 2 dimensional Mott Insulator that also exhibits strong electron phonon interaction, making it a suitable model system to address such a problem. Using femtosecond time resolved photoemission spectroscopy we monitor the transient population of the upper Hubbard band, showing that doublon dynamics occur on a time scale of one or few hopping cycle, ruling out any interaction with the lattice. This finding leads to a reduction in complexity in the formulation of theoretical modeling, as, at least at early stages after photo perturbation, only the electronic part of the system can be considered, while the phononic part is still frozen. From results of a theoretical modeling obtained with a nonequilibrium dynamical mean field theory approach, we concluded that the dynamics of the transient population of the doublon states are governed by the effective band filling and our results are best reproduced in the case of a slightly hole doped system. Financial support by the Deutsche Forschungsgemeinschaft through SFB 616, SPP 1458, SFB 1242 and from ERC Starting Grant No. 278023 are gratefully acknowledged.
References 1. C. Giannetti et al., Advance Physics 65, 58 (2016) http://dx.doi.org/10.1080/00018732.2016.1194044
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24.2
Dynamical phase transition to a charge transfer state
N. Kirova1 and S. Brazovskii2 1 LPS, CNRS, Univ. Paris Sud, Université Paris–Saclay 91405, Orsay, France 2 LPTMS, CNRS, Univ. Paris Sud, Université Paris–Saclay 91405, Orsay, France
Email: natacha.kirova@u psud.fr Keywords: optical pumping, excitons, excitonic insulator, pump induces phase transition
A dynamical phase transition can be provoked by a short optical pumping to excitons. We consider a system prone to a thermodynamic instability towards a charge ordered state of electrons like in neutral ionic transitions of donor acceptor structures. We notice that here the density of pumped excitons contributes additively to the thermodynamic order. To describe both thermodynamic and dynamical effects on equal footing, we adopt for the phase transition a view of the “excitonic insulator” and suggest a formation of the macroscopic quantum state for the pumped excitons. The double nature of the ensemble of excitons leads to an intricate time evolution: the dynamical transition between number–preserved and phase–locked regimes, macroscopic quantum oscillations from interference between the Bose condensate of excitons and the ground state of the excitonic insulator. Modelling of an extended sample shows also stratification in domains of low and high densities which evolve through local dynamical phase transitions and a sequence of domains’ merging.
Formation of domains of the new phase.
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References 1. S. Brazovskii and N. Kirova, “The excitonic insulator rout trough a dynamical phase transition induced by an optical pulse”, JETP, 122, (2016) 412; arxiv.org/abs/1512.06200 2. S. Brazovskii and N. Kirova “Dynamical phase transitions and patterns formation induced by pulse pumping of excitons to a system near a thermodynamic instability”, Phys. Rev. B 94 (2016) 054302.
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24.3
Ultrafast orbital manipulation in copper oxides
Claudio Giannetti
Email: [email protected]
The short range interactions among the electrons occupying the copper and oxygen orbitals represent the universal underlying mechanism of many exotic properties of copper oxides, such as the intrinsic nanoscale electronic inhomogeneity, the ubiquitous antinodal pseudogap and the onset of high temperature superconductivity. Recently, the use of ultrashort light pulses has been introduced as a "non conventional" control parameter to transiently manipulate the electronic occupation of the Cu 3d and O 2p orbitals and investigate the fundamental interactions that drive the relaxation towards the correlated ground state. Here I will review the most recent discoveries obtained via the ultrafast manipulation of the orbital occupation in cuprates. I will discuss the existence of a high temperature crossover at optimal doping between the physics of a doped Mott insulator to that of a more coherent metal. The underdoped correlated ground state constitutes the fertile ground for the onset of the low temperature symmetry breaking instabilities, such as the onset of charge order.
References 1. S. Peli et al. The room temperature prodrome of charge order in copper oxides. arXiv:1508.03075 (2016).
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24.4
Collective electronic orders under strong optical drive studied by means of time resolved multipulse optical spectroscopy
A. Pogrebna (1,2), I. Madan (1), P. Kusar (1), M. Naseska (1), V. V. Kabanov (1), T. Mertelj (1,3), Z. A. Xu (4), M. Oda (5), D. Mihailovic (1,3) (1) Complex Matter Department, Jozef Stefan Institute, Jamova 39, SI 1000 Ljubljana, Slovenia (2) Radboud University, Institute for Molecules and Materials, Nijmegen 6525 AJ, The Netherlands (3) Center of Excellence on Nanoscience and Nanotechnology – Nanocenter (CENN Nanocenter), Jamova 39, SI 1000 Ljubljana, Slovenia (4) Department of Physics, Zhejiang University, Hangzhou 310027, People’s Republic of China (5) Department of Physics, Hokkaido University, Sapporo 060 0810, Japan
Email: [email protected] Keywords: ultrafast nonequilibrium phase transitions, cuprates, iron based superconductors, superconductivity, spin density wave
Ultrafast phase transitions from and into electronically ordered states, which occur during the quench following a strong femtosecond laser excitation, have become a rather hot research topic during the last decade. Experimentally various electronic orders were investigated with emphasis on ferromagnetism[1], charge and orbital ordering[2], charge density waves[3] as well as superconductivity[4]. Despite a significant occurrence frequency of antiferromagnets the collinear antiferromagnetism and the related spin density wave (SDW) order were among the less studied orders[5] in this context, perhaps due to the absence of the linear coupling of the order parameter to photons. Despite the lack of momentum sensitivity and in general complicated response functions all optical time resolved spectroscopy can give some insight into ultrafast optical quenches of electronic order parameters. I will present some of our recent efforts reaching beyond the standard 2 pulse pump probe technique applied to the cuprate superconductors and the antiferromagnetic spin density wave in undoped iron based pnictides.
References 1. A. Kirilyuk, A. V. Kimel, T. Rasing, Rev. Mod. Phys. 82, 2731 (2010). 2. T. Ogasawara, T. Kimura, T. Ishikawa, M. Kuwata Gonokami, and Y. Tokura, Phys. Rev. B 63, 113105 (2001). 3. P. Kusar, V. V. Kabanov, J. Demsar, T. Mertelj, S. Sugai, and D. Mihailovic, Phys. Rev. Lett. 101, 22700 (2008). 4. F. Schmitt et al., Science 321, 1649 (2008). 5. A. V. Kimel, R. V. Pisarev, J. Hohlfeld, and Th. Rasing, Phys. Rev. Lett. 89, 287401 (2002).
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25.1
Unraveling the ultrafast dynamics of spatially confined phonons and plasmons in low dimensional nanosystems
Giovanni Maria Vanacore and Fabrizio Carbone Institute of Physics, Laboratory for Ultrafast Microscopy and Electron Scattering (LUMES), Ecole Polytechnique Fédérale de Lausanne (EPFL), Lausanne, Switzerland
Email: [email protected] Keywords: Ultrafast electron microscopy; quantum materials; ultrafast dynamics; phononics; plasmonics
Understanding the ultrafast evolution of low dimensional materials under non equilibrium conditions plays a fundamental role in deciphering the mechanism governing chemical and physical functions. With direct visualization, the technological development of new generation nanoscale devices would become feasible. Although an enormous effort has been devoted to the comprehension and improvement of these materials and devices, the capability of investigating their dynamic behavior is hindered by the difficulty of simultaneously studying their evolution in space and time at the appropriate scales. Instead, a novel approach for visualization of matter with high temporal and spatial resolutions, together with momentum and energy selection, is indispensable to fully exploit their potential. Ultrafast electron microscopy (UEM) has been recently developed with the capability of performing time resolved imaging, diffraction and electron spectroscopy [1], making this technique a unique tool for the dynamic investigation of surfaces, interfaces and nanostructures. In this contribution, we will address several recent applications to the investigation of elementary excitations, such as plasmons and phonons, in low dimensional nanosystems. In particular, it is now possible to visualize and control the dynamics of the plasmonic near field optically created in the vicinities of single nanostructures or arrays of nanocavities with nanometer spatial and femtosecond temporal resolutions [2,3]. Also, ultrafast diffraction is used to unveil the effect of the reduced dimensionality on the non equilibrium dynamics of lattice vibrations (phonons) and their transport regimes [4,5].
References 1. G.M. Vanacore, et al., Nano Today 11, 228 249 (2016). 2. L. Piazza, et al., Nat. Commun. 6, 6407 (2015). 3. T.T.A. Lummen, et al., Nat. Commun. 7, 13156 (2016). 4. G.M. Vanacore, et al., Nano Lett. 14, 6148 6154 (2014). 5. J. Hu, G. M. Vanacore, et al., Proc. Natl. Acad. Sci. USA 113, E6555 E6561 (2016).
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25.2
Nonequilibrium quasiparticle dynamics in Bi based superconductors measured by modulation photoexcitation spectroscopy
Y. Toda1, S. Tsuchiya1, T. Kurosawa2, M. Oda2, T. Mertelj3, I. Madan3, D. Mihailovic3 1 Department of Applied Physics, Hokkaido University, Sapporo, 060 8628, Japan 2 Department of Physics, Hokkaido University, Sapporo, 060 0810, Japan 3 Complex Matter Department, Jozef Stefan Institute, Ljubljana, SI 1000, Slovenia.
Email: [email protected] Keywords: time resolved spectroscopy; polarimetry; pseudogap.
Optical pump probe (Pp) spectroscopy using femtosecond pulse laser is a unique method to separate the quasiparticle (QP) dynamics associated with superconducting (SC) and pseudogap (PG) states in the time domain, where the nonequilibrium QPs excited by the pump are characterized by the reflectivity changes of the probe pulse with variable delay times between the two pulses [1]. The method can also clarify the condensation dynamics of superconductors within the photoexcited volume when the pump fluence is strong enough to destroy the SC state. In the previous studies on underdoped Bi2212, we found that the QP dynamics shows a delay of the SC recovery whose duration time increases with increasing the fluence. Since the observed delay time is comparable to the relaxation time of the PG QPs, we concluded that the PG is responsible for the formation of high Tc superconductivity [2]. We also performed the polarized Pp experiments, which can separate the QP dynamics into isotropic and anisotropic modes with respect to the probe polarization [3]. Since the pump polarization shows almost no distinct anisotropies, the probe anisotropies can be associated with the presence of a spontaneous breaking of the rotational symmetry. Here the anisotropic SC and PG signals are identified to be polarized along the crystalline axes and Cu O bond directions, respectively, which are associated with B1g and B2g like symmetries of the dielectric tensor in analogy with Raman spectroscopy. The B2g symmetry breaking can originate in the weak orthorhombicity of the crystal (BiO chain ordering) while the B1g symmetry breaking can be associated with the softness of the CuO2 planes towards stripe ordering or similar textures. The conventional Pp spectroscopy including the above employs lock in detection by chopping the pump pulse, where we can detect the differences of the probe reflectivity with and without the pump pulse (upper part of Fig. 1 (a)). In this work, we employ the modulation of the pump polarization/chirality for the lock in detection (lower part of Fig. 1 (a)). The modulation of the pump polarization was realized by using a liquid crystal variable retarder. The combination with a vortex waveplate can provide additional modulations of the chirality. Because of the nearly constant pump fluence, improvements of the sensitivity to the local/global anisotropies induced by the pump
141 Superstripes 2017, Ischia June 4 10, 2017 can be expected. In the weak excitation condition, no additional change to the QP dynamics was detected while anomalous transients were observed above the saturation condition of the SC (Fig. 1 (b)). We will discuss the results from the viewpoint of the symmetry breaking in the ground states of Bi based superconductors.
Figure 1: (a) schematic illustrations of the lock in detections for Pp spectroscopy, (b) DR/R obtained by polarization modulation Pp spectrocopy with various pump fluences. The data were measured for UD Bi2212 at 10K.
References 1. YH. Liu et al., Phys. Rev. Lett. 101, 137003 (2008). 2. Y. Toda et al., Phys. Rev. B 84, 174516 (2011). 3. Y. Toda et al., Phys. Rev. B. 90, 094513 (2014).
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25.3
Delocalized charge carriers in strongly disordered t–J model
Janez Bonca (1, 2) and Marcin Mierzejewski (3) 1) Jozef Stefan Institute, SI 1000 Ljubljana, Slovenia 2) Faculty of Mathematics and Physics, University of Ljubljana, SI 1000 Ljubljana, Slovenia 3) Institute of Physics, University of Silesia, 40 007 Katowice, Poland
Email: [email protected] Keywords: many body localisation, sub diffusion, t J model
We show that electron magnon interaction delocalizes the particle in a strongly disordered system. The analysis is based on results obtained for a single hole in the one–dimensional t–J model. Unless there exists a mechanism that localizes spin excitations, the charge carrier remains delocalized even for a very strong disorder and shows subdiffusive motion up to the longest accessible times. Moreover, upon inspection of the propagation times between neighboring sites as well as a careful finite–size scaling we conjecture that the anomalous subdiffusive transport may be transient and should eventually evolve into a normal diffusive motion.
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25.4
Superconductivity emerging from an electronic phase separation in the charge ordered phase of RbFe2As2
M. Moroni1, E. Civardi1, M. Babij2, Z. Bukowski2, P. Carretta1 1 Dipartimento di Fisica ed Unità CNISM di Pavia, I 27100 Pavia, Italy 2 Institute of Low Temperature, Polish Academy of Sciences, 50 422 Wroclaw, Poland
Email: [email protected] Keywords: charge order, iron based superconductor, orbital selective Mott transition.
Half band filling, a necessary requisite for Mott insulators, can be approached in BaFe2As2 iron based superconductors (IBS) by replacing Ba with an alkali atom A=K, Rb or Cs, resulting in 5.5 electrons per Fe atom [3]. Transport measurements show that AFe2As2 compounds are still metallic [5] but with sizable electronic correlations and with a low Tc superconducting transition [2] (for RbFe2As2 Tc = 2.7 K). Nuclear quadrupole resonance (NQR) is a powerful tool to probe the local charge 75 distribution. Upon cooling the sample below T0≃140 K the As NQR [1] spectrum is observed to progressively broaden with decreasing temperature and below 50 K one clearly observes that the spectrum is actually formed by two peaks nearly symmetrically shifted with respect to the center. This shape recalls the one expected for an incommensurate charge density wave, which causes a periodic modulation of the electric field gradient (EFG) at the nuclei and gives rise to two symmetrically shifted peaks in the spectrum. However the EFG modulation could also be due to the onset of an orbital order. A single exponential recovery function describes very well the recovery of the 75As NQR nuclear magnetization at T ≥ 20K. Below T∗≃ 20 K one observes the appearance of a second component characterized by much longer relaxation times. The appearance of different relaxation rates below T∗ arise from a phase separation causing marked differentiation in the low energy excitations which starts to be significant at low temperature once the effect of electronic correlations is relevant. This behavior could possibly be explained in terms of the orbital selective Mott transition predicted for IBS [4]. The observation of a phase separation in the hole doped IBS is also supported by recent theoretical works [6].
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75 Figure 1: As NQR spectrum in RbFe2As2 at different temperatures between 5 K and 300 K.
References 1. E. Civardi et al., Phys.Rev.Lett. 117, 217001 (2016). 2. Y. P. Wu et al., Phys.Rev.Lett. 116, 147001 (2016). 3. F. F. Tafti et al., Phys. Rev. B 91, 054511 (2015). 4. L. de’ Medici et al., Phys.Rev.Lett. 102, 126401 (2009). 5. F. Eilers et al., Phys. Rev. Lett. 116, 237003 (2016). 6. L. de’ Medici, arXiv:1609.01303v1
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26.1
High temperature superconductivity in hydrides at high pressures
M. I. Eremets, A. Drozdov Max Planck Institute for Chemistry
Email: [email protected] Keywords: high tempearture superconductivity, high pressure
We will present our recent results on the high temperature superconductivity up to 203 K[1] in different hydrides. The superconductivity has been proved by observation of zero resistance, Meissner effect, isotope effect, and X ray diffraction studies [2]. Recent results on infrared and Raman studies will be presented. Pure hydrogen also will be discussed. The observed apparently conventional superconductivity will be discussed in view of numerous theoretical works. Recent proposals of new superconducting materials and prospects for achieving higher critical temperatures of superconducting transition will be discussed too.
References 1. Drozdov, A.P., et al., Conventional superconductivity at 203 K at high pressures. Nature 2015. 525: p. 73 77. 2. Einaga, M., et al., Crys
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26.2
Stable high pressure phases in the H S system determined by chemically reacting hydrogen and sulfur up to 140 GPa
Alexander F. Goncharov 1 Key Laboratory of Materials Physics, Institute of Solid State Physics CAS, Hefei 230031, China 2 Geophysical Laboratory, Carnegie Institution of Washington, Washington, DC 20015, USA
Email: [email protected] Keywords: H S system, structure, high pressure, superconductivity
Synchrotron X ray diffraction and Raman spectroscopy have been used to study chemical reactions of molecular hydrogen with sulfur at high pressures. We find theoretically predicted Cccm and Im 3m H3S to be the reaction products at 50 and 140 GPa, respectively. Im 3m H3S is a stable crystalline phase above 140 GPa and it transforms to R3m H3S on pressure release below 140 GPa. The latter phase is (meta)stable down to at least 70 GPa where it transforms to Cccm H3S upon annealing (T
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26.3
Search for Pressure Induced Superconductivity in Other Hydrides
Katsuya Shimizu1, Harushige Nakao1, Akiyoshi Masuda1, Mari Einaga1, Masafumi Sakata1, Naohisa Hirao2, Saori Kawaguchi2, Yasuo Ohishi2 1 KYOKUGEN, Grad. Sch. Eng. Sci., Osaka University, 1 3 Machikaneyama, Toyonaka, Osaka 560 8531, Japan 2 JASRI, 1 1 1, Sayo cho, Sayo gun, Hyogo 679 5198, Japan
Email: [email protected] u.ac.jp Keywords: high Tc; H2S; pressure
Superconductivity above 200 K was recently reported in the highly compressed hydrogen sulfide (H2S) [1]. The crystal structure of the superconductor was studied by using the synchrotron x ray diffraction at room temperature and the superconducting temperature [2]. The creation of the superconductor from pure H2S was experimentally confirmed. The sample was compressed in a diamond anvil cell (DAC) with the same process with the ref.1, and cooled down to 10 K in the cryostat in SPring 8. The critical temperature and zero resistivity were observed around 180 K. Recently other candidates of the high Tc superconductor in other hydrides were theoretically predicted [3]. We conducted the synthesis of other/new hydrides by compression of some elements in pure hydrogen under low temperature. This work was supported by JSPS KAKENHI Grant Number 26000006.
References 1. A. Drozdov et al., Nature 525, 73 (2015). http://dx.doi.org/10.1038/nature14964. 2. M. Einaga et al., Nature Physics 12, 835 (2016). http://dx.doi.org/10.1038/nphys3760. 3. Y. Li et al., Scientific Reports 5, 9948 (2015). http://dx.doi.org/10.1038/srep09948.
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26.4
Optical Spectroscopy of H3S: Evidence of a new Energy Scale for superconductivity
Thomas Timusk4,5, F. Capitani1, B. Langerome1, J. B. Brubach1, A. Drozdov2, M.I. Eremets2, E. J. Nicol3, J. P. Carbotte4,5, and P.Roy1 1Synchrotron SOLEIL, AILES Beamline, Saint Aubin, 91190, France 2Biogeochemistry Department, Max Planck Institute for Chemistry, PO Box 3060, 55020 Mainz, Germany 3Department of Physics, University of Guelph, Guelph, N1G 2W1 ON Canada 4Department of Physics and Astronomy, McMaster University, Hamilton, ON L8S 4M1, Canada 5The Canadian Institute for Advanced Research, Toronto, ON M5G 1Z8 Canada
Email: [email protected] Keywords: superconductors, high pressure, infrared. reflectance, H3S.
The discovery of a superconducting phase in sulfur hydride under high pressure with a critical temperature above 200 K by Drozdov et al. [1] has provided a new impetus to the search for even higher Tc. Theory predicted and experiment confirmed that the phase involved is H3S with Im 3m crystal structure. The observation of a sharp drop in resistance to zero at Tc, its downward shift with magnetic field and a Meissner effect confirm superconductivity but the mechanism involved remains to be determined. Using the AILES beamline at Soleil, we provide a first optical spectroscopy study of this new superconductor.[2] Experimental results for the optical reflectivity of H3S, under high pressure, for several temperatures and over the range 60 to 600 meV of photon energies, are compared with theoretical calculations based on Eliashberg theory using DFT results for the electron phonon spectral density. Two significant features stand out: some remarkably strong infrared active phonons at approximately 160 meV and a band with a depressed reflectance in the superconducting state in the region from 450 meV to 600 meV. In this energy range, as predicted by theory, H3S is found to become a better reflector with increasing temperature. This temperature evolution is traced to superconductivity originating from the electron phonon interaction. The shape, magnitude, and energy dependence of this band at 150 K agrees with our calculations. This provides strong evidence of a conventional mechanism. However, the unusually strong optical phonon suggests a contribution of electronic degrees of freedom.
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Figure 1: Reflectance ratio R(T)/R(200 K) of H3S in a diamond anvil cell. Solid blue curve is the measured ratio, normalized at 600 meV. The dashed curves are calculated ratios. The strong between 100 and 600 meV are structures are due to bosons. The step at 175 meV is due to the energy gap.
References 1. A.P. Drozdov, M.I. Eremets, I.A. Troyan, V. Ksenofontov, and S.I. Shylin, “Conventional superconductivity at 203 Kelvin at high pressures in the sulfur hydride system,” Nature 525, 73–76 (2015). http://dx.doi.org/10.1038/nature14964. 2. F.Capitani, B. Langerome, J. B. Brubach, P. Roy, A. Drozdov, M.I. Eremets, E. J. Nicol, J. P. Carbotte, and T. Timusk, Spectroscopy of H3S: evidence of a new energy scale for superconductivity, arXiv:1612.0673v2
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26.5
Fano Resonances at Lifshitz transitions driving high Tc superconductivity: from iron based superconductors to the case of H3S and p Terphenyl
Antonio Bianconi 1,2,3 1RICMASS, Rome International Centre for Material Science Superstripes, via dei Sabelli 119A, 00185 Rome, Italy 2 Institute of Crystallography, CNR, via Salaria Km 29.300, Roma, I 00015, Italy 3 National Research Nuclear University MEPhI 115409 Moscow Russia
Email: [email protected] Keywords: superlattices of atomic layers or atomic wires; Lifshitz transitions, Fano resonances, Shape resonances, Feshbach resonances
In 1993 it has been proposed that particular metallic heterostructures at the atomic limit made of superconducting units (layers, or stripes, or wires, or spheres) having a nanoscale size of the order the wavelength of electrons at the Fermi level (see panel A in Fig.1) could show high temperature superconductivity (HTS) if the chemical potential EF is tuned near a Lifshitz transition (see panel A in Fig.2)
i) ii) Figure Panel:i) the drawing of the heterostructure in the patent [1] and the structure or p Terphenyl Panel ii) the drawing of DOS for HTS from ref.[1], and the tuning of the chemical potential in K dopecd p Terphenyl ref. [2]
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This scenario has been called the superstripes scenario where a striped landscape promotes HTS where the chemical potential is tuned by chemical doping, strain or pressure [2]. The maximum Tc amplification is driven by "Fano resonance" between the pairs in the BCS BEC crossover in the n th new appearing band with low Fermi energy and BCS like pairs in the other (n 1) bands with large Fermi energies. This scenario has been recently proposed for plastic superconductors like p terphenyl [3] and for H3S [4]. Fig. 1 shows structure (a superlattice of stripes) of p terphenyl and the tuning the chemical potential at a Lifshitz transition in the conduction band of p terphenyl by K doping. However the synthesis of HST tuned at a Lifshitz transition is very difficult task since in strongly correlated multiband systems tuning the chemical potential at a Lifshitz transition gives a frustrated or arrested multiscale phase separation from nano scale to micron scale [5] . This is the driving force for the emerging of granular matter with percolating pathways at the interphase between multiple puddles where a complex non Euclidean geometry promotes quantum coherence at high temperature at optimum doping [6]. Therefore a similar complex structural landscape is expected for p Terphenyl at optimum doping.
References 1. A. Bianconi, “Process of increasing the critical temperature Tc of a Bulk Superconductor by Making Metal Heterostructures at the Atomic Limit” US Patent 6,265,019 (2001) priority date Dec 7, 1993. 2. A. Bianconi, Nature. Phys. 9, 536 (2013) 3. M.V. Mazziotti, A. Valletta, G. Campi, D. Innocenti, A. Perali, A. Bianconi (May 26, 2017) Arxiv: arXiv:1705.09690 4. A. Bianconi, T. Jarlborg EPL (Europhysics Letters 112, 37001 (2015) 5. N. Poccia, et al., Proc. Nat. Acad. Sci. 109, 15685 (2012). 6. G. Campi, A. et al., Nature 525, 359 (2015).
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27.1
Compressed H2S, superfluid density and the quest for room temperature superconductivity
Jeff Tallon1,2, Evgeny Talantsev1, Wayne Crump1, James Storey1 1Robinson Research Institute, Victoria University of Wellington, P.O. Box 33436, Lower Hutt 5046, New Zealand. 2 MacDiarmid Institute for Advanced Materials and Nanotechnology, Victoria University of Wellington, P.O. Box 33436, Lower Hutt 5046, New Zealand.
Email: [email protected] Keywords: high pressure, fluctuations, H2S, room temperature superconductivity, superfluid density.
Fifty years ago New Zealand physicist Neil Ashcroft predicted that hydrogen at very high pressure would superconduct at room temperature [1]. Now that prediction is close to being realized. Recently sulphur hydride when compressed to 1.5 million atmospheres was shown to superconduct with Tc = 203 K, the current record [2]. But at such temperatures thermal fluctuations might be expected to break up Cooper pairs. For example in the cuprates fluctuations reduce Tc by 30% or more below the mean field value which in Bi2212 is as high as 150 K [3]. Similar effects are found in iron pnictides. How does superconductivity survive in sulphur hydride at such balmy temperatures?
Figure 1: The penetration depth and superfluid density of highly compressed H3S is calculated from the critical current density. It implies a very high phase fluctuation temperature scale (1470 K) arising from the 3D character of H3S.
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The key parameter underlying fluctuations in these materials is the superfluid density [4]. We show how this can be measured in any superconductor from the self field critical current density [5]. This leads to a remarkable scaling behaviour observed for all superconductors of any type or symmetry or anisotropy, including single atomic layer superconductors. In this way we measure the superfluid density in compressed sulphur hydride in order to determine the fluctuation temperature scale Tfluc. We find that Tfluc for phase fluctuations exceeds 1400 K [6] and it is shown that dimensionality plays a key role in suppressing or enhancing thermal fluctuations to the benefit of hydrogen sulphide and the detriment of its more layered 2D competitors. At the same time we find that Tfluc for amplitude fluctuations is around 300 K and this has important implications for the quest for room temperature superconductivity. Appealing to the way in which superfluid density, Tfluc and Tc each scale it seems that room temperature superconductivity is nearly ruled out – but not quite.
References 1. N.W. Ashcroft, Phys. Rev. Lett. 21, 1748 (1968). https://doi.org/10.1103/PhysRevLett.21.1748. 2. A.P. Drozdov et al., Nature 525, 73 (2015). http://dx.doi.org/10.1038/nature14964. 3. J.L. Tallon, J.G. Storey and J.W. Loram, Phys. Rev. B 83, 092502 (2011). https://doi.org/10.1103/PhysRevB.83.092502. 4. V.J. Emery and S.A. Kivelsen, Nature 374, 434 (1995). http://dx.doi.org/10.1038/374434a0. 5. E.F. Talantsev, J.L. Tallon, Nature Commun., 6, 7820 (2105). https://dx.doi.org/10.1038%2Fncomms8820. 6. E.F. Talantsev, W.P. Crump, J.G. Storey, J.L. Tallon, Annalen der Physik, 529 (3),1600390 (2017). http://dx.doi.org/10.1002/andp.201600390.
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27.2
High Temperature Superconductivity in H3S why so high?
Frank Marsiglio1* 1University of Alberta Department of Physics
Email: [email protected] Keywords: high Tc, superconductivity, microscopic mechanism
H3S superconducts at unprecedented high temperature under extreme pressures. It is important to understand why, particularly if we are to optimize the possibility of achieving the necessary conditions through chemical pressure by way of substitution. In this talk we will discuss possible mechanisms and the role of the electronic density of states in achieving high Tc.
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27.3
Formation Process of High Tc Phase of Sulfur Hydride
Mari Einaga1, Masafumi Sakata1, Katsuya Shimizu1, Alexander Drozdov2, Mikhail Eremets2, Saori Kawaguchi3, Naohisa Hirao3, and Yasuo Ohishi3. 1KYOKUGEN, Graduate School of Engineering Science, Osaka University, Machikaneyamacho 1 3, Toyonaka, Osaka, 560 8531, Japan. 2Max Planck Institute for Chemistry, Hahn Meitner Weg 1, 55128 Mainz, Germany. 3JASRI, 1 1 1, Sayo cho, Sayo gun, Hyogo 679 5198.
Email: [email protected] u.ac.jp Keywords: Superconductivity; Synchrotron X ray Diffraction; Sulfur Hydride.
The cooperation between theoretical and experimental investigation broke the record for superconducting critical temperature Tc in hydrogen sulfide under high pressure at the end of 2014[1, 2]. The material improved the highest Tc by more than 30 K and shows the conventional superconductivity. By compression at low temperature 200 K, a superconducting phase named low Tc phase appears above 100 GPa, and Tc increases up to 150 K with increase pressure to 200 GPa. High Tc phase showing Tc over 200 K is obtained after the low Tc phase is annealed at near room temperature. Several theoretical groups proposed the crystal structures and the value of Tc in some sulfur hydrides HxSy under pressure [3 6]. According to the results of their theoretical calculation, it is considered that H2S dissociates into H3S and elemental sulfur through other stoichiometric compounds HxSy, and the H3S which has cubic structure shows the high Tc over 200 K [2, 3]. However, the phase boundary and the crystal structures above 50 GPa were not determined experimentally yet. Here we report our recent results of synchrotron X ray diffraction studies on formation process of the superconducting phases in sulfur hydride and deuteride. Our results suggest that H2S dissociates into H3S and elemental sulfur under high pressure through metastable phases, and the high Tc phase corresponds to theoretically predicted cubic H3S.
References 1. A. P. Drozdov et al., Nature, 525, 73 (2015). 2. Y. Li et al., J. Chem. Phys., 140, 174712 (2014). 3. D. Duan et al., Sci. Rep., 4, 6968 (2014). 4. I. Errea et al., Phys. Rev. Lett., 114, 157004 (2015). 5. T. Ishikawa et al., Sci. Rep., 6, 23160 (2016). 6. R. Akashi et al., Phys. Rev. Lett., 117, 075503 (2016). 7. M. Einaga et al., Nature Phys. 12, 835 (2016).
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28.1
Impurity dependent superconductivity, Berry phase and bulk Fermi surface of the Weyl type II semi metal candidate MoTe2
D. Rhodes†,1, 2 Q. Zhou†,1, 2 R. Schoenemann,1, 3 Q. R. Zhang,1, 2 E. Kampert,3 Y. c. Chiu,1, 2 Y. Lai,1, 2 Y. Shimura,1, 4 G. T. McCandless,5 J. Y. Chan,5 J. Lee,6 J. P. C. 6 1, 2 7 1,∗ Ruff, S. Das, E. Manousakis,2, 1 M. D. Johannes, and L. Balicas 1Rome International Centre for Material Science Superstripes, RICMASS, via dei Sabelli 119A, 00185 Rome, Italy 2 Institute of Crystallography, CNR, via Salaria Km 29.300, Monterotondo Roma, I 00015, Italy.
Email: [email protected] Keywords: Weyl type II semimetals; Fermi surface; Berry phase.
The electronic structure of semi metallic transition metal dichalcogenides, such as WTe2 and orthorhombic MoTe2, are claimed to be characterized by a non trivial Z2 topological invariant [1]. In addition, their Fermi surfaces are predicted to contain pairs of linearly touching electron and hole pockets each associated with a non trivial Chern number [2]. For this reason, these compounds were recently claimed to conform to a new class, deemed type II, of Weyl semi metalic systems [2]. A series of very recent angle resolved photoemission experiments (ARPES) seem to display a broad agreement with these last predictions detecting, for example, topologically non trivial Fermi arcs [3]. In an attempt to validate these predictions, through measurements of their bulk Fermi surface (FS) via quantum oscillatory phenomena, we synthesized high quality single crystals of semi metallic MoTe2 [4]. We find that its superconducting transition temperature depends on disorder as quantified by the ratio between the room and low temperature resistivities, suggesting the possibility of a non trivial superconducting pairing symmetry. Similarly to WTe2, its magnetoresistivity does not saturate at high magnetic fields and can easily surpass 106 %. An analysis of the quantum oscillatory signal superimposed onto the magnetic susceptibility extracted from the measurements of the magnetic torque, indicates a non trivial Berry phase quite close to the value of ≃ π predicted for Weyl type II systems. Quite surprisingly, the geometry of the Fermi surface (FS) as extracted from the quantum oscillatory phenomena, is markedly distinct from the calculated one and therefore from the FS recently revealed by ARPES. A broad anomaly seen in the heat capacity and in the Hall effect suggests that the crystallographic and the electronic structures might evolve upon cooling below 100 K, perhaps explaining the discrepancy between predictions, ARPES and our experimental observations.
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1000 1.5 )
e a c 5 H ll c 100 T = 1.7 K %)
6 1.0 0 #1; RRR = 385
cm) 10 (10 ( #2; RRR = 518 0 ρ ρ -5 / #3; RRR = 1020 0.5 SdHSignal ( 1 ρ H ll c 0.025 0.050 0.075 T = 1.7 K 0 100 200 300 ( H) -1 (T -1) T (K) 0.0 0 10 d f ∂(τ/H)/∂H
b %)
2 3 4 LK-fit (10
0 o ρ 5 θ ∼ 3 / cm) 1 ρ ( 0 H ll b (Arb. Units)
ρ T = 25 mK
T = 1.7 K χ 0 0 0.0 0.2 0.4 0.6 0.8 0 20 40 60 0.1 0.2 ( H) -1 (T -1) T (K) 0H (T) 0
Figure 1: (a) Resistivity ρ, for currents flowing along the a−axis, as a function of the temperature T for three representative single crystals displaying resistivity ratios ρ(300 K)/ρ(2 K) between 380 and ∼ 1000. (b) ρ as a function of T for each single crystal indicating that Tc depends on sample quality. The apparent hysteresis is due to a non ideal thermal coupling between the single crystals, the heater and the thermometer. (c) ρ as a function of the field H applied along the c axis at a temperature T = 1.7 K. Notice i) the non
saturation of ρ(H) and ii) that ρ ( 0H)/ρ0 = (ρ( 0H) − ρ0)/ρ0, where ρ0 = ρ( 0H = 0 T; T = 6 2 K) surpasses 1.4 × 10 % at 0H = 60 T. (d) ρ as a function of 0H applied along the b−axis also at T = 1.7 K and for the same single crystal. (e) Shubnikov de Haas signal
superimposed onto the magnetoresistivity for 0H∥c axis and for three temperatures, T = 8 K (blue line), 4.2 K (red line) and 1.7 K (black line), respectively. (f) Oscillatory signal
(black line) superimposed onto the magnetic susceptibility χ= ∂(τ/ 0H)=∂( 0H), where τ is the magnetic torque. Red line is a fit to four Lifshitz Kosevich oscillatory components, i.e. two fundamental frequencies plus their harmonics, from which one extracts the respective Berry phases.
References 1. X. F. Qian, J. W. Liu, L. Fu, and J. Li, Quantum spin Hall effect in two dimensional transition metal dichalcogenides, Science 346, 1344 (2014). 2. A. A. Soluyanov, D. Gresch, Z. Wang, Q. Wu, M. Troyer, X. Dai and B. A. Bernevig, A New Type of Weyl Semimetals, Nature 527, 495 498 (2015). 3. L. Huang, et al, Spectroscopic evidence for type II Weyl semimetal state in MoTe2, Nat. Mater. 15, 1155 1160 (2016); K. Deng et al, Experimental observation of topological Fermi arcs in type II Weyl semimetal MoTe2, Nat. Phys. 12, 1105 (2016). 4. D. Rhodes et al., Impurity dependent superconductivity, Berry phase and bulk Fermi surface of the Weyl type II semi metal candidate MoTe2, arXiv:1605.09065 (2016).
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28.2
Resonant X ray Inelastic Scattering and nanoscale inhomogeneity in FeSe1 xTex
Jose Mustre de León, Diego Mulato 1 Departamento de Física Aplicada, Cinvestav Mérida, Mérida, Yucatán, México
Email: [email protected] Keywords: Fe based calchogenide superconductors, density of states, x ray absorption, FeSe monolayers
Reports of superconductivity in few layers of FeSe deposited in SrTiO3 substrates, with critical temperatures reaching Tc = 65 K [1,3] have renewed the interest in Fe chalcogenide superconductors. We report real space calculations of electronic density of states of 1 and 2 layers of FeSe deposited on SrTiO3. For these calculations we have used a Density Functional Theory approach, based on a one electron approximation, spherically symmetric self consistent pseudopotentials, previously used in X ray absoption spectroscopy calculations in Fe chalcogenide superconductors[4]. We have used structural models based on experimental reports,[1] which assume a I4/mcm crystal structure for the substrate, which leads to a 1% expansion of the structural parameters of the FeSe layers. We compare the electronic density of states, in the vicinity of the Fermi energy, EF, assuming a nonmagnetic configuration of the FeSe monolayer and two different antiferromagnetic (AF) configurations. We find that the density of states at the Fermi level ρ(EF), is dominated by the Fe 3d states contributions, although the Ti 3d states contribute up to 10%. For the AF order configurations, we find that ρ (EF) exhibits a maximum value for the 1 layer case, with a decrease for the two layer and bulk values, consistent with a possible increase in Tc, with respect to the bulk case (see Fig. 1).
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Figure 1. Electronic density of states for the system FeSe/SrTiO3 using a Density Functional Theory approach.
References 1. D. Liu, et al, Nature Communications 3, 931 (2012) http://nature.com/dx.doi.org/10.1038/ncomms1946. 2. W. Qing Yan, et al, Chinese Physics Lett 29 037402 (2013) stacks.iop.org/0256 307X/29/i=3/a=037402. 3. S. He, et al, Nature Materials 12,605 (2013), http://dx.doi.org/10.1038//nmat 3648. 4. A. Vega Flick, J. Mustre de Leon, N.L. Saini, Journal of Superconductivity and Novel Magnetism 28, 1355 (2015). DOI: 10.1007/s10948 015 2955 3.
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28.3
Phenomenological theory of switching of electronic phases by optical, current, voltage and STM pulses in TaS2.
Serguei Brazovskii1,2* 1LPTMS CNRS, University Paris Sud, Orsay, France 2 Jozef Stefan Institute, Ljubljana, Slovenia
Email: [email protected] psud.fr Keywords: polaron, Wigner crystal, Mott insulator, hidden state, switching
The recent mainstream in strongly correlated electronic systems is a quest for so called “hidden states”. A success came recently from observations of ultrafast (~ps) switching by means of optical [1] and current or voltage [1,2] pulses, as well by local manipulations by the STM tip [3,1,4]. These observations have been done upon the most popular layered material 1T TaS2 which is an enigmatic “polaronic Wigner crystalline Mott insulator”. The presented phenomenological theory focuses upon equilibration among electrons and holes as mobile charge carriers, and the crystallized electrons modifiable by intrinsic defects (anti polaronic voids and their walls). The dynamical exchange among these reservoirs proceeds by formation of a network of charged domain walls [5] originated by the intrinsic Coulomb instability of the super lattice of self trapped electrons – the polarons.
References 1. L. Stojchevska, et al., Science, 344, 177 (2014); I. Vaskivskyi, et al., Science Advances, 1, 1500168 (2015); I. Vaskivskyi, et al., Nature Comm., 7, 11442 (2016). 2. M. Yoshida, et al., Science Reports, 4, 7302 (2014). 3. D. Cho, et al., Nature Comms 7, 10453 (2016). 4. L. Ma, et al., Nature Comms 7, 10956 (2016). 5. P. Karpov and S. B., Phys. Rev. B 94, 125108 (2016)
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28.4
Collective modes of the excitonic condensate in 1T TiSe2
Jasper van Wezel University of Amsterdam
Email: [email protected] Keywords: dichalcogenides, excitons, charge order
Light absorbed by a semiconductor can create an electron hole bound state called an exciton. In the 1960s it was realized that, if the exciton binding energy were larger than the semiconductor band gap, excitons would spontaneously proliferate. The resulting “excitonic insulator” is a macroscopic condensate of electron hole pairs with non zero centre of mass momentum, or in other words, a charge density wave. For 50 years, no experimental technique has been able to unambiguously identify an excitonic insulator phase in any material, despite many candidate materials being investigated. The reason is that its only tell tale signature—an electronic “soft mode” with non zero momentum—could not be detected with any technique. In this talk I will describe how momentum resolved EELS (electron energy loss spectroscopy) was recently used to demonstrate the existence of an electronic soft mode in the transition metal dichalcogenide TiSe2. This study represents the first observation of a soft electronic mode in any material, and the first unambiguous evidence for the existence of an excitonic phase.
References arXiv, 1611.04217 (2016)
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29.1
Intrinsic inhomogeneity of 2D crystalline superconductors
Sergio Caprara, Gianluca Dezi, Niccolò Scopigno, Marco Grilli* Department of Physics University of Rome “Sapienza”
Email: [email protected] Keywords: twodimensional superconductors, transition metal dichalcogenides, electronic phase separation
Recent progress in the fabrication of 2D highly ordered thin films and in increasing their electron density both by chemical doping or ionic gating has opened a new field with a wealth of interesting physical effects. These range from superconductivity in monolayers, possibly with an Ising like order parameter, sizable spin orbit coupling, competition with spatially ordered phases like CDW, and so on. In this framework, we analyzed transport properties in terms of a phenomenological model of Random Resistor Network representing an inhomogeneous system, where superconducting regions are embedded in a normal metal matrix. Fitting the resistance curves of several systems like TiSe2, MoS2, ZrNCl, we find that these systems are electronically inhomogeneous despite their high electron mobility and nearly perfect crystalline structure [1]. This finding, not only is relevant per se in systems of such broad interest, but naturally explains the quantum metallic phase taking place, e.g., in ZrNCl. Moreover, this raises the crucial question of the general mechanism(s) leading to this electronic inhomogeneity. We propose two general, possibly cooperative, mechanisms based on the electrostatic confinement and/or the density dependence of the superconducting critical temperature [1]. While similar mechanisms have been proposed in the past in the context of superconducting oxide interfaces [2,3], we find that they have a more general character and may be adjusted to account for the inhomogeneity formation in 2D superconducting films in general.
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(Left) Experimental (solid lines) and calculated (points) resistivity of a ionic gated ZrNCl film. (Right) Same as the left panel, but for the resistivity of ionic gated TiSe2 film [1]
References 1. S. Caprara, G. Dezi, N. Scopigno, and M. Grilli, preprint. 2. N. Scopigno, D. Bucheli, S. Caprara, J. Biscaras, N. Bergeal, J. Lesueur, and M. Grilli, Phys. Rev. Lett. 116, 026804 (2016). 3. N. Bovenzi, et al., J. Superc. Nov. Magn. 28, 1273 (2015), DOI 10.1007/s10948 014 2903 7, 2014.
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29.2
Exploiting multiorbital physics to achieve high temperature superconductivity: Fullerene and beyond
M. Capone International School for Advanced Studies (SISSA) and CNR IOM, Trieste
Email: [email protected] Keywords: Fullerides, multiorbital physics, Hund's coupling, electron phonon interaction
Alkali metal doped fullerides are surprising materials, where electron phonon driven superconductivity survives and lives prosper close to a transition to a Mott insulator, in constrast with intuition. We show that this surprising result relies on the multi orbital electronic structure of these molecular crystals, which allows to form local s wave pairs despite a strong short ranged Coulomb repulsion. The Jahn Teller phonons give rise to an inverted Hund’s coupling which favors low spin states which are not harmed by Coulomb repulsion. This, together with the reduction of the kinetic energy due to strong correlations, leads to an enhanced superconducting order parameter with respect to a system without Coulomb repulsion. We briefly discuss several anomalies of these superconductors which descend from strong correlations. This suggest that one can define a broader class of strongly correlated superconductors regardless of the pairing mechanism. In this light, we discuss how this mechanism can be relevant for other classes of superconductors including the cuprates and the iron based superconductors and its relation with non equilibrium properties of superconductors.
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Theoretical and experimental phase diagram for alkali doped fullerides as a function of the lattice spacing
References 1. M. Capone, M. Fabrizio, C. Castellani and E. Tosatti, Science 296, 2364 (2002). 2. M. Capone, M. Fabrizio, C. Castellani and E. Tosatti, Rev. Mod. Phys. 81, 943 (2009). 3. Y. Nomura, S. Sakai, M. Capone and R. Arita, Science Advances, 1 e1500568 (2015). 4. L. de' Medici, G. Giovannetti and M. Capone, Phys. Rev. Lett. 112, 177001 (2014).
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29.3
Eliashberg equations with antiferromagnetic ‘hidden order’ induced pairing boson in cuprates
Sergei I. Mukhin Department for Theoretical physics and quantum technologies, Moscow Institute for Steel and Alloys, Moscow, Russia
Email: [email protected] Keywords: Eliashberg equations for antiferromagnetic ‘hidden order’ induced pairing boson in cuprates
An emergence of the ‘magnetic boson’ providing Cooper pairing ‘glue’ is considered in the model of superconducting cuprates with antiferromagnetically fluctuating electron hole quasi classical condensate an instantonic “crystal”. The “crystal” manifests broken Matsubara time translational symmetry of the correlated Fermi system and plays the role of its ‘hidden order’. Usually unstable [1], the ‘soft mode’ of the “crystal” is shown to be stabilized in the presence of superconducting condensate of Cooper pairs. This ‘soft mode boson’ is considered as an origin of the Cooper pairing “glue” in the initially repulsive Fermi system. Thus, the two competing orders: antiferromagnetic and superconducting coexist (below some Tc) in the form of superconductor with ‘hidden order’. The ‘hidden order’ scenario based on the Euclidean “crystallization” was proposed earlier in [2] [4], where a spin density wave (SDW) with Matsubara time periodic amplitude was considered. It was demonstrated analytically in [2], that the SDW with an amplitude that behaves as a snoidal Jacobi function of the Matsubara time, leads to zero scattering cross section [2] for weakly perturbing external probes, like neutrons, etc., thus representing ‘hidden order’. In the present work the set of extended Eliashberg like equations with bosonic ‘glue’ in the presence of instantonic “crystal” is derived and solved self consistently for the case of a single lowest “crystal” vibration band. This new picture is discussed in relation with the different experiments in high Tc superconductors.
References 1. A.M. Polyakov, “Guage fields and strings”, Harwood Academic Pub., 1987. 2. S. I. Mukhin, «Spontaneously broken Matsubara’s time invariance in fermionic system: macroscopic quantum ordered state of matter», J. Supercond. Nov. Magn., vol. 24, 1165 1171 (2011).
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3. S. I. Mukhin, «Euclidean action of fermi system with “hidden order”, Physica B: Physics of Condensed Matter, vol. 460, 264 (2015). 4. S. I. Mukhin, «Euclidian Crystals in Many Body Systems: Breakdown of Goldstone’s Theorem», J. Supercond. Nov. Magn., vol.27, 945 950 (2014).
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29.4
Topological structures in a model cuprate
A.S. Moskvin, Yu.D. Panov Ural Federal University,620083, Ekaterinburg, Russia
Email: [email protected] Keywords: cuprates, pseudospin formalism, topological structures, skyrmions
The origin of high Tc superconductivity and other unconventional properties of cuprates is presently still a matter of great controversy mainly due to a complex interplay of charge, orbital, spin, and lattice degrees of freedom. Recently we have introduced a minimal model to describe the charge degree of freedom with the on site Hilbert space reduced to only the three effective valence centers [CuO4]7 ,6 ,5 (nominally Cu1+;2+;3+), where the electronic and lattice degrees of freedom get strongly locked together, and made use of the S=1 pseudospin formalism [1]. Effective pseudospin Hamiltonian does incorporate all the on site and inter site couplings with a charge density constraint: , where n is a deviation from the half filling. Here we make use of conventional spin operators, T±={Sz, S±}, 2D=Ueff is a correlation parameter, Vij intersite electron hole attraction, nij intersite coupling correction, m chemical potential, t,t’,t” are the three types of the the correlated single particle transfer integrals, tb is a two particle transfer integral. The Hamiltonian implies further possible simplifications, in particular, so called negative U model given large negative D [2]. The 2D pseudospin system is prone to a creation of different topological structures from domain walls, in plane and out of plane vortices to single centered and multi centered skyrmions which form topologically protected inhomogeneous distributions of the eight local S=1 pseudospin order parameters including charge density and superfluid order parameters. Different nontrivial skyrmion like topological defects for 2D (pseudo)spin S=1 systems were considered in Ref [3]. Hereafter, we focus on the so called quadrupole skyrmion [3] which is believed to be a candidate for a topological charge excitation in parent or underdoped cuprates. Fig.1 demonstrates the radial distribution of different order parameters for such a skyrmion. Puzzlingly, such an unconventional structure is characterized by an uniform distribution of the mean on site charge (
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We suppose that the parent insulating antiferromagnetic cuprates may be unstable with regard to nucleation of topological defects in the unconventional form of the one or multi center skyrmion like object with ring shaped superfluid regions.
*Supported by Act 211 Government of the Russian Federation, agreement № 02.A03.21.0006 and by the Ministry of Education and Science, projects 2277 and 5719.
Figure 1 Radial distribution of the local order parameters for a quadrupole pseudospin 2 2 skyrmion: (1
References 1. A.S. Moskvin, Low Temp. Phys. 33, 234 (2007); Phys. Rev. B 84, 075116 (2011); J. Phys.: Condens. Matter 25, 085601 (2013); J. Phys: Conf. Ser. 592, 012076 (2015); JETP, 121, 477 (2015). 2. A.S. Moskvin, Yu.D. Panov, F.N. Rybakov, A.B. Borisov, J. Supercond. Nov. Magn., 30(1), 43 (2017). 3. N.A. Mikushina, A.S. Moskvin, Phys. Lett. A 302/1, 8 (2002).
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30.1
Spin Peierls dimerization caused by Jahn Teller effect in NaTiSi2O6
E. Joon, I. Heinmaa, R. Stern, R. Rästa* National Institute of Chemical Physics and Biophysics
Email: [email protected] Keywords: Mott insulator, Spin Peierls dimerization, Jahn Teller effect, Quantum magnetism
The Spin Peierls (SP) effect is the crystal lattice dimerization with the formation of a singlet ground state from the paramagnetic high temperature state. It takes place in low dimensional crystals, like one dimensional (1D) Heisenberg ½ spin chains, with antiferromagnetic (AF) exchange coupling. The essence of Jahn Teller (JT) effect is the lifting of degeneracy of the symmetric state by lowering of crystal lattice symmetry. Both phenomena are dynamic at high temperature T≥ Tc and become static in low temperature phase T≤ Tc, where Tc is the structural phase transition temperature. According to the existing point of view these effects act separately and do not coexist. In this report we demonstrate the opposite; the JT effect causes SP dimerization in 1D Ti3+ magnetic chains of NaTiSi2O6. NaTiSi2O6 is a ½ spin member of quasi 1D magnets of pyroxene family. It is a Mott insulator, which crystallizes in the monoclinic space group C2/c at high temperatures [1,2,3]. Its crystal lattice consists of slightly distorted TiO6 octahedra, which are skew edge connected into zigzag chains, bridged by SiO4 tetrahedra. Using local coordinates, defined in [4], the threefold t2g level of Ti3+ splits due to the crystal field into low lying doublet with dxy and dyz orbitals and a single irrelevant dxz orbital removed to higher energy. This orbital degeneracy causes cooperative JT effect through strong electron lattice coupling [4]. At Tc= 210 K the lattice undergoes structural phase transition into triclinic P1Ī space group [2,3] with the dimerization of Ti chains and the forming of the spin singlet ground state. As a result a spin gap of order 500 700 K [1, 5] and 53 meV [6] opens and the magnetic susceptibility starts rapidly to decrease. In order to gain more insight on local spin structure and its dynamics, we have performed 29Si and 23Na NMR studies of NaTiSi2O6 [7, 8]. At low temperatures we found a high amount of undimerized Ti3+ ions, whose concentration c(T) follows activation type temperature dependence: , with the energy . We relate Ea with soliton energy Ea =2/π* , where =470K is the amplitude of the spin gap in our case. As a result solitons act as paramagnetic impurities and spins between them form SP phase. The detailed analysis of the NMR line shapes and their temperature dependencies allows us to elucidate the distribution of singlets and solitons. We also demonstrate that JT distortions of the neighbour TiO6 octahedra lead directly to the dimerization of Ti spins and SP state.
References 1. M. Isobe et al., Novel phase transition in spin 1/2 linear chain systems: NaTiSi2O6 and LiTiSi2O6, J. Phys. Soc. Japan 71, 1423 (2002).
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2. E. Ninomiya et al., Observation of lattice dimerization in spin singlet low temperature phase of NaTiSi2O6, Physica B, 329 333, 884 (2003). 3. G. J. Redhammer, et al., Single crystal structure refinement of NaTiSi2O6 clinopyrexene at low temperatures (298 ent of the spin gap in a quasi one dimensional clinopyroxene: NaTiSi2O6, Phys. Rev. B90, 140402(R) (2014). 4. R. Rästa, I. Heinmaa, E. Joon, R. Stern, 29Si NMR study of NaTiSi2O6 (unpublished) 5. E. Joon, R. Rästa, I. Heinmaa, R. Stern, Two level behavior of Ti3+ d orbitals in NaTiSi2O6 (unpublished).
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30.2
Quantum spin liquid in a molecular Mott system based on Pd(dmit)2
Reizo Kato Condensed Molecular Materials Laboratory, RIKEN, Wako shi, Saitama 351 0198, Japan
Email: [email protected] Keywords: quantum spin liquid; Mott insulator; dimer; charge disproportionation.
A series of anion radical salts of a metal complex Pd(dmit)2 (dmit = 1,3 dithiol 2 thione 4,5 dithiolate), X[Pd(dmit)2]2 (X: monovalent cation), belong to a Mott system – with a quasi triangular lattice of [Pd(dmit)2]2 dimers. We found that β' EtMe3Sb[Pd(dmit)2]2 is a promising candidate for quantum spin liquid (QSL) [1, 2]. The ground state of the Pd(dmit)2 salts is classified by the anisotropy of the triangular lattice that can be tuned by the choice of the counter cation X. The cation effect on the degree of frustration is associated with the arch shaped distortion of the Pd(dmit)2 molecule [3].
Figure 1: Crystal structure of β' EtMe3Sb[Pd(dmit)2]2 (left) and phase diagram of the Pd(dmit)2 salts (right).
The QSL phase is near the Mott transition and is situated between the antiferromagnetic long range order (AFLO) phase and the charge order (CO) phase. The AFLO phase in the vicinity of the QSL phase exhibits very small magnetic moment. The AFLO state in the Pd(dmit)2 salts is accompanied by intramolecular antiparallel spin configuration and charge disproportionation.
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On the other hand, the CO state in the Et2Me2Sb salt is understood in terms of the formation of a closed shell octamer composed of two charge rich dimers and two charge poor dimers [4]. In connection with this, the valence bond order (VBO) state observed in the EtMe3P (monoclinic and triclinic) salts is characterized by the formation of a closed shell tetramer composed of two equivalent dimers with intradimer charge disproportionation [5]. Vibrational spectra of the QSL salt indicate competition between the tetramerization and octamerization, suggesting that the charge degree of freedom is important for the emergence of the QSL state. We will also discuss an incommensurate modulated phase in the Et2Me2Sb salt that appears above the CO transition temperature. The modulation is coupled to the arch shaped distortion of the Pd(dmit)2 molecule and thus to the anisotropy of the triangular lattice.
References 1. (a) K. Kanoda and R. Kato, Annu. Rev. Condens. Matter Phys., 2, 167 (2011). http://www.annualreviews.org/doi/10.1146/annurev conmatphys 062910 140521 (b) R. Kato, Bull. Chem. Soc. Jpn., 87, 355 (2014). http://www.journal.csj.jp/doi/10.1246/bcsj.20130290 2. (a) T. Itou, et al., Phys. Rev. B, 77, 104413 (2008). http://journals.aps.org/prb/abstract/10.1103/PhysRevB.77.104413 (b) M. Yamashita, et al., Science, 328, 1246 (2010). http://science.sciencemag.org/content/328/5983/1246 (c) T. Itou, et al., Nature Phys., 6, 673 (2010). http://www.nature.com/nphys/journal/v6/n9/full/nphys1715.html (d) S. Yamashita, et al., Nature Commun., 2, 275 (2011). http://www.nature.com/articles/ncomms1274 (e) D. Watanabe, et al., Nature Commun., 3, 1090 (2012). http://www.nature.com/articles/ncomms2082 3. R. Kato and H. Cui, Crystals, 2, 861 (2012). http://www.mdpi.com/2073 4352/2/3/861 4. T. Yamamoto et al., J. Phys. Soc. Jpn., 85, 104711 (2016). http://journals.jps.jp/doi/10.7566/JPSJ.85.104711 5. T. Yamamoto et al., J. Phys. Soc. Jpn., 83, 053703 (2014). http://journals.jps.jp/doi/10.7566/JPSJ.83.053703
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30.3
Half filled anizotropic triangular Hubbard model and organic charge transfer salts based on BEDT TTF
Jure Kokalj1 and Ross H. McKenzie2 1 Jozef Stefan Institute, Ljubljana, Slovenia and Faculty for Civil and Geodetic Engineering, University of Ljubljana, Slovenia 2 University of Queensland, Brisbane, Australia
Email: [email protected]
We numerically calculated several quantities for the half filled anisotropic triangular Hubbard model with the aim to describe the behavior of organic charge transfer salts based on BEDT TTF. In particular, the Mott metal insulator transition is observed via charge susceptibility, the bad metallic regime is characterized with large entropy and local moment, while below the relatively low coherence temperature the Fermi liquid phase is strongly renormalized as seen, e.g., in specific heat and spin susceptibility. Further the DMRG results suggest possible gapless spin liquid phase between the metallic and 120 degree ordered AFM Neel state. The calculated results will be discusses in the light of experiments on the organic charge transfer salts.
References 1. J. Kokalj and R. H. McKenzie, Phys. Rev. Lett. 110, 206402 (2013). 2. T. Shirakawa, T. Tohyama, J. Kokalj, S. Sota and S. Yunoki, arXiv:1606.06814. 3. J. Kokalj and R. H. McKenzie, Phys. Rev. B 91, 125143 (2015). 4. J. Kokalj and R. H. McKenzie, Phys. Rev. B 91, 205121 (2015). 5. P. Prelovsek, J. Kokalj, Z. Lenarcic and R. H. McKenzie, Phys. Rev. B 92, 235155 (2015).
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31.1
Nematic electronic structure of the iron based superconductor FeSe
Takahiro Shimojima RIKEN Center for Emergent Matter Science (CEMS), Wako 351 0198, Japan
Email: [email protected] Keywords: electronic structure; iron based superconductor; angle resolved photoemission.
Most of the parent compounds of the iron based superconductors exhibit the tetragonal orthorhombic structural transition at Ts and the stripe type antiferromagnetic order below TN (toemission spectroscopy (ARPES). Experimental and theoretical studies suggested that the tetragonal orthorhombic phase transition (nematic order) is caused by the spin or orbital degrees of freedoms1. FeSe is a good example to examine the role of orbital degrees of freedom, since it shows the structural and superconducting transitions at Ts ≈ 90 K and Tc ≈ 9 K without any magnetic order2. In order to understand the role of orbital degrees of freedom on the nematicity, it is required to clarify how the electronic structure breaks four fold symmetry in the entire Brillouin zone. In this talk, we report the electronic reconstruction across Ts of FeSe by employing ARPES with several photon sources on detwinned single crystals. We observed highly two fold symmetric Fermi surfaces (FSs) below 90 K around both the G and M points. The polarization between xz and yz orbitals at M point was found to be more than five times larger than that expected from the orthorhombic lattice distortion, thus indicative of the orbital driven nematicity3. Polarization dependent ARPES further revealed that the xz orbital shifts upward at the G point, while it moves downward at the M point. Such momentum dependent sign inversion of orbital polarization modifies the FSs at the G and M point into elliptical shapes elongating along ky and kx, respectively4. We further investigated the dynamics of the nematic electronic structure by employing time resolved ARPES. We observed the complete suppression and recovery of the ellipticity in the nematic FS after a femtosecond photoexcitation. We will also discuss the orbital dependence in the relaxation process of the photoexcited carriers.
References 1. R. M. Fernandes et al., Nature Physics 10, 97 (2014). 2. A. E. Böhmer et al., Phys. Rev. B 87, 180505(R) (2013). 3. T. Shimojima et al., Phys. Rev. B 90, 121111(R) (2014). 4. Y. Suzuki et al., Phys. Rev. B 92, 205117 (2015).
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31.2
ARPES of iron based superconductors
Sergey Borisenko IFW Dresden
Email: S.Borisenko@ifw dresden.de Keywords: ARPES, Iron Based Superconductors, Gap Functions
I will overview our most recent ARPES results on iron based superconductors. In particular, we have determined both the 3D electronic structure and superconducting energy gaps with a new precision. Multiorbital nature of these superconductors makes itself evident in the gap functions and provides new constraints for the successful theoretical models of high Tc superconductivity.
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31.3
Non Fermi liquid behavior, Lifshitz transitions, and Hund’s metal behavior of iron based superconductors and related compounds from ARPES
Jörg Fink1, 2,3 1Leibnitz Institute Dresden, Germany 2Technische Universität Dresden, Germany 3Max Planck Institute for Chemical Physics of Solids, Dresden, Germany
Email: J.Fink@ifw dresden.de Keywords: high Tc, ferropnictides, ferrochalcogenides, Lifshitz transitions, correlation effects
Using ARPES, we have investigated the electronic band structure and many body properties of iron based high Tc superconductors and related compounds in a large range of the occupation of the 3d shell, starting from Cr compounds via the ferropnictides and ferrochalcogenides until Cu pnictide. For those compounds having the highest superconducting transition temperatures, we find Lifshitz transitions for those bands exhibiting the highest superconducting gaps. Furthermore, from the measured scattering rates we observe the strongest correlation effects for compounds near a half filled 3d shell (Fe based high Tc superconductors), while the correlation effects are strongly reduced for smaller 3d count (Cr compounds) or larger 3d count (Co, Ni, Cu compounds). This indicates that the correlation effects in these multi orbital systems are strongly influenced by Hund’s exchange interaction. From these results we conclude that the high superconducting transition temperatures and the strange normal state properties are influenced both by band structure properties and by correlation effects [1 3].
References 1. J. Fink, E. D. L. Rienks, S. Thirupathaiah, J. Nayak, A. van Roekeghem, S. Biermann, T. Wolf, P. Adelmann, H. S. Jeevan, P. Gegenwart, S. Wurmehl, C. Felser, and B. Büchner, Phys. Rev. 95, 144513 (2017). 2. J. Fink, A. Charnukha, E. D. L. Rienks, Z. H. Liu, S. Thirupathaiah, I. Avigo, F. Roth, H. S. Jeevan, P. Gegenwart, M. Roslova, I. Morozov, S. Wurmehl, U. Bovensiepen, S. Borisenko, M. Vojta, and B. Büchner, Phys. Rev. 92, 201106 (R) (2015). 3. I. Avigo, S. Thirupathaiah, E. D. L. Rienks, L. Rettig, A. Charnukha, M. Ligges, R. Cortes, J. Nayak, H. S. Jeevan, T. Wolf, Y. Huang, S. Wurmehl, M. I. Sturza, P. Gegenwart, M. S. Golden, L. X. Yang, K. Rossnagel, M. Bauer, B. Büchner, M. Vojta, M. Wolf, C. Felser, J. Fink, and U. Bovensiepen, Phys. Status Solidi B 254, 1600382 (2016).
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31.4
Electron electron correlation in iron Pnictides, revealed by ARPES
Ming Shi Paul Scherrer Institute, CH 5232 Villigen, Switzerland
Email: [email protected] Keywords: superconductivity, Pnictides, AFM insulator, correlation, ARPES
The effects of electron electron correlations on the low energy electronic structure and their relationship with unconventional superconductivity are important aspects in the research on the iron based pnictide superconductors. Here we use angle resolved photoemission spectroscopy (ARPES) to investigate how electronic correlations evolve in different chemically substituted iron pnictides. We revealed 1) the electronic structure of the antiferromagnetic iron pnictide insulator is very similar to that of the parent compound of cuprates [1], 2) in transition metal pnictides electron electron correlations are intrinsically related to the effective filling of the correlated orbitals, rather than to the filling obtained by valence counting [2,3], and 3) modifying the spacer layer between FeAs layers, the common building block of iron pnicides, could result in a staggered combination of a quantum spin Hall insulator and a high temperature superconductor.
References 1. C. E. Matt et al., Phys. Rev. Lett. 117, 097001 (2016). 2. E. Razzoli et al., Phys. Rev. B. 91, 214502 (2015). 3. E. Razzoli et al., Phys. Rev. Lett. 108, 257005 (2012).
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32.1
The new frontiers of the Josephson effect in novel unconventional nano scale and magnetic systems
F. Tafuri 1,2*, R. Caruso 1,2, D. Massarotti 1,2,3, D. Stornaiuolo 1,2, G.P. Pepe 1,2, L. Longobardi 3,4, F. Lombardi 5, P. Lucignano 1,2, G. Campagnano 1, G. Rotoli 3, and A. Tagliacozzo1,2 1 Dipartimento di Fisica “E. Pancini”, Università di Napoli Federico II, Napoli Italy 2 CNR SPIN UOS Napoli, Italy 3 Dipartimento di Ingegneria Industriale e dell’Informazione, Università della Campania L. Vanvitelli, Aversa (CE) Italy 4 American Physical Society, 1 Research Road, Ridge, New York 11961, USA 5 Chalmers University of Technology, Gotenborg, Sweden
Email: [email protected] Keywords: Hybrid Josephson junctions, quantum devices, nanoscale
Josephson Junctions (JJs) provide unique solutions to frontier fundamental problems and very advanced applications in quantum technologies. We have investigated various unconventional systems including junctions with graphene or topological insulator or ferromagnets as barriers and found significant anomalous behaviors. This evidence partly invalidates standard approaches to the Josephson effect in these systems and confirm the presence of competing mechanisms induced by the special nature of the superconductors or of the barriers or of their interfaces. Effects due to nano engineering of the junctions and weak links contribute to enhance specific effects, manifesting themselves through special fingerprints in the phenomenology of the Josephson effect. All this has to be taken into account to use these junctions as quantum sensors in a variety of experiments.
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32.2
Superconducting weak links created by electromigration
X. Baumans, J. Lombardo, V. Zharinov, J. Scheerder, D. Massarotti, R. Caruso, J. Yuan, B.Y. Zhu, K. Jin, R. B.G. Kramer, F. Tafuri, V. V. Moshchalkov, J. Van de Vondel, and A. V. Silhanek Experimental Physics of Nanostructured Materials, Q MAT, CESAM, Université de Liège, B 4000 Sart Tilman, Belgium INPAC – Institute for Nanoscale Physics and Chemistry, Nanoscale Superconductivity, and Magnetism Group, K.U. Leuven, Celestijnenlaan 200D, B–3001 Leuven, Belgium Dipartimento di Fisica, Università degli Studi di Napoli ’Federico II’, Monte S. Angelo, I 80126 Napoli, Italy Dipartimento di Ingegneria Industriale e dell´Informazione, Seconda Università degli Studi di Napoli, I 81031 Aversa (Ce), Italy CNR SPIN UOS Napoli, Monte S. Angelo via Cinthia, I 80126 Napoli, Italy Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China Université Grenoble Alpes, Institut NEEL, F 38000 Grenoble, France and CNRS, Institut NEEL, F 38000 Grenoble, France
Email: [email protected] Keywords: electromigration, phase slips, weak links
In this presentation, we explore in situ controlled electromigration to fabricate superconducting weak links. We show evidence that in Al a transition from thermally assisted phase slips (TAPS) to quantum phase slips may takes place when the effective cross section becomes smaller than ~150 nm2. In the regime dominated by quantum phase slips the nanowire loses completely its capacity to carry current without dissipation, even at the lowest possible temperature. We also discuss the origin of negative magnetoresistance at low magnetic fields in the bow tie shaped constrictions. Strikingly, the detrimental effect caused by the repeated electromigration can be healed by simply inverting the current direction. These findings reveal perspectives of the proposed fabrication method for exploring various fascinating superconducting phenomena in atomic size constrictions.
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Al nanoconstriction as fabricated by electron beam lithography (virgin) and after two consecutive electromigration procedures (EM1 and EM2).
References 1. Baumans, X. D. A., Cerbu, D., Adami, O. A., Zharinov, V. S., Verellen, N., Papari, G., Scheerder, J. E., Zhang, G., Moshchalkov, V. V., Silhanek A. V., and Van de Vondel. J. Nat. Commun. 7, 10560 (2016).
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32.3
Quantum decay of supercurrent in transparent nanojunctions
Andrei D. Zaikin Institute of Nanotechnology, Karlsruhe Institute of Technology (KIT), 76021 Karlsruhe, Germany
Email: [email protected] Keywords: Macroscopic quantum tunneling, dissipation, quantum phase slips
Making use of the effective action theory [1,2] we demonstrate that the problem of macroscopic quantum tunneling of the superconducting phase in highly transparent superconducting nanojunctions can be exactly mapped onto that of a quantum particle in a dissipative environment formed by a collection of harmonic oscillators with parameters directly related to those of subgap Andreev levels inside the junction. We evaluate both quantum and thermally activated supercurrent decay rates in such nanojunctions and identify crossover conditions between these regimes. We also predict the possibility for non monotonous dependence of the switching current distributions on temperature and elucidate the physics behind this non trivial effect.
References 1. A.V. Galaktionov and A.D. Zaikin, Phys. Rev. B 82, 134508 (2010). 2. A.V. Galaktionov and A.D. Zaikin, Phys. Rev. B 92, 214511 (2015).
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32.4
Resonant inelastic x ray scattering to measure short range magnetic order
Claude Monney University of Zurich
Email: [email protected] Keywords: RIXS, spin chain, cuprate
I will present resonant inelastic x ray scattering (RIXS) data obtained at O K edge on the quasi one dimensional spin chains Li2CuO2 and CuGeO3. In these edge sharing cuprates having a standard Cu d9 electronic configuration, RIXS can create a particular excitation called a Zhang Rice singlet (ZRS) in its final state. The ZRS consists in a double hole occupation on a CuO4 plaquette, which occurs via an effective hole transfer from one plaquette to another. The intensity of this excitation depends on the ground state spin configuration and is a measure of the nearest neighbour spin arrangement. This effect is used here to monitor the intrachain short range spin correlations in Li2CuO2 and CuGeO3 as a function of temperature [1]. I will also present results on Li2CuO2 showing that not only the intrachain, but also the interchain short range spin correlations can be extracted via the chemical and site selectivity of RIXS by tuning the x ray incident energy [2]. I will finally argue that the charge transfer energy obtained from this material is not only due to a purely electronic effect, but has a large contribution due to the deformation of the underlying lattice [3].
References 1. C. Monney et al., PRL 110, 087403 (2013). 2. C. Monney et al., PRB 94, 165118 (2016). 3. S. Johnston, C. Monney et al., Nature Commun. 10653 (2016).
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33.1
Studying Silicene mono and multilayers with soft X ray spectroscopy and DFT
Alexander Moewes and Neil Johnson Department of Physics, University of Saskatchewan, Canada
Email: [email protected] Keywords: Silicene, band gap, X ray absorption and emission spectroscopy, DFT
We study the hexagonal honeycomb of Si atoms – referred to as Silicene [1] – deposited on Ag(111) with synchrotron based soft X ray spectroscopy (XAS & XES) at the Si L edge. When compared to our electron density functional theory calculations, we unambiguously show that the Si valence and conduction states are continuous across the Fermi energy; i.e. that the silicene overlayer was indeed metallic [2]. If Si monolayers are to come into use, they must be all at once isolated from their substrates. One suggested way of achieving these characteristics is to produce a multilayer of silicene on the Ag(111) surface. Our DFT calculations predict a stable, AA stacked silicene bilayer on Ag(111) that corresponds nicely to the scanning tunnelling microscopy (STM) bilayer observations. Unfortunately, these same DFT calculations predict a similar electronic structure as that of the monolayers, namely metallic and bound to the Ag(111). Our measurements indicate a transition to bulk Si beginning shortly after the completion of a monolayer [3]. When studying the oxidation of Silicene, our calculations indicate that moderate levels of oxidation do not cause a significant bandgap opening in the epitaxial silicene monolayer. In addition, moderate oxidation is calculated to strongly distort the hexagonal Si lattice, causing it to cluster in regions of highest oxygen adatom concentration but retain its 2D sheet structure. Our experiments reveal that beam induced oxidation is consistent with the formation of islands of bulk like SiO2 [4].
References 1. P. Vogt, P. De Padova, C. Quaresima, J. Avila, E. Frantzeskakis, M.C. Asesnsio, A. Resta, B. Ealet and G. Le Lay, Phys. Rev. Lett. 108, 155501 (2012). 2. N.W. Johnson, P. Vogt, A. Resta, P. De Padova, I. Perez, D. Muir, E. Z. Kurmaev, G. Le Lay and A. Moewes, Adv. Funct. Mater. 24, 5253 (2014). 3. N.W. Johnson, D. Muir, E.Z. Kurmaev, and A. Moewes Adv. Funct. Mat. 25, 4083 (2015). 4. N.W. Johnson, D.I. Muir and A. Moewes, Sci. Rep. 6, 22510 (2016).
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33.2
Doping effects on electronic properties of bilayer graphene
Hidenori Goto1, Takaki Uchiyama1, Yoko Nakashima1, Hidehiko Akiyoshi1, Ritsuko Eguchi1, Hiroshi Osada2, Takao Nishikawa2, Yoshihiro Kubozono1 1 Research Institute for Interdisciplinary Science, Okayama University, Japan 2 Iwate University, Japan
Email: hgoto@okayama u.ac.jp Keywords: bilayer graphene, energy gap, electric field effect, doping effect
Graphene exhibits unique electronic properties resulting from the linear dispersion relation, whereas zero energy gap between the valence and conduction bands makes it difficult to develop practical graphene devices. One solution to this problem is to apply electric field perpendicular to bilayer graphene (BLG). Two methods are known to produce the electric field. One is a conventional gating method using double gate structure. The other is a doping method which utilizes electron transfer between graphene and surface adsorbates. However, it is not yet conclusive whether the doping method can actually produce uniform electric field[1,2]. In this study, we investigated the presence of band gap of doped BLG by measuring temperature dependence of the conductivity. BLG devices were prepared on self assembled monolayers (NH2 SAMs), on which 2,3,5,6 tetrafluoro 7,7,8,8 tetracyanoquinodimethane (F4TCNQ) molecules were deposited. NH2 SAMs donate electrons, while F4TCNQ molecules donate holes, which can generate effective electric field through the BLG. As a result, some devices showed an energy gap, while the others no gap. Even in the former sample, the energy gap was reduced after subsequent deposition of F4TCNQ molecules. It is inferred that random doping from NH2 SAMs and F4TCNQ molecules does not always lead to uniform electric field. The potential fluctuation by adsorbed molecules decreases scattering length and prevents the energy gap from opening.
References 1. S. Xiao et al., Phys. Rev. B 82, 041406(R) (2010). 2. J. Park et al., Adv. Mater. 24, 407 (2012).
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33.3
Superconductivity of K doped FeSe ultra thin films on SrTiO3(001) substrate
Canhua Liu Shanghai Jiao Tong University
Email: [email protected] Keywords: superconductive phase diagram, FeSe thin film, electron doping
Single unit cell layer of FeSe film grown on a SrTiO3 substrate was found to have a superconductive transition at a temperature much higher than FeSe bulk crystal, which stimulated a great deal of research interest in revealing the mechanism of the interface enhanced superconductivity. One of the key ingredients for the superconductivity enhancement is charge transfer from SrTiO3 substrate to the FeSe thin film, i.e., electrons doped to the FeSe thin film due to oxygen vacancies in the SrTiO3 substrate. Inspired by this idea, researchers found in both ARPES and STM experiments that K doped FeSe thin films also exhibit K coverage dependent superconductive energy gaps ( ), which are much larger than that of FeSe bulk crystal and thus indicate much higher Tc. However, the superconductivity of K doped FeSe thin films haven’t been confirmed in experiments yet, since neither its zero resistance nor diamagnetism could have been measured. We recently invented a piezo scanner tube with four electrodes for a special scanning tunneling microscope (STM), based on which, we developed a four point probe and a double coil mutual inductance head for in situ measurements of electrical and magnetic properties of a sample in an ultra high vacuum chamber, respectively. The original STM function is fully sustained, which enables us to investigate the surface morphology, surface atomic arrangement and surface electronic structure while doing electrical and magnetic property measurement of a same sample. Using this setup, we succeeded for the first time in measuring the diamagnetism of K doped FeSe thin films. By comparing the evolution of Tc and as function of K coverages, we found that the Tc is not determined by the pair potential in the overdoped region.
This work was in cooperation with Ming Chao Duan, Gang Yao, Yan Fu We, Yao Yi Li, Dong Qian, and Jin Feng Jia.
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34.1
Multicomponent electron hole superfluidity and the BCS BEC crossover in double bilayer graphene
David Neilson, Sara Conti, and Andrea Perali Dipartimenti di Fisica e di Farmacia, Università di Camerino, 62032 Camerino (MC), Italy.
Email: [email protected] Keywords: Multicomponent electron hole superfluidity; BCS BEC crossover; double bilayer graphene
The recent fabrication of a pair of very close, but electrically independent, conducting bilayer graphene sheets, one containing electrons and the other holes [1],raises exciting possibilities of observing high temperature superfluidity [2]. In bilayer graphene, by decreasing the densities, the system can be moved from the region of weak interactions to the region where the Coulomb interactions dominate over kinetic energies [3]. In addition, an electric field applied perpendicular to the bilayer graphene sheets opens up a tuneable energy band gap between its conduction and valence bands [4].
We investigate the effect of the two bands of the bilayer graphene sheets on the BCS BEC crossover regime and the BEC regime of the multicomponent superfluid in the conduction and valence bands. We find that the crossover properties depend sensitively not only on the densities of the carriers but also on the tuneable energy band gap.
The regimes of the crossover phenomena are characterized by the superfluid condensate fraction c, the fraction of carriers in pairs relative to the total number of carriers [5]. We recall the usual classification, c > 0.8 for the BEC regime, 0.2 188 Superstripes 2017, Ischia June 4 10, 2017 Figure 1: Condensate fraction and the chemical potential as functions of density for different band gaps, Eg. Upper panels, solid and dashed lines are condensate fractions in conduction band and valence band. Lower panels, solid lines are the chemical potential and dashed lines the effective Fermi energy. The horizontal shaded area is the energy band gap. Screening suppresses superfluidity at high densities (vertical shaded area). The inset shows the limiting value at low density of the chemical potential as a function of band gap Eg . The Figure shows that even at the highest carrier densities at which screening does not suppress superfluidity (n~5×1011 cm 2), the conduction band is already in the crossover regime. For larger band gaps EG, the behaviour with decreasing density is similar to a one band system, the conduction band enters the BEC regime, the chemical potential is less than the Fermi energy, becoming negative at the BEC boundary and approaching half the exciton binding energy, εB/2, for zero density [6]. However, the valence band is trapped in the BEC regime over the full range of densities because for large EG there are so few anti particles in the valence band. For smaller band gaps, the conduction band does not enter the BEC regime. An interesting new property for the multicomponent superfluid is that the behaviour of the chemical potential in the small density limit depends on the size of the energy band gap EG (see inset of Figure). For large band gaps, the limiting behaviour of is the familiar → εB/2, but when the energy band gap drops below εB, the limiting behaviour smoothly switches over to the midpoint of the band gap, → EG/2. References 1. A. K. Geim and I. V. Grigorieva, Nature 499, 419 (2013); K. Lee, et al., Phys. Rev.Lett. 117, 046803 (2016); J. Li, et al., Phys.Rev.Lett. 117, 046802 (2016). 2. A. Perali, D. Neilson, A.R. Hamilton, Phys.Rev.Lett. 110, 146803 (2013). 3. M. Zarenia, A. Perali, D. Neilson, F. Peeters, Sci. Reports 4, 7319 (2014). 4. K. Lee, et al., Science 345, 58 (2014). 5. S. Giorgini, L. Pitaevskii, S. Stringari, Phys. Rev.A 54, 4633 (1996); L.Salasnich, N. Manini, A. Parola, Phys. Rev. A 72, 023621 (2005). 6. G. Strinati, Physics Essays 13, 427 (2000). 189 Superstripes 2017, Ischia June 4 10, 2017 34.2 High temperature quantum oscillations in graphene superlattices L. A. Ponomarenko1, R. Krishna Kumar1, X. Chen2, G. H. Anton2, S. V. Morozov4,5, A. Mishchenko3, A. V. Kretinin2, Y. Cao2, E. Khestanova3, D. A. Bandurin3, M. Ben Shalom3, K. S. Novoselov2, L. Eaves6, I. V. Grigorieva1, V. I. Fal'ko2, A. K. Geim2,3 1 Department of Physics, University of Lancaster, Lancaster LA1 4YW, United Kingdom 2 National Graphene Institute, University of Manchester, Manchester M13 9PL, United Kingdom 3 School of Physics & Astronomy, University of Manchester, Oxford Road, Manchester M13 9PL, United Kingdom 4 Institute of Microelectronics Technology and High Purity Materials, RAS, Chernogolovka 142432, Russia 5 National University of Science and Technology ‘MISiS’, Leninsky Pr. 4, 119049 Moscow, Russia 6 School of Physics and Astronomy, University of Nottingham NG7 2RD, United Kingdom Email: [email protected] Keywords: Graphene, Superlattice Cyclotron motion of charge carriers in metals and semiconductors leads to Landau quantization and oscillatory behavior in their properties. Liquid helium temperatures are usually required to observe such oscillations. We show that graphene superlattices support another kind of oscillations that do not rely on Landau quantization and are extremely robust with respect to thermal smearing. The oscillations persist up to 100 C (370 K) in magnetic fields of only several T, with the temperature range being limited by thermal stability of current graphene devices. The phenomenon is attributed to the repetitive formation of Brown Zak minibands at unit fractions of the flux quantum per superlattice unit cell. Our work points at much of unexplored physics in Hofstadter butterflies in the regime of high temperatures. 190 Superstripes 2017, Ischia June 4 10, 2017 34.3 Governing energies of graphene Josephson junctions from dirty to ultra clean regimes Ivan Borzenets, Francois Amet, Chung Ting Ke, Anne Draelos, Kenji Watanabe, Takashi Taniguchi, Yuriy Bomze, Gleb Finkelstain, Michihisa Yamamoto, Seigo Tarucha The University of Tokyo, Appalachian State University, Duke University, National Institute for Material Science Email: [email protected] Keywords: Graphene, Josephson junctions, ballistic regime We analyze the diffusive, short ballistic and long ballistic regimes in superconductor normal Josephson junctions made of encapsulated graphene/boron nitride heterostructures. By examining the junction length L and gate dependence of diffusive samples we show that, over a range of up to three orders of magnitude, the critical current is proportional to the Thouless energy ETH. In ballistic devices the temperature dependence of the critical current allows us to identify and observe the crossover from the short to the long junction regimes. (Defined by the ratio of the superconducting coherence length ξ to the junction length L). In the short regime, the energy is consistent with the expected superconducting gap . While in the long regime, the governing energy δE is independent of the carrier density and proportional to the level spacing of the ballistic cavity, as determined from Fabry Perot oscillations of the junction normal resistance. At low temperatures, we show that the critical current saturates at a level determined by the product of (or δE) and the number of the junction's transversal modes. This is the first demonstration of all three regimes in the same system. 191 Superstripes 2017, Ischia June 4 10, 2017 Map of differential resistance versus bias current and gate voltage. The data are shown for a short ballistic graphene Josephson junction at a temperature T = 1.5K. The superconducting region of zero resistance can be observed around I = 0. The P doped region shows oscillations in the critical current, consistent with that of a Fabry Perot cavity. References 1. I.V. Borzenets, F. Amet, C.T. Ke, A.W. Draelos, M.T. Wei, A. Seredinski, K. Watanabe, T. Taniguchi, Y. Bomze, M. Yamamoto, S. Tarucha, and G. Finkelstein, Phys. Rev. Lett. 117, 237002 (2016). 2. C.T. Ke, I.V. Borzenets, A.W. Draelos, F. Amet, Yu. Bomze, G. Jones, M. Craciun, S. Russo, M. Yamamoto, S. Tarucha and G. Finkelstein, Nano Lett. 16 (8), 4788 (2016). 3. F. Amet, C.T. Ke, I.V. Borzenets, Y. Wang, K. Watanabe, T. Taniguchi, R.S. Deacon, M. Yamamoto, Y. Bomze, S. Tarucha, and Finkelstein, Science 352 (6288), p.966 (2016). 192 Superstripes 2017, Ischia June 4 10, 2017 34.4 Superconducting fluctuations in a thin NbN film probed by the Hall effect Daniel Destraz,1,* Konstantin Ilin,2 Michael Siegel,2 Andreas Schilling,1 and Johan Chang1 1Physik Institut, Universität Zürich, Winterthurerstrasse 190, CH 8057 Zürich, Switzerland 2Institut für Mikro und Nanoelektronische Systeme (IMS), Karlsruher Institut für Technologie, Germany Email: [email protected] Keywords: superconducting fluctuations; thin films Superconducting fluctuations above the critical temperature provide valuable insight in the pairing mechanisms of superconductivity. The recent discovery of a pseudogap phase in NbN has opened many new questions [1, 2]. In this study [3] we measure the paraconductivity and the Hall effect response in NbN originating from superconducting fluctuations. These experimental results are compared to a recent theoretical study on the influence of superconducting fluctuations on the Hall response [4]. The presented study demonstrates experimentally how Gaussian fluctuations of superconductivity contribute to the conductivity tensor. References 1. Mintu Mondal et al., Phys. Rev. Lett. 106, 047001 (2011) https://doi.org/10.1103/PhysRevLett.106.047001 2. Madhavi Chand et al., Phys. Rev. B 85, 014508 (2012) https://doi.org/10.1103/PhysRevB.85.014508 3. Daniel Destraz et al., submitted to Phys. Rev. Lett. (2017). 4. Karen Michaeli et al., Phys. Rev. B 86, 014515 (2012) https://doi.org/10.1103/PhysRevB.86.014515 193 Superstripes 2017, Ischia June 4 10, 2017 35.1 Electron count and chemical complexity in high entropy alloy superconductors Fabian von Rohr 1, Michał J. Winiarski 2, Jing Tao 3, Tomasz Klimczuk 2, and Robert Joseph Cava 1 1 Department of Chemistry, Princeton University, Princeton, NJ 08544; 2 Faculty of Applied Physics and Mathematics, Gdansk University of Technology, Gdansk 80 233, Poland; 3 Condensed Matter Physics Department, Brookhaven National Laboratory, Upton, NY 11973 Email: [email protected] Keywords: High entropy alloys High entropy alloys are a new class of materials that consist of several principal elements arranged on simple lattices. These structures are stabilized by the high configurational entropy of the random mixing of the elements. HEAs can display novel, highly tunable properties such as, for example, excellent specific strength, superior mechanical performance at high temperatures, and fracture toughness at cryogenic temperatures, making them promising candidates for future applications. The recently discovered body centered cubic (BCC) Ta Nb Hf Zr Ti high entropy alloy superconductor appears to display properties of both simple crystalline intermetallics and amorphous materials; e.g., it has a well defined superconducting transition along with an exceptional robustness against disorder. In this presentation, we will show that the properties of this superconducting high entropy alloy are strongly related to the valence electron count and that the superconducting transition temperatures Tc of these alloys fall between those of analogous crystalline and amorphous materials. We find that despite the large degree of randomness and disorder in these alloys, the superconducting properties are nevertheless strongly dependent on the chemical composition and complexity. We argue that high entropy alloys are excellent model systems for understanding how superconductivity and other collective quantum states evolve from crystals to amorphous solids. 194 Superstripes 2017, Ischia June 4 10, 2017 35.2 Extensive study of the superfluid density of oxypnictides Samuele Sanna Department of Physics and Astronomy, University of Bologna, Bologna, Italy Email: [email protected] Keywords: Oxypnictides, Superfluid Density, Uemura plot An extensive study of the phenomenological behaviour of the superfluid density, ns, is given for oxy pnictide compounds as a function of hole doping, impurity, pressure and magnetic field as measured by muon spin rotation measurements. It is shown that for REFeAsO1 xFx (RE1111, RE=La, Ce, Nd, Sm) in the F underdoped regime the superconducting temperature, Tc, does not follow the linear behaviour observed for cuprates in the ‘Uemura plot’, Tc vs ns, (left panel in figure from Ref. [1]). The results will be compared to the behaviour expected within different theoretical approaches such as multiband BCS, phase fluctuations around a quantum critical point, coexistence of magnetism and superconductivity [2]. Figure 1: Uemura plot (left) for REFeAsO1 xFx for 0.04 < x < 0.11 and (right) for optimally F doped REFe1 yRuyAsO0.89F0.11 with 0 195 Superstripes 2017, Ischia June 4 10, 2017 The Tc(ns) behaviour shows a linear dependence when Fe is partially substituted by diamagnetic Ru impurities in optimally F doped samples (right panel in figure). Considering that magnetic regions coexisting with superconductivity on a nanoscopic scale are induced by Ru in REFe1 yRuyAsO0.89F0.11 [3,4], this effect can be described within the ‘Swisse cheese’ model, resembling the behaviour observed in Zn doped cuprates [5,7]. It will be also presented an anomalous dramatic increase of the superfluid density by ∼30% while Tc is substantially constant as measured by applying hydrostatic pressure up to ∼2.5 GPa. The effect of nonmagnetic impurities on multiband superconductivity must be taken into account to explain this effect [6]. References 1. P. Carretta, R. De Renzi, G. Prando, S. Sanna, Phys. Scr. 88, 068504 (2013). 2. Paper in preparation. 3. S. Sanna et al., Phys. Rev. B 87, 134518 (2013). 4. S. Sanna et al., Phys. Rev. Lett. 107, 227003 (2011). 5. H. Alloul, J. Bobroff, M. Gabay, P. Hirschfeld, Rev. Mod. Phys. 81, 45 (2009). 6. G. Prando et al., Phys. Rev. Lett. 114, 247004 (2015). 7. Caivano, R. et al., Superconductor Science and Technology 22, 014004 (2009). 196 Superstripes 2017, Ischia June 4 10, 2017 35.3 Quantum critical points in iron based superconductors Yuta Mizukami Department of Advanced Materials Science, University of Tokyo Email: [email protected] tokyo.ac.jp Keywords: iron based superconductor; quantum critical point; electron nematicity The relationship between the quantum critical point (QCP) of a broken symmetry phase and unconventional superconductivity is a long standing issue in condensed matter physics. In iron based superconductors BaFe2(As1 xPx)2, there is clear evidence for an antiferromagnetic (AFM) QCP at the optimal composition[1]. Although it is widely believed that the quantum critical fluctuations which originate from the QCP are related to the unconventional superconductivity, there is no direct evidence for the scenario that they help to enhance superconductivity. One of the most direct way to this issue is to investigate how the superconducting dome traces when the QCP is shifted. By introducing controlled disorder, we investigate the change of the resistive transitions without changing carrier concentration or band width for a wide range of compositions. The obtained phase diagram after introducing disorder shows that the AFM QCP and the superconducting dome are simultaneously shifted by the same amount toward low P compositions, suggesting that the quantum critical fluctuations play an essential role in enhancing superconductivity in this high Tc family. In FeSe, on the other hand, tetragonal to orthorhombic structural transition (nematic transition) occurs around 90 K, but there is no AFM order in contrast with other iron based superconductors[4]. The nematic transition is monotonically suppressed when Se is substituted by isovalent S[5,6], which makes it possible to study the relationship between nematicity and superconductivity without magnetism. We have measured the elastoresistance in Fe(Se,S) to obtain the nematic susceptibility, and it exhibits divergent like behavior around the compositions where the nematic transition is completely suppressed, evidencing a nonmagnetic nematic QCP[7]. The relationship between the nematic QCP and superconductivity is also discussed. References 1. T. Shibauchi et al., “A Quantum Critical Point Lying Beneath the Superconducting Dome in Iron Pnictides” Annu. Rev. Condens. Matter Phys. 5, 113 (2014). 197 Superstripes 2017, Ischia June 4 10, 2017 http://www.annualreviews.org/doi/abs/10.1146/annurev conmatphys 031113 133921 2. Y. Mizukami et al., “Disorder Induced Topological Change of the Superconducting Gap Structure in Iron Pnictides” Nature Communications 5, 5657 (2014). http://www.nature.com/articles/ncomms6657 3. R. Khasanov et al., “Evidence of nodeless superconductivity in FeSe0.85 from a muon spin rotation study of the in plane magnetic penetration depth” Phys. Rev. B 78, 220510 (2008). http://journals.aps.org/prb/abstract/10.1103/PhysRevB.78.220510 4. Y. Mizuguchi et al., “Substitution Effect on FeSe Superconductor” J. Phys. Soc. Jpn. 78, 074712 (2009). http://journals.jps.jp/doi/abs/10.1143/JPSJ.78.074712 5. M. D. Watson et al., “Suppression of orbital ordering by chemical pressure in FeSe1 xSx” Phys. Rev. B 92, 121108 (2015). http://journals.aps.org/prb/abstract/10.1103/PhysRevB.92.121108 6. S. Hosoi et al., “Nematic Quantum Critical Point without Magnetism in FeSe1 xSx Superconductors” Proc. Natl. Acad. Sci. USA 113, 8139 (2016). http://www.pnas.org/content/113/29/8139 198 Superstripes 2017, Ischia June 4 10, 2017 35.4 How different are the iridates from the cuprates? Insights from the RIXS and ARPES spectroscopies Krzysztof Wohlfeld University of Warsaw Email: [email protected] Keywords: iridates, cuprates, spin orbit coupling, orbitals, spectroscopies The quasi 2D iridates (such as e.g. Sr2IrO4 or Ba2IrO4) have recently attracted a lot of attention, for they seem to resemble the “high Tc” cuprates. Indeed, despite some fundamental differences between these two classes of compounds (like the implicit inclusion of the orbital degrees of freedom or the strong on site spin orbit coupling), there exist striking similarities between these oxides. In particular, various RIXS experiments on quasi 2D iridates observed, e.g.: (i) the onset of dispersive collective magnetic excitations [1], (ii) the strong coupling between excitons and magnons [2], (iii) the persistence of magnon excitations upon doping [3, 4]. Nevertheless, as will be discussed in this talk, recent theoretical studies, backed by RIXS and ARPES experiments, show crucial differences between the iridates and the cuprates: (i) the excitons found in the undoped iridates may be strongly affected by the Jahn Teller effect [5], and (ii) in the hole doped iridate the many body (“multiplet”) 5d4 configurations form, strongly affecting the way such a “5d4 hole” moves. The latter phenomenon makes the hole doped iridates not only fundamentally different from tho iridates doped with electrons but also from both electron and hole doped cuprates [6]. References 1. J. Kim et al., Phys. Rev. Lett. 108, 177003 (2012). 2. J. Kim et al., Nat. Commun. 5, 4453 (2014). 3. H. Gretarsson et al., Phys. Rev. Lett. 117, 107001 (2016). 4. X. Liu et al., Phys. Rev. B 93, 241102(R) (2016). 5. E. M. Plotnikova, M. Daghofer, J. van den Brink, K. Wohlfeld, Phys. Rev. Lett. 116, 106401 (2016). 6. E. M. Paerschke, K. Wohlfeld, K. Foyevtsova, J. van den Brink, submitted (2017). 199 Superstripes 2017, Ischia June 4 10, 2017 36.1 Principles of holographic duality in the laboratory J. Zaanen Instituut Lorentz for Theoretical Physics, Leiden University Email: [email protected] Keywords: Quantum matter, High Tc superconductivity, Holographic duality. New mathematical machinery has entered the condensed matter stage in the form of the holographic duality of string theory [1]. This is presently understood as a method describing the collective properties of states of matter that are characterised by extreme many body quantum entanglement. Among others it predicts holographic strange metals: quantum critical phases characterized by novel types of scaling properties which appear to be surprisingly similar to what is observed in the strange metals found in high Tc superconductors [2] and related systems. The challenge is to find out whether this is just a coincidence or signalling a revolution in fundamental physics. A major research got funded in the Netherlands aiming at (dis)proving holographic principle by condensed matter experiment. I will discuss some of the main ideas behind this affair. References 1. J. Zaanen, Y. W. Sun, Y. Liu and K. Schalm, "holographic duality in condensed matter physics" (Cambridge Univ. Press, 2015). 2. B. Keimer et al., Nature 518, 179 (2015). 200 Superstripes 2017, Ischia June 4 10, 2017 36.2 Gauge theory of the BKT transition in disordered systems M. G. Vasin, V. N. Ryzhov, V. M. Vinokur M. G. Vasin: Physical Technical Institute, Ural Branch of Russian Academy of Sciences, 426000 Izhevsk, Russia; 2Institute for High Pressure Physics of Russian Academy of Sciences, 108840 Moscow, Russia. V. N. Ryzhov: 2Institute for High Pressure Physics of Russian Academy of Sciences, 108840 Moscow, Russia. V. M. Vinokur: Materials Science Division, Argonne National Laboratory, 9700 S. Cass Ave, Lemont, IL 60439, USA Email: [email protected] Keywords: disordered BKT transition, gauge theories, superinsulators We develop a gauge theory of the topological defects driven phase transition in the weakly disordered XY model, the harbor of the Berezinskii Kosterlitz Thouless (BKT) physics. We find that while in two dimensions the liquid of topological defects freezes according to the BKT scenario, the three dimensional topological liquid exhibits more singular Vogel Fulcher Tamman (VFT) criticality signaling that the system freezes into a nonergodic glassy state. We discuss the far reaching implications of the existence of the nonergodic confined BKT state, ranging from properties of a superinsulator to the development of the universe according to the Kibble Zürek scenario. A sketch of phase diagram of the frustrated 3D XY model in the topological defects density (solitons) – temperature coordinates. The red line marks the renormalized temperature of the second order phase transition and the blue line depicts the confinement deconfinement transition line. The transition occurs according to the mechanism of the larger transition temperature. 201 Superstripes 2017, Ischia June 4 10, 2017 36.3 Multi orbital Hamiltonian for Iron Chalcogenides Adriana Moreo University of Tennessee and ORNL. Email: [email protected] Keywords: Nematic phase, orbital lattice coupling, spin lattice coupling The bicollinear antiferromagnetic ground state experimentally observed in FeTe, the parent compound of the chalcogenide high Tc superconductor FeTe1 xSex, is stabilized by spin lattice coupling in a three orbital (xz, yz, xy) spin fermion model studied with Monte Carlo techniques[1,2,3]. Monoclinic lattice distortions coupled to a spin nematic parameter with B2g symmetry via a dimensionless coupling parameters g12 stabilize a monoclinic bicollinear, (π/2,π/2), AF phase experimentally observed in FeTe. This shows that both magnetic and structural properties can be controlled by a magneto ellastic interaction. The planar resistivity was studied and it was found, in agreement with experiments for Fe chalcogenides with bicollinear AF ground states, that the resistivity is larger along the antiferromagnetic direction for the bicollinear state. This reversed anisotropy, compared with the one observed in pnictides, increases with the Hund coupling. These results indicate that the magnetic, structural, and transport properties observed in Fe chalcogenides can be reproduced via the coupling between the magnetic and lattice degrees of freedom [3]. It is also found that coupling a B2g orbital order parameter to the monoclinic lattice distortion with a coupling lambda12, produces a novel, not yet experimentally observed, nematic phase above the AF bicollinear state characterized by spin and orbital nematic order.[4] 202 Superstripes 2017, Ischia June 4 10, 2017 Phase diagram as a function of the orbital lattice coupling, lambda12, and the temperature. The monoclinic nematic phase appears between the structural transition at TS and the magetic transition at TN. References 1. S. Liang et al., Phys. Rev. Lett. 109, 047001 (2012). 2. Shuhua Liang, Adriana Moreo, and Elbio Dagotto, Phys. Rev. Lett. 111, 047004 (2013). 3. Chris Bishop, Adriana Moreo, and Elbio Dagotto, Phys. Rev. Lett. 117, 117201 (2016). 4. Chris Bishop, Adriana Moreo, and Elbio Dagotto, in preparation. 203 Superstripes 2017, Ischia June 4 10, 2017 36.4 Non destructive high resolution three dimensional imaging of intelligent matter G. Aeppli Department of Physics, ETH Zürich, Zürich CH 8093, Switzerland Institut de Physique, EPFL, Lausanne CH 1015, Switzerland Paul Scherrer Institut, Villigen CH 5232, Switzerland Email: [email protected] Conventional high resolution microscopy for imaging the interior of three dimensional matter typically entails destructive sample preparation followed by electron microscopy of resulting surfaces or sections. Here we describe X ray ptychography, a mixed real space/reciprocal space technique, which is non destructive and provides three dimensional images to depths given by the penetration of the X rays at the wavelength used. Applications to artificial intelligence implemented in silicon is described, and perspective will be provided concerning possible applications to natural intelligence, implemented in wetware, and other problems, including self assembled stripes in multiphase matter. Reference 1. Holler et al. Nature 543, 402–406 (16 March 2017) http://www.nature.com/nature/journal/v543/n7645/abs/nature21698.html 204 Superstripes 2017, Ischia June 4 10, 2017 36.5 Elastic Effects at the Mott Transition Peter Littlewood, RIchard Brierley, Gian Guzman Verri University of Chicago University of Costa Rica Yale University Email: [email protected] The boundary between metal and insulator remains a fruitful source of emergent phenomena in materials, ranging from oxides, to cold atoms. Typically the insulating side of this boundary is occupied by an electronic crystal (though often disordered), and at higher temperatures a polaronic liquid or bad metal. While the paradigm Hamiltonian for this transition involves only short –range electronic correlations, in practice the transition is tuned by disorder, by screening of longer range Coulomb forces, and by coupling to the lattice. While electric charges can be screened, the same is not true of strain fields, which have intrinsic long range interactions that cannot be screened. When strain fields are produced as a secondary order parameter in phase transitions as for example in ferroelectrics this produces unexpected consequences for the dynamics of order parameter fluctuations, including the generation of a gap in what would otherwise have been expected to be Goldstone modes. In some cases, e.g. manganites and nickelates, other intra cell modes can nonlinearly screen the order parameter, which produces a strong sensitivity of ordering to octahedral rotations, essentially a jamming transition. This is relevant for tuning entropic effects at phase transitions, perhaps to enhance electro caloric and magneto electric effects. References 1. Elastic interactions and control of the Mott transition, G. G. Guzmán Verri, R. T. Brierley, P. B. Littlewood arXiv:1701.02318 2. Why is the electrocaloric effect so small in ferroelectrics? G. G. Guzmán Verri, P. B. Littlewood, APL Mater. 4, 064106 (2016) 205 Superstripes 2017, Ischia June 4 10, 2017 37.1 Effect of electron phonon interaction on the doping and temperature dependent spectral function in cuprates I.A. Makarov, S.G. Ovchinnikov Kirensky Institute of Physics, Federal Research Center KSC SB RAS, 660036 Krasnoyarsk, Russia Email: [email protected] Keywords: strong electron correlations, cluster perturbation theory, polaron band structure The generalized tight binding (GTB) method to calculate the electronic structure of strongly correlated electrons in cuprates is modified to incorporate also strong electron phonon interaction. By exact diagonalization of the p d Holstain model Hamiltonian for a separate CuO6 unit cell we find the multelectron and multiphonon local eigenstates that are used to construct a set of local Hubbard operators. Then we treat the intercell electron hopping t by the perturbation approach over small ratio t/U, where U is the charge transfer excitation energy. Without electron phonon interaction we obtain the band of spin polaron and a set of local multiphonon Franck Condon excitations. The electron phonon interaction results in the hybridization of spin polaron and Franck Condon excitations that forms the polaronic band structure with strong temperature dependence. The temperature dependence of the polaronic band structure and Fermi surface is discussed. The peak of a spectral function at the top of the valence band has large width typical to the ARPES data and determined by a large number of the multiphonon excitations. 206 Superstripes 2017, Ischia June 4 10, 2017 37.2 Robust determination of the superconducting gap sign structure via quasiparticle interference Ilya Eremin Ruhr Universität Bochum Email: [email protected] Phase sensitive measurements of the superconducting gap in Fe based superconductors have proven more difficult than originally anticipated. While quasiparticle interference (QPI) measurements based on scanning tunneling spectroscopy are often proposed as definitive tests of gap structure, the analysis typically relies on details of the model employed. Here we point out that the temperature dependence of momentum integrated QPI data can be used to identify gap sign changes in a qualitative way, and present an illustration for s± and s++ states in a system with typical Fe pnictide Fermi surface. 207 Superstripes 2017, Ischia June 4 10, 2017 37.3 Magnetotransport Signatures of Competing Ground States and Critical Scaling in Strongly Correlated Superconductors Fedor F. Balakirev National High Magnetic Field Laboratory, Los Alamos National Laboratory Email: [email protected] Keywords: high Tc, phase transitions, cuprates, unconventional superconductivity A large number of unconventional superconductors exhibit signatures of density wave instabilities and Fermi surface reconstruction beneath the superconducting order. Similar traits associated with resulting transformations of the electronic structure are found in magnetoreasistance and Hall response in a variety of strongly correlated superconducting materials ranging from electron and hole doped high Tc superconductors to heavy fermion compounds. The instability driven competition among alternate ground states can provide the essential ingredients governing the physics of the strongly correlated superconductors. Extremely high magnetic fields help to reveal newly formed ordered states and emergence of universal critical scaling behavior. References 1. F.F. Balakirev et al., Nature 424, 912 (2003). 2. F.F. Balakirev et al., Phys. Rev. Lett. 102, 017004 (2009). 3. P.Li et al., Phys. Rev. Lett. 99, 047003 (2007). 4. Y. Kohama et al., Phys. Rev. B 79, 144527 (2009). 5. P.J.W. Moll et al., "Nature communications 6, 6663 (2015). 208 Superstripes 2017, Ischia June 4 10, 2017 38.1 Conventional vortices in the high temperature superconductor YBa2Cu3O7 δδδ I. Maggio Aprile, Ch. Berthod, J. Bruér, Ch. Renner* Department of Quantum Matter Physics, University of Geneva, 1211 Geneva 4, Switzerland Email: [email protected] Keywords: HTS, vortex core, STM, tunneling spectroscopy The electronic vortex core structure in cuprate high temperature superconductors has remained an open question for the past 30 years. It was recently found [1] that the tunnelling spectra of YBa2Cu3O7 δ in zero field could be perfectly reproduced within a standard BCS d wave symmetry pairing model, assuming a coherent and an incoherent contribution to the tunnelling current. The coherent contribution is fully consistent with a weak coupling d wave BCS local density of states. In this presentation, we show that in a finite applied magnetic field, the coherent contribution to the tunnelling current reveals standard Caroli–de Gennes–Matricon vortex core states. We observe significant variations in the core signatures of adjacent vortices, which we can fully explain by considering the effect of neighbouring vortices and disorder in the vortex lattice (Ref[2] and talk by Ch.Berthod). These latest scanning tunnelling microscopy studies show that the superconducting condensate of copper oxides is conventional, but does not look so because superconducting electrons are minority. References 1. Bruér, J., et al., Nat Commun 7, 11139 (2016). 2. C. Berthod, Phys. Rev. B 94, 184510 (2016). 209 Superstripes 2017, Ischia June 4 10, 2017 38.2 SU(2) Gauge Theory Description of the Current Induced Spin Polarizations in an Electron Gas Roberto Raimondi, Cosimo Gorini, Amin Maleki, Ka Shen, Ilya V. Tokatly, Giovanni Vignale Dipartimento di Matematica e Fisica, Università Roma Tre, Via della Vasca Navale 84, 00146 Rome, Italy; Institut für Theoretische Physik, Universität Regensburg, 93040 Regensburg, Germany; Kavli Institute of NanoScience, Delft University of Technology, Lorentzweg 1, 2628 CJ Delft, The Netherlands; Nano bio Spectroscopy group and ETSF Scientific Development Centre, Dpto. Física de Materiales, Universidad del País Vasco, E 20018 San Sebastian, Spain IKERBASQUE, Basque Foundation for Science, 48011 Bilbao, Spain; Department of Physics and Astronomy, University of Missouri, Columbia, Missouri 65211, USA Email: [email protected] Spin charge conversion mechanisms are currently a focus of intensive experimental and theoretical research. In particular the spin galvanic effect, also known as the inverse Edelstein effect, is the generation of a charge current by a non equilibrium spin polarization. Viceversa, its Onsager reciprocal effect is the generation of a spin polarization by an applied electric field. The effect occurs thanks to the Rashba spin orbit coupling which arises as a consequence of the breaking of inversion symmetry. This may occur in semiconducting quantum wells and at surfaces and interfaces. In this talk, considering the general model of a two dimensional electron gas, I will discuss how the simultaneous presence of spin orbit coupling from impurities potential modifies the picture valid when only the Rashba spin orbit coupling is present. These modifications are relevant for the interpretation of experimental results. I will sketch how the description of the Rashba spin orbit coupling as an effective SU(2) gauge field allows the derivation of an effective Boltzmann equation, by which the Bloch equations for the spin dynamics can be derived. In particular, I will show how the interplay of the Rashba guage field and the Elliott Yafet spin relaxation yields a new spin generation term. The effects of the Dresselhaus bulk inversion asymmetry spin orbit coupling is also considered. 210 Superstripes 2017, Ischia June 4 10, 2017 38.3 Insights into the spin orbital entanglement in complex iridium oxides from high field ESR spectroscopy Vladislav Kataev Email: v.kataev@ifw dresden.de Keywords: iridates, spin orbital Mott insulators, ESR spectroscopy Complex iridium oxides have attracted recently a lot of attention due to an intimate entanglement of spin and orbital degrees of freedom which may give rise to a novel spin orbital Mott insulating behavior and exotic quantum spin liquid phases. Electron spin resonance (ESR) spectroscopy is known to be an instructive tool for studying the spin orbital coupling (SOC) effects as it can directly access the relevant parameters sensitive to SOC, such as the g factor tensor, magnetic anisotropy gaps and spin dynamics. In this talk, our recent results on multi frequency sub THz ESR spectroscopy on iridium oxides in strong magnetic fields will be discussed: (1) Evidence for the inversion of the orbital states in the prototypical spin orbital Mott insulator Sr2IrO4 due to the long range crystal field effects [1]; (2) Observation of the collective magnetic resonance mode of coupled Cu2+ spins s = 1/2 and Ir4+ pseudo spins jeff = 1/2 in the aniferromagnetic double perovskite La2CuIrO6 [2]; (3) Origin of the unexpected magnetism in the double perovskite Ba2YIrO6 [3]. References 1. Bogdanov, N. A. et al. , Nat. Commun. 6:7306 doi: 10.1038/ncomms8306 (2015). 2. K. Manna et al., Phys. Rev. B 94, 144437 (2016). 3. S. Fuchs et al., to be published, (2017). 211 Superstripes 2017, Ischia June 4 10, 2017 38.4 Electronic Structure Study of Filled Skutterudites Khandker Quader1, Michael Widom2, Lucian Pascut3 1 Kent State University 2 Carnegie Mellon University 3 Rutgers University Email: [email protected] Keywords: Skutterudites, f electrons, DFT electronic structure, Fermi surface, superconductivity Over the past few years there has been considerable interest in the class of compounds called “filled” skutterudites RGe4Pt12, which belong to the general class MT4X12, where T is a transition metal, X a pnictogen or Group 14/16 element, and the filler M (or R) a rare earth element. Interest stem from the array of physical behavior exhibited : conventional as well as unconventional superconductivity with non s wave and multi band or multi gap pairing, antiferromagnetism, intermediate valence behavior, etc. These are also promising candidates for thermoelectric applications. First principle density functional theory (DFT) calculations can provide useful information about the Fermi surface topology, bands crossing Fermi energy, density of states, and magnetism. These in turn may shed light on the nature of superconductivity and other behavior. We first give an overview of features of the skutterudites, and principles underlying DFT. Then we present our recent systematic, comparative study of RGe4Pt12 (R = La, Ce, Pr), as we progress across the periodic table. Our calculations utilize both VASP and WIEN2k codes. To elicit possible role of the lanthanide f electrons and f f interaction U, we calculate band structures, Fermi surfaces and density of states (DOS) for different scenarios: (a) frozen f electron Generalized Gradient Approximation (GGA); (b) GGA + U with and without spin –orbit coupling; (c) unfrozen f electron GGA. Comparing our DFT DOS with experimental electronic heat capacity, we obtain values of effective mass enhancement, m*/m_band. Our calculated Fermi surface topology near Fermi energy may provide clues into the nature of superconductivity in some of these compounds. Our calculation of magnetic order (f electron moment) suggest that Dynamical Mean field Theory (DMFT) may be necessary to reproduce experimental magnetic behavior in these materials. We also explore whether the experimentally observed variation of superconducting Tc with pressure in the Pr compound can be accounted for in terms the variation of DOS with pressure. Finally, I shall discuss our ongoing DMFT calculations on these materials. 212 Superstripes 2017, Ischia June 4 10, 2017 Our calculated Fermi surfaces for LaPt4Ge12 at different symmetry points in the 1st Brillouiun zone (BZ). The points are shown in the accompanying BZ figure. References 1. R. Gumeniuk, W. Schnelle, H. Rosner, M. Nicklas, A. Leithe Jasper, and Yu. Grin, Phys. Rev. Lett. 100, 017002 (2008). 2. I. Jeon, K. Huang, D. Yazici, N. Kanchanavatee, B. D. White, P. C. Ho, S. Jang, N. Pouse, and M. B. Maple, Phys. Rev. B 93, 104507 (2016). 3. K. Quader, M. Widom, G.L. Pascut, Bulletin of the APS, Abstract: H39.00008 (2017). 213 Superstripes 2017, Ischia June 4 10, 2017 39.1 Spin susceptibility of the correlated 2D electron system Vladimir Pudalov1, Michael Gershenson2, Michael Reznikov3 1 P. N. Lebedev Physics Institute, 119991 Moscow, Russia 2 Serin Physics Lab, Rutgers University, Piscataway, NJ 08854, USA 3 Solid State Institute, Technion, 32000 Haifa, Israel Email: * [email protected] Key words: strongly correlated electrons; two dimensional electron systems. Dilute two dimensional (2D) electron systems provide an opportunity for exploring the physics of strongly interacting charged fermions. A number of theoretical predictions were made on the temperature behavior of the interaction renormalized spin susceptibility, including its divergence [1 3]. To test this issue experimentally, we studied the interference pattern of Shubnikov de Haas oscillations in weak crossed magnetic fields, for the strongly interacting electrons in Si inversion layers. From this data we deduced the temperature and magnetic field dependence of the renormalized spin susceptibility χ*(T,B) for itinerant electrons [4]. We found the weak χ*(T) dependence, only a few percent over the range T = (0.05 1)K, which seems to qualitatively agree with the theoretical predictions for the interaction corrections [5], δχ*(T). However, this dependence does not vanish, and even grows in a strong in plane magnetic fields B > T. In sharp contrast to δχ*(T), the total spin susceptibility χtot(T)T, obtained from thermodynamic magnetization measurements, diverges as T 2 with decreasing temperature. This difference suggests that the thermodynamic response in spin magnetization is dominated by the localized spins which are attributed to collective spin droplets coexisting with 2D Fermi liquid [6]. In its turn, the χ*(T) dependence of itinerant electrons, reflects the thermodynamic response of the itinerant electrons subsystem to the spin magnetization of the subsystem of localized electrons. References 1. A.Camjayi, K. Haule, V. Dobrosavljevic, G. Kotliar, Nat. Phys. 4, 932 (2008). 2. C. Castellani, C. Di Castro, P. A. Lee, M. Ma, S. Sorella, and E. Tabet, Phys. Rev. B 30, 1596 (1984). 3. A. Punnoose, A.M.Finkel'stein, Science 310, 289 (2005). 4. V. M. Pudalov, M. E. Gershenson, H. Kojima, N. Butch, E. M. Dizhur, G. Brunthaler, A. Printz, G. Bauer, Phys. Rev. Lett. 88, 196404 (2002). 5. B. L. Altshuler, A. G. Aronov, A. Yu. Zyuzin, JETP Lett. 35, 16 (1982). 6. N.Teneh, A.Yu. Kuntsevich, V. M. Pudalov, M. Reznikov, Phys. Rev.Lett. 109, 226403 (2012). 214 Superstripes 2017, Ischia June 4 10, 2017 39.2 INS study of single and entangled rings Tatiana Guidi ISIS facility, Rutherford Appleton Laboratory, UK Email: [email protected] Keywords: molecular magnetism, quantum bits, entanglement Entanglement is a crucial resource for quantum information processing and its detection and quantification is of paramount importance in many areas of current research. Weakly coupled molecular nanomagnets provide an ideal test bed for investigating entanglement between complex spin systems. However, entanglement in these systems has only been experimentally demonstrated rather indirectly by macroscopic techniques or by fitting trial model Hamiltonians to experimental data. We have exploited the capabilities of four dimensional inelastic neutron scattering (INS) to portray entanglement in weakly coupled molecular qubits and to quantify it [1]. The INS measurements on the prototype (Cr7Ni)2 supramolecular dimer has allowed us to demonstrate the potential of this approach, which allows one to extract the concurrence in eigenstates of a dimer of molecular qubits. References 1. E. Garlatti, T. Guidi, S. Ansbro, P. Santini, G. Amoretti, J. Ollivier, H. Mutka, G. Timco, I.J. Vitorica Yrezabal, G.F.S. Whitehead, R.E.P. Winpenny, & S. Carretta Nat. Comm. 8, 14543 (2017). 215 Superstripes 2017, Ischia June 4 10, 2017 39.3 Enhancement of electron phonon interaction in bilayer graphene with optically driven lattice E. Pomarico,1,2 M. Mitrano,2,3 H. Bromberger,2 M. A. Sentef,2 A. Al Temimy,4 C. Coletti,4 A. Stöhr,5 S. Link,5 U. Starke,5 C. Cacho,6 R. Chapman,6 E. Springate,6 G. M. Vanacore,1 F. Carbone,1 A. Cavalleri,2,7 and I. Gierz2 1 Laboratory for Ultrafast Microscopy and Electron Scattering, Institute of Physics, École Polytechnique Fédérale de Lausanne (EPFL), Lausanne, Switzerland 2 Max Planck Institute for the Structure and Dynamics of Matter, Center for Free Electron Laser Science, Hamburg, Germany 3 Department of Physics and Frederick Seitz Materials Research Laboratory, University of Illinois, Urbana, Illinois 61801, USA 4 Center for Nanotechnology @ NEST, Istituto Italiano di Tecnologia, Pisa, Italy 5 Max Planck Institute for Solid State Research, Stuttgart, Germany 6 Central Laser Facility, STFC Rutherford Appleton Laboratory, Harwell, United Kingdom 7 Department of Physics, Clarendon Laboratory, University of Oxford, Oxford, United Kingdom Email: [email protected] Keywords: nanoscale materials; graphene; time resolved dynamics of complex materials The electron phonon coupling determines the stability of orders like superconductivity, charge and spin density waves and its control in non equilibrium configurations may provide new ways to change materials’ functionalities. Here, we investigate whether optical lattice modulation can change the electron phonon coupling constant λ in bilayer graphene, whose response upon excitation of the in plane E1u phonon with pulses at 6.3 m is probed via terahertz time domain and time and angle resolved photoemission spectroscopy (tr ARPES) [1]. Drude scattering times in the optical conductivity significantly increase, as well as momentum integrated relaxation rates of hot quasi particles. These observations can be explained by a transient three fold enhancement of λ, leading to an increase of the carriers' effective mass and thermal capacity. The observed cooling of the electronic temperature and acceleration of the quasi particle relaxation upon phonon excitation are quantitatively reproduced [2]. A mechanism of phonon non linearity, which reduces the electronic bandwidth, could be responsible of the enhancement of λ [3]. New tests with ultrafast electron based techniques will be performed to elucidate the structural dynamics and the anharmonic phonon couplings stemming from the phonon excitation. Our results indicate that a control of the electron phonon interaction through phonon pumping may be possible 216 Superstripes 2017, Ischia June 4 10, 2017 and provide useful perspective for understanding the enhancement of superconductivity in K3C60 [4]. (a) Pump induced changes of the real part of the optical conductivity as a function of frequency, together with Drude fits, and (b) Drude scattering time (left axis) and electron phonon coupling constant (right axis) as a function of pump wavelength. (c) Relaxation rate 1/(2τ) as a function of energy for different pump wavelengths. (d) Electronic peak temperature and fast relaxation time as a function of pump wavelength together with a simulation based on a two temperature model. References 1. E. Pomarico et al, Phys. Rev. B 95, 024304 (2017). 2. I. Gierz et al, Phys. Rev. Lett. 114, 125503 (2015). 3. M. Knap et al, Phys. Rev. B 94, 214504 (2016). 4. M. Mitrano et al, Nature 530, 461 (2016). 217 Superstripes 2017, Ischia June 4 10, 2017 39.4 Detailed optical spectroscopy of hybridization gap and hidden order transition in high quality URu2Si2 single crystals N. Bachar (1), D. Stricker (1), S. Muleady (1), K. Wang (1), J. A. Mydosh (2), Y. K. Huang (3), and D. van der Marel (1) (1) Department of Quantum Matter Physics, University of Geneva, CH 1211 Geneva 4, Switzerland (2) Kamerlingh Onnes Laboratory, Leiden University, 2300RA Leiden, The Netherlands (3) Van der Waals Zeeman Institute, University of Amsterdam, 1018XE Amsterdam, The Netherlands Email: [email protected] We present a detailed temperature and frequency dependence of the optical conductivity measured on clean high quality single crystals of URu2Si2 of ac and ab plane surfaces. Our data demonstrate the itinerant character of the narrow 5f bands, becoming progressively coherent as the temperature is lowered below a crossover temperature T*~75 K. T* is higher than in previous reports as a result of a different sample preparation, which minimizes residual strain. We furthermore present the density response (energy loss) function of this compound, and determine the energies of the heavy fermion plasmons with a and c axis polarization. Our observation of a suppression of optical conductivity below 50 meV along both the a and c axes, along with a heavy fermion plasmon at 18 meV, points toward the emergence of a band of coherent charge carriers crossing the Fermi energy and the emergence of a hybridization gap on part of the Fermi surface. The evolution towards coherent itinerant states is accelerated below the hidden order temperature THO=17.5 K. In the hidden order phase the low frequency optical conductivity shows a single gap at ~6.5 meV, which closes at THO. 218 Superstripes 2017, Ischia June 4 10, 2017 Colormap of the optical conductivity of high quality URu2Si2 single crystals showing the emergence of the 5f heavy electrons coherent state at 75K and the hidden order state at 17.5K along a and c axes. References 1. N. Bachar et al., Phys. Rev. B 94, 235101 (2016). 219 Superstripes 2017, Ischia June 4 10, 2017 40.1 Phase dynamics and macroscopic quantum phenomena in unconventional Josephson junctions D. Massarotti1,2,3*, R. Caruso1,2, A. Pal4, D. Stornaiuolo1,2, P. Lucignano1,2, G. P. Pepe1,2, G. Rotoli3, L. Longobardi3,5, A. Tagliacozzo1,2, M. G. Blamire4, F. Tafuri2,3 1 Dipartimento di Fisica “E. Pancini”, Università Federico II di Napoli, Italy 2 CNR SPIN UOS Napoli, Italy 3 Dipartimento di Ingegneria Industriale e dell’Informazione, Seconda Università di Napoli, Italy 4 Department of Materials Science and Metallurgy, University of Cambridge, Cambridge, UK 5 American Physical Society, 1 Research Road, Ridge, New York 11961, USA Email: [email protected] Keywords: Hybrid Josephson junctions, phase dynamics, macroscopic quantum tunneling. Progress in material science in producing a larger variety of interfaces and in nanotechnologies applied to superconductivity is promoting a rethinking of the phase dynamics of Josephson junctions (JJs). Unconventional properties of the Josephson effect and different dissipation mechanisms can arise, thus a self consistent method for the study of the electrodynamics parameters is necessary in order to fully exploit the real functionalities of the emergent class of hybrid Josephson devices. We will report on a comparative study of the transport properties of unconventional JJs, ranging from high critical current density YBCO grain boundary junctions to ferromagnetic spin filter JJs and coplanar junctions with extended graphene sheets. Measurements of switching current distributions provide the key tool to distinguish the fingerprints of different dissipation sources, whose origin may depend on the geometry of the device and on the nature of the interface [1]. The first evidence of macroscopic quantum phenomena in spin filter JJs [2] paves the way for their possible use in quantum hybrid circuits, while in junctions characterized by large values of critical current density, local heating processes come into play and hinder the possible occurrence of MQT [3], imposing severe limitations for the quantum functionalities of these systems. A phase diagram valid in a wide range of junction energies and parameters will be discussed. References 1. D. Massarotti, et al. Physical Review B 94, 054525 (2016). 2. D. Massarotti, et al. Nature Communications 6, 7376 (2015). 3. D. Massarotti, et al. Physical Review B 92, 054501 (2015). 220 Superstripes 2017, Ischia June 4 10, 2017 40.2 Voltage noise in short superconducting bridges Andrew G. Semenov (1,3) and Andrei D. Zaikin(2,1) 1 I.E. Tamm Department of Theoretical Physics, P.N. Lebedev Physical Institute, 119991 Moscow, Russia 2 Institute of Nanotechnology, Karlsruhe Institute of Technology (KIT), 76021 Karlsruhe, Germany 3 National Research University Higher School of Economics, 101000 Moscow, Russia Email: [email protected] Keywords: Quantum phase slips, Shot noise At low temperatures non equilibrium voltage fluctuations can be generated in current biased superconducting nanowires due to proliferation of quantum phase slips (QPS) or, equivalently, due to quantum tunneling of magnetic flux quanta across the wire [1]. In our talk we will review theoretical results related to this phenomenon and present our recent calculations of the voltage noise generated by quantum phase slips in short superconducting bridges. In this case the main source of dissipation is an external dissipative environment which makes this situation markedly different from that of long superconducting wires [2 4]. We will demonstrate that quantum phase slips generate quantum shot noise in short superconducting nanowires which vanishes at frequencies beyond some threshold value in the zero temperature limit. We will also discuss the relation between QPS induced shot noise in ultrathin superconducting bridges and that in ultrasmall Josephson junctions [5]. The results of our theoretical analysis can be directly tested in future experiments with superconducting nanowires. References 1. K.Yu. Arutyunov, D.S. Golubev, and A.D. Zaikin, Phys. Rep. 464, 1 (2008). 2. A.G. Semenov and A.D. Zaikin, Phys. Rev. B 94, 014512 (2016). 3. A.G. Semenov and A.D. Zaikin, Fortschr. Phys. 64, XXX (2016). 4. A.G. Semenov and A.D. Zaikin, J. Supercond. Nov. Magn. 30, 139 (2017). 5. G. Schon and A.D. Zaikin, Phys. Rep. 198, 237 (1990). 221 Superstripes 2017, Ischia June 4 10, 2017 40.3 Small NbN superconducting nanonetwork fabricated using porous silicon templates Carmine Attanasio Email: [email protected] Keywords: one dimensional superconductivity Superconducting NbN nanonetworks with a very small number of interconnected nanowires, each having an effective diameter of 5 nm, are fabricated combining a bottom up (use of porous silicon nanotemplates) with a top down technique (high resolution electron beam lithography). The method is cheap and easy to control and allows to fabricate on a very robust support a system whose electrical properties are those of a one dimensional superconductor that can be fruitfully used as asuperconducting nanodevice. 222 Superstripes 2017, Ischia June 4 10, 2017 41.1 On superconducting stripes of the two dimensional Hubbard model R. Frésard1, O. Juillet2, and A. Leprévost1,2 1 Laboratoire CRISMAT, UMR CNRS ENSICAEN(ISMRA) 6508, Caen, France 2 Laboratoire LPC Caen, ENSICAEN, Université de Caen, CNRS/IN2P3, Caen, France Email: [email protected] Keywords: Two dimensional Hubbard model. Intertwining of spin , charge , and pair density waves. Variational approach The intertwining of spin , charge , and pair density waves embedded in a uniform wave superfluid background is highlighted in the strongly correlated regime of the two dimensional Hubbard model. As the lattice filling increases, this striped phase emerges from homogenous states exhibiting spiral magnetism and evolves towards a doped antiferromagnet. A concomitant enhancement of long ranged d wave pairing correlations is also found. Our variational results are obtained by mixing unrestricted Hartree Fock and BCS wave functions with symmetry restoration before variation. The approach is shown to be exact for a four site cluster [1], and to compare very favorably against existing exact results or numerical simulations [2,3]. References 1. A. Leprévost, O. Juillet, and R. Frésard, Ann. Phys. (Berlin) 526, 430 (2014). 2. O. Juillet and R. Frésard, Phys. Rev. B. 87, 115136 (2013). 3. A. Leprévost, O. Juillet, and R. Frésard, New J. Phys. 17, 103023 (2015). 223 Superstripes 2017, Ischia June 4 10, 2017 41.2 Magnetic ground state of the pyrochlore iridate Nd2Ir2O7 H. Guo1, C. Ritter2, K. Matsuhira3, I. Watanabe4, L. H. Tjeng1 and A. C. Komarek1 1 Max Planck Institute for Chemical Physics of Solids, Dresden 2 Institute Laue Langevin (ILL), Grenoble, France 3 Kyushu Institute of Technology, Japan 4 RIKEN, Japan Email: [email protected] Keywords: iridates Pyrochlore iridates (R2Ir2O7, R = Y and rare earth elements) are of great interest due to the interplay between the relatively large spin orbit coupling and electron electron correlations which may induce novel phases such as topological Mott insulators, axion insulators and Weyl semimetals. One important task for understanding the properties of these compounds is the determination of the magnetic structure which is challenging due to the small size of Ir4+ ions and strong neutron absorption from Ir atoms. Here, we studied the magnetic ground state of Nd2Ir2O7 by means of muon spin relaxation (muSR) [1] and powder neutron diffraction technique [2]. The study of muSR clearly showed spontaneous muon spin precession below the metal insulator transition temperature about 30 K and the internal field increases again below about 9 K after exhibiting a plateau below ~20 K, evidencing the magnetic ordering of the Ir and Nd sublattices, respectively. For the exact magnetic structure determination, we perform the powder neutron diffraction experiment at D20, ILL. Our magnetic structure refinement unravels a so called all in/all out magnetic structure that appears in both the Nd and the Ir sublattices. The ordered magnetic moments at 1.8 K amount to 0.34(1) B/Ir4+ and 1.27(1) B/Nd3+. The Nd3+ moment size at 1.8 K is smaller than that expected for the Nd3+ ground state doublet [3]. On the other hand, the size of the ordered moments of the Ir4+ ions at 1.8 K agrees well with the value expected for a Jeff = 1/2 state based on the presence of strong spin orbit coupling and hybridization between the Ir 5d and O 2p orbitals in this system [4]. Finally, our measurements reveal a parallel alignment of the Nd3+ moments with the net moment of its six nearest neighboring Ir4+ ions. References 1. H. Guo, K. Matsuhira, I. Kawasaki, M. Wakeshima, Y. Hinatsu, I. Watanabe, and Z. Xu, Phys. Rev. B, 88, 060411 (R) (2013). 2. H. Guo, C. Ritter and A. C. Komarek, Phys. Rev. B 94, 161102(R) (2016). 3. M. Watahiki, K. Tomiyasu, K. Matsuhira, K. Iwasa, M. Yokoyama, S. Takagi, M. Wakeshima, and Y. Hinatsu, J. Phys.: Conf. Ser. 320, 012080 (2011). 4. X.Wan, A.M. Turner, A. Vishwanath, and S. Y. Savrasov, Phys. Rev. B 83, 205101 (2011). 224 Superstripes 2017, Ischia June 4 10, 2017 41.3 Spin orbital frustration in Mott insulators George Jackeli MPI FKF and University of Stuttgart Email: [email protected] Keywords: spin orbit coupling, frustrated magnetism, quantum spin liquid In Mott insulators, unquenched orbital degrees of freedom often frustrate the magnetic interactions and lead to a plethora of interesting phases with unusual spin patterns or non magnetic states without long range order. I will review from this perspective the theoretical concepts and experimental data on late transition metal compounds, mostly focusing on iridates. In the second part, I will present our recent theoretical study of interplay of spin and orbital degrees in double perovskite compounds with spin one half ions occupying the frustrated fcc sublattice, such as molybdenum and osmium oxides. I will argue that this interplay might lead to a rich variety of the phases that include non collinear ordered patterns with or without net moment, and, most remarkably, non magnetic disordered spin orbit dimer state. 225 Superstripes 2017, Ischia June 4 10, 2017 41.4 Observing Interactions As They Happen: Ultrafast X ray and THz Studies of Charge Ordered Materials Giacomo Coslovich 1 SLAC National Accelerator Laboratory, 2575 Sand Hill Road, Menlo Park, CA 94025, U.S.A. 2 Materials Sciences Division, Lawrence Berkeley National Laboratory, 1 Cyclotron Road, Berkeley, CA 94720, U.S.A. Email: [email protected] Keywords: charge order, nickelates, cuprates ultrafast spectroscopy, THz, X ray Ultrashort X ray and optical pulses offer new opportunities to study fundamental interactions in materials exhibiting exotic quantum states, such as stripes, charge density waves and high temperature superconductivity. In this talk I will present two examples where ultrafast techniques provide unique insight in the dynamical forces governing the formation of charge order. The first example I will discuss is recent experiments on the nickelate compound La1.75Sr0.25NiO4 where broadband THz pulses reveal the complex relaxation of the folded Ni O bending vibrations following the quench of electronic stripes order1. Longitudinal and transverse vibrations react with different speeds, indicating a strong directionality of the electron phonon interaction. Moreover, ultrafast measurements in the mid infrared spectral range probe the dynamics of electronic pseudogap correlations and their relationship to the Fano asymmetry of Ni O stretching vibrations2. These experiments reveal the hidden complexity of the electron phonon interaction in stripes systems. In the second part of my talk I will briefly discuss very recent ultrafast resonant X ray scattering (RXS) results on underdoped ortho VIII YBa2Cu3O6+x (YBCO) single crystals performed at the LCLS. In this experiment an ultrashort laser pulse is used to transiently quench the superconducting state while the FEL probe detects the reaction of the CDW order, directly revealing the interaction between the two order parameters in real time. References 1. G. Coslovich, A.F. Kemper, S. Behl, B. Huber, H. A. Bechtel, T. Sasagawa, M. C. Martin, A. Lanzara, and R. A. Kaindl, arXiv:1603.07819 (2015). 2. G. Coslovich, B. Huber, W. S. Lee, Y. D. Chuang, Y. Zhu, T. Sasagawa, Z. Hussain, H.A. Bechtel, M.C. Martin, Z.X. Shen, R.W. Schoenlein, and R.A. Kaindl, Nature Comm. 4, 2643 (2013). 226 Superstripes 2017, Ischia June 4 10, 2017 42.1 Topological Kondo semi metals M. M. Wysokinski (1,2), M. Fabrizio (1) (1) International School for Advanced Studies (SISSA), via Bonomea 265, IT 34136, Trieste, Italy (2) Marian Smoluchowski Institute of Physics, Jagiellonian University, ul. Lojasiewicza 11, PL 30 348 Krakow, Poland. Email: [email protected] Keywords: topological Kondo insulators, Kondo semi metal; non local effects of correlations The Anderson lattice model with spin orbit coupling encoded in the hybridization form is known to efficiently portray topological Kondo insulators [1]. In our recent work [2] we have analysed role of the non local effects of the correlations on this state; in other words we have supplemented the self energy of the interacting f electrons with the momentum dependence. In result we have obtained strong arguments that dependently on the interaction strength the indirect hybridization gap can either open or close. Namely, above a critical interaction strength the topological Kondo insulator with an indirect gap undergoes transition to the metallic state, an intriguing result opposite to the conventional Mott phenomenon where increasing interaction instead favours the onset of an insulating state. Finally our results are very encouraging in light of possible existence of the topologically non trivial systems among wide group of materials called Kondo semi metals, or failed Kondo insulators, with the CeNiSn being the most promising candidate. The work has been supported by Polish Ministry of Science and Higher Education under the “Mobility Plus” program, Agreement No. 1265/MOB/IV/2015/0 as well as by European Union under the H2020 Framework Programme, ERC Advanced Grant No. 692670 “FIRSTORM”. 227 Superstripes 2017, Ischia June 4 10, 2017 U vs. εf phase diagram of the two dimensional topological Anderson lattice model [1] at half filling, with the value (in units of the conduction band hopping amplitude) of the emergent indirect gap marked on a colour scale. The phase diagram comprises three topologically distinct phases, a trivial topological insulator (TTI) and two non trivial ones, TKI(Γ) and TKI(M). Along the two red dashed lines the f occupancy is constant, with nf = 0.9 and nf = 1.1. (b) The continuation of the phase diagram for larger U where the TKI can undergo a transition to a metallic state. The region where the f occupancy locks at nf = 1 with negligible fluctuations, df→0, is denoted as an orbital selective (OS) Mott regime. References 1. M. Dzero, K. Sun, V. Galitski, and P. Coleman, Phys. Rev. Lett. 104, 106408 (2010). 2. M. M. Wysokinski, M. Fabrizio, Phys. Rev. B 94, 121102(R) (2016). 228 Superstripes 2017, Ischia June 4 10, 2017 42.2 Magnetic Lifshitz transition in iron based superconductors Andrzej Ptok 1),2), Konrad J. Kapcia 3),*), Agnieszka Cichy 4), Andrzej M. Oleś 5),6), Przemysław Piekarz 2) 1) Institute of Physics, Maria Curie Skłodowska University, Plac M. Skłodowskiej Curie 1, PL 20031 Lublin, Poland 2) Institute of Nuclear Physics, Polish Academy of Sciences, ul. E. Radzikowskiego 152, PL 31 342 Kraków, Poland 3) Institute of Physics, Polish Academy of Sciences, Aleja Lotników 32/46, PL 02 668 Warsaw, Poland 4) Institut für Physik, Johannes Gutenberg Universität Mainz, Staudingerweg 9, D 55099 Mainz, Germany 5) Marian Smoluchowski Institute of Physics, Jagiellonian University, ul. prof. S. Łojasiewicza 11, PL 30348 Kraków, Poland 6) Max Planck Institute for Solid State Research, Heisenbergstrasse 1, D 70569 Stuttgart, Germany *) presenting author Email: [email protected] Keywords: iron based superconductors, Lifshitz transition, magnetic field, multi band superconductivity In this lecture we address Lifshitz transition induced by applied external magnetic field in a case of iron based superconductors, in which a difference between the Fermi level and the edges of the bands is relatively small [1]. We introduce and investigate a two band model with intra band pairing in the relevant parameters regime to address a generic behavior of a system with hole like and electron like bands in external magnetic field [2,3,4]. Our results show that two Lifshitz transitions can develop in analyzed systems and the first one occurs in the superconducting phase and takes place at approximately constant magnetic field [3]. The chosen sets of the model parameters can describe characteristic band structure of iron based superconductors and thus the obtained results can explain the experimental observations in FeSe and Co doped BaFe2As2 compounds [5,6]. 229 Superstripes 2017, Ischia June 4 10, 2017 The main idea of the magnetic Lifshitz transition for a two band system with hole and electron like bands, which are realized in the iron based superconductors. (a) The application of the relatively small magnetic field leads to the splitting of the Fermi surfaces in both bands. Panels (b–d) show the band structure and the Fermi surfaces in the presence of an external magnetic field above the first (two possibilities b,c), and the second (d), magnetic Lifshitz transition. In all cases, the solid line represents the Fermi surfaces, while the blue (red) color corresponds to electron states with spin (anti)parallel to the magnetic field. References 1. I. M. Lifshitz, Zh. Eksp. Teor. Fiz. 38, 1569 (1960) [Sov. Phys. JETP 11, 1130–1135 (1960)]. 2. X. Liu, L. Zhao, S. He, J. He, D. Liu, D. Mou, B. Shen, Y. Hu, J. Huang, and X. J. Zhou, J. Phys.: Condens. Matter 27, 183201, (2015). 3. A. Ptok, K. J. Kapcia, A. Cichy, A. M. Oleś, and P. Piekarz, Scientific Reports 7, 41979 (2017). 4. A. Ptok, D. Crivelli, and K. J. Kapcia, Supercond. Sci. Technol. 28, 045010 (2015). 5. A. A. Kordyuk, Low Temp. Phys. 38, 888 (2012). 6. S. Kasahara, T. Watashige, T. Hanaguri, Y. Kohsaka, T. Yamashita, Y. Shimoyama, Y. Mizukami, R. Endo, H. Ikeda, K. Aoyama, T. Terashima, S. Uji, T. Wolf, H. von Löhneysen, T. Shibauchi, and Y. Matsuda, PNAS 111, 16309 (2014). 230 Superstripes 2017, Ischia June 4 10, 2017 42.3 The ab initio study of unconventional superconductivity in CeCoIn5 and FeSe Andrzej Ptok 1,2, Konrad J. Kapcia 3, Przemysław Piekarz 2 and Andrzej M. Oleś 4,5 1 Institute of Physics, Maria Curie Skłodowska University, Plac M. Skłodowskiej Curie 1, PL 20031 Lublin, Poland 2 Institute of Nuclear Physics, Polish Academy of Sciences, ul. E. Radzikowskiego 152, PL 31342 Kraków, Poland 3 Institute of Physics, Polish Academy of Sciences, Aleja Lotników 32/46, PL 02668 Warsaw, Poland 4 Max Planck Institute for Solid State Research, Heisenbergstrasse 1, D 70569 Stuttgart, Germany 5 Marian Smoluchowski Institute of Physics, Jagiellonian University, ul. prof. S. Łojasiewicza 11, PL 30348 Kraków, Poland Email: [email protected] Keywords: FFLO, ab initio Physical properties of real materials are very sensitive to the band structure and the shape of the Fermi surface [1]. These properties are known to be of fundamental importance for the superconducting instability in the system. For instance, an external magnetic field or a change in the band structure can trigger the onset of an unconventional superconducting phase of the Fulde Ferrell Larkin Ovchinnikov (FFLO) type [2,3], in which the Cooper pairs with non zero total momentum exist. We present a method which merges the Cooper pair susceptibility and the realistic model of bulk materials in Wannier orbitals from ab initio calculation [4]. As an example, we implement this method to study a heavy fermion compound CeCoIn5 [5] and an iron based superconductor FeSe [6]. The results obtained for both materials indicate the occurrence of the FFLO superconducting phase. References 1. A. A. Kordyuk, Low Temp. Phys. 38, 888 (2012). 2. P. Fulde and R. A. Ferrell, Phys. Rev. 135, A550 (1964). 3. A. I. Larkin and Y. N. Ovchinnikov, Zh. Eksp. Teor. Fiz. 47, 1136 (1964) [Sov. Phys. JETP 20, 762 (1965)]. 4. N. Marzari, A. A. Mostofi, J. R. Yates, I. Souza and D. Vanderbilt, Rev. Mod. Phys. 84, 1419 (2012). 5. Y. Matsuda and H. Shimahara, J. Phys. Soc. Jpn. 76, 051005 (2007). 6. S. Kasahara S et al., Proc. Natl. Acad. Sci. USA 111, 16309 (2014). 231 Superstripes 2017, Ischia June 4 10, 2017 42.4 Modeling low energy electronic excitations in the background of spin vortex checkerboard Pavel Dolgirev1,2, Vivek Bhartiya1, Boris V. Fine1,3 1 Skolkovo Institute of Science and Technology, Skolkovo Innovation Center, Nobel Str. 3, Moscow 143026, Russia 2 Department of General and Applied Physics, Moscow Institute of Physics and Technology, Institutskiy per. 9, Dolgoprudny, Moscow Region, 141700, Russia 3 Institute for Theoretical Physics, University of Heidelberg, Philosophenweg 12, 69120 Heidelberg, Germany Email: [email protected] Keywords: cuprate superconductors, stripes, checkerboards, pseudogap We investigate the properties of low energy electronic excitations in the background of a magnetic texture called "spin vortex checkerboard"[1,2,3]. This texture was proposed as a possible alternative to stripes to interpret the experimental phenomenology of 1/8 doped lanthanum cuprates. We mimic the spin texture by a 8x8 periodic pattern of staggered local fields acting on the spin variables of charge carriers. This leads to reconstructed electronic bands, which we use to identify the pseudogap and analyse its geometry. We show that, for quite realistic parameters, the pseudogap would vanish along the nodal directions in the CuO2 planes. Such a geometry[3,4] is very challenging to explain starting from one dimensional stripe modulations. We further discuss how the above electronic bands can explain other known transport properties. Finally we present our results for a two component superconductivity model that generalizes the previous analysis of the grid checkerboard[5,6] to the spin vortex checkerboard. Spin vortex checkerboard 232 Superstripes 2017, Ischia June 4 10, 2017 References 1. B. V. Fine, Phys. Rev. B 75, 060504R (2007) 2. B. V. Fine, J. Supercond. Nov. Magn. 24, 1207 (2011) 3. T. Valla et al., Science 314, 1914 (2006) 4. R. He et al., Nat. Phys. 5, 119 (2009) 5. B. V. Fine, Phys. Rev. B 70, 224508 (2004) 6. B. V. Fine, Phys. Rev. Lett. 94, 157005 (2005) 233 Superstripes 2017, Ischia June 4 10, 2017 43.1 Local probing of magnetic order and excitations in iron based superconductors Peter Wahl University of St Andrews Email: wahl@st andrews.ac.uk Keywords: iron based superconductors, inelastic excitations, spin polarized scanning tunneling microscopy and spectroscopy The proximity of magnetic order to superconductivity in the phase diagrams of many of the iron based superconductors indicates an intimate relationship between the two. In my talk, I will discuss local measurements by low temperature scanning tunnelling microscopy and spectroscopy of the magnetic order and magnetic excitations in iron based superconductors. I will discuss detection of magnetic order and magnetic excitations in the non superconducting parent compound, FeTe, of the iron chalcogenides by inelastic tunnelling spectroscopy. I will then show the influence of inelastic tunnelling on spectra obtained in the superconducting state and how the inelastic signal can be used to image the spin resonance mode of the iron based superconductors in real space, information not available from other methods. 234 Superstripes 2017, Ischia June 4 10, 2017 Schematic image of inelastic tunnelling process probing the spin resonance in LiFeAs in real space. References 1. Shun Chi, et al., Imaging the Real Space Structure of the Spin Fluctuations in an Iron based superconductor, under review. 2. M. Enayat, et al., Science 345, 653 (2014). 235 Superstripes 2017, Ischia June 4 10, 2017 43.2 Local spectroscopy of vortices in the presence of disorder: application to YBCO C. Berthod Department of Quantum Matter Physics, University of Geneva, 24 quai Ernest Ansermet, 1211 Geneva, Switzerland Email: [email protected] Keywords: Vortex core, HTS, STM, disorder We study the electronic structure of vortex cores at intermediate fields in the presence of positional disorder in the vortex lattice, for clean type II superconductors with d wave pairing symmetry and short coherence length. Our model targets the copper oxide high Tc materials for which the peculiar spectra measured [1,2] by scanning tunneling spectroscopy inside vortices have not received any convincing interpretation so far. In order to describe infinite disordered vortex configurations within the Bogoliubov de Gennes formalism, we have recently proposed an asymmetric singular gauge in which each vortex is represented by a short range disturbance of the order parameter [3]. Using model parameters appropriate for optimally doped YBa2Cu3O7 δ (YBCO) and a field of ~ 5~T, we find that in a perfect vortex lattice the local density of states depends strongly on the relative orientations of the vortex and crystal lattices. Introducing disorder, we also find that the core spectra depend on the positions of nearby vortices and are therefore different in each vortex. These results, together with new measurements in YBCO that will be presented by Ch. Renner at this conference, lead to the first positive identification of conventional d wave vortex core spectroscopic signatures in a cuprate. References 1. I. Maggio Aprile, Ch. Renner, A. Erb, E. Walker, and Ø. Fischer, Phys. Rev. Lett. 75, 2754 (1995). 2. Ch. Renner, B. Revaz, K. Kadowaki, I. Maggio Aprile, and Ø. Fischer, Phys. Rev. Lett. 80, 3606 (1998). 3. C. Berthod, Phys. Rev. B 94, 184510 (2016). 236 Superstripes 2017, Ischia June 4 10, 2017 43.3 RIXS study on charge order and magnetic excitations in superconductor Bi2201 Yingying Peng1 1 Dipartimento di Fisica, Politecnico di Milano, Piazza Leonardo da Vinci 32, I 20133 Milano, Italy Email: [email protected] Keywords: superconductor; charge order; magnetic excitations. Charge density fluctuations have been observed in several families of hole doped cuprates and are considered to be intrinsic in underdoped materials. Resonant soft x ray scattering has emerged as the most sensitive method that uncover charge density wave (CDW) correlations competing with superconductivity [1]. Here, by utilizing the high resolution RIXS we have directly observed charge density modulation in the optimally doped Bi2201, with smaller intensity and correlation length with respect to the underdoped sample (Figure 1). This demonstrates the short range charge order in Bi2201 persists up to optimal doping, as in other hole doped cuprates [2]. We also detected, quite unexpectedly, a signal of CDW in overdoped Bi2201. Figure 1: The charge order in Bi2201 observed by resonant inelastic x ray scattering (RIXS). 237 Superstripes 2017, Ischia June 4 10, 2017 In cuprate high temperature superconductors, superconductivity emerges from doping the antiferromagnetic Mott insulator thus intense research has been focused on the evolution of the spin excitation spectrum on doping [3 4]. Here, we explored the evolution of spin excitation dispersion upon doping in Bi2201 from heavily underdoping to heavily overdoping. We notice that the spin wave excitations detected in the parent compounds gets strongly broadened (damped) along (1,1) direction in the SC compounds. Surprisingly, the undamped frequency disperses similarly along the magnetic Brillouin Zone boundary. In addition, we have utilized the polarimeter [5] to fully disentangle the charge or spin flip components. References 1. G. Ghiringhelli et al., Long Range Incommensurate Charge Fluctuations in (Y,Nd)Ba2Cu3O6+x. Science 337, 821 (2012). 2. Y. Y. Peng et al., Direct observation of charge order in underdoped and optimally doped Bi2(Sr,La)2CuO6+δ by resonant inelastic x ray scattering. Phys. Rev. B 94, 184511 (2016). 3. M. Le Tacon et al., Intense paramagnon excitations in a large family of high temperature superconductors. Nat. Phys. 7, 725 (2011). 4. M. P. M. Dean et al., Persistence of magnetic excitations in La2−xSrxCuO4 from the undoped insulator to the heavily overdoped non superconducting metal. Nat. Mater. 12, 1019 (2013). 5. L. Braicovich et al., The simultaneous measurement of energy and linear polarization of the scattered radiation in resonant inelastic soft x ray scattering. Rev. Sci. Instrum. 85, 115104 (2014). 238 Superstripes 2017, Ischia June 4 10, 2017 44.1 Berezinskii–Kosterlitz–Thouless in curved space Leopoldo R. Gómez, Nicolás García and José Lorenzana Department of Physics, Universidad Nacional del Sur IFISUR CONICET, 8000 Bahı́a Blanca, Argentina. Institute for Complex Systems Consiglio Nazionale delle Ricerche, and Physics Department, University of Rome La Sapienza, I 00185 Rome, Italy. Email: [email protected] Keywords: Berezinskii Kosterlitz Thouless Transition, curved surfaces We consider the XY model on a curved surface. We discuss how the model on the surface can be mapped to model with inhomogeneous parameters in a planar geometry and show numerical simulations and analytical results that show non trivial effects of surface curvature on the Berezinskii Kosterlitz Thouless transition. The balance between energetic effects and entropic effects changes as a function of temperature giving rise to dramatic effects in the distributions of vortices. We discuss several experimental probes that can be used to verify the predictions. Snapshots of a Monte Carlo simulation of the XY model on a Gaussian surface. The colors indicate the phase of the angular variable. White dots are vortices. 239 Superstripes 2017, Ischia June 4 10, 2017 44.2 Effect of Nanoperforation on critically disordered NbTiN films M. V. Burdastyh1,2, S. V. Postolova1,2, D. A. Nasimov1, T. Proslier3, T. I. Baturina1,2, V. M. Vinokur4, A. Yu. Mironov1,2,* 1 A. V. Rzhanov Institute of Semiconductor Physics SB RAS, 630090, Novosibirsk, Russia 2 Novosibirsk State University, 630090, Novosibirsk, Russia 3 Institut de recherches sur les lois fundamentales de l'univers, CEA Saclay, 91400, Gif sur Yvette, France 4 Materials Science Division, Argonne National Laboratory, IL 60439, Argonne, USA Email: [email protected] Keywords: phase transitions, vortex matter, superconducting array We present the results of the study of low temperature non linear transport properties of disordered nanoperforated NbTiN film. Nanopatterning transforms a thin superconducting NbTiN film into an array of superconducting superconducting islands coupled by weak links, with the period 100 nm. The island’s sizes vary randomly. Nanopatterning drives the critically disordered superconducting film into an insulating state, which transits into a superinsulating one upon decreasing temperature. Appearance of the superinsulator is detected by the changes from the monotonic to threshold behavior of current voltage characteristics evidencing formation of the zero conducting state at finite temperature. In the insulating state, we observe the periodic dependence of the resistance upon the external magnetic field, with the period B0 2 corresponding to the magnetic flux quantum per unit cell (B0 = Φ0/a = 206 mT). In the superinsulating state we find oscillations of the threshold voltage with the same period. The observed oscillations indicate the defining role of Josephson energy in formation of the insulating and superinsulating states, as was predicted in [1]. (a) SEM images of the disordered nanoperforated NbTiN film, (b) Color plot of the differential conductance as function of the magnetic field and the dc bias. References 1. T. I. Baturina & V. M. Vinokur, Annals of Physics 331, 236 257 (2013). 240 Superstripes 2017, Ischia June 4 10, 2017 44.3 BKT phases in disordered systems, past and present Thomas Nattermann Institute for Theoretical Physics, University of Cologne, Zulpicher Str. 77A, 50937 Köln, Germany Email: [email protected] koeln.de Keywords: Vortices, superconductor, disorder, magnets BKT phases in clean systems are characterized by a power law decay of correlations with exponents depending on the fluctuation strength (thermal or quantum). They appear in many 2D classical and 1D quantum systems. The transition to the disordered phase originates from dissociation of vortices or quantum phase slips. This scenario can be extended to disordered systems, but some modifications apply. If the coupling between the order parameter and disorder is of random field type, quasi long range order (QLRO) occurs in 3 dimension, with the vortex lattice as a prominent example. The QLRO phase is here stable against the formation of vortex loops in a certain range of the H T diagram. If the disorder couples to the gradient of order parameter, as in some magnetic systems, BKT phases occur in 2 dimensions. At sufficiently low temperatures, vortex unbinding is triggered by disorder. Vortices show in this region fermionic features, altering the transition to the disordered phase to a universality class different from BKT. Finally, some recent results on quantum phase slips in 1 dimensional disordered superfluids will be discussed. 241 Superstripes 2017, Ischia June 4 10, 2017 44.4 Disordered BKT criticality and superinsulation Sarath Sankar, Valerii Vinokur and Vikram Tripathi S. S. and V. T.: Tata Institute of Fundamental Research, India, V. V.: Argonne National Laboratory, USA Email: [email protected] Keywords: disordered BKT transition, superinsulators, many body localization In lateral Josephson junction arrays and strongly disordered superconducting films, the charge vortex duality leads to the formation of superconducting and superinsulating states that mirror each other. These states respectively form at dual vortex and charge Berezinskii Kosterlitz Thouless (BKT) transitions that terminate each other at the self dual point of the zero temperature superconductor insulator transition (SIT). There is an extensive lore on the vortex BKT and the associated two dimensional (2D) superconductivity, but the nature of the finite temperature zero conductance superinsulating state at the insulating side of the SIT is far less understood [1 3]. Here we report our results on the critical behaviour of the charge BKT transition in disordered systems. We show that the 2D systems of Coulomb interacting charges with strong charge disorder exhibit glass like Vogel Fulcher (VF) critical behaviour and freeze into a nonergodic superinsulating state, whereas systems with weak charge disorder show a less singular BKT criticality and form an ergodic superinsulator at the BKT transition temperature. Our findings reveal a striking parallel between recent developments in quantum many body localization and the BKT theory of superinsulation shedding new light on the intriguing nature of disordered topological BKT phases. 242 Superstripes 2017, Ischia June 4 10, 2017 A sketch of the phase diagram of the superinsulating state and critical behaviours of a two dimensional Josephson junction disordered array in disorder – temperaure coordinates. Disorder stems from the quenched random dipole moments of the (charge) neutral grains. In the superinsulating phase, the probability of single charge excitations is zero. The transition to the conducting state occurs via the proliferation of the single charge excitations generated either thermally or by disorder. The former leads to the usual BKT criticality, while the latter results in a Vogel Fulcher (VF) behaviour. The dotted line separates a nonergodic region (shaded green), where the charge dipoles freeze (their free energy becomes independent of temperature), from the ergodic region (shaded blue) where a finite entropy is associated with the charge dipoles which can appear anywhere. Likewise, the VF critical region is nonergodic and conducting, while the BKT critical region is ergodic and conducting. References 1. V. M. Vinokur et al., Nature 452, 613 (2008). 2. M. Ovadia et al., Scientific reports 5, Article:13503 (2015). 3. T. I. Baturina and V. M. Vinokur, Annals of Physics 331, 236 (2013). 243 Superstripes 2017, Ischia June 4 10, 2017 45.1 BCS Bose Crossover Extended with Hole Cooper Pairs I. Chávez1, L.A. García1, M. Grether2, M. de Llano1 1 Instituto de Investigaciones en Materiales, UNAM, Circuito Exterior, Ciudad Universitaria, Coyoacán, 04510, México City, México 2 Facultad de Ciencias, UNAM, Circuito Exterior, Ciudad Universitaria, Coyoacán, 04510, México City, México. Email: [email protected] Keywords: BCS Bose crossover, hole Cooper pairs Applying the generalized Bose Einstein condensation (GBEC)[1] theory we extend the BCS Bose crossover[2] theory by explicitly including hole Cooper pairs (2hCPs). This leads to a phase diagram with two pure phases, one with 2hCPs and the other with electron Cooper pairs (2eCPs), plus a mixed phase with arbitrary proportions of 2eCPs and 2hCPs. The special case phase when there is perfect symmetry, i.e., with ideal 50 50 proportions between 2eCPs and 2hCPs, gives the usual unextended BCS Bose crossover. The extended crossover predicts Tc/TF values (with Tc and TF the critical and the Fermi temperatures for each superconductor) for some well known conventional superconductors comparing quite well with experiment and, notably, much better than BCS predictions. The BCS gap equation dimensionless coupling constant λBCS is compared with the Bogoliubov et al.[3] upper limit λBCS ≤ 1/2. In turn, these results are compared with theoretical curves associated with the extended crossover for the special case of perfect symmetry holding at n/nf = 1, where n is the total number particle in the system and nf is the number of unbound electrons at T = 0. Remarkably, for 50 50 symmetry all extended crossover results lie below the Bogoliubov et al. upper limit and thus affords corroboration of their results. References 1. V.V. Tolmachev, Phys. Lett. A 266, 400 (2000); M. de Llano and V.V. Tolmachev, Physica A 31, 546 (2003); M. de Llano and V.V. Tolmachev, Ukrainian J. Phys. 55, 79 (2010); M. Grether, M. de Llano, and V.V. Tolmachev, Int. J. Quant. Chem. 112, 3018 (2012). 2. J.R. Schrieffer, Theory of Superconductivity (Benjamin, New York, 1963) p. 41; L.V. Keldysh and Yu. V. Kopaev, Sov. Phys. Sol. St. 6, 2219 (1965); V.N. Popov, Sov. Phys. JETP 50, 1034 (1966); J. Labbé, F. Barisic, and J. Friedel, Phys. Rev. Lett. 19, 1039 (1967); D.M. Eagles, Phys. Rev. 186, 456 (1969), A.J. Leggett, J. Phys. (Paris). Colloq. 41 C7 19 (1980). 3. N.N. Bogoliubov, V.V. Tolmachev, and D.V. Shirkov, Fortschr. Phys. 6, 605 (1958); A New Method in the Theory of Superconductivity (Consultants Bureau, NY, 1959); V.V. Tolmachev and S.V. Tyablikov, Sov. Phys. JETP, 34, 46 (1958). 244 Superstripes 2017, Ischia June 4 10, 2017 45.2 Dimensionless Coupling Constants in Superconductivity I. Chávez1, L.A. García1, M. Grether2, M. de Llano1 1Instituto de Investigaciones en Materiales, UNAM, Circuito Exterior, Ciudad Universitaria, Coyoacán, 04510, México City, México 2 Facultad de Ciencias, UNAM, Circuito Exterior, Ciudad Universitaria, Coyoacán, 04510, México City, México. Email: [email protected] Keywords: boson fermion gas, weak coupling, strong coupling A critique is given of four dimensionless coupling constants: a) the familiar BCS λ ≥ 0 but limited to 1/2 according to the Bogoliubov school [1], b) the inverse of the Fermi wavenumber kF times the S wave scattering length as characterizing the two body interaction [2]; c) the well known Pippard coherence length ξ0 times kF [3]; and d) the new dimensionless coupling constant: n/nf emerging from the recent GBEC theory [4] where n is the total electron number density and nf the number density of unbound electrons at zero temperature in a binary or ternary boson fermion gas model. This new dimensionless coupling constant is analyzed here in greater detail; it includes the two coupling extremes, n/nf = 1 (weak coupling) and n/nf → ∞ (strong coupling) and, of course, intermediate coupling when 1 < n/nf < ∞. In principle, n/nf can be related with any other dimensionless coupling constant. Here we detail its relation with the BCS λ. Also shown is the phase diagram of Tc/TF vs. n/nf (where Tc and TF respectively are the superconducting and Fermi temperatures of a superconductor). Lastly, its relation with the superconducting gap to Tc ratio is also discussed. References 1. N.N. Bogoliubov, V.V. Tolmachev, and D.V. Shirkov, Fortschr. Phys. 6, 605 (1958); and A New Method in the Theory of Superconductivity (Consultants Bureau, NY, 1959); V.V. Tolmachev and S.V. Tyablikov, Sov. Phys. JETP, 34, 46 (1958). 2. R. Haussmann, Phys. Rev. B 49, 12975 (1994). 3. Cf. e.g., M. Casas, J.M. Getino, M. de Llano, A. Puente, R.M. Carter, H. Rubio, and D.M. van der Walt, Phys. Rev. B 50, 15945 (1994).; R.M. Carter, M. Casas, J.M. Getino, M. de Llano, A. Puente, H. Rubio, and D. van der Walt, Phys. Rev. B 52, 16149 (1995). 4. V.V. Tolmachev, Phys. Lett. A 266, 400 (2000); M. de Llano and V.V. Tolmachev, Physica A 317, 546 (2003); M. de Llano and V.V. Tolmachev, Ukrainian J. Phys. 55, 79 (2010); M. Grether, M. de Llano, and V.V. Tolmachev, Int. J. Quant. Chem. 112, 3018 (2012). 245 Superstripes 2017, Ischia June 4 10, 2017 45.3 Quantum size effects in superconducting nanostripes with step edge L. Flammia, L. F. Zhang, A. Perali, and M. V. Milosevic Physics Department, University of Camerino, Camerino, Italy Department of Physics, University of Antwerp, B 2020 Antwerpen, Belgium Email: [email protected] Keywords: nanoscale superconductors, multiband superconductivity, quantum confinement, quantum size effects, shape resonances, step edge, structural disorder. When the dimensions of a superconductor are of the order of the Fermi wavelength, the superconducting properties are influenced by quantum confinement that discretes the energy levels near the Fermi level, leading to the variation of the density of states, and induces a reconfiguration of the pairing interaction leading to multigap effects. Therefore the number of Cooper pairs and the superconducting energy gap become dependent on the size and the shape of the specimen, i.e., quantum size effects and shape resonance effects. In this regime we expect quantum size oscillations in T c and the superconducting order parameter accompanied by enhancement of superconductivity. The microscopic Bogoliubov de Gennes (BdG) equations are a theoretical starting point for nanoconfined systems. Results contain information on the full quasi particle energy spectrum so that they can be compared with scanning tunneling microscopy (STM) experiments. Our goal is to investigate the effect of a step edge in superconducting nanostripes. Recently, its effect was found to be pronounced in experiments on ultrathin superconducting films [1]. Here, we show that the step edge induces scattering on quasiparticle states and how it causes important modifications on the order parameter and the local density of states. References 1. C. Brun, T. Cren, V. Cherkez, F. Debontridder, S. Pons, D. Fokin, M. C. Tringides, S. Bozhko, L.B. Ioffe, B.L. Altshuler, and D. Roditchev, “Remarkable effects of disorder on superconductivity of single atomic layers of lead on silicon, Nat Phys 10, 444 450 (2014). 246 Superstripes 2017, Ischia June 4 10, 2017 45.4 Competition between Intraband Pairing and Crosspairing A. A. Vargas Paredes, A. A. Shanenko, M. V. Milošević, and A. Perali University of Camerino, Universidade Federal de Pernambuco and University of Antwerp Email: alfredo.vargas [email protected] Keywords: Multigap, Interband Pairing and Interband Superconductivity. We investigate the coexistence of intraband and interband pair formation in a two band superconductor. The self consistent complex gap equation is obtained at mean field using the Nambu Gor'kov formalism. We found two solutions at weak coupling for bound states with zero momentum. One solution correspond to all pairings in phase and the other presents a phase difference of π between the intraband pairings of different bands. Both solutions describe a competitive behaviour of intraband with interband pairing and reduce the system to a one component superconductor. Coexistence region for the intraband pairing and crosspairing when the interaction between bands is repulsive. 247 Superstripes 2017, Ischia June 4 10, 2017 References 1. F.G. Korchorbé and M.E. Palistrant, Zh. Eksp. Teor. Fiz. 104, 442 (1993). 2. A.A. Shanenko, J.A. Aguiar, A. Vagov, M.D. Croitoru, and M.V. Milosevic, Superconductor Science and Technology 28, 054001 (2015). 3. Y. Tanaka, Superconductor Science and Technology 28, 034002 (2015). 4. A. Moreo, M. Daghofer, A. Nicholson, and E. Dagotto, Phys. Rev. B 80, 104507 (2009). 5. M. Iskin and C.A.R. Sá de Melo, Phys. Rev. B 74, 144517 (2006). 248 Superstripes 2017, Ischia June 4 10, 2017 46.1 Topological Crystalline Materials Masatoshi Sato, Yukawa Institute for Theoretical Physics, Kyoto Univeristy, Kitashirakawa Oiwakecho, Sakyo ku, Kyoto 606 8502, Japan Email: [email protected] u.ac.jp Keywords: topological states of matter; space group symmetry Symmetry is a key to realize new topological states of matters. For instance, breaking of spin rotation symmetry is necessary to realize Majorana fermions in topological superconductors, which is a reason why one needs the spin orbit coupling to have Majorana modes in s wave pairing states [1,2]. Here we discuss a variety of interplays between topology and symmetry. In particular, we discuss roles of crystalline symmetry in topological materials. It is shown that the nonsymmorphic crystalline symmetry such as glide and screw make it possible to realize a novel Z4 topological phase with Mobius twisted surface states [3], of which the existence has been confirmed experimentally [4]. Also superconductivity in Dirac semimetals is found to support a Majorana quartet [5,6], which could be relevant to recently discovered superconductors Cd3As2, and Sr3 xSnO [7]. Furthermore, in the presence of nonsymmorphic symmetry, stable topological nodal superconductivity is obtained naturally, which resolves a long standing puzzle of the Blount’s theorem in the heavy fermion odd parity superconductor UPt3 [8]. We propose a systematic and unified framework to explore topological crystalline materials on the basis of K theory [9]. References 1. M. Sato, Phys. Lett. B575, 126 (2003); M. Sato, Y. Takahashi, S. Fujimoto, Phys. Rev. Lett. 103, 020401 (2009). 2. M. Sato, and Y. Ando, arXiv:1608.03395. 3. K. Shiozaki, M. Sato, and K. Gomi, Phys. Rev. B91, 155120 (2015); K. Shiozaki, M. Sato, and K. Gomi, Phys. Rev. B93, 195413 (2016). 4. J. –Z. Ma et al, arXiv:1605.06824. 5. S. Kobayashi, and M. Sato, Phys. Rev. Lett. 115, 187001 (2015). 6. T. Hashimoto, S. Kobayashi, Y. Tanaka, and M. Sato, Phys. Rev. B94, 014512 (2016). 7. M. Oudah, et. al, Nature Communications 7,13717 (2016). 249 Superstripes 2017, Ischia June 4 10, 2017 8. S. Kobayashi, K. Shiozaki, Y. Tanaka, and M. Sato, Phys. Rev. B90, 024516 (2014); S. Kobayashi, Y. Yanase, and M. Sato, Phys. Rev. B94, 134512 (2016). 9. K. Shiozaki, and M. Sato, Phys. Rev. B90, 165114; K. Shiozaki, M. Sato, and K. Gomi, in preparation. 250 Superstripes 2017, Ischia June 4 10, 2017 46.2 Dirty multi band superconductors: time reversal symmetry breaking, multiple coherence lengths, type 1.5 superconductivity and vortex matter Egor Babaev, Julien Garaud, Mihail Silaev Royal Institute of Technology/KTH Email: [email protected] Keywords: multicomponent superconductors, type 1.5 superconductivity I will discuss the effect of disorder and dirt on symmetry breaking, multiple coherence lengths and magnetic response of multiband superconductors. References 1. Mihail Silaev, Julien Garaud, Egor Babaev Phase diagram of dirty two band superconductors and observability of impurity induced s+is state arXiv:1610.05846 2. Egor Babaev, Johan Carlstrom, Mihail Silaev, Martin SpeightType 1.5 superconductivity in multicomponent systems arXiv:1608.02211 251 Superstripes 2017, Ischia June 4 10, 2017 46.3 Low temperature thermoelectric power of strongly correlated quantum dot M.M. Wysokiński, U. Eckern, K.I. Wysokiński Scuola Internazionale Superiore di Studi Avanzati (SISSA), Via Bonomea 265, 34136 Trieste, Italy Institute of Physics, University of Augsburg, 86135 Augsburg, Germany Institute of Physics, M. Curie Sklodowska University, ul. Radziszewskiego 10, 20 031 Lublin, Poland Email: [email protected] Keywords: Quantum transport, Kondo effect, quantum dot The transport through the junctions with a molecule or a quantum dot is frequently studied within the Anderson impurity [1] model. One of the hallmarks of the system is the appearance of the Kondo phenomenon at low temperature. It severely influences the transport of the nanostructure. Here we shall analyse the model by using simple and accurate method based on the analytic approximation of the appropriate Green function [2]. Conductance and other transport coefficients of the system are calculated in the linear response and in far from equilibrium situation [3] and compared with the results obtained via other techniques. References 1. M. Krawiec, K.I. Wysokiński Thermoelectric effects in strongly interacting quantum dot coupled to ferromagnetic leads Phys. Rev. B 73, 075307 (2006). 2. R. Van Rermund, S. Shiau, M. Lavagna, Anderson model out of equilibrium: decoherence effects in transport through a quantum dot Phys. Rev. B 81, 165115 (2010). 3. G. Benenti, G. Casati, K. Saito, R.S. Whitney, “Fundamental aspects of steady state conversion of heat to work at the nanoscale” arXiv:1608.05595 252 Superstripes 2017, Ischia June 4 10, 2017 46.4 Enhancement of Superconductivity by Shape Resonances: from Nano films to Nano stripes Andrea Perali1,2 1School of Pharmacy, Physics Unit, University of Camerino, 62032 Camerino, Italy 2INFN – Sezione di Perugia, Italy Email: [email protected] Keywords: BCS BEC crossover, multigap superconductivity, shape resonances, band edge, atomic step, nanofilms, nanostripes Ultrathin superconductors of different materials are becoming a powerful platform to find mechanisms for enhancement of superconductivity, exploiting shape resonances in different superconducting properties. Since 2004, the observation of shape resonances in superconducting nanofilms of Pb and first evidences of shape resonances in the superconducting critical temperature in metallic nanowires of Sn and Al [1–2] clearly established the importance of the interplay between quantum size effects, leading to multiple bands, and superconductivity, when the lateral dimensions of the system are reduced to the order of the interparticle distance. Moreover, superconductivity in iron based, magnesium diborides, and other high Tc superconductors has a strong multi band and multi gap character [3,4]. Recent experiments support the possibility for a BCS BEC crossover induced by the proximity of the chemical potential to the band edge of one of the bands, with evidences for Lifshitz transitions associated with changes in the Fermi surface topology [5, 6]. Here we present the simplest theoretical model which accounts for superconducting shape resonances and the BCS BEC crossover in a multi band / multi gap superconductor, considering tunable interactions and nanostructured geometries. When the gap is of the order of the local chemical potential, superconductivity is in the crossover regime of the BCS BEC crossover and the Fermi surface of the small band is completely smeared by the gap opening. In this situation, small and large Cooper pairs coexist in the total condensate, which is the optimal condition for high Tc or even for room temperature superconductivity [7,8]. As a realizable example of enhancement of superconductivity in nanostructured materials, we consider here superconducting stripes organized in a parallel pattern (Superstripes), in which shape resonances and multigap physics at the band edge play a cooperative role in enhancing superconductivity in the crossover regime of pairing, while allowing for a sizable screening of the detrimental superconducting fluctuations [7,8,9]. A key prediction of 253 Superstripes 2017, Ischia June 4 10, 2017 this physics is the following: the isotope effect of the superconducting critical temperature in the vicinity of a Lifshitz transition, which has a unique dependence on the energy distance (or density) between the chemical potential and the Lifshitz transition point [10,11]. Finally we discuss a more complex nanostructure: recent experiments show that an atomic step on the surface of atomically thin metallic films can strongly affect electronic transport. Here we reveal multiple and versatile effects that such a surface step can have on superconductivity in ultrathin films [12]. References 1. A.A. Shanenko, M.D. Croitoru, M. Zgirski, F.M. Peeters, K. Arutyunov, Phys. Rev. B 74, 052502 (2006). 2. F. Altomare, A.M. Chang, One Dimensional Superconductivity in Nanowires, WILEY VCH. Weinheim, Germany (2013). 3. S.V. Borisenko et al., Symmetry 4, 251 (2012). See also the International Network MultiSuper: http://www.multisuper.org 4. A. Bianconi, T. Jarlborg, EPL (Europhysics Letters) 112, 37001 (2015). 5. D. Innocenti, N. Poccia, A. Ricci, A. Valletta, S. Caprara, A. Perali, and A. Bianconi, Phys. Rev. B 82, 184528 (2010). 6. A. Bianconi, Nature Phys. 9, 536 (2013). 7. A. Perali, C. Castellani, C. Di Castro, M. Grilli, E. Piegari, and A. A. Varlamov, Phys. Rev. B 62, R9295 (2000). 8. A. Guidini and A. Perali, Supercond. Sci. Technol. 27, 124002 (2014). 9. A. Perali, A. Bianconi, A. Lanzara, N.L. Saini, Solid State Comm. 100, 181, (1996). 10. A. Perali, D. Innocenti, A. Valletta, A. Bianconi, Supercond. Sci. Technol. 25, 124002 (2012). 11. M. V. Mazziotti, A. Valletta, G. Campi, D. Innocenti, A. Perali, A. Bianconi, arXiv:1705.09690 (2017); to be published in EPL (Europhysics Letters) (2017). 12. L. F. Zhang, L. Flammia, L. Covaci, A. Perali, and M.V. Milosevic, arxiv: 1702.02370 (2017). 254 Superstripes 2017, Ischia June 4 10, 2017 46.5 Topological phases emerging from spin orbital physics Wojciech Brzezicki,a Fiona Forte,a Mario Cuoco, a Andrzej M. Olesb,c a CNR SPIN and Dipartimento di Fisica "E. R. Caianiello", Università degli Studi di Salerno, 84084 Fisciano (SA), Italy b Marian Smoluchowski Institute of Physics, Jagiellonian University, prof. S. Lojasiewicza 11, PL 30348 Krakow, Poland c Max Planck Institute for Solid State Research, Heisenbergstrasse 1, D 70569 Stuttgart, Germany Email: [email protected] Keywords: spin orbital physics, topological phase, pairing center Strong Coulomb interactions in transition metal oxides lead to low energy superexchange with entangled spin orbital states [1]. Doping of such systems introduces inhogeneities which lead to stripes for hole doping [2]. Neutral doping, as e.g. in Ca2Ru1 xCrxO4, shows surprising negative volume thermal expansion. Such doping introduces hybrid d4 d4 n bonds in correlated insulators with: (i)~orbital dilution for n=1 realized by 3d3 impurities, and (ii) hole doublon pairs in case of n=2 and 3d2 doping. In case of orbital dilution superexchange favors doubly occupied active orbitals along the hybrid bond leading to orbital polarons [3]. The spin orbital order within the host is totally modified by hybrid bonds at doping x=1/4 [4]. For doublon dilution the derived + + spin orbital interactions on the hybrid bonds contain Ti Tj terms responsible for double hole doublon excitations which generate enhanced quantum fluctuations [5]. In the one dimensional (1D) case this model maps onto spinless itinerant electrons with randomly distributed p wave pairing centers and has interesting topological properties. We derive the topological invariant and demonstrate the existence of stable topological domains in a broad parameter range. Work supported by Narodowe Centrum Nauki (NCN) Project No. 2012/04/A/ST3/00331. References 1. A. M. Oles, Journal of Physics: Condensed Matter 24, 313201 (2012). 2. A. Bianconi and A. Ricci, J. Supercond. Novel Magn. 29, 3013 (2016). 3. W. Brzezicki, A. M. Oles, and M. Cuoco, Phys. Rev. X 5, 011037 (2015). 4. W. Brzezicki, M. Cuoco, and A. M. Oles, J. Supercond. Novel Magn. 29, 563 (2016). 5. W. Brzezicki, M. Cuoco, and A. M. Oles, J. Supercond. Novel Magn. 30, 129 (2017). 255 Superstripes 2017, Ischia June 4 10, 2017 47.1 Ground state oxygen holes and the metal–insulator transition in the negative charge transfer rare earth nickelates Thorsten Schmitt Paul Scherrer Institut, Swiss Light Source, CH 5232 Villigen PSI, Switzerland Email: [email protected] Perovskite rare earth (Re) nickelates ReNiO3 continue to attract a lot of interest thanks to their intriguing physical properties like sharp metal to insulator transition (MIT), unusual magnetic order [1] and expected superconductivity in nickelate based heterostructures [2]. Full understanding of these materials, however, remains still today elusive being hampered by the difficulties in describing their electronic ground state (GS). Taking a NdNiO3 thin film as a representative example, we reveal with x ray absorption (XAS) and resonant inelastic x ray scattering (RIXS) at the Ni L3 edge an unusual coexistence of bound and continuum excitations providing a strong evidence for the abundance of O 2p holes (L) in the GS of these materials [3]. Using cluster calculations and Anderson impurity model interpretation, we show that the specific nature of the orbital excitations and the energy dispersing spectral signatures both arise from a Ni 3d8 configuration along with holes in the O 2p valence band. This finding confirms that these materials exhibit a negative charge transfer energy with O 2p states extending across the Fermi level [4]. In this scenario, the metallic GS configuration is described as Ni 3d8Ln (n=1), realizing the MIT by bond disproportionation leading to two Ni site environments: Ni 3d8 (n=0, S=1) and Ni 3d8L2 (n=2, S=0), differing in the hybridization with the O 2p hole states yet leaving the charge at the nickel sites almost equal. References 1. M. L. Medarde, J. Phys. Cond. Matt. 9, 1679 (1997); G. Catalan, Phase Transitions: A Multinational Journal, 81:7 8, 729 749 (2008). 2. Chaloupka et al., Phys. Rev. Lett. 100, 016404 (2008). 3. Valentina Bisogni, Sara Catalano, Robert J. Green, Marta Gibert, Raoul Scherwitzl, Yaobo Huang, Vladimir N. Strocov, Pavlo Zubko, Shadi Balandeh, Jean Marc Triscone, George Sawatzky, and Thorsten Schmitt, Nature Communications 7, 13017 (2016). doi: 10.1038/ncomms13017. 4. T. Mizokawa et al., Phys. Rev. B 61, 11263 (2000); H. Park et al., Phys. Rev. Lett. 109, 156402 (2012); S. Johnston et al., Phys. Rev. Lett. 112, 106404 (2014). 256 Superstripes 2017, Ischia June 4 10, 2017 47.2 In situ EXAFS studies of metal to insulator transition in ReO3 WO3 and related electrochromic materials Juris Purans,1,2 1Institute of Solid State Physics University of Latvia, Riga, LV 1063, Latvia 2 Institute of Crystallography, CNR, via Salaria Km 29.300, Monterotondo Roma, I 00015, Italy. Email: * [email protected] Key words: local structure; EXAFS, WO3, ReO3, perovskites, phase transitions. The anharmonicity of lattice dynamics is very important on the atomic scale of quantum systems showing high local structural fluctuations and formation of heterostuctures [1]. In the strongly anharmonic systems the so called explicit anharmonicity effect links the phonon frequencies and interatomic forces to the amplitude of the atomic vibrations. We have demonstrated that ab initio calculations beyond quasiharmonic approximation (BQHA) are well correlated with reconstructed local structure by femtometer scale X ray absorption fine structure (XAFS) spectroscopy [2 4]. Complimentary XAFS spectra were measured at the W and Re L edges and and at the O K edge at the synchrotron radiation beam lines. With this complementary data on the local structure around two selected metal ions and oxygen ions it is then possible to give a better view of the mixed electrochromic solid solutions and thin films ReOx WO3, especially concerning the electronic structure and distribution of the two ions in such nanocrystalline films. The dependence of local structure on composition, probed with femtometer accuracy, and new possibilities of XAFS data analysis will be presented. Finally, we present recent results on structural investigations of hydrogen intercalation in perovskite type ReO3 and WO3. In situ x ray absorption spectroscopy at the Me L1 and L3 edges was used to study a modification of the local atomic and electronic structure around rhenium in perovskite type ReO3 upon hydrogen intercalation. The analysis of both EXAFS and XANES parts of the x ray absorption spectra shows an evidence of the charge disproportionation phenomenon in hydrogenated rhenium (HxReO3) and tungsten trioxides (HxWO3). The analysis of the x ray absorption spectra shows that the formation of so called rhenium bronze HxReO3 leads to a strong distortion of the ReO6 octahedra and a large deviation of the Re O Re angles from 180°. On the other hand, formation of tungsten bronze HxWO3 leads to a strong decrease of distortion of the WO6 octahedra and a large increase of the W O W angles 257 Superstripes 2017, Ischia June 4 10, 2017 to 180°. The details of distortion and possible models of small polaron (W5+) structure will be presented and discussed. References 1. A. Bianconi, “Process of increasing the critical temperature Tc of a Bulk Superconductor by Making Metal Heterostructures at the Atomic Limit” US Patent 6,265,019 (2001). 2. J. Purans et al., Phys. Rev. B 93, 214101 (2016) https://doi.org/10.1103/PhysRevB.93.214101. 3. J. Purans, et al., 92, 014302 (2015) https://doi.org/10.1103/PhysRevB.92.014302. 4. J. Purans et al., Phys. Rev. Lett. 100, 055901 (2008) https://doi.org/10.1103/PhysRevLett.100.055901. 5. J. Timoshenko et al., J. Phys.: Condens. Matter 26 055401 (2014) https://doi.org/10.1088/0953 8984/26/5/055401 258 Superstripes 2017, Ischia June 4 10, 2017 47.3 Room temperature ferroelectricity in SrTiO3 ultrathin films on silicon: Infrared and ab initio study Wei wei Peng1, Robert Tétot2,1, Gang Niu3 , Emilie Amzallag2, Bertrand Vilquin4, Jean Blaise Brubach1 and Pascale Roy1,* 1Synchrotron SOLEIL, AILES Beamline, Saint Aubin, 91190, France 2 CNRS Université paris Sud, ICMMO(SP2M) UMR 8182, Bât 410, F 91405 Orsay Cedex, France 3Electronic Materials Research Laboratory, Key Laboratory of the Ministry of Education & International Center for Dielectric Research, Xi'an Jiaotong University, Xi'an 710049, China 4Ecole Centrale de Lyon, (INL), CNRS UMR 5270, Ecully, France Email: pascale.roy@synchrotron soleil.fr Keywords: SrTiO3 ultrathin films, Infrared spectroscopy, ab initio, ferroelectricity. Due to the remarkable possibilities of epitaxially growing strontium titanate (SrTiO3 or STO) on silicon, this oxide is widely used as a buffer layer for integrating other perovskite oxides which allows for the development of various functional electronic devices on silicon. Moreover, STO is known to be an incipient ferroelectric in bulk [1] but may become ferroelectric when in the form of strained ultrathin films [2]. Given the importance of the potential applications for electronics if this property is demonstrated, we performed a spectroscopic study of STO on Si(001) templates coupling experimental infrared and ab initio investigations. Both measured and calculated spectra are presented Fig. 1. The experimental infrared absorbance was measured on six samples of ultrathin films: three strained samples (of thickness 4, 9 and 48 nm) and three relaxed samples (of equivalent thickness). Their infrared spectra show that both the mechanical stress and the thickness play major roles: higher energy modes evolve as soft modes in thinner strained films. In order to support these observations, the dynamical ab initio calculations allowed deriving the conditions for STO films to become ferroelectric at room temperature as shown by the development of a soft mode and the divergence of the in plane dielectric constant. (see figure 2). This study demonstrates for the first time, that a large in plane dielectric constant can develop in ultra thin films for strains between a critical value (~ 1.23% for a thickness of 1.2 nm) up to 1.69%. 259 Superstripes 2017, Ischia June 4 10, 2017 Figure 1| a, IR absorbance of the unstrained STO/Si(001) films of thickness 50, 10 and 4 nm. The three phonon structures TO1, TO2 and TO4 correspond to the classification of the bulk phonon modes. b, IR absorbance of the strained (as grown on Si) STO/Si(001) films of thickness 48, 9 and 5 nm. The phonon structures of the films are bulk like modes (T1, T2, T3) and surface and/or soft mode (SM). c, Calculated absorbance of STO bulk and fully relaxed STO slabs of 7 layers (2.5 nm), 5 layers (2 nm) and 3 layers (1.2 nm). The presence of modes at negative values (imaginary modes) demonstrates that all slabs are metastable. d, Calculated absorbance of STO slabs with 1.69% strain corresponding to the lattice mismatch between STO and Si(001). Figure 2: Results of DFT calculations for a STO slab of 7 layers under various in plane strains between 1.69 % and 1.30 %. Variations of the Soft Mode frequency and of the static dielectric constant parallel to the slab as a function of the strain. The values of both the soft mode and the in plane static dielectric constant diverge for strain values under 1.305%. References 1. Setter, N. et al. Ferroelectric thin films: Review of materials, properties, and applications. J. Appl. Phys. 100, 051606 (2006). 2. Warusawithana, M. P. et al. A Ferroelectric Oxide Made Directly on Silicon. Science 324, 367 (2009). 260 Superstripes 2017, Ischia June 4 10, 2017 48.1 Bose condensation of excitons in a transition metal dichalcogenide Peter Abbamonte University of Illinois, Urbana, IL, USA Bose condensation has shaped our understanding of macroscopic quantum phenomena, having been realized in superconductors, atomic gases, and liquid helium. Excitons are bosons that have been predicted to condense into either a superfluid or an insulating electronic crystal. But definitive evidence for a thermodynamically stable exciton condensate has never been achieved. In this talk I will describe our use of momentum resolved electron energy loss spectroscopy (M EELS) to study the valence plasmon in the transition metal dichalcogenide semimetal, 1T‐TiSe2. Near the phase transition temperature, TC = 190 K, the plasmon energy falls to zero at nonzero momentum, indicating dynamical slowing down of plasma fluctuations and crystallization of the valence electrons into an exciton condensate. At low temperature, the plasmon evolves into an amplitude mode of this electronic crystal. Our study represents the first observation of a soft plasmon in any material, the first definitive evidence for exciton condensation in a three dimensional solid, and the discovery of a new form of matter, “excitonium.” 261 Superstripes 2017, Ischia June 4 10, 2017 48.2 Unconventional superconductivity in uranium compounds Dai Aoki IMR, Tohoku University Email: [email protected] Keywords: Ferromagnetism, Superconductivity The coexistence of ferromagnetism and superconductivity is an interesting topics, because the spin triplet state with equal spin pairings may be realized. We present the experimental results on three uranium ferromagnets, UGe2, URhGe and UCoGe, using high quality single crystals. Extremely large upper critical field Hc2 is explained by the ferromagnetic fluctuations and the Fermi surface instabilities. We also show our recent results on unconventional/conventional superconductivity in uranium compounds. References 1. D. Aoki and J. Flouquet: J. Phys. Soc. Jpn. 83, 061011 (2014). 262 Superstripes 2017, Ischia June 4 10, 2017 48.3 Two dimensional topological superconductivity in Pb/Co/Si(111) Gerbold C. Ménard1, Sébastien Guissart2, Christophe Brun1, Mircea Trif2, François Debontridder1, Raphaël T. Leriche1, Dominique Demaille1, Dimitri1,3, Pascal Simon2 and Tristan Cren1 1Institut des Nanosciences de Paris, Université Pierre et Marie Curie (UPMC),CNRS UMR 7588, 4 place Jussieu, 75252 Paris, France 2Affiliation Laboratoire de Physique des Solides, CNRS, Univ. Paris Sud, Université Paris Saclay, 91405 Orsay Cedex, France 3Laboratoire de physique et d’étude des matériaux, LPEM UMR8213/CNRS ESPCI ParisTech UPMC, 10 rue Vauquelin, 75005 Paris, France Email: [email protected] Keywords: 2D superconductivity; atomic monolayers; topological superconductivity. Majorana fermions are very peculiar quasiparticles that are their own antiparticle. They obey non abelian statistics: upon exchange, they behave differently from fermions (antisymmetric) and bosons (symmetric). Their unique properties could be used to develop new kind of quantum computing schemes. Majorana states are predicted to appear as edge states of topological superconductors, in a similar way as Dirac surface states appears at the edge of topological insulators. Spectroscopic signatures of Majorana bound states were claimed to be observed in one dimensional (1D) InAs nanowires proximity coupled to a bulk superconductor [1]. Then Nadj Perge et al. [2] have realized a chain of Fe adatoms on a Pb(110) crystal that is supposed to induce locally a 1D topological p wave superconductivity. Zero energy bound states were observed at the extremity of some the Fe chain and interpreted as Majorana excitations [2]. Nevertheless this interpretation is challenged by close to zero energy Shiba states [3]. We have recently decided to follow a different strategy using a two dimensional superconducting system consisting in a monolayer of Pb atoms grown on Si(111) [4]. We have shown that the strong spin orbit coupling of Rashba type present in the superconductivity of the Pb/Si(111) monolayer can be revealed through the filling of in gap quasiparticle states by scattering from non magnetic disorder at 300 mK [5]. Following Rashba and Gor’kov this shows that a mixed singlet triplet superconductivity exists in our Pb monolayer [6]. Nano magnetic disks made of Cobalt deposited below the Pb/Si(111) monolayer were grown to induce locally 2D topological superconductivity by combining a strong local Zeeman field with a mixed singlet triplet 2D superconductor. We have observed that dispersive edge states appear in the superconducting gap around the magnetic domains [7]. We have interpreted these spectroscopic features as signatures of a locally induced topological superconductivity in our 2D system consisting in Pb/Co/Si(111). Indeed, we expect to 263 Superstripes 2017, Ischia June 4 10, 2017 get some propagative Majorana edge states around 2D topological domains since the edges have a 1D character. References 1. V. Mourik et al., “Signatures of Majorana Fermions in Hybrid Superconductor Semiconductor Nanowire Devices” Science 346, 602 (2012). 2. S. Nadj Perge et al., “Observation of Majorana fermions in ferromagnetic atomic chains on a superconductor” Science 336, 1003 (2014). 3. M. Ruby, F. Pientka, Y. Peng, F. Von Oppen, B.W. Heinrich, and K. Franke, “End States and Subgap Structure in Proximity Coupled Chains of Magnetic Adatoms” PRL 115, 197204 (2015). 4. T. Zhang et al. “Superconductivity in one atomic layer metal films grown on Si(111) ” Nature Phys. 444, 10 (2014). 5. C. Brun et al., “Remarkable effects of disorder on superconductivity of single atomic layers of lead on silicon” Nature Phys. 444, 10 (2014). 6. E.I. Rashba and L.V. Gor’kov, ”Superconducting 2D System with Lifted Spin Degeneracy: Mixed Singlet Triplet State” PRL 444, 10 (2010). 7. G. C. Ménard, S. Guissart, C. Brun, M. Trif, F. Debontridder, R. T. Leriche, D. Demaille, D. Roditchev, P. Simon, T. Cren, “Two dimensional topological superconductivity in Pb/Co/Si(111)”, arXiv:1607.06353 (2016). 264 Superstripes 2017, Ischia June 4 10, 2017 48.4 Ultrafast Surface Dirac Fermion Dynamics of Sb2Te3 based Topological Insulators Kazuki Sumida1, Yukiaki Ishida2, Tomoki Yoshikawa1, Jiahua Chen1, Munisa Nurmamat1, Konstantin Kokh3,4,5, Oleg Tereshchenko4,5,6, Shik Shin2, Akio Kimura1 1 Graduate School of Science, Hiroshima University, 1 3 1 Kagamiyama, Hiroshima 739 8526, Japan 2 Institute for Solid State Physics, University of Tokyo, 5 1 5 Kashiwa no ha, Kashiwa, Chiba 277 8581, Japan 3 Institute of Geology and Mineralogy, Siberian Branch, Russian Academy of Sciences, Koptyuga pr. 3, 630090 Novosibirsk, Russia 4 Novosibirsk State University, ul. Pirogova 2, 630090 Novosibirsk, Russia 5 Saint Petersburg State University, Saint Petersburg, 198504, Russia 6 Institute of Semiconductor Physics, Siberian Branch, Russian Academy of Sciences, pr. Akademika Lavrent'eva 13, 630090 Novosibirsk, Russia Email: sumida1126@hiroshima u.ac.jp Keywords: topological insulator; time and angle resolved photoemission spectroscopy; ultrafast carrier dynamics Three dimensional (3D) topological insulators (TIs) possess spin polarized massless Dirac fermions on their edge. The edge mode occurs due to the topology of the bulk band structure, and exists as long as time reversal symmetry is preserved. Thus, the exotic two dimensional (2D) metal on the edge of the 3D insulator is robust against nonmagnetic defects/impurities, and are expected to exhibit novel phenomena where conventional 2D metals cannot meet. Recently, the ternary TIs (Sb1 xBix)2Te3 have attracted a great deal of attention due to its tunable bulk carrier [1]. In addition, the quantum Hall effect (QHE) that stems from surface Dirac Fermions was observed in (Sb1 xBix)2Te3 films under a magnetic field [2]. Furthermore, Cr or V doped films have been found to show the anomalous QHE [3,4]. Therefore, the ternary TIs (Sb1 xBix)2Te3 are the most promising candidate for the dissipationless device applications. In order to reveal the transport properties, we have performed time and angle resolved photoemission spectroscopy (TARPES) implementing pump probe method [5] for (Sb1 xBix)2Te3. Figure 1 shows the band dispersion and the temperature dependence of recovery time at bulk conduction band (BCB), upper Dirac cone (UDC) and lower Dirac cone (LDC) of (Sb0.73Bi0.27)2Te3. It clearly indicates that the recovery time drastically elongated upon increasing temperature. Concerning the mechanism of the recovery, we consider that the electron phonon scatterings are playing a minor role because the recovery time elongated upon increasing the temperature. If such a decaying channel was dominant, the recovery time should have shortened because the electron phonon scattering rate increases at elevated temperatures. Thus, the electron hole recombination may be the 265 Superstripes 2017, Ischia June 4 10, 2017 dominant channel in ~10 ps to ~100 ps time domains. Moreover, this temperature induced long duration is also due to the Pauli blocking effect at Dirac cone. In the presentation, we also show the prolonged duration of the intrinsic TIs. Figure 1: (a) Photo excited band dispersion of (Sb0.73Bi0.27)2Te3 recorded at pump probe delay time t = 1.33 ps. Temperature dependence of recovery time at bulk conduction band (b), upper Dirac cone (c) and lower Dirac cone (d). References 1. D. Kong et al., Nat. Nanotech. 6, 705 (2011). DOI: 10.1038/NNANO.2011.172 2. R. Yoshimi et al., Nat. Commun. 6, 6627 (2015). DOI: 10.1038/ncomms7627 3. C. Z. Chang et al., Science 340, 167 (2013). DOI: 10.1126/science.1234414 4. C. Z. Chang et al., Nat. Mater. 14, 473 (2015). DOI: 10.1038/NMAT4204 5. Y. Ishida et al., Rev. Sci. Instrum. 85, 123904 (2014). DOI: 10.1063/1.4903788 266 Superstripes 2017, Ischia June 4 10, 2017 49.1 STS studies on correlated f electron systems: Kondo lattice, quantum criticality and topological Kondo insulator Wirth S. MPI for Chemical Physics of Solids Dresden Email: [email protected] Electronic correlations give rise to a plethora of interesting phenomena and phases. For example, hybridization between 4f and conduction electrons in heavy fermion metals may result in the generation of low energy scales that can induce quantum criticality and unconventional superconductivity. One of the most important techniques that helped shaping our understanding of nonlocal correlations, both magnetic and superconducting, has been scanning tunneling spectroscopy (STS) with its unique ability to give local, microscopic information that directly relates to the one particle Green's function. We combine STS with bulk measurements to obtain complementary information on different length scales. We studied the temperature evolution of hybridization effects and Kondo lattice coherence as observed by STS, focusing on the model heavy fermion metal YbRh2Si2 and the intermediate valence insulator SmB6. For the former, the evolution of the signatures of Kondo lattice coherence upon lowering the temperature is studied. We also show how Kondo coherence connects with quantum criticality. These results by STS are compared to magnetotransport and thermodynamic measurements. In case of SmB6, different surface terminations were found upon cleaving giving rise to marked differences in the STS results. We investigate the low temperature evolution of the tunneling spectra which indicates a suppressed Kondo effect at the surface. References 1. S. Wirth and F. Steglich, Nature Rev. Mat. 1 (2016) 16051 2. Lin Jiao et al., Nature Commun. 7 (2016) 13762 267 Superstripes 2017, Ischia June 4 10, 2017 49.2 Field induced Lifshitz transitions in heavy fermion systems G. Bastien, A. Gourgout, D. Aoki, A. Pourret, i. Sheikin, G. Seyfahrt, J. Flouquet, G. Knebel UGA CEA, Inac, Pheliqs, Grenoble, France LNCMI EMFL, CNRS, UGA, Grenoble, France Email: [email protected] Keywords: Fermi surface, Lifshitz transition, ferromagnetic supercondutors, heavy fermion We present a detailed study of the Fermi surface of the ferromagnetic superconductor UCoGe. For magnetic field applied along the easy magnetization axis c of the orthorhombic crystal we observe a series of anomalies in the magnetoresistance and thermoelectric power. Significant changes in the quantum oscillation frequencies and in the effective masses have been observed indicating successive Fermi surface instabilities induced by the strong magnetic polarization under magnetic field. The effect of the strong polarization of the flat bands near the Fermi level will be discussed for other heavy fermion systems showing field induced changes of the Fermi surface. References 1. G. Bastien, A. Gougour, D. Aoki, A. Pourret, I. Sheikin, G. Seyfahrt, J. Flouquet, G. Knebel, Phys. Rev. Lett. 117, 206401 (2016). 2. A. Gourgout, A. Pourret, G. Knebel, D. Aoki, G. Seyfahrt, J. Flouquet, Phys. Rev. Lett. 117, 046401 (2016). 3. A. Pourret, G. Knebel, T.D. Matsuda, G. Lapertot, J. Flouquet J. Phys. Soc. Jpn. 82, 116404 (2013). 268 Superstripes 2017, Ischia June 4 10, 2017 49.3 Transport spectroscopy and Electronic Topological Transitions in heavy fermion materials Gertrud Zwicknagl Institut fuer Mathematische Physik, TU Braunschweig, Mendelssohnstr. 3, 38106 Braunschweig, Germany Email: g.zwicknagl@tu bs.de Key words: Lifshitz transitions, heavy fermions, transport properties Many heavy fermion materials exhibit pronounced anomalies in the variation with magnetic field of their thermodynamic and transport properties. In YbRh2Si2, the observed anomalies could be related to magnetic field induced reconstructions of the Fermi surface, i. e., Electronic Topological (Lifshitz) transitions. [1,2]. Here, we demonstrate that the analysis of the Seebeck coefficient allows for detailed transport spectroscopy of the strongly renormalized quasiparticle bands in the vicinity of critical points [3]. The calculations start from the renormalized bands [4] in high magnetic fields from which the variation with magnetic field of the electron scattering time is calculated [5,6]. References 1. H. Pfau et al, Phys. Rev. Lett. 110, 256403 (2013); H. R. Naren et al, New J. Phys. 15, 093032 (2013) . 2. A. Pourret et al.,J. Phys. Soc. Jpn. 82 , 053704 (2013). 3. A. Pourret, S.G. Sharapov, G. Knebel, A.A. Varlamov, and G. Zwicknagl, (to be published). 4. Gertrud Zwicknagl, Rep. Prog. Phys. 79 124501 (2016) 5. G. Zwicknagl, J. Phys.: Condens. Matter 23, 094215 (2011. 6. A.A. Varlamov, V.S. Egorov, A.V. Pantsulaya, Adv. In Phys. 38, 469 (1989) 269 Superstripes 2017, Ischia June 4 10, 2017 49.4 Physical properties of LaNiO3 single crystals Z. Li1, H. Guo1, Z. Hu1, L. Zhao1, C. Y. Kuo1, W. Schmidt2,3, A. Piovano2, T. W. Pi4, L. H. Tjeng1 and A. C. Komarek1 1 Max Planck Institute for Chemical Physics of Solids, Nöthnitzer Str. 40, Dresden D 01187, Germany 2 Institut Laue Langewin (ILL), 71 avenue des Martyrs, F 38042 Grenoble Cedex 9, France 3 Jülich Centre for Neutron Science JCNS, Forschungszentrum Jülich GmbH, Outstation at ILL, CS 20156, 71 avenue de Martyrs, 38042 Grenoble, France 4 National Synchrotron Radiation Research Center (NSRRC), 101 Hsin Ann Road, Hsinchu 30077, Taiwan Email: [email protected] Keywords: nickelates, charge density wave, metal insulator transition The high oxidation state rare earth nickelates have generated long standing interest due to the occurrence of a metal insulator transition from a bad metal to an insulating state that arises from charge order and the appearance of non collinear magnetic phases within this insulating regime. However, the difficulties in single crystal growth of these highly oxidized nickelates hampered a more deeper study of the physical properties of these intriguing materials. Here, we for the first time report on the successful single crystal growth of cm sized LaNiO3 single crystals by the floating zone technique and on subsequent studies of the physical properties of these interesting materials. Especially, the availability of cm sized single crystals allowed us to study these nickelates by means of elastic and inelastic neutron scattering. 270 Superstripes 2017, Ischia June 4 10, 2017 50.1 Orbital Degeneracy Lifting and Short Range Orbital Order in CuIr2S4 Emil S. Bozin1*, Milinda Abeykoon1, Yew San Hor2, Rongwei Hu1, Cedomir Petrovic1, J.F. Mitchell2, Simon J.L. Billinge1,3 1Brookhaven National Laboratory, Upton, NY, USA 2Argonne National Laboratory, Argonne, IL, USA 3Columbia University, New York, NY, USA Email: [email protected] Keywords: iridates, dimerization, short range orbital order Transition metal chalcogenides (TMC) with partially filled d bands exhibit rich physical phenomena, displaying orders in orbital, charge and spin sectors, as well as structural, electronic and magnetic transitions. Such systems are hosts to emergent responses including high temperature superconductivity, colossal magnetoresistance, formation of spin dimerized lattices, and spin and charge glass states. Most studies of these systems focus on the observed behaviors in the low temperature regime, where symmetry broken states order over long range, originating from subtle interplays of competing and/or cooperating tendencies with possible new fundamental interactions. Less is known about what happens upon heating when the long range order melts or disappears upon doping or other excitation, yet this is possibly more crucial to understand the physics governing the behavior than the much lower energy effects responsible for the ordering of the broken symmetry states. In most of the TMCs of interest the high temperature regime is characterized by a high crystallographic symmetry structure where, due to partial filling of the d orbitals, orbital states are degenerate and are prone to symmetry breaking to lift the degeneracy. Mechanisms of lifting the degeneracy could be numerous, such as the crystal field (CF) effects, the well known orbital lattice Jahn Teller (JT) effect, the superexchange interactions between the orbitals, as well as the relativistic spin orbit coupling (SOC), and could in principle also arise from some combination of these effects. We refer to this as “Orbital Degeneracy Lifting” (ODL) to emphasize the very general nature of the phenomenon regardless of origin. Studies exploring the character of the ODL state at high temperature, above the temperature where the broken symmetry states order (i.e., the spin or orbital ordering) are therefore of great importance as they could provide important missing pieces of the puzzle. CuIr2S4 (CIS) thiospinel is a TMC system well known for displaying long range dimerized insulating ground state on pyrochlore sublattice of Ir, as well as metal to insulator transition (MIT) at around 230 K [1], assigned as orbitally driven Peierls transition [2]. In this talk we take the ODL spectacles to explore possible reasons behind the observed poor metallicity of CuIr2S4 in its cubic high temperature phase [3]. Early studies suggested that persistence of some form of short range Ir dimer order 271 Superstripes 2017, Ischia June 4 10, 2017 may be behind the unusual transport properties at high temperature [4, 5]. However, local structural studies utilizing X ray total scattering based atomic pair distribution function (xPDF) approach unambiguously rejected such a scenario [6]. Interestingly, xPDF study of Cr substituted CIS evidenced that long range order is in fact not required for dimerization, as signatures of Ir dimers were seen at low temperature on a nanometer length scale even when the long range dimer order is crystallographically prohibited [7]. However, this study clearly demonstrated that local dimer order is a privilege of the low temperature regime only (T≤TMI), and that dimers do not exist on any length scale at elevated temperature. Under a yet tighter grip of the xPDF analysis the data of CuIr2S4 finally reveal a subtle secret of the high temperature regime: the existence of short range orbital order. This order comes about due to the presence of presumably dynamic local ODL state that persists above the MIT. Thanks to fortuitous scattering contrast, the nearest Ir neighbor xPDF peak effectively provides a direct view of the Ir d orbital overlap and shows presence of tetragonal like distribution of 2 short and 4 long nearest neighbor Ir Ir distances on a pyrochlore, consistent with c/a>1 and short range orbital ordering on a length scale limited to one unit cell at best. The effect is robustly observed up to the highest measured temperature (~800 K). Cr doping induced strain fields are found to stabilize the effect seen in parent CuIr2S4, but ordering remains poorly spatially correlated. On the other hand, xPDF analysis of Zn doped samples, in which the MIT is suppressed and superconductivity occurs [8], confirms underlying orbital origin of the observed effects via electron filling induced destabilization of the short range orbital order (and concomitant changes of the local structure) that ultimately disappear for higher Zn content. The observations provide a rationale for a long standing puzzle of reportedly poor and unusual metallicity of CuIr2S4 at high temperature – existence of orbital liquid like state. More importantly the observations further suggest that the MIT in this system can be seen, at least in part, as a crystallization of orbital liquid like state into a long range orbitally ordered lattice. In this regard CuIr2S4 displays a surprising similarity to a seemingly unrelated TMC system LaMnO3 (LMO) [9] where short range orbital fluctuations were also observed up to the highest measured temperature and which crystallize upon cooling into a long range orbital order at ~720 K. In both LMO and CIS the high T behavior could be attributed to local ODL state and short range orbital order. The apparent differences relate to the mechanisms of ODL – JT in LMO, and CS or SOC in CIS [10]. Ubiquity of ODL concepts is to be validated by coordinated experimental and theoretical efforts. References 1. P.G. Radaelli et al., Nature 416, 155 (2002). 2. D.I. Khomskii and T. Mizokawa, Phys. Rev. Lett. 94, 156402 (2005). 3. A.T. Burkov et al., Phys. Rev. B 61 10049 (2000). 4. K. Yagasaki et al., J. Phys. Soc. Jpn. 75, 074706 (2006). 5. K. Takubo et al., Phys. Rev. B 78, 245117 (2008). 6. E.S. Bozin et al., Phys. Rev. Lett. 106, 045501 (2011). 7. E.S. Bozin et al., Sci. Rep. 4, 4081 (2014). 8. G. Cao et al., Phys. Rev. B 64, 214514 (2001). 9. X. Qiu et al., Phys. Rev. Lett. 94, 177203 (2005). 10. J. Nasu and Y. Motome, Phys. Rev. B 90, 045102 (2014). 272 Superstripes 2017, Ischia June 4 10, 2017 50.2 Spin split surface states of transition metal delafossite oxides Veronika Sunko,1,2 H. Rosner,2 P. Kushwaha,2 L. Bawden,1 O. J. Clark,1 J. M. Riley,1,3 D. Kasinathan,2 M. W. Haverkort,2 A. P. Mackenzie,1,2 and P. D. C. King1 1SUPA, School of Physics and Astronomy, University of St. Andrews, St. Andrews KY16 9SS, United Kingdom 2Max Planck Institute for Chemical Physics of Solids, Nothnitzer Straße 40, 01217 Dresden, Germany 3Diamond Light Source, Harwell Campus, Didcot, OX11 0DE, United Kingdom Email: vs61@st andrews.ac.uk Keywords: ARPES, delafossites, spin orbit, spin splitting Delafossite oxides have recently attracted considerable attention because of their fascinating transport properties [1, 2]. As well as having extremely long low temperature mean free paths, PdCoO2 and PtCoO2 are the most conductive oxides known at room temperature, with resistivities comparable to those of silver, copper or gold [3, 4]. This high conductivity is attributed to a single broad band crossing the Fermi level [4, 6]. However, due to the polarity of the structure the electronic properties at the crystal surfaces can be very different to those of the bulk[5, 6]. Here we use angle resolved photoemission (ARPES) to show that the CoO2 terminated surfaces of (Pd,Pt)CoO2 indeed host a set of states which do not appear in the bulk, with much higher masses and apparently stronger interactions. Intriguingly, we find that those Co derived states exhibit a large spin splitting at the Fermi level of ∆kF = 0.1Å 1, comparable to the giant Rashba system BiTeI, and unexpected in a 3d system. Comparing ARPES with density functional theory (DFT) and model tight binding calculations allows us to understand the origin of the large splitting, as well as to suggest general ways to maximise the effects of spin orbit coupling at surfaces and interfaces. References 1. Moll, P.J.W. et al, 2016. Evidence for hydrodynamic electron flow in PdCoO2. Science 351, 1061–1064. doi:10.1126/science.aac8385 2. Kikugawa, N. et al, 2016. Interplanar coupling dependent magnetoresistivity in high purity layered metals. Nat Commun 7, 10903. doi:10.1038/ncomms10903 3. Hicks, C.W. et al, 2012. Quantum oscillations and high carrier mobility in the delafossite PdCoO2. Physical Review Letters 109, 116401. doi:10.1103/PhysRevLett.109.116401 4. Kushwaha, P. et al, 2015. Nearly free electrons in a 5d delafossite oxide metal. Science Advances 1, e1500692. doi:10.1126/sciadv.1500692 273 Superstripes 2017, Ischia June 4 10, 2017 5. Kim, K. et al, 2009. Fermi surface and surface electronic structure of delafossite PdCoO2. Physical Review B Condensed Matter and Materials Physics 80, 1–4. doi:10.1103/PhysRevB.80.035116 6. Noh, H. J. et al., 2009. Orbital character of the conduction band of delafossite PdCoO2 studied by polarization dependent soft x ray absorption spectroscopy. Physical Review B 80, 73104. doi:10.1103/PhysRevB.80.073104 274 Superstripes 2017, Ischia June 4 10, 2017 50.3 Electrochemical intercalation of alkali metal ions into the layered structure of iron chalcogenides Anna Krzton Maziopa, Edyta Pęśko Warsaw University of Technology, Faculty of Chemistry, Warsaw, Poland Email: [email protected] Keywords: layered chalcogenides, electrochemical intercalation, structure, electrosynthesis Superconducting layered FeSe1 xChx (Ch = S, Te) materials are the subject of continuous interest with respect to their unique properties and remarkable ability for accommodating various species that may be inserted between the iron chalcogenide layers. Anion substitution significantly alters the unit cell parameters and critical temperature of superconductivity, that can be explained by deformation of FeSe tetrahedron in crystal structure [1]. On the other hand similar effects can be achieved by exertion of chemical pressure by intercalation of organic molecular spacer between Fe Se sheets. This brings even more spectacular effect as more than fourfold enhancement of critical temperature is observed in comparison to the parent compound [2]. It has been shown that low temperature intercalation form various liquid media is a quite convenient way of controlling the properties of the material, however with some restrictions related to the amount of the intercalated species [2]. The other possibility, which offers better control of the process is the electrochemical intercalation and, more importantly, the direct electrosynthesis of iron chalcogenide layers and their subsequent electrochemical intercalation with alkali metals. In the current paper the problems related to electrochemical approach to the intercalation and electrosynthesis of the layered iron chalcogenides will be discussed. References 1. F. C. Hsu et al., Proc. Natl. Acad. Sci. USA, 105, 14262 (2008) https://doi.org/10.1073/pnas.0807325105 2. A Krzton Maziopa et al.J. Phys.: Condens. Matter 28, 293002 (2016) https://dx.doi.org/10.1088/0953 8984/28/29/293002 275 Superstripes 2017, Ischia June 4 10, 2017 51.1 Structure and dynamics of composite vortex states in multiband superconductors Mikhail Silaev Department of Physics and Nanoscience Center, University of Jyväskylä, P.O. Box 35 (YFL), FI 40014 University of Jyväskylä, Finland Email: [email protected] Keywords: multiband superconductors, composite vortices, type 1.5 superconductivity, flux flow resistive state. Resistive properties of type II superconductors are determined by the dynamics of vortices. The microscopic kinetic theory of flux flow resistivity in conventional superconductors has been developed in seminal works by Gor’kov and Kopnin [1]. Many of the recently discovered superconducting materials including MgB2, Sr2RuO4, iron pnictides, the pairing of electrons is supposed to take place in several sheets of a Fermi surface formed by overlapping electronic bands. Unusual behaviour of flux flow resistivity in multiband superconductors cannot be explained by the exisitng single band models [2]. Moreover in strong contrast to the single component type I or type II superconductors some of multiband materials feature complicated vortex clusters, chains and gossamer patterns in low magnetic field. An explanation of this behavior was proposed that they may belong to a completely new "type 1.5" class of superconductors [3]. In this talk I will discuss how the observed anomalies can be explained by the composite structure of vortices, consisting of to the order parameter phase windings in different superconducting bands [4]. Composite vortex states are naturally described by several coherence lengths which results in the follwoing intriguing phenomena: (i) non monotonic interaction between vortices at low magnetic fields [4,5]; (ii) diverse behaviour of magnetization curves at high magnetic fields [6]; (iii) large deviations of the flux flow resistivity from the single band Bardeen Stephen law [7]. The calculation of flux flow conductivity presented in [7] is a generalization of the single component kinetic theory [1] for multiband systems. References 1. L.P. Gor’kov and N.B. Kopnin, Zh. Eksp. Teor. Fiz. 65, 396 (July 1973) [ Sov. Phys. JETP, 38, 195 (1974)]; L.P. Gor’kov and N.B. Kopnin, Zh. Eksp. Teor. Fiz. 64 356 (1973) [Sov. Phys. JETP, 37, 183 (1973)]. 276 Superstripes 2017, Ischia June 4 10, 2017 2. T. Okada, F. Nabeshima, H. Takahashi, Y. Imai, and A. Maeda, Phys. Rev. B 91, 054510 (2015); A. Shibata, M. Matsumoto, K. Izawa, Y. Matsuda, S. Lee, and S. Tajima Phys. Rev. B 68, 060501(R) (2003). 3. V. Moshchalkov, et al., Phys. Rev. Lett., 102, 117001 (2009); C.W. Hicks, et al. Phys. Rev. B, 81, 214501 (2010); S. J. Ray, et al., Phys. Rev. B, 89, 094504 (2014). 4. E. Babaev and M. Speight, Phys. Rev. B, 72, 180502(R) (2005); E. Babaev, J. Carlström, and M. Speight, Phys. Rev. Lett., 105, 067003 (2010). 5. M. Silaev, E. Babaev, Phys. Rev. B 84, 094515 (2011). 6. M. Silaev, Phys. Rev. B 93, 214509 (2016). 7. M. Silaev, A. Vargunin, Phys. Rev. B 94, 224506 (2016). 277 Superstripes 2017, Ischia June 4 10, 2017 51.2 Quantized Massive Gauge Fields and Anomalous Angle resoluved Photoemission Spectra in HIgh Tc Cuprates I. Kanazawa and R. Maeda Department of Physics, Tokyo Gakugei University, Koganeishi, Tokyo 184 8501, Japan Email: kanazawa@u gakugei.ac.jp Keywords: high Tc cuprates, gauge fields, ARPES Angle resoluved photoemission spectra in high Tc cuprates are quite unusual [1]. A broad 'hump' at 100 300 meV is present in photoemission spectra near the hot spots in underdoped high Tc cuprates. Tacon et al [2] have observed by means of resonant inelastic x ray scattering that damped magnetic excitations are present inside the electron hole spin flip continuum (up to about 300 meV) in doped high Tc cuprates. They have suggested that these damped magnetic excitation, whose half width at height maximum(HWHM) is about 200 meV, are mediating Cooper Pairing in high Tc cuprates. The present author and coworkers[3 6] have introduced quantized collective massive gauge fields around the doped hole as collective modes, which contain effects of spin fluctuation, charge fluctuation, and phonons, and have suggested strongly that the quantized massive gauge fields are mediating Cooper pairing in high Tc cuprates. In this study, we have analyzed anomalous ARRPES spectra in high Tc cuprates, using quantized massive gauge fields, and will discuss the relation between quantized massive gauge fields and anomalous ARPES spectra. References 1. Z. X. Shen and D. Dessau, Phys. Rep.,253,1(1995). 2. M. Le Tacon et al., Nat. Phys. 4,696(2008). 3. I. Kanazawa, Physica C 185 189,1703(1991). 4. I. Kanazawa, J. Phys. A36,9371(2003). 5. I. Kanazawa, J. Phy. Chem. Solids 66,1388(2005). 6. I. Kanazawa and T. Sasaki, Phys. Scr. T165,014038(2015). 278 Superstripes 2017, Ischia June 4 10, 2017 51.3 Asymmetry of critical temperatures in e and h doped cuprates Mikhail Eremin Institute of Physics, Kazan (Volga region) Federal University Email: [email protected] Keywords: e and h doped cuprates, t J T model, singlet correlated band It was widely believed that spin fluctuation mechanisms play crucial role in all h Tc cuprates. However resent RIXS data displayed that frequency of high energy collective spin excitations in e doped cuprates even higher then in h doped curates [1]. Basic features of such spin excitation in Pr0.88LaCe0.12CuO4−x can be reproduced using effective Hamiltonian ,00, σσ l −− σσ '1 −− σσσσ ',0',0, (1) H −− TJt = ∑ , jiji + ∑ [() nnssJXXt jijiij 4. ] ∑Tij ()−−− 1 li XXX j ji ,, σ > ji jli σσ ',,,, Here the first two terms correspond to well known t J model. Last one takes into account the so called three site terms. The parameters and have the same orders of magnitude [2]. The asymmetry between phase diagrams of e and h doped cuprates originated from fundamentally different nature of carriers. In the first case the d hole is distributed over copper positions. The Fermi level is placed in the low Hubbard Cu band. Whereas in h doped cuprates the carriers are spread over the oxygen positions (p hole). Strong exchange coupling between d and p holes yield new band between and energy levels. We call it as a singlet correlated band. Corresponding quasiparticle operators (creation) is written as pd ,↑ ↑↓↑ ↓↑↑ 0,,0,, dd,↑ pp,↑ ψ d = − PXPXc 2/ − Xc d − Xc d (2) 1 2 3 Here is creation operator of oxygen p hole near Cu site. Using widely accepted set of parameters (in eV); Idd=8, Ipp=6, tpd=1.3, Vpd=1, Jpd=1, and we found c1= , c2=0.29, c3 =0.23. The first term in (2) corresponds to quasiparticle operator with respect to exchange coupling energy between d and p–holes, i.e. . The effective Hamiltonian for singlet correlated band is written as follows pa σ σ ,, pd H = ∑ t ψ ψ + ∑ J [()ss − n n 4/ ] (3) sc ji ,, σ , iji j > ji jiij i j The three site term is absent here, but all spin indexes refer to Cu spins. This Hamiltonian allowed describing basic features of collective spin excitations in 279 Superstripes 2017, Ischia June 4 10, 2017 optimally doped YBaCuO [3]. Keeping in mind that three site terms in (1) destroys the superexchange pairing mechanism [4], we able to understand way Tc in e doped low with respect to Tc in h doped cuprates. References 1. W. S. Lee, J. J. Lee, E.A. Nowadnick et al., Nature Physics 10, 883 (2014). 2. M.V. Eremin, M.A. Malakhov. JETP Lett. 104, pp. 15–19 (2016). 3. M.V. Eremin, I.M. Shigapov, I.M. Eremin, Magnetic Resonance in Solids. Electronic J. 16, 14206 (2014). 4. V.V. Val’kov, T.A. Val’kova, D.M. Dzebisashvili, S.G. Ovchinnikov, JETP Lett.75, 378 (2002). 280 Superstripes 2017, Ischia June 4 10, 2017 51.4 Detailed Simulation of Vortex Crossing Andreas Glatz, Vitalii Vlasko Vlasov, George Crabtree Materials Science Division, Argonne National Laboratory, Argonne, Illinois 60439, USA Email: [email protected] Keywords: Ginzburg Landau simulations, vortex dynamics, magnetoresistance, vortex crossing Vortex crossing and reconnection is a complex and intricate physical phenomenon [1,2,3], which emerges in many classical and quantum hydrodynamic systems including turbulence in liquids and astrophysical plasmas, Bose condensates, and DNA assemblies. It is an intrinsic part of the dynamics of nonparallel vortices in superconductors and is practically important for their power applications and superconducting machinery. In spite of numerous theoretical efforts, until the problem still lacks even a qualitative understanding. We address the vortex crossing in superconductors using Time Dependent Ginzburg Landau (TDGL) simulations [4] and elucidate consecutive steps of the crossing events in arrays of vortices subject to orthogonal magnetic fields. We suggest important future directions in TGDL modeling that will allow to understand the role of the material properties, sample geometry, and anisotropy, in the complex vortex crossing effects. Vortex crossing event – two vortices approach, locally twist, intersect, and cross by exchanging their tails References 1. A. Glatz, V. K. Vlasko Vlasov, W. K. Kwok, and G. W. Crabtree Phys. Rev. B 94, 064505 (2016). 2. V. Vlasko Vlasov, A. Koshelev, A. Glatz, C. Phillips, U. Welp, and W. Kwok, Phys. Rev. B 91, 014516 (2015). 281 Superstripes 2017, Ischia June 4 10, 2017 3. V. K. Vlasko Vlasov, A. Glatz, A. E. Koshelev, U. Welp, and W. K. Kwok, Phys. Rev. B 91, 224505 (2015). 4. I. A. Sadovskyy, A. E. Koshelev, C. L. Phillips, D. A. Karpeev, A. Glatz, J. of Comp. Phys. 294, 639 (2015). 282 Superstripes 2017, Ischia June 4 10, 2017 52.1 Engineering the functional properties of 2 dimensional electron gases at oxide interfaces Fabio Miletto Granozio CNR SPIN, Napoli Email: [email protected] Keywords: oxide interfaces, two dimensional electron gases, photoconductivity, superconductivity, magnetism. 2 Dimensional electron gases (2DEGs) at oxide interfaces hold promise to combine the specific physics of low dimensional systems with extraordinary functional properties as superconductivity, magnetism and ferroelectricity, that are commonly found in transition metal oxides, and are typically missing in semiconductors. In this talk, the phenomenology of oxide 2DEGs will be first revised. We will show that the properties of the LaAlO3/SrTiO3 interface, as originally discovered in Bell labs over a decade ago, can be suitably engineered by modifying, resorting to atomically controlled growth, the layers present either on the nominally polar or on the nominally non polar side if the interfaces. As a result, the response of our samples to light [1,2] as well as to magnetic [2] and electric fields can be suitably adjusted, thus allowing for the potential implementation of novel device concepts. Figure 1: (a) Normal photoconductivity of a LaAlO3 interface under red light (625nm). (b) “Colossal” photoconductivity of a amorphous LaGaO3/SrTiO3 interface, previously brought in retention state by a backgate voltage pulse, under the same photon beam. 283 Superstripes 2017, Ischia June 4 10, 2017 References 1. Non volatile, reversible metal insulator transition in oxide interfaces controlled by gate voltage and light, Mian Akif Safeen, F. Miletto Granozio et al., arXiv:1701.03660 [cond mat.str el] 2. Persistent Photoconductivity in 2D Electron Gases at Different Oxide Interfaces, Emiliano Di Gennaro, Fabio Miletto Granozio, et al., Adv. Opt. Mat. DOI:10.1002/adom.201300150 (2013) 3. Tunable spin polarization and superconductivity in engineered oxide interfaces, D. Stornaiuolo, F. Miletto Granozio, et al., Nature Materials 15, 278 (2016) doi:10.1038/nmat4491 284 Superstripes 2017, Ischia June 4 10, 2017 52.2 Josephson junctions based on LAO/STO 2DEG D. Stornaiuolo1,2, D. Massarotti1,2, R. Di Capua1,2, P. Lucignano2, G.P. Pepe1,2, M. Salluzzo2, and F. Tafuri1,2,3 1 Department of Physics, University of Naples “Federico II”, Italy 2 CNR SPIN Napoli, Italy 3 Dipartimento di Ingegneria dell’Informazione, Seconda Università degli Studi di Napoli (SUN), Italy. Email: [email protected] Keywords: oxide 2DEG, Josephson effect The nature and properties of the superconducting phase of the 2 dimensional electron gas (2DEG) at the LaAlO3/SrTiO3 (LAO/STO) interface are still largely unexplored. We realized LAO/STO based nanoscale Josephson junctions and used them as an ultrasensitive spectroscopic probe to gain information about the superconducting order parameter [1]. Conductance spectra and critical current vs. temperature data reveal the presence of two gap structures and the junctions’ magnetic patterns show anomalies that can be accounted for only assuming the presence of a non conventional order parameter. These results are in agreement with theoretical predictions of mixed singlet triplet superconducting order parameter in 2D superconducting systems hosting Rashba spin orbit coupling, and pave the way to a deeper understanding of these systems [2]. Our data confirm the complexity and richness of engineered oxide 2DEG structures and the exceptional opportunities they offer for the study of exotic excitations and novel quantum electronics [3]. References 1. D. Stornaiuolo et al., under review. 2. L.P. Gor’kov, E.I. Rashba, Physical Review Letters 87, 037004 (2001). 3. D. Stornaiuolo et al., Nature Materials 15, 278 (2016). 285 Superstripes 2017, Ischia June 4 10, 2017 52.3 Orbital selectivity and Hund's physics in Iron based superconductors Laura Fanfarillo, Massimo Capone International School for Advanced Studies SISSA/ISAS and CNR IOM Democritos Email: [email protected] Keywords: orbital selectivity, Hund metal, superconductuctivity, nematicity The description of electronic correlation in iron based superconductors is complicated by their multi orbital character. For long time the nature and degree of local correlations, as well as the relation between the so call Hund's coupling and the Mott physics has been highly debated. I will show that in iron based superconductors correlations are orbital selective and I will clarify the connection between Hund metal physics and half filled Mott physics [1, 2]. I will also explain that contrary to what happens in Mott systems, the atomic spin polarization promoted by Hund's coupling induces strong correlations, without necessary leading to an increase in the localization of total charge. Indeed, in some cases the polarization may even promote itineracy [2]. I will then discuss the interplay between local correlations and ordered phases of iron based systems. As a matter of fact, although a number of experiments calls for a prominent role of local correlations and place iron superconductors at the entrance of a Hund metal state, the effect of the local correlations on the nematic, superconducting and magnetic states of iron materials has been theoretically poorly investigated. I will discuss the nematicity at the Hund's metal crossover [3]. I will show how correlations severely constrain the precise nature of the feasible orbital ordered state and induces a differentiation in the effective masses of the zx/yz orbitals in the nematic phase. The latter effect leads to distinctive signatures in different probes, so far overlooked in the interpretation of experiments. I will then discuss the consequences of the orbital selectivity on the superconducting phase, in particular concerning the symmetry of the pairing [4]. References 1. L. De Medici, G. Giovannetti and M. Capone, Phys. Rev. Lett., 112, 177001 (2014). 2. L. Fanfarillo and E. Bascones, Phys. Rev. B, 92, 075136 (2015). 3. L. Fanfarillo, G. Giovannetti, M. Capone and E. Bascones, arXiv:1609.06672 (2016). 4. L. Fanfarillo, M. Capone in preparation (2017). 286 Superstripes 2017, Ischia June 4 10, 2017 52.4 Temperature dependent quasiparticle interference of LiFeAs C. Hess, Z. Sun, J.M. Guevara, S. Sykora, P.K. Nag, D. Baumann, R. Kappenberger, R. Beck, U. Gräfe, S. Wurmehl, S. Borisenko, B. Büchner IFW Dresden, Helmholtzstraße 20,01069 Dresden, Germany Email: c.hess@ifw dresden.de The nature of superconductivity of LiFeAs remains an open problem, particularly in view of its electronic structure, which is far away from the canonical picture of strong Fermi surface nesting. Upon extending our previous temperature dependent studies of the superconducting state using scanning tunneling spectroscopy, we present here temperature dependent results for the quasiparticle interference (QPI) as a high resolution tool to access the fermiology in the both the superconducting and the normal state at small scattering momenta. Our data reveal a so far not detected enhancement of the QPI at q~0, providing fresh input with respect to a putative electronic instability of the electronic system. 287 Superstripes 2017, Ischia June 4 10, 2017 53.1 Superconductivity in noncentrosymmteric low dimensional materials Toshiya Ideue,1* and Yoshihiro Iwasa1,2 1 Quantum Phase Electronics Center (QPEC) and Department of Applied Physics, The University of Tokyo, Tokyo 113 8656, Japan 2 RIKEN Center for Emergent Matter Science (CEMS), Wako, Saitama 351 0198, Japan. Email: * [email protected] tokyo.ac.jp Key words: superconductivity; ionic liquid gating, transition metal dichalcogenides; nanotube; inversion symmetry breaking. The effect of lattice symmetry breaking on superconductivity has been explored over the years [1,2]. One of the manifestations of lattice symmetry breaking in the electric transport is the nonreciprocal electric transport, in which the forward and backward supercurrent flows are not equivalent because of inversion symmetry breaking [3,4]. In this presentation, I will talk about the recent progress on the observation of the nonreciprocal superconducting transport in noncentrosymmetric low dimensional materials. Such superconductivity without space inversion symmetry is realized in nanostructures of transition metal dichalcogenides via ionic liquid gating. Figure 1: Illustrations of the nonreciprocal superconducting transport in noncentrosymmetric sueprconductors. Left and right figures show the superconductivity in a two dimensional MoS2 and chiral WS2 nanotube, respectively. In two dimensional MoS2, second harmonic voltage signals corresponding to the nonreciprocal electric trasnport are largely enhanced in electric field induced superconducting state, showing the characteristic selection rule (presence of absence of signals as a function of electric current directions) [5]. 288 Superstripes 2017, Ischia June 4 10, 2017 We further observed the electric field induced superconductivity in a chiral WS2 nanotube. Second harmonic signals originating from the tube chirality also show the large enhancement in superconducting region and characteristic quantum oscillations due to the interference of supercurrent along the circumference of the nanotube have been observed. These results clearly indicate the first observation of unidirectional superconducting transport and its quantum nature, providing a powerful approach for probing the exotic superconducting state in a variety of noncentrosymmetric systems. References 1. E. Bauer, and M. Sigrist, Non centrosymmetric Superconductors: Introduction and Overview (Springer, 2012). 2. L. P. Gor'kov, and E. I. Rashba, Phys. Rev. Lett. 87, 037004 (2001) https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.87.037004 3. F. Pop, P. Auban Senzier, E. Canadell, G. L. J. A. Rikken, and N. Avarvari, Nature Communications 5, 3757 (2014). https://www.nature.com/articles/ncomms4757. 4. T. Ideue, et al., Nature Physics, Advanced Online Publication (2017). http://www.nature.com/nphys/journal/vaop/ncurrent/full/nphys4056.html. 5. R. Wakatsuki, et al., Science Advances 3, e1602390 (2017). http://advances.sciencemag.org/content/3/4/e1602390. 6. F. Qin, et al., Nature Communications 8, 14465 (2017). https://www.nature.com/articles/ncomms14465. 289 Superstripes 2017, Ischia June 4 10, 2017 53.2 Strong peak in Tc of Sr2RuO4 under uniaxial pressure Alexander Steppke1,2, Lishan Zhao1,2, Mark Barber1,2, Thomas Scaffidi3, Fabian Jerzembeck1, Helge Rosner1, Alexandra Gibbs4, Yoshiteru Maeno5, Steven Simon3, Andrew Mackenzie1,2 and Clifford Hicks1 1Max Planck Institute für Chemische Physik fester Stoffe, Dresden, Germany 2University of St Andrews, School of Physics and Astronomy, St Andrews, UK 3Rudolf Peierls Centre for Theoretical Physics, Oxford, UK 4ISIS Facility, Rutherford Appleton Laboratory, United Kingdom 5Department of Physics, Kyoto University, Kyoto, Japan Email: [email protected], [email protected] Keywords: uniaxial pressure; Lifshitz transitions; odd parity superconductivity The unconventional superconductor Sr2RuO4 challenges the current level of understanding of strongly correlated materials. On the one hand, the high purity of available samples has allowed precise knowledge of the Fermi surfaces from quantum oscillations, while on the other hand the superconducting order parameter and pairing mechanism are not known with certainty. The most likely possibility is a chiral, odd parity order parameter. The superconductivity is highly sensitive to disorder, so it is not possible to tune the superconductivity through chemical substitution [1]. Here we applied, using a novel piezoelectric apparatus, uniaxial strains on the order of 1% to high quality single crystals of Sr2RuO4. While the unstrained material exhibits a Tc of 1.5K, at a compression of approximately 0.6% along a <100> direction Tc peaks at 3.4K [2], and the c axis upper critical field Hc2 is enhanced by a factor of more than twenty. We show evidence, from uncorrelated band structure calculations, that the Fermi level at or near this compression passes through a Van Hove singularity in one of the three electronic bands. We discuss implications of our results, especially the dramatic increase in Hc2, for the order parameter of Sr2RuO4. 290 Superstripes 2017, Ischia June 4 10, 2017 Figure 1: (Left) Tc of three samples of Sr2RuO4 shown against uniaxial strain. Negative values of εxx denote compression. (Right) Drawing of the experimental apparatus with the sample clamped mounted as a beam and held in place by epoxy. The susceptibility is measured by a pair of concentric coils placed on the centre of the sample. References 1. C.W. Hicks, M.E. Barber, S.D. Edkins, D.O. Brodsky, and A.P. Mackenzie. Piezoelectric based apparatus for strain tuning. Rev. Sci. Inst. 85 065003 (2014). 2. A. Steppke, L. Zhao, M. Barber, T. Scaffidi, F. Jerzembeck, H. Rosner, A. Gibbs, Y. Maeno, S. Simon, A. Mackenzie and C. Hicks, Strong peak in Tc of Sr2RuO4 under uniaxial pressure, Science, 255, 148 (2017). 3. T. Scaffidi, J.C. Romers, and S.H. Simon. Pairing symmetry and dominant band in Sr2RuO4. Phys. Rev. B 89 220510R (2014). 291 Superstripes 2017, Ischia June 4 10, 2017 53.3 Topological Excitations and Bound States in a Quantum Dimer Antiferromagnet P. A. McClarty (1), F. Kruger (1,2), T. Guidi (1), S. F. Parker (1), K. Refson (1,3), A. W. Parker (4), D. Prabhakaran (5), and R. Coldea (5) (1) ISIS, Science and Technology Facilities Council, Rutherford Appleton Laboratory, Didcot OX11 0QX, United Kingdom. (2) London Centre for Nanotechnology, University College London, Gordon Street, London, WC1H 0AH, United Kingdom. (3) Department of Physics, Royal Holloway, University of London, Egham TW20 0EX, United Kingdom. (4) Central Laser Facility, Science and Technology Facilities Council, Rutherford Appleton Laboratory, Didcot OX11 0QX, United Kingdom. (5) Clarendon Laboratory, University of Oxford, Parks Road, Oxford OX1 3PU, United Kingdom Email: [email protected] Keywords: Quantum Dimer Magnet; Topological Chern Insulator; Bound States Using inelastic neutron scattering along with theoretical calculations we demonstrate that, in a weak magnetic field, the dimerized quantum magnet SrCu2(BO3)2 is a bosonic analogue of a topological Chern insulator with topologically protected chiral edge modes of triplon excitations. In addition to the triplon bands we find a dispersive two triplon S=0 bound state, reflecting that the system is strongly correlated. The bound state strongly hybridises with the triplon excitations. Interestingly, it does not destroy the topological nature of the excitations but instead makes it much richer, leading to a sequence of topological transitions. 292 Superstripes 2017, Ischia June 4 10, 2017 Evolution of the low energy magnetic excitations of SrCu2(BO3)2 in a field along the [001] direction with cut taken in the [−1 + H, 1 + H] direction. (a) Panels show data taken at at zero field, 0.7 T, 1.4 T, and 2.8 T. In addition to six triplon bands, the data show a relatively dispersive, field independent mode. We identify this mode as a singlet bound state of two triplons, visible in the magnetic structure factor only through the strong hybridization with the triplon excitations. (b) Calculated spectra using a model of interacting triplons that is derived from a bond operator expansion of the initial spin Hamiltonian. 293 Superstripes 2017, Ischia June 4 10, 2017 54.1 Imaging the insulator metal phase transition with resonant soft X ray holography Luciana Vidas1, Bastian Pfau2, Stefan Eisebitt2, Simon Wall1 1 ICFO Institut de Ciencies Fotòniques, The Barcelona Institute of Science and Technology, 08860 Castelldefels (Barcelona), Spain 2 Institut für Optik und Atomare Physik, Technische Universität Berlin, 10623 Berlin, Germany Email: [email protected] Keywords: Phase separation, insulator metal, nanoscale Vanadium dioxide (VO2) in ambient conditions resides close to a solid state triple point between the insulating M1 and M2 phases and the metallic R phase [1]. As a result, small changes in the strain profile can modify the transition pathway from the insulating to metallic phase. This is particularly true in thin film samples in which an inhomogeneous strain can dramatically modify the energy landscape on the nanoscale. Recently, a separation between electronic and structural aspects of the phase transition have been claimed in thin films [2,3]. These experiments have lacked the ability to observe the spatial distribution of the undistorted metallic phase. In this talk I will present our technique of resonant soft X ray holography to image the insulator metal phase transition in VO2 on the nanoscale. By imaging on the vanadium and oxygen edges we can achieve contrast between the insulating and metallic phases and observe domain growth with 50 nm spatial resolution [4]. 294 Superstripes 2017, Ischia June 4 10, 2017 X ray pseudo colour Image of VO2 at 338 K high lighting nanoscale phase coexistence and inhomogeneity in the sample. Each colour channel (red, green, blue) is sensitive to specific regions of the VO2 absorption spectrum. The blue channel is sensitive to shifts at the vanadium edge, the green channel corresponds to the d// state, and the red channel corresponds to the π* state. Five distinct regions of the sample can be clearly identified. The XAS spectra of the four regions relative to the spectra of region M1 are plotted in b (offset for clarity). References 1. J. H. Park et al. Nature 500, 431 (2013). 2. J. Laverock Phys. Rev. Lett. 113, 216402 (2014). 3. A. X. Gray et al. Phys. Rev. Lett. 116, 116403 (2016). 4. L. Vidas et al. arXiv 1612.07998 (2016). 295 Superstripes 2017, Ischia June 4 10, 2017 54.2 Thickness and Temperature Driven Metal Insulator Transitions in CaVO3: A Resonant Inelastic X ray Scattering Study D.E. McNally, Xingye Lu, J. Pelliciari, M. Dantz, M. Naamneh, T. Shang, Z. Wang, G. Sclauzero, S. Beck, C. Ederer, M. Radovic and T. Schmitt Paul Scherrer Institute; ETH Zurich Email: [email protected] Keywords: metal insulator transition; vanadate thin films; correlated electrons Bulk CaVO3 is a correlated paramagnetic metal. Thin film CaVO3 undergoes a metal insulator transition when the thickness is reduced below around 20 u.c. We present resonant inelastic x ray scattering and x ray absorption measurements at the vanadium L edge that reveal a large reduction in the charge excitation bandwidth across the thickness and temperature driven metal insulator transitions in thin film CaVO3. Our measurements further show that a decreased V O covalency accompanies this correlation assisted metal insulator transition. RIXS energy maps across the metal insulator transition in CaVO3. Thick films are metallic and thinner films are insulating. 296 Superstripes 2017, Ischia June 4 10, 2017 54.3 Spin transfer torque induces parity time symmetry breaking Alexey Galda, V. Vinokur Materials Science Division, Argonne National Laboratory; James Franck Institute, University of Chicago Email: [email protected] Keywords: magnetism, spin transfer torque, symmetry breaking, parity time symmetry The understanding of out of equilibrium physics, especially dynamic instabilities and dynamic phase transitions, is one of the major challenges of contemporary science, spanning the broadest wealth of research areas that range from quantum optics to living organisms. Focusing on nonequilibrium dynamics of an open dissipative spin system, we introduce a non Hermitian Hamiltonian approach, in which non Hermiticity reflects dissipation and deviation from equilibrium. The imaginary part of the proposed spin Hamiltonian describes the effects of Gilbert damping and applied Slonczewski spin transfer torque. In the classical limit, our approach reproduces Landau Lifshitz Gilbert Slonczewski dynamics of a large macrospin. We reveal the spin transfer torque driven parity time symmetry breaking phase transition corresponding to a transition from precessional to exponentially damped spin dynamics. Micromagnetic simulations for nanoscale ferromagnetic disks demonstrate the predicted effect. Our findings can pave the way to a general quantitative description of out of equilibrium phase transitions driven by spontaneous parity time symmetry breaking. References 1. Alexey Galda, V.M. Vinokur, Parity time symmetry breaking in magnetic systems, Physical Review B 94, 020408(R) (2016). 2. Alexey Galda, V.M. Vinokur, Linear dynamics of classical spin as Möbius transformation, arXiv:1610.00762 (2016). 297 Superstripes 2017, Ischia June 4 10, 2017 54.4 Optical control of skyrmions in helimagnetic FeGe. Berruto Gabriele*, Ivan Madan*, Murooka Yoshie*, Damien McGrouther**, Fabrizio Carbone* *Laboratory for Ultrafast Microscopy and Electron Scattering, ICMP, École Polytechnique Fédérale de Lausanne, CH 1015 Lausanne, Switzerland **Department of Physics and Astronomy, University of Glasgow, Scotland, United Kingdom, G12 8QQ Email: [email protected] Keywords: Skyrmions, optical control, helimagnet, ultrafast, Lorentz TEM Magnetic skyrmions are topologically non trivial metastable spin configurations with particle like properties and a number of characteristics promising for spintronic applications[1]. In the thin films of helical magnets they appear together with topologically trivial helical and ferromagnetic phases coexisting over the large range of the phase diagram[2]. Previous experiments on the control of skyrmions in helical magnets included electrical [3], [4] and magnetic control [5]. Here we report on a real space observation of the creation of skyrmions by a nanosecond optical pulse. The experiment is conducted on the thin 50 nm films of FeGe. Skyrmions creation is observed over a large region of the phase diagram with moderate variation in threshold fluence. In the talk we will consider possible mechanisms responsible for skyrmion formation and discuss experimental evidences supporting them. References 1. N. Nagaosa and Y. Tokura, “Topological properties and dynamics of magnetic skyrmions.,” Nat. Nanotechnol., vol. 8, no. 12, pp. 899–911, 2013. 2. X. Z. Yu et al., “Near room temperature formation of a skyrmion crystal in thin films of the helimagnet FeGe.,” Nat. Mater., vol. 10, no. February, pp. 106–109, 2011. 3. J. S. White et al., “Electric field control of the skyrmion lattice in Cu2OSeO3.,” J. Phys. Condens. Matter, vol. 24, p. 432201, 2012. 4. F. Jonietz et al., “Spin Transfer Torques in MnSi,” Science (80 . )., no. September, pp. 1648–1652, 2011. 5. S. Woo et al., “Observation of room temperature magnetic skyrmions and their current driven dynamics in ultrathin metallic ferromagnets,” Nat. Mater., vol. 15, no. 5, pp. 501–506, Feb. 2016. 298 Superstripes 2017, Ischia June 4 10, 2017 55.1 Nonlinear Terahertz Spectroscopy of Cuprates – A Probe of the “Hidden” Pair Density Wave Order Srivats Rajasekaran Email: [email protected] Cuprates along the c axis are a set of intrinsic Josephson junctions consisting of superconducting Cu O planes separated by insulating layers. The tunneling of superconducting Cooper pairs between the planes characterizes the c axis electrodynamics in the superconducting state [1]. This Josephson tunneling is highly nonlinear and therefore, strong field THz pulses could be used to achieve nonlinear control of the Josephson phase fluctuations. Further, such nonlinearities could be used to reveal the superconducting correlations in “hidden” phases like the Pair Density Wave state. I would discuss few nonlinear phenomena such as the amplification of the phase fluctuations and third harmonic frequency generation (THG) in La2 xBaxCuO4, x = 9.5 % [2]. Further, I would present our recent work where we utilized the THG as a spectroscopic probe for revealing Josephson phase correlations above Tc in stripe ordered x = 11.5 %. The third harmonic promptly disappears at Tc in the x=9.5% sample, however for the strongly striped x=11.5% sample, it is present throughout the stripe and charge order, i.e. upto T = Tco (55 K) > Tc (13 K). Our results provide compelling evidence for the presence of pair density wave order and interlayer phase coherence in the stripe ordered state of the La214 family above Tc [3]. References 1. Basov, D. and Timusk, T. Rev. Mod. Phys.77,121 (2005). 2. Rajasekaran, S. et al. Nat. Phys., 12, 1012–1016 (2016). 3. Berg, E. et al. Phys. Rev. Lett. 99, 127003 (2007). 299 Superstripes 2017, Ischia June 4 10, 2017 55.2 Remarkable energy dependent domain formation in the CDW of 1T CuxTiSe2 M. Spera, A. M. Novello, A. Scarfato, A. Ubaldini, E. Giannini, D. R. Bowler, and Ch. Renner All except D.R. Bowler: Department of Quantum Matter Physics, University of Geneva, 24 Quai Ernest Ansermet, CH 1211 Geneva 4, Switzerland D.R. Bowler: London Centre for Nanotechnology and Department of Physics and Astronomy, University College London, London WC1E 6BT, United Kingdom Email: [email protected] Keywords: Dichalcogenides, CDW, Charge Density Wave, Superconductivity, Exciton condensate, Jahn Teller distortion, Stripes The charge density wave (CDW) formation mechanism in 1T TiSe2 has been matter of debate since its first observation in 1976. Despite the large amount of data available, it is still unclear whether it is a purely electronic or elastic mechanism, or a combination of both. The appearance of superconductivity upon Cu intercalation (2006) and high pressure application (2009) triggered further interest in understanding the microscopic mechanisms governing the CDW ground state, seemingly in competition with superconductivity. We present a detailed scanning tunnelling microscopy and spectroscopy study of the impact of Cu intercalation on the CDW in 1T CuxTiSe2 [1]. Cu atoms, identified through density functional theory modelling, are found to intercalate randomly on the octahedral site in the van der Waals gap. Tunnelling spectroscopy shows Cu to shift the chemical potential and dope delocalized electrons near the Fermi level. The CDW modulation period does not depend on Cu content, but we observe the formation of charge stripe domains at low Cu content (x 300 Superstripes 2017, Ischia June 4 10, 2017 Left: STM topography and spectroscopic locations (coloured points) of CuxTiSe2 (x=0.01). Right: Scanning Tunneling Spectroscopy of TiSe2 and different regions of CuxTiSe2. T=1.2 K. References 1. A.M. Novello et al. Phys. Rev. Lett. 118, 017002 2. Hildebrand et al. arXiv:1609.04164 301 Superstripes 2017, Ischia June 4 10, 2017 55.3 X ray magnetic circular dichroism at the K edge of Cu in Bi2Sr2CaCu2O8+x 1,2 Antonio Bianconi, 3 Valentin G. Ivanov, 3 Andrey A. Ivanov, 3 Alexey P. Menushenkov, 4 Fabrice Wilhelm, 4 Andrei Rogalev, 5 B. Joseph, 6 Xu Wei, 7 A. Marcelli 1 Rome International Centre for Material Science Superstripes, RICMASS, via dei Sabelli 119A, 00185 Rome, Italy 2 Institute of Crystallography, CNR, via Salaria, Km 29.300, 00015 Monterotondo Roma, Italy 3 National Research Nuclear University MEPhI (Moscow Engineering Physics Institute), Kashirskoe sh. 31, 115409 Moscow, Russia 4 European Synchrotron Radiation Facility (ESRF), CS40220, F 38043 Grenoble Cedex 9, France 5 Sincrotrone Elettra, Strada Statale 14 Km 163,5 Area Science Park, 34149 Basovizza, Trieste, Italy 6 Beijing Synchrotron Radiation Facility Institute of High Energy Physics Chinese Academy of Sciences Beijing, 100049 P. R. China 7 Istituto Nazionale di Fisica Nucleare, Laboratori Nazionali di Frascati, 00044 Frascati (RM), Italy Email: [email protected] Keywords: XMCD, high Tc superconductors, CDW We present a study of X ray magnetic circular dichroism (XMCD) at K edge of Cu in high temperature superconductor Bi2Sr2CaCu2O8+x (Bi2212). The measurements were carried out at ID12 beamline of ESRF in Grenoble, France in fluorescence mode. The wave vector of an x ray beam was parallel to c axis of Bi2212 single crystal. A magnetic field of 17 T was applied in direction parallel to incident beam. XMCD spectra were recorded consecutively by reversing the helicity of the incident beam or by reversing the magnetic field at temperature points of 80, 100 and 200K that are below and above the points of different phase transitions in Bi2212. A special care was taken to exclude the influence of energy shift of XANES spectra measured at different helicities. The measurements revealed an XMCD signal of magnitude about 9*10 4 a.u. Its shape and magnitude didn't change in temperature range of 80 200K. No trace of x ray natural circular dichroism was detected. Figure shows XMCD spectra and typical XANES spectrum at Cu K edge normalized to a total edge jump of 1. The size of XMCD is given in the normalized scale. Numerical simulations of the XMCD signal for a series of Bi2212 lattice distortions showed that only rhombic one may be a reason for non zero XMCD signal in Bi2212 for our geometry of measurements. 302 Superstripes 2017, Ischia June 4 10, 2017 Normalized XANES and XMCD at K edge of Cu in Bi2212 at different temperatures under an applied magnetic field of 17T. 303 Superstripes 2017, Ischia June 4 10, 2017 55.4 Picometer scale determination of 3D local atomic structure parameters in nanostructured materials Soldatov A. V. Southern Federal University Email: [email protected] Keywords: local atomic structure, synchrotron radiation, XANES spectroscopy, nanostructured materials Nanoscale local atomic structure determines most of unique properties of novel materials without long range order. To study its fine details one has to use both computer nanodesign and advanced experimental methods for nanodiagnostics. Novel in situ technique for picodiagnostics extracting of 3D structure parameters on the basis of advanced quantitative analysis of X ray absorption near edge structure (XANES) has been developed. The possibility to extract information on bond angles and bond lengths (with accuracy up to 1 picometer) is demonstrated and it opens new perspectives of quantitative XANES analysis as a 3D local structure probe for any type of materials without long range order in atoms positions (all nanostructured materials and free clusters belong to this class of materials). The review of results obtained by this method for a wide class of nanostructured magnetic objects is presented. Another interesting application of this method is the possibility to analyze the time dependent processes, in particular, to study the dynamics of nanoscale atomic and electronic structure of materials with high temporal resolution. micrometer for nanoworld 304 Superstripes 2017, Ischia June 4 10, 2017 56.1 Nanoscale phase separation and lattice complexity in VO2, a complex multiphase correlated electron systems A. Marcelli*1,2,3, M. Coreno3, A. Bianconi2,4, A. D’Elia5,6, M. Stredansky5,6, A. Cossaro6, Wei Xu7,2, Lele Fan8, Chongwen Zou8 and A. Ricci9 1INFN Laboratori Nazionali di Frascati, Via E. Fermi 40, 00044, Frascati, Italy 2Rome International Centre for Material Science Superstripes, RICMASS, via dei Sabelli 119A, 00185 Rome, Italy 3CNR ISM, Basovizza Area Science Park, 34149 Trieste, Italy 4CNR IC, via Salaria Km 29.300, Monterotondo Roma 00015, Italy 5Department of Physics, University of Trieste, via A. Valerio 2, 34127 Trieste, Italy 6CNR IOM, Laboratorio TASC, SS 14, km 163.5, 34149 Basovizza, Trieste, Italy 7Beijing Synchrotron Radiation Facility, IHEP, Beijing, 100049, P.R. China 8University of Science and Technology of China, CAS, Hefei 230026, P.R. China 9Deutsches Elektronen Synchrotron DESY, Notkestraße85, D 22607 Hamburg, Germany Email: [email protected] Keywords: VO2, Metal insulator transition, phase separation, transition metal oxides, x ray absorption spectroscopy, resonant photoemission Vanadium dioxide (VO2) is a transition metal oxide that undergoes upon heating or cooling through a temperature range near room temperature (~340 K) to a hysteretic metal insulator transition (MIT). This phenomenon is accompanied to a structural phase transition from monoclinic to rutile phase, with a change in the electrical conductivity by several orders of magnitude due to interplay between lattice and electronic charge [1]. VO2 is highly sensitive to chemical and physical local perturbations [2] such as strain/stress that affects the MIT temperature and the resistance of the two main insulating phases: M1 and M2. Actually, the metallic and insulating phases and the transition changes across the MIT are controlled by the electronic orbital occupations regulated by local strain [3,4]. The emerging features of nanoscale inhomogeneity at the MIT make this system similar to other transition metal (TM) oxides that offer a wide spectrum of phase separated systems where anomalies can be detected in different observable quantities such as the resistivity and/or the optical transmission [5 8]. All these phenomena originate from interactions among spin, lattice, and charge degrees of freedom. In TM oxides the appearance of domains with distinct structural, magnetic, and electronic properties is described as a (dynamic) phase separation that occurs where two or more phases with comparable free energies and a large coherence length coexist [8]. All domains play a role in the dynamics of phase transformations, transport, magnetic and structural changes and are at the origin of the strong anomalies in the properties characteristic of phase separated systems. Among these systems, VO2 is 305 Superstripes 2017, Ischia June 4 10, 2017 certainly one of the most challenging and studied systems where changes corresponds to a V V dimerization along the rutile c axis forming homo polar bonds associated to a structural twist of edge sharing octahedrons. An electron correlation driven Mott transition and a structure distortion driven Peierls transition, or cooperation of these two mechanisms, have been proposed to explain the MIT. However, in spite of decades of great efforts the driving mechanism of this transition remains an open question and new important discoveries still occur [9]. XANES spectroscopy has the sensitivity to probe the local structure and the electronic changes associated with a MIT transition. Moreover, a local probe such as XANES may investigate simultaneously both the MIT and the structural phase transition. Figure 1: Comparison of X ray Absorption spectra of a VO2 film of 16 nm grown on TiO2. V L23 and O K edges were measured through the detection of the Auger electron yield at 464 eV (left) and at 507 eV (right) across the MIT transition. Experiments have been performed at the Aloisa beamline at Elettra. We will present here data collected on VO2 films using XAS and photoemission, measurements as a function of temperature across the metal insulator transition. In particular, we will report results of Resonant Photoemission and XANES spectra collected with the Auger yield (see Fig. 1) in order to establish a correlation between electronic and morphological properties and the presence of intermediate electronic configurations. We thank the Aloisa staff for the support at Elettra during the run of the Proposal N. 20160373 (Dynamic competition between insulating and metallic phase in VO2). References 1. J. Cao, J. Wu, Mat. Sci. Eng. 2011, R71, 35 52 doi:10.1016/j.mser.2010.08.001 2. E. Dagotto, Science 2005, 309, 257 262 doi:10.1126/science.1107559 3. N.B. Aetukur et al., Nature Physics 2013, 9, 661 666 doi:10.1038/nphys2733 4. H. Yoon et al., Nature Materials 2016, 15, 1113 1119 doi:10.1038/nmat4692 5. N. Poccia et al., Proc. Natl. Acad. Sci. U.S.A. 2012, 109, 15685 15690 doi:10.1073/pnas.1208492109 6. D. Di Gioacchino et al., Phys. Chem. Chem. Phys. 2016, 18, 12534 12540 doi:10.1039/c6cp01400c 7. G. Campi, et al., Nature 2015, 525, 359 362 doi:10.1038/nature14987 306 Superstripes 2017, Ischia June 4 10, 2017 8. A. Marcelli, Acta Phys. Pol. A 2016, 129, 264 269 doi:10.12693/APhysPolA.129.264 9. Sangwook Lee et al., Science 2017, 355, 371–374 doi:10.1126/science.aag0410 307 Superstripes 2017, Ischia June 4 10, 2017 56.2 Metal Insulator transitions in calcium ferrite compounds Akinori Irizawa 1, Hiroya Sakurai 2 1. Osaka University, Japan 2. NIMS, Japan Email: [email protected] u.ac.jp Keywords: calcium ferrite, MIT The crystal structure of both NaV2O4 and CaV2O4 is calcium ferrite type. It is reported that CaV2O4 is an insulator and shows an antiferromagnetic order at 78 K [1] and NaV2O4 undergoes antiferromagnetic transition while keeping the metal state at 140 K [2]. Calcium ferrite type vanadium oxide is characterized by a structure in which VO6 octahedrons are connected in a duplex chain with ridge sharing, so interesting physical properties are expected from both magnetic and electrical conductivity like the hollandite type vanadium oxide. These solid solution systems of Ca1 xNaxV2O4 can be synthesized in the whole range of x=0 to 1, and exhibit metal insulator transition in the intermediate solid solution region [3, 4]. In this study, optical measurement was performed on the change in the electronic state accompanying the difference in composition and temperature in this system. As a result, it was found that the size of the band gap estimated from the optical conductivity changes in the wide temperature range in the intermediate solid solution region as well as the change from the metallic state to the insulating state according to the composition. References 1. X. Zong, B. J. Suh, A. Niazi, J. Q. Yang, D. L. Schlagel, T. A. Lograsso and D. C. Johnston, Phys. Rev. B 77 014412 (2008). 2. K. Yamaura, M. Arai, A. Sato, A. B. Karki, D. P. Young, R. Movshovich, S. Okamoto, D. Mandrus and E. Takayama Muromachi, Phys. Rev. Lett. 99 196601 (2007). 3. H. Sakurai, Phys. Rev. B 78 094410 (2008). 4. H. Sakurai, A. Irizawa and T. Nanba, J. Phys.: Conf. Ser. 344 012013 (2012). 308 Superstripes 2017, Ischia June 4 10, 2017 56.3 Metal Insulator Transitions in Complex Oxides Probed by x ray inelastic scattering Bernardo Barbiellini Northeastern University Email: [email protected] Keywords: Metal Insulator Transitions, Complex Oxides, x ray Compton scattering The Coulomb repulsion in transition metal oxides (TMO) tends to localize individual d electrons on metal atoms while the hybridization with the oxygen p electron states de localizes these same electrons. These competing effects explain the metal insulating transition (MIT) in a TMO. Several theories have been put forward to explain the MIT, some generalize the concept of the Fermi liquid, while others attempt to describe highly correlated behavior by using Hubbard models. In this context, the comparison of the measured electron momentum density with the predictions of theories gives an indication of their correctness. Detecting the energy of photons scattered at a fixed angle in back scattering geometry from a mono energetic beam incident on the sample gives access to the Compton profile (CP), which is a projection onto one dimension of the electron momentum density. Here, we will provide examples for the Cuprates [1], the Manganites [2] and the Lithium battery materials [3]. 309 Superstripes 2017, Ischia June 4 10, 2017 Theoretical electronic structure of LSCO from Ref. [1]: (A) Band structure; (B) anisotropy of Compton profiles; (C) 2D EMD contribution between –0.4 eV and +0.1 eV; (D) 2D EMD contribution between –0.8 eV and –0.4 eV; and (E) 2D EMD contribution between –0.8 eV and +1.3 eV. Error bars in (B) indicate SEM. a.u., atomic units. References 1. Y. Sakurai, M. Itou, B. Barbiellini, P. E. Mijnarends, R. S. Markiewicz, S. Kaprzyk, J. M. Gillet, S. Wakimoto, M. Fujita, S. Basak, Y. J. Wang, W. Al Sawai, H. Lin, A. Bansil, and K. Yamada, Science 332, 698 (2011). 2. B. Barbiellini, A. Koizumi, P. E. Mijnarends, W. Al Sawai, H. Lin, T. Nagao, K. Hirota, M. Itou, Y. Sakurai, and A. Bansil, Phys. Rev. Lett. 102, 206402 (2009). 3. B Barbiellini, K Suzuki, Y Orikasa, S Kaprzyk, M Itou, K Yamamoto, Yung Jui Wang, H Hafiz, R Yamada, Y Uchimoto, A Bansil, Y Sakurai, H Sakurai, Appl. Phys. Lett. 109, (2016). 310 Superstripes 2017, Ischia June 4 10, 2017 56.4 Non local equation for the superconducting gap parameter S. Simonucci and G.C. Strinati The University of Camerino, Department of Physics Email: [email protected] Keywords: Superconducting gap parameter, non local effects, Cooper pair size A non local (integral) equation for the superconducting gap parameter is presented, which is obtained by a coarse graining procedure applied to the Bogoliubov deGennes (BdG) equations over the whole coupling vs temperature phase diagram associated with the superfluid phase. It is found that the limiting size of the coarse graining procedure, which is dictated by the range of the kernel of this integral equation, corresponds to the size of the Cooper pairs over the whole coupling vs temperature phase diagram up to the critical temperature, even when Cooper pairs turn into composite bosons on the BEC side of the BCS BEC crossover. A practical method is also implemented to solve numerically this integral equation in an efficient way, which is based on a novel algorithm for calculating the Fourier transforms. This method is tested for the case of an isolated vortex throughout the BCS BEC crossover and for all temperatures in the superfluid phase, which clarifies the kind of details that are disposed off by the coarse graining procedure on the BdG equations. Where the non local (integral) equation is expected to have its most exclusive applications, however, is in the context of the proximity effect, for which the finite size of Cooper pairs plays a crucial role and cannot be dealt with by using a local (differential) equation. A direct connection with experiments can be established in this context. Work along these lines is in progress. References 1. S. Simonucci and G.C. Strinati, Phys. Rev. B 89, 054511 (2014). 2. S. Simonucci, P. Pieri, and G.C. Strinati, Nature Phys. 11, 941 (2015). 3. S. Simonucci, P. Pieri, and G.C. Strinati, Phys. Rev. B 87, 214507 (2013). 4. S. Simonucci and G.C. Strinati (unpublished). 311 Superstripes 2017, Ischia June 4 10, 2017 56.5 Soft spins and Higgs mode in ruthenates Giniyat Khaliullin Max Planck Institute for Solid State Research, Stuttgart, Germany Email: [email protected] Keywords: spin orbit coupling I will discuss a special class of Mott insulators, where spin orbit coupling dictates a nonmagnetic ground state and the magnetic response is given by gapped singlet triplet excitations. Exchange interactions as well as crystalline electric fields may close the spin gap, resulting in a Bose condensation of spin orbit excitons. In addition to usual magnons, a Higgs amplitude mode, most prominent near quantum critical point, is expected. Upon electron doping, ferromagnetic correlations and triplet superconductivity may emerge. These predictions [1,2] will be discussed in the context of recent neutron and Raman light scattering experiments [3] in ruthenium oxides. References 1. G. Khaliullin, Phys. Rev. Lett. 111, 197201 (2013). 2. J. Chaloupka and G. Khaliullin, Phys. Rev. Lett. 116, 017203 (2016). 3. A. Jain et al., arXiv: 1510.07011; M. Souliou et al., (unpublished). 312 Superstripes 2017, Ischia June 4 10, 2017 57.1 Interplay of superconductivity and magnetism in Fe based superconductors under high pressure V. Ksenofontov1*, S. Shylin1, S. A. Medvedev2, P. Naumov2, G. Wortmann3, C. Felser2 1 Institut für Anorganische und Analytische Chemie, Johannes Gutenberg Universität, Mainz, Germany 2 Max Planck Institut für Chemische Physik fester Stoffe, Dresden, Germany 3 Department Physik, Universität Paderborn, Paderborn, Germany Email: ksenofon@uni mainz.de Keywords: pairing mechanism, iron based superconductors, Mössbauer effect, pressure The family of iron based superconductors is being intensively studied but the mechanism of superconductivity in these materials still remains enigmatic disputed. The currently available experimental data reveals that the structure, magnetism, and superconductivity strongly correlate in the iron based superconductors. One of the main aspects is the widely acknowledged scenario that magnetic fluctuations are responsible for the superconducting pairing. The application of pressure is a versatile and elegant tool to induce structural changes and consequently to investigate the interplay between magnetic and superconducting properties. Our study is focused on the simplest systems based mainly on FeSe, where magnetism, or nematic order, could be „switched off“ by doping or intercalation. The studies were conducted on Li/NH3 intercalated FeSe with Tc up to 44 K, and FeSe related compounds, namely the A1 xFe2 ySe2 (A = K, Rb, Cs, Tl) series of compounds belonging to the ThCr2Si2 type of structure with Tc values up to 33 K. The emergence of the superconducting state under pressure was investigated in conjunction with the magnetic properties of the respective material in the normal state. 313 Superstripes 2017, Ischia June 4 10, 2017 STM study of germanene Jincheng Zhuang, Xun Xu, Shi Xue Dou, and Yi Du Institute for Superconducting & Electronic Materials Email: [email protected] Keywords: germanene, STM, Raman We performed STM, ARPES, and in situ Raman spectroscopy studies combined with first principles calculations on the atomic structures, and the electronic and phonon properties of germanene on both Au(111) and Ag(111) substrates. The low buckled 1×1 germanene honeycomb lattice was explored. The linear dispersion of energy momentum and large Fermi velocity are derived from the pronounced quasiparticle interferences patterns in √3×√3 germanene. Moreover, a cone like dispersion with cone point locating at around 0.8 eV below the Fermi level is identified in the Brillion zone center due to the band folding effect by ARPES measurements. Our results present clear evidence for the existence of epitaxial germanene, and elucidate the massive Dirac fermions characteristics of germanene. 314 Superstripes 2017, Ischia June 4 10, 2017 Poster Session Micro XAS measures of the local structure changes in BaPb1 xBixO3 as a function of temperature Ruben Albertini1, Salvatore Macis2, Michael Di Gioacchino3,4, Andrej Ivanov5, Valentin Ivanov5, Alessandro Puri6, Virginia Monteseguro6, Gaetano Campi4, Augusto Marcelli3,7 P. Giraldo Gallo8, I.R. Fisher8 and Antonio Bianconi3 11Department of Mathematics and Physics, University of Rome Tre, Via della Vasca Navale 84, 00146 Rome, Itlay 2Department of Mathematics and Physics, University di Rome Tor Vergata, Via della Ricerca Scientifica 1, 00133 Rome, Italy 3Rome International Centre for Material Science Superstripes, RICMASS, via dei Sabelli 119A, 00185 Rome, Italy 4Institute of Crystallography, CNR, via Salaria Km 29.300, Monterotondo Roma, I 00015, Italy 5National Research Nuclear University MEPhI, Moscow Engineering Physics Institute, 115409 Moscow Kashirskoe shosse 31, Russia 6European synchrotron radiation facility, 71 Avenue des Martyrs, 38000 Grenoble, France 7Istituto Nazionale di Fisica Nucleare Laboratori Nazionali di Frascati, 00044, Frascati, Italy 8 Geballe Laboratory for Advanced Materials, Stanford University, Stanford, California 94305, USA Department of Physics, Stanford University, Stanford, California 94305, USA Email: [email protected] Keywords: Scanning micro XANES, superconductivity, BaPb1 xBixO3 It has been proposed that the multiscale fluctuations of the lattice structure are extremely important for the understanding of high temperature superconductivity and emergence of quantum coherence in biological matter. Recently, novel experimental approaches, like scanning micro x ray diffraction [1 7] and scanning micro XANES [8], have been developed to unveil statistical distribution of inhomogeneity extending from nanoscale to microscale. Micro XANES technique is the proper tool to investigate the local lattice structure probing multiple scattering resonances at the nanoscale [9]. In this work we investigate the local lattice spatial fluctuations in BaPb1 xBixO3 at the Pb L3 edge [10]. We have used the ID24 beamline at ESRF synchrotron in Grenoble [11] equipped with an energy dispersive XAS spectrometer and a unique setup for real space scanning and low temperature measurements with high quality data. The beamline setup (Figure 1) is composed by a set of mirrors in a Kirkpatrick–Baez geometry (vertical and horizontal focusing mirrors) that focus the white beam on a polychromator crystal, which split the beam. A second vertical mirror focuses the splitted beam on the sample, with a photon flux of 1014 ph/s . Passed through the sample, the beam is finally acquired by a 315 Superstripes 2017, Ischia June 4 10, 2017 Ge strip detector, equipped with an acquisition electronics with a readout time of 2.8 µs and minimum integration time of ∼80 ns. The absence of moving parts, due to the particular setup of the beamline, provides a 2 small and stable focal spot (5×5 m , at Pb and Bi L3 edges) necessary for the scanning micro XAS. The samples have been prepared at Stanford University. In order to span the superconducting dome and get evidence for the formation of local stripe like charge order we investigate a single crystal with x=0.19 as a function of temperature. As a matter of fact the bismuthate superconductors, similar to cuprates, seem characterized by a strong interplay between local distortion and electronic properties, so, for this reason, we are focusing our research on the real space distribution of the local lattice distortions as a function of temperature. The data show new features shading light on the relation between the superconductivity phase of the material and the distribution of the local lattice fluctuations. Figure 1: Beamline setup for scanning micro XANES. It is possible to see the three focusing mirrors, the polycromator crystal and the CCD Detector . References 1. N. Poccia, et al., Proc. of the Nat. Acad. Sci.109, 15685 15690 (2012). 2. A. Ricci, et al., Phys. Rev. B 84, 060511 (2011) 3. A. Ricci, et al., New Journal of Physics 16, 053030 (2014). 4. A. Ricci, et al., Scientific Reports 3, 2383 (2013). 5. N. Poccia, et al, Phys. Rev. B 84, 100504 (2011). 6. A. Ricci, et al, J. Supercond. Nov. Magn. 22, 305 308 (2009). 7. G. Campi, M. Di Gioacchino et al. arXiv:1705.09730 (2017) 8. N. Poccia et al., Applied Physics Letters 104, 221903 (2014). 9. A. Bianconi, S. Doniach, D. Lublin Chem. Phys. Lett. 59, 121 124 (1978). 10. P. Giraldo Gallo et al, Nature Communications 6, 8231 (2015) 11. S. Pascarelli, et al, J. Synchrotron Rad. 23, 353 368 (2016). 316 Superstripes 2017, Ischia June 4 10, 2017 Poster Session Levy flight distribution of fluctuation supramolecular structure of myelin Michael Di Gioacchino1,2, Gaetano Campi2, Antonio Bianconi1,2. 1Rome International Centre for Material Science Superstripes, RICMASS, via dei Sabelli 119A, 00185 Rome, Italy 2 Institute of Crystallography, CNR, via Salaria Km 29.300, Monterotondo Roma, I 00015, Italy. Email: [email protected] Keywords: micro X Ray Diffraction, Myelin, Correlated disorder, Levy flight distribution, Axon fluctuation. While the ultrastructure of the myelin, that surround the axons within the nerve has been considered to be a lyotropic liquid crystal, today it is crucial understanding its multiscale complex dynamics to relevant for its function, the degeneration and repair processes following neurological diseases and trauma. We focus our attention on the axons interactions, associated to the nerve functionality, measuring the spatial distribution of the orientational fluctuations of axons. Scanning micro X ray Diffraction (S XRD) is a technique already applied to layered superconducting materials [1,2], and biomaterials [3] but it is the ideal tool for investigation of the myelin sheath [4 7]. Here we use the S XRD as unique non invasive probe for mapping both k space and real space to visualize spatial statistical fluctuations of the orientation of axons bundle in a Xenopus laevis sciatic nerve. We find that the probability density function (PDF) of orientational spatial fluctuations of fresh axons shows a mesoscale correlated disorder described by Levy flight distribution. This marks the nerve functionality in fresh state of the just extracted nerve. We analyse also how this correlated disorder evolves during the degeneration of the nerve. We find that the spatial distribution of orientational fluctuations in unfresh axons shows a Gaussian behaviour. This indicates the loss of interaction between the axons. This work allows a deeper understanding of nerve states and paves the way to study other biomaterials with the same technique to detect and characterize their states and supramolecular structure, associated with dynamic structural changes at the nanoscale and mesoscale. 317 Superstripes 2017, Ischia June 4 10, 2017 Figure 1: Left panel) Two maps of axons orientation fluctuations given by Φ normalized to their mean value Φ0 of PNS myelin in axons of the sciatic nerve of a Xenopus Laevis in the fresh state, to the left, and unfresh state, to the right. Right panel) Probability density function (PDF) of the orientation fluctuations Φ/ Φ0 for fresh (red circles) and unfresh (blue squares) sample in semi log plot. References 1. G. Campi et al. , Inhomogeneity of charge density wave order and quenched disorder in a high Tc superconductor. Nature 525, 359 362 (2015). 2. A. Ricci et al. Networks of superconducting nano puddles in 1/8 doped YBa2Cu3O6.5+ y controlled by thermal manipulation. New Journal of Physics 16, 053030 (2014). 3. G. Campi. et al. Imaging collagen packing dynamics during mineralization of engineered bone tissue. Acta Biomaterialia 23, 309 316 (2015). 4. T. Ducic, et al. Structure and composition of myelinated axons: A multimodal synchrotron spectro microscopy study. Journal of Structural Biology 173, 202 212 (2011). 5. N. Poccia, et al. Changes of statistical structural fluctuations unveils an early compacted degraded stage of PNS myelin. Scientific Reports 4, 5430 (2014), doi:10.1038/srep05430 . 6. H. Inouye, et al. Myelin organization in the nodal, paranodal, and juxtapa ranodal regions revealed by scanning X Ray microdiffraction. PLOS ONE 9, e100592 (2014). 7. G. Campi, M. Di Gioacchino, N. Poccia, A. Ricci, M. Burghammer, A. Bianconi, Intrinsic dynamical fluctuation of PNS myelin ultrastructure. arXiv:1705.09730 (2017). 318 Superstripes 2017, Ischia June 4 10, 2017 Poster Session Low temperature scanning probe microscopy investigation of FeSe single crystals C. Di Giorgio1, A. Putilov1, E. Lechner1, D. Trainer1, A. Aladyshkin2, A. Melnikov2, O. S. Volkova3,4,5, A. N. Vasiliev3,4,5, D. A. Chareev4, 6 and M. Iavarone1 1 Department of Physics, Temple University, Philadelphia (USA) 2 Institute for Physics of Microstructures, Russian Academy of Sciences, Nizhni Novgorod (Russia) 3 Physics Faculty, M.V. Lomonosov Moscow State University, Moscow (Russia) 4 Theoretical Physics and Applied Mathematics Department, Ekaterinburg (Russia) 5 National University of Science and Technology “MISiS,” Moscow (Russia) 6 Institute of Experimental Mineralogy, Russian Academy of Sciences, Moscow District (Russia) Email: [email protected] FeSe is the most attracting material among the Fe based superconductors because it owns the simplest crystal structure as well as peculiar electronic and physical properties. It undergoes a tetragonal to orthorhombic structural transition at ~90K and a normal to superconducting transition at ~9K. Low temperature scanning tunneling microscopy and spectroscopy (STM/STS) experiments allow measurements of the local quasiparticle density of states as well as the visualization of the vortex lattice by spatially mapping the electronic local density of states at the Fermi energy. Here, we present STM/STS experiments on high quality FeSe single crystal. Multiband superconductivity, symmetry of the order parameter, role of disorder and vortex matter in this system will be discussed. Moreover, we will detail the occurrence of a vortex lattice transition. 319 Superstripes 2017, Ischia June 4 10, 2017 Poster Session Spin excitations in cuprates from spin cluster calculations Oleg Lychkovskiy, Boris Fine Skolkovo Institute of Science and Technology Email: [email protected] We theoretically study spin excitations in cuprate superconductors under the assumption that the system is divided into weakly interacting finite clusters of spins 1/2, possibly forming a checkerboard or a more disordered superstructure. We find that that some of the main features of the dynamic magnetic susceptibility computed on the basis of such a simple model exhibit promising agreement with the magnetic response measured in neutron scattering experiments. 320 Superstripes 2017, Ischia June 4 10, 2017 Poster Session High Tc in the organic superconductor Kx p Terphenyl by Fano resonances in superconducting gaps at the Lifshitz transition M.V. Mazziotti1, D. Innocenti2, A. Valletta3, G. Campi4, A. Bianconi1,4,5 A. Perali6 1RICMASS, Rome International Centre for Material Science Superstripes, Rome, Italy 2Department of Chemistry, University of Liverpool, UK 3 IMM, CNR, Roma, Italy 4IC, CNR, 00015 Monterotondo Roma, Italy 5National Research Nuclear University MEPhI (Moscow Engineering Physics Institute) Moscow Russia 6 School of Pharmacy, Physics Unit, University of Camerino, Camerino, Italy Email: [email protected] Keywords: superlattices; atomic layers; atomic wires; Lifshitz transitions. A potassium doped aromatic hydrocarbon p Terphenyl shows the highest critical temperature for the onset of superconductivity between 43 K and 123 K in organic materials [1 2]. This achievement provides the record for the highest Tc in an organic superconductor overcoming the previous record of Tc=38 K in organics [3,4]. Here we propose that the driving mechanism is the quantum resonance between superconducting gaps near a Lifshitz transition which belongs to the class of Fano resonances called shape resonances [5 8]. For the case of Kx p Terphenyl our numerical solutions of the multi gap equation shows that high Tc is driven by tuning the chemical potential by K doping and it appears only in a narrow energy range near a Lifshitz transition in the conduction band [9]. Results of the Bianconi Perali Valletta BPV theory [5 8].for the superconducting state properties as a function of the energy separation from the Lifshitz transition for the appearing of a new Fermi surface are plotted in Fig. 1. Panel (A) of Fig. 1 shows the superconducting critical temperature for Kx p Terphenyl and corresponding isotope coefficient is plotted as a function of the reduced Lifshitz parameter ξ= ( En)/ω0, where is the chemical potential, which is tuned by increasing potassium content, En is the energy of the bottom of the n th band and ω0=145 meV is the energy cut off for the pairing interaction. The critical temperature is below 1 K but reaches a maximum of 123 K only over a limited range of potassium doping such that the energy range of the chemical potential is about 300 meV around the Lifshitz transition. The maximum of Tc is located at the Lifshitz transion for opening a neck which is a 2D 1D topological crossover. At the maximum critical temperature, Tc=123 K, the condensate in the appearing new small Fermi surface pocket is in the BCS BEC crossover while the Tc drops below 0.3 K in the BEC regime. Finally we predict the experimental results which can support or falsify our proposed mechanism: the variation of the gap ratios as a function of the critical temperature of Tc, shown in panel B). Finally we 321 Superstripes 2017, Ischia June 4 10, 2017 want to remark that tuning the chemical potential of a strongly correlated metal near the Lifshitz transition a frustrated phase separation occurs [9,10] as it has been observe in diborides [11], cuprates [12,13] therefore it is predicted to show up in Kx p Terphenyl. A) B) Figure 1: Panel A) The critical temperature Tc and isotope coefficient of Kx p Terphenyl as a function of the Lifshitz parameter ξ= ( En)/ω0, is the chemical potential, En is band edge energy of the n th band and ω0=145 meV is the energy cut off for the pairing interaction. Panel B) The gap ratios as a function of Tc . References 1. R. S. Wang et al. (March 2017) Arxiv:1703.06641 2. H. Li et al. (April 2017) Arxiv:1704.04230 3. A. Y. Ganin et al. Nature Materials 7, 367 (2008). 4. Y. Kubozono et al. Physical Chemistry Chemical Physics, 13, 16476 (2011). 5. A. Perali et al. Supercond. Sci. Technol., 25, 124002 (2012). 6. R. Caivano et al. Supercond. Sci. Technol., 22, 014004 (2009). 7. D. Innocenti et al. Supercond. Nov. Magn., 24, 1137 (2011). 8. A. Bianconi, Nature Physics, 9, 536 (2013). 9. M.V. Mazziotti, A. Valletta, G. Campi, D. Innocenti, A. Perali, A. Bianconi (May 2017) arXiv:1705.09690 10. K.I. Kugel et al. Phys. Rev. B, 78, 165124 (2008). 11. A. Bianconi et al. Supercond. Sci. Technol. 28, 024005 (2015). 12. G. Campi et al., Eur. Phys. J. B, 52, 15 (2006). 13. G. Campi et al. Nature, 525, 359 (2015). 14. A. Ricci, et al. New Journal of Physics 16, 053030 (2014). 322 Superstripes 2017, Ischia June 4-10, 2017 Authors Index Abbamonte P...... 261 Aeppli G...... 204 Alarco J.A...... 52 Albertini R...... 315 Aoki D...... 262 Attanasio C...... 222 Avigo I...... 135 Babaev E...... 251 Bachar N...... 218 Badoux S...... 122 Balakirev F.F...... 208 Balicas L...... 157 Bao W...... 72 Barbiellini B...... 309 Berciu M...... 121 Berthod C...... 236 Bianconi A...... 151 Billinge S.J.L...... 100 Bonca J...... 143 Boris A...... 114 Borisenko S...... 177 Borzenets I...... 191 Bozin E.S...... 271 Brazovskii S...... 161 Brun C...... 263 Bussmann-Holder A...... 20 Capone M...... 165 Carlström J...... 85 Chang J...... 32 Chávez I...... 245 Chu P.C.W...... 94 Conradson S.D...... 13 Coslovich G...... 226 Crisan A...... 128 Daghero D...... 69 de Llano M...... 244 de’ Medici L...... 81 Dean M. P. M...... 104 Degiorgi L...... 14 Destraz D...... 193 Deutscher G...... 12 Di Gioacchino M...... 317 Di Giorgio C...... 319 Dobrosavljevic V...... 111 Drechsler S.L...... 86 323 Superstripes 2017, Ischia June 4 10, 2017 Efremov D...... 89 Egami T...... 22 Einaga M...... 156 Eremets M.I...... 146 Eremin I...... 207 Eremin M...... 279 Fanfarillo L...... 286 Farina D...... 93 Feng S...... 109 Fine B.V...... 232 Fink J...... 178 Flammia L...... 246 Frésard R...... 223 Fujimori A...... 95 Fujita M...... 35 Galda A...... 297 Giannetti C...... 138 Glatz A...... 281 Goncharov A.F...... 147 Goto H...... 186 Goto Y...... 57 Gray A.X...... 115 Grilli M...... 163 Grochala W...... 59 Guguchia Z...... 126 Guidi T...... 215 Guo H...... 224 Guzman Verri G.G...... 73 Hanaguri T...... 118 Hayden S...... 30 Hess C...... 287 Huecker M...... 107 Iavarone M...... 132 Ideue T...... 288 Imada M...... 99 Irizawa A...... 308 Ivanov A.A...... 302 Jackeli G...... 225 Joon E...... 171 Jurkutat M...... 48 Kanazawa I...... 278 Kapcia K.J...... 229 Kataev V...... 211 Kato R...... 173 Khaliullin G...... 312 Khomskii D.I...... 29 Kimura A...... 41 324 Superstripes 2017, Ischia June 4 10, 2017 Kimura T...... 74 Kirova N...... 136 Knebel G...... 268 Kokalj J...... 175 Kolodziej J.J...... 83 Komarek A.C...... 270 Kontani H...... 28 Kresin V...... 27 Kruger F...... 292 Krzton Maziopa A...... 275 Ksenofontov V...... 313 Kubozono Y...... 39 Langerome B...... 75 Larkin T.I...... 61 Leridon B...... 70 Littlewood P...... 205 Liu C...... 187 Lorenzana J...... 239 Louca D...... 65 Luo J...... 62 Lychkovskiy O...... 320 Madan I...... 298 Maeno Y...... 18 Marcelli A...... 305 Markiewicz R.S...... 67 Marsiglio F...... 155 Massarotti D...... 220 Mazziotti M.V...... 321 Mazzoli C...... 101 McNally D.E...... 296 Mertelj T...... 139 Mesaros A...... 108 Miletto Granozio F...... 283 Mironov A. Yu...... 240 Miyasaka S...... 119 Mizuguchi Y...... 56 Mizukami Y...... 197 Moewes A...... 185 Momono N...... 33 Monney C...... 184 Moreo A...... 202 Moroni M...... 144 Moskvin A.S...... 169 Mukhin S.I...... 167 Mustre de León J...... 159 Nattermann T...... 241 Neilson D...... 188 325 Superstripes 2017, Ischia June 4 10, 2017 Nissinen J...... 113 Oda M...... 133 Oles A.M...... 255 Orgad D...... 45 Orth P.P...... 124 Ovchinnikov S.G...... 206 Pelliciari J...... 79 Peng Y...... 237 Perali A...... 253 Perring T...... 110 Pomarico E...... 216 Ponomarenko L.A...... 190 Popović D...... 43 Prassides K...... 16 Ptok A...... 231 Pudalov V...... 214 Purans J...... 257 Puzniak R...... 130 Quader K...... 212 Raimondi R...... 210 Rajasekaran S...... 299 Renner Ch...... 209 Reznik D...... 17 Robinson I.K...... 102 Roy P...... 259 Sanna S...... 195 Sato M...... 249 Schmitt T...... 256 Schneider W. D...... 54 Seibold G...... 116 Semenov A.G...... 221 Shengelaya A...... 51 Shi M...... 179 Shimizu K...... 148 Shimojima T...... 176 Silaev M...... 276 Silhanek A.V...... 181 Soh Y. Ah ...... 63 Soldatov A.V...... 304 Spera M...... 300 Spivak B...... 82 Steppke A...... 290 Stornaiuolo D...... 285 Strinati Calvanese G...... 311 Sumida K...... 265 Sunko V...... 273 Sushkov O.P...... 112 326 Superstripes 2017, Ischia June 4 10, 2017 Tafuri F...... 180 Tallon J...... 153 Tanatar B...... 92 Tanner D.B...... 106 Teitel’baum G...... 97 Terao T...... 77 Timusk T...... 149 Toda Y...... 141 Tortello M...... 55 Tripathi V...... 242 Truccato M...... 46 Tsuchiizu M...... 84 Uemura Y.J...... 24 van der Marel D...... 37 van Wezel J...... 162 Vanacore G.M...... 140 Vargas Paredes A.A...... 247 Vinokur V.M...... 201 von Rohr F...... 194 Wahl P...... 234 Wall S...... 294 Wirth S...... 267 Wohlfeld K...... 199 Wysokiński K.I...... 252 Wysokinski M.M...... 227 Yanagisawa T...... 90 Yoshida Y...... 117 Zaanen J...... 200 Zaikin A.D...... 183 Zhigadlo N.D...... 49 Zhuang J...... 314 Zwicknagl G...... 269 327