DOCSLIB.ORG

Electronic and Transport Properties of Weyl Semimetals

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text

Load more

Electronic and Transport Properties of Weyl Semimetals Dissertation Presented in Partial Fulfillment of the Requirements for the Degree Doctor of Philosophy in the Graduate School of The Ohio State University By Timothy M. McCormick, B.S. Graduate Program in Physics The Ohio State University 2018 Dissertation Committee: Professor Nandini Trivedi, Advisor Professor Yuri Kovchegov Professor Mohit Randeria Professor Rolando Valdes Aguilar c Copyright by Timothy M. McCormick 2018 Abstract Topological Weyl semimetals have attracted substantial recent interest in con- densed matter physics. In this thesis, we theoretically explore electronic and transport properties of these novel materials. We also present results of experimental collabora- tions that support our theoretical calculations. Topological Weyl semimetals (TWS) can be classified as type-I TWS, in which the density of states vanishes at the Weyl nodes, and type-II TWS, in which an electron pocket and a hole pocket meet at a singular point of momentum space, allowing for distinct topological properties. We consider various minimal lattice models for type-II TWS. We present the discovery of a type II topological Weyl semimetal (TWS) state in pure MoTe2, where two sets of WPs (W2±, W3±) exist at the touching points of electron and hole pockets and are located at different binding energies above EF . Using ARPES, modeling, DFT and calculations of Berry curvature, we identify the Weyl points and demonstrate that they are connected by different sets of Fermi arcs for each of the two surface terminations. Weyl semimetals possess low energy excitations which act as monopoles of Berry curvature in momentum space. These emergent monopoles are at the heart of the extensive novel transport properties that Weyl semimetals exhibit. We show how the Nernst effect, combining entropy with charge transport, gives a unique signature for the presence of Dirac bands. The Nernst thermopower of NbP (maximum of 800 ii µV·K−1 at 9 T, 109 K) exceeds its conventional thermopower by a hundredfold and is significantly larger than the thermopower of traditional thermoelectric materials. The Nernst effect has a pronounced maximum near TM = 90±20K = µ0=kB (µ0 is chemical potential at T = 0 K). A self-consistent theory without adjustable parameters shows that this results from electrochemical potential pinning to the Weyl point energy at T ≥ TM , driven by charge neutrality and Dirac band symmetry. We propose that Fermi arcs in Weyl semimetals lead to an anisotropic magne- tothermal conductivity, strongly dependent on externally applied magnetic field and resulting from entropy transport driven by circulating electronic currents. The circu- lating currents result in no net charge transport, but they do result in a net entropy transport. This translates into a magnetothermal conductivity that should be a unique experimental signature for the existence of the arcs. We analytically calculate the Fermi arc-mediated magnetothermal conductivity in the low-field semiclassical limit as well as in the high-field ultra-quantum limit, where only the chiral Landau levels are involved. By numerically including the effects of higher Landau levels, we show how the two limits are linked at intermediate magnetic fields. This work pro- vides the first proposed signature of Fermi arc-mediated thermal transport and sets the stage for utilizing and manipulating the topological Fermi arcs in experimental thermal applications. iii To my parents, who inspired my love of science. iv Acknowledgments There are many people who have been indispensible during my time in graduate school. First and foremost, I extend my deepest thanks to my advisor, Professor Nandini Trivedi. Her guidance and support were invaluable during my time here and she was a superb role model for how one should attack an unstructured problem. I can only hope that I picked up some of her physical insight during my time here. I am particularly indebted to her for the many opportunities that I had to collaborate with excellent experimentalists and theorists, as well as to attend several truly amazing conferences in the US and abroad. My time here would have been much less productive had it not been for the won- derful collaborations that I have been apart of. I thank Professor Adam Kaminski for the opportunity to collaborate on the ARPES discovery of type-II Weyl semimetal MoTe2. I am deeply grateful to Professor Jos Heremans and his student Sarah Watz- man for our many collaborations on transport phenomena in Weyl semimetals. From them I learned how truly messy yet rewarding studying transport can be. Much of this thesis was inspired by their excellent experiments. I am thankful to Professor Mohit Randeria, whose precise questions always got to the heart of a matter and were the source of many illuminating discussions on anomalous transport in Skyrmions. I also had the pleasure of collaborating with a very hard-working undergraduate student, Robert McKay, who was as ideal a mentee as I could ask for. v The Trivedi and Randeria groups were close to a second family to me during my time here. I follow in the footsteps of Will Cole, Mason Swanson, Eric Duchon, Onur Erten, and Nganba Meetei, who all helped to shape my physical intuition. I am particularly thankful for their infinite patience in answering the many questions of a new member of the group. I thank Hasan Khan, James Rowland, Tamaghna Hazra, Po-Kuan Wu, Wenjuan Zhang, Tim Gao, Kyungmin Lee, Kyusung Hwang, David Nozadze, Mehdi Kargarian, and Sumilan Banerjee for their discussions and companionship. I was also fortunate to have the best office-mates that I could ask for in Blythe Moreland and Jiaxin Wu. The condensed matter theory group is particularly lively at Ohio State. My time here was greatly enriched by the many interactions with other students, postdocs, and professors. I extend my thanks to Professor Ilya Gruzberg, Professor Jason Ho, and Professor Yuan-Ming Lu for teaching several excellent classes. I always found their doors open for questions and discussion. My friends and family provided a backbone of support while I completed my dissertation. I thank Jon Zizka, Andrew Hausman, Jake Kerrigan, Drew Gallagher, Chris Wolfe, Marci Howdyshell, Adam Ahmed, Simran Singh, Jyoti Katoch, Igor Pinchuk, Chris Ehemann, Dennis Bazow, and Dante O'Hara for always always being there for me. I thank my wife, Beth McCormick, for her love and support. I also thank my parents for their constant love and encouragement. Last but certainly not least, I would like to thank the NSF and the Center for Emergent Materials for funding the majority of my research. I also acknowledge the OSU presidential fellowship for funding my final year. vi Vita January 24, 1990 . Born - Wilmington, DE, USA 2012 . .B.S. Physics Publications Research Publications Timothy M. McCormick, Sarah J. Watzman, Joseph P. Heremans, Nandini Trivedi, \Fermi arc mediated entropy transport in topological semimetals" Phys. Rev. B 97, 195152 (2018). Sarah J. Watzman, Timothy M. McCormick, Chandra Shekhar, Shu-Chun Wu, Yan Sun, Arati Prakash, Claudia Felser, Nandini Trivedi, Joseph P. Heremans, \Dirac dispersion generates unusually large Nernst effect in Weyl semimetals" Phys. Rev. B 97, 161404 (2018). Timothy M. McCormick, Robert C. McKay, Nandini Trivedi, \Semiclassical the- ory of anomalous transport in type-II topological Weyl semimetals" Phys. Rev. B 96, 235116 (2017) Joseph R. Smith, Amber Byrum, Timothy M. McCormick, Nathan Young, Christo- pher Orban, and Christopher D. Porter, \A controlled study of stereoscopic virtual re- ality in freshman electrostatics" Physics Education Research Conference Series 2017, 363 (2017). Timothy M. McCormick, Itamar Kimchi, Nandini Trivedi, \Minimal models for topological Weyl semimetals" Phys. Rev. B 95, 075133 (2017). Lunan Huang, Timothy M. McCormick, Masayuki Ochi, Zhiying Zhao, Michi-to Suzuki, Ryotaro Arita, Yun Wu, Daixiang Mou, Huibo Cao, Jiaqiang Yan, Nandini vii Trivedi, Adam Kaminski, \Spectroscopic evidence for type II Weyl semimetal state in MoTe2" Nature Materials 15, 1155-1160 (2016). Timothy M. McCormick, Nandini Trivedi, \Tuning the Chern number and Berry curvature with spin-orbit coupling and magnetic textures" Phys. Rev. A 91, 063609 (2015). Fields of Study Major Field: Physics viii Table of Contents Page Abstract . ii Dedication . iv Acknowledgments . .v Vita......................................... vii List of Tables . xii List of Figures . xiii 1. Introduction . .1 2. Topology in Solid State Systems . .5 2.1 Berry Phase . .6 2.1.1 Berry Curvature . .8 2.1.2 Chern Number . 10 2.2 Chern Insulators . 11 2.2.1 Berry Curvature of a 2-Band Hamiltonian . 12 2.2.2 Chern Insulator on the Square Lattice . 13 2.2.3 Chiral Edge Modes . 15 3. Introduction to Weyl Semimetals . 18 3.1 Weyl Fermions . 19 3.1.1 Weyl Fermions in Quantum Materials . 21 3.2 Lattice Models for Weyl Semimetals . 26 3.3 Type II Weyl Semimetals . 30 ix 3.3.1 Time Reversal Breaking Model . 33 3.3.2 Inversion Breaking Model . 42 3.3.3 Surface States: Topological and Track . 46 3.3.4 Comparison with Experiments . 53 3.3.5 Conclusions . 55 3.4 Experimental Discovery of Weyl Semimetal MoTe2 ......... 56 3.4.1 ARPES Results . 59 3.4.2 DFT and Topological Analysis . 65 4. Thermoelectric Transport in Weyl Semimetals . 67 4.1 Boltzmann Transport Theory . 68 4.1.1 Definition of Transport Coefficients . 68 4.1.2 Boltzmann formalism . 71 4.2 Nernst Effect of Isotropic Weyl Nodes . 75 4.2.1 Numerical Results . 80 4.2.2 Analytic Results . 81 4.2.3 Nernst Thermopower in Weyl Semimetal NbP . 83 4.3 Anomalous Transport in Type-II Weyl Semimetals . 86 4.3.1 Model . 88 4.3.2 Anomalous Transport . 94 4.3.3 Relation to Measurable Quantities . 102 4.3.4 Discussion and Conclusion . 103 5. Fermi Arc-Mediated Entropy Transport in Weyl Semimetals . 106 5.1 Fermi arc-mediated magnetothermal transport .
Recommended publications
  • DFT Quantization of the Gibbs Free Energy of a Quantum Body

    DFT Quantization of the Gibbs Free Energy of a Quantum Body

    DFT quantization of the Gibbs Free Energy of a quantum body S. Selenu (Dated: December 2, 2020) In this article it is introduced a theoretical model made in order to perform calculations of the quantum heat of a body that could be acquired or delivered during a thermal transformation of its quantum states. Here the model is mainly targeted to the electronic structure of matter[1] at the nano and micro scale where DFT models have been frequently developed of the total energy of quantum systems. De fining an Entropy functional S[ρ] makes us able optimizing a free energy G[ρ] of the quantum system at finite temperatures. Due to the generality of the model, the latter can be also applied to several first principles computational codes where ab initio modelling of quantum matter is asked. INTRODUCTION thermal transformations at a fi nite temperature T . This work could then be consid- This article will be focused on a study based on the ered as the begining part of a more general theory can derivation of the quantum electrical heat absorbed or ei- include an ab initio modelling of the first law and second ther released by a physical system made of atoms and law of thermodynamics[13], where heat and free energy electrons either at the nano or at the microscopic scale, variations of a quantum body are taken into account. In extending to it the concept of thermal heat within a DFT fact it is actually considered a quantum system of elec- model. Also, the latter being fundamental in physics, can trons at a given temperature T in thermal equilibrium be employed for a full understanding of the thermal phase with its surrounding.
  • Resonance As a Measure of Pairing Correlations in the High-Tc

    Resonance As a Measure of Pairing Correlations in the High-Tc

    letters to nature ................................................................. lost while magnetic (spin) ¯uctuations centred at the x =0 6±11 Resonance as a measure of pairing antiferromagnetic Bragg positionsÐoften referred to as Q0 = (p, p)±persist. For highly doped (123)O6+x, the most prominent feature in the spin ¯uctuation spectrum is a sharp resonance that correlations in the high-Tc appears below Tc at an energy of 41 meV (refs 6±8). When scanned superconductor YBa Cu O at ®xed frequency as a function of wavevector, the sharp peak is 2 3 6.6 centred at (p, p) (refs 6±8) and its intensity is unaffected by a 11.5- 19 Pengcheng Dai*, H. A. Mook*, G. Aeppli², S. M. Hayden³ & F. DogÏan§ T ®eld in the ab-plane . In our underdoped (123)O6.6 (Tc = 62.7 K)9, the resonance occurs at 34 meV and is superposed on a * Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831-6393, USA continuum which is gapped at low energies11. For frequencies below ² NEC Research Institute, Princeton, New Jersey 08540, USA ³ H. H. Wills Physics Laboratory, University of Bristol, Bristol BS8 1TL, UK § Department of Materials Science and Engineering, University of Washington, Seattle, Washington 98195, USA B rotated 20.6° from the c-axis B along the [3H,-H,0] direction 2.0 2.0 .............................................................................................................................................. a d [H,3H,0] One of the most striking properties of the high-transition-tem- 1.5 1.5 perature (high-Tc) superconductors is that they are all derived [H, (5-H)/3, 0] from insulating antiferromagnetic parent compounds. The inti- 1.0 B ∼ i c-axis 1.0 B i ab-plane mate relationship between magnetism and superconductivity in these copper oxide materials has intrigued researchers from the [0,K,0] (r.l.u.) [0,K,0] (r.l.u.) 0.5 0.5 outset1±4, because it does not exist in conventional superconduc- 20.6° tors.
  • A Simple Method to Estimate Entropy and Free Energy of Atmospheric Gases from Their Action

    A Simple Method to Estimate Entropy and Free Energy of Atmospheric Gases from Their Action

    Article A Simple Method to Estimate Entropy and Free Energy of Atmospheric Gases from Their Action Ivan Kennedy 1,2,*, Harold Geering 2, Michael Rose 3 and Angus Crossan 2 1 Sydney Institute of Agriculture, University of Sydney, NSW 2006, Australia 2 QuickTest Technologies, PO Box 6285 North Ryde, NSW 2113, Australia; [email protected] (H.G.); [email protected] (A.C.) 3 NSW Department of Primary Industries, Wollongbar NSW 2447, Australia; [email protected] * Correspondence: [email protected]; Tel.: + 61-4-0794-9622 Received: 23 March 2019; Accepted: 26 April 2019; Published: 1 May 2019 Abstract: A convenient practical model for accurately estimating the total entropy (ΣSi) of atmospheric gases based on physical action is proposed. This realistic approach is fully consistent with statistical mechanics, but reinterprets its partition functions as measures of translational, rotational, and vibrational action or quantum states, to estimate the entropy. With all kinds of molecular action expressed as logarithmic functions, the total heat required for warming a chemical system from 0 K (ΣSiT) to a given temperature and pressure can be computed, yielding results identical with published experimental third law values of entropy. All thermodynamic properties of gases including entropy, enthalpy, Gibbs energy, and Helmholtz energy are directly estimated using simple algorithms based on simple molecular and physical properties, without resource to tables of standard values; both free energies are measures of quantum field states and of minimal statistical degeneracy, decreasing with temperature and declining density. We propose that this more realistic approach has heuristic value for thermodynamic computation of atmospheric profiles, based on steady state heat flows equilibrating with gravity.
  • Holographic Topological Semimetals Arxiv:1911.07978V1 [Hep-Th]

    Holographic Topological Semimetals Arxiv:1911.07978V1 [Hep-Th]

    Holographic Topological Semimetals Karl Landsteiner Instituto de Física Teórica UAM/CSIC, C/ Nicolás Cabrera 13-15, Campus Cantoblanco, 28049, Spain E-mail: [email protected] Yan Liu Center for Gravitational Physics, Department of Space Science, Beihang University, Beijing 100191, China Key Laboratory of Space Environment Monitoring and Information Processing, Ministry of Industry and Information Technology, Beijing, China E-mail: [email protected] Ya-Wen Sun School of physics & CAS Center for Excellence in Topological Quantum Computation, University of Chinese Academy of Sciences, Beijing 100049, China Kavli Institute for Theoretical Sciences, University of Chinese Academy of Sciences, Beijing 100049, China E-mail: [email protected] Abstract The holographic duality allows to construct and study models of strongly cou- pled quantum matter via dual gravitational theories. In general such models are characterized by the absence of quasiparticles, hydrodynamic behavior and Planck- ian dissipation times. One particular interesting class of quantum materials are ungapped topological semimetals which have many interesting properties from Hall transport to topologically protected edge states. We review the application of the holographic duality to this type of quantum matter including the construction of holographic Weyl semimetals, nodal line semimetals, quantum phase transition to arXiv:1911.07978v1 [hep-th] 18 Nov 2019 trivial states (ungapped and gapped), the holographic dual of Fermi arcs and how new unexpected transport properties,
  • Hear the Sound of Weyl Fermions

    Hear the Sound of Weyl Fermions

    PHYSICAL REVIEW X 9, 021053 (2019) Featured in Physics Hear the Sound of Weyl Fermions Zhida Song1,2 and Xi Dai1,* 1Department of Physics, Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong 2Department of Physics, Princeton University, Princeton, New Jersey 08544, USA (Received 4 February 2019; revised manuscript received 10 April 2019; published 17 June 2019) Quasiparticles and collective modes are two fundamental aspects that characterize quantum matter in addition to its ground-state features. For example, the low-energy physics for Fermi-liquid phase in He-III is featured not only by fermionic quasiparticles near the chemical potential but also by fruitful collective modes in the long-wave limit, including several different sound waves that can propagate through it under different circumstances. On the other hand, it is very difficult for sound waves to be carried by electron liquid in ordinary metals due to the fact that long-range Coulomb interaction among electrons will generate a plasmon gap for ordinary electron density oscillation and thus prohibits the propagation of sound waves through it. In the present paper, we propose a unique type of acoustic collective mode in Weyl semimetals under magnetic field called chiral zero sound. Chiral zero sound can be stabilized under the so-called “chiral limit,” where the intravalley scattering time is much shorter than the intervalley one and propagates only along an external magnetic field for Weyl semimetals with multiple pairs of Weyl points. The sound velocity of chiral zero sound is proportional to the field strength in the weak field limit, whereas it oscillates dramatically in the strong field limit, generating an entirely new mechanism for quantum oscillations through the dynamics of neutral bosonic excitation, which may manifest itself in the thermal conductivity measurements under magnetic field.
  • Arxiv:2008.10628V3 [Cond-Mat.Str-El] 14 Jan 2021

    Arxiv:2008.10628V3 [Cond-Mat.Str-El] 14 Jan 2021

    Prediction of Spin Polarized Fermi Arcs in Quasiparticle Interference of CeBi Zhao Huang,1 Christopher Lane,1, 2 Chao Cao,3 Guo-Xiang Zhi,4 Yu Liu,5 Christian E. Matt,5 Brinda Kuthanazhi,6, 7 Paul C. Canfield,6, 7 Dmitry Yarotski,2 A. J. Taylor,2 and Jian-Xin Zhu1, 2, * 1Theoretical Division, Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA 2Center for Integrated Nanotechnology, Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA 3Department of Physics, Hangzhou Normal University, Hangzhou 310036, China 4Department of Physics, Zhejiang University, Hangzhou 310013, China 5Department of Physics, Harvard University, Cambridge, Massachusetts 02138, USA 6Ames Laboratory, Iowa State University, Ames, Iowa 50011, USA 7Department of Physics and Astronomy, Iowa State University, Ames, Iowa 50011, USA (Dated: January 15, 2021) We predict that CeBi in the ferromagnetic state is a Weyl semimetal. Our calculations within density func- tional theory show the existence of two pairs of Weyl nodes on the momentum path (0,0,kz) at 15 meV above and 100 meV below the Fermi level. Two corresponding Fermi arcs are obtained on surfaces of mirror- symmetric (010)-oriented slabs at E = 15 meV and both arcs are interrupted into three segments due to hy- bridization with a set of trivial surface bands. By studying the spin texture of surface states, we find the two Fermi arcs are strongly spin-polarized but in opposite directions, which can be detected by spin-polarized ARPES measurements. Our theoretical study of quasiparticle interference (QPI) for a nonmagnetic impurity at the Bi site also reveals several features related to the Fermi arcs.
  • Proximity to a Critical Point Driven by Electronic Entropy in Uru2si2

    Proximity to a Critical Point Driven by Electronic Entropy in Uru2si2

    www.nature.com/npjquantmats ARTICLE OPEN Proximity to a critical point driven by electronic entropy in URu2Si2 ✉ Neil Harrison 1 , Satya K. Kushwaha1,2, Mun K. Chan 1 and Marcelo Jaime 1 The strongly correlated actinide metal URu2Si2 exhibits a mean field-like second order phase transition at To ≈ 17 K, yet lacks definitive signatures of a broken symmetry. Meanwhile, various experiments have also shown the electronic energy gap to closely resemble that resulting from hybridization between conduction electron and 5f-electron states. We argue here, using thermodynamic measurements, that the above seemingly incompatible observations can be jointly understood by way of proximity to an entropy-driven critical point, in which the latent heat of a valence-type electronic instability is quenched by thermal excitations across a gap, driving the transition second order. Salient features of such a transition include a robust gap spanning highly degenerate features in the electronic density of states, that is weakly (if at all) suppressed by temperature on approaching To, and an elliptical phase boundary in magnetic field and temperature that is Pauli paramagnetically limited at its critical magnetic field. npj Quantum Materials (2021) 6:24 ; https://doi.org/10.1038/s41535-021-00317-6 1234567890():,; INTRODUCTION no absolute requirement for the magnitude of a hybridization gap URu2Si2 remains of immense interest owing to the possibility to vanish at a phase transition, it need not be thermally of it exhibiting a form of order distinct from that observed
  • Interaction and Temperature Effects on the Magneto-Optical Conductivity Of

    Interaction and Temperature Effects on the Magneto-Optical Conductivity Of

    Interaction and temperature effects on the magneto-optical conductivity of Weyl liquids S. Acheche, R. Nourafkan, J. Padayasi, N. Martin, and A.-M. S. Tremblay D´epartement de physique; Institut quantique; and Regroupement qu´eb´ecois sur les mat´eriauxde pointe; Universit´ede Sherbrooke; Sherbrooke; Qu´ebec; Canada J1K 2R1 (Dated: July 29, 2020) Negative magnetoresistance is one of the manifestations of the chiral anomaly in Weyl semimetals. The magneto-optical conductivity also shows transitions between Landau levels that are not spaced as in an ordinary electron gas. How are such topological properties modified by interactions and temperature? We answer this question by studying a lattice model of Weyl semimetals with an on-site Hubbard interaction. Such an interacting Weyl semimetal, dubbed as Weyl liquid, may be realized in Mn3Sn. We solve that model with single-site dynamical mean-field theory. We find that in a Weyl liquid, quasiparticles can be characterized by a quasiparticle spectral weight Z, although their lifetime increases much more rapidly as frequency approaches zero than in an ordinary Fermi liquid. The negative magnetoresistance still exists, even though the slope of the linear dependence of the DC conductivity with respect to the magnetic field is decreased by the interaction. At elevated temperatures, a Weyl liquid crosses over to bad metallic behavior where the Drude peak becomes flat and featureless. We comment on the effect of a Zeeman term. I. INTRODUCTION nodes.11,12 This is a consequence of the parabolic density of states. It has been observed in the low-temperature, low-frequency optical spectroscopy of the known Weyl Weyl semimetals are three-dimensional (3D) analogs of 13 graphene with topologically protected band crossings and semimetal TaAs.
  • It's Been a Weyl Coming

    It's Been a Weyl Coming

    CONDENSED MATTER It’s been a Weyl coming Condensed-matter physics brings us quasiparticles that behave as massless fermions. B. Andrei Bernevig “Mathematizing may well be a creative activity of man, like language or music”1 — so said Hermann Weyl, the German physicist whose penchant for mathematical elegance prompted his prediction that a new particle would arise when the fermionic mass in the Dirac equation vanished2. Such a particle could carry charge but, unlike all known fermions, would be massless. During the course of his career, Weyl actually fell out of love with his prediction, largely because it implied the breaking of a particular symmetry, known as parity, which at the time was thought to be obeyed. More to the point, no such particle was observed during his lifetime. After his death, the Weyl fermion was proposed to describe neutrinos, which are now known to have mass. For some time, it seemed that the Weyl fermion was destined to be just an abstract concept from another beautiful mind. That was until the Weyl fermion entered the realm of condensed-matter physics. For several years this field has been considered fertile ground for finding the Weyl fermion. Now, three papers in Nature Physics3–5 have cemented earlier findings6,7 to confirm the predictions8,9 of Weyl physics in a family of nonmagnetic materials with broken inversion symmetry. In condensed-matter physics, specifically in solid-state band structures, Weyl fermions appear when two electronic bands cross. The crossing point is called a Weyl node, away from which the bands disperse linearly in the lattice momentum, giving rise to a special kind of semimetal.
  • Electronic Entropy Contribution to the Metal Insulator Transition in VO$ 2

    Electronic Entropy Contribution to the Metal Insulator Transition in VO$ 2

    Electronic entropy contribution to the metal insulator transition in VO2 The MIT Faculty has made this article openly available. Please share how this access benefits you. Your story matters. Citation Paras, J. and A. Allanore. "Electronic entropy contribution to the metal insulator transition in VO₂" Physical Review B 102, 16 (October 2020): 165138. © 2020 American Physical Society As Published http://dx.doi.org/10.1103/physrevb.102.165138 Publisher American Physical Society (APS) Version Final published version Citable link https://hdl.handle.net/1721.1/131098 Terms of Use Article is made available in accordance with the publisher's policy and may be subject to US copyright law. Please refer to the publisher's site for terms of use. PHYSICAL REVIEW B 102, 165138 (2020) Electronic entropy contribution to the metal insulator transition in VO2 J. Paras and A. Allanore Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA (Received 11 June 2020; revised 31 August 2020; accepted 1 September 2020; published 21 October 2020) VO2 experiences a metal-insulator transition at 340 K. Discontinuities in electronic transport properties, such as the Seebeck coefficient and the electronic conductivity, suggest that there is a significant change in the electronic structure upon metallization. However, the thermodynamic nature of this transformation remains difficult to describe using conventional computational and experimental methods. This has led to disagreement over the relative importance of the change in electronic entropy with respect to the overall transition entropy. A method is presented that links measurable electronic transport properties to the change in electronic state entropy of conduction electrons. The change in electronic entropy is calculated to be 9.2 ± 0.7J/mol K which accounts for 62%–67% of the total transition entropy.
  • Electronic Properties of Type-II Weyl Semimetal Wte2. a Review Perspective

    Electronic Properties of Type-II Weyl Semimetal Wte2. a Review Perspective

    Electronic properties of type-II Weyl semimetal WTe2. A review perspective. P. K. Das1, D. Di Sante2, F. Cilento3, C. Bigi4, D. Kopic5, D. Soranzio5, A. Sterzi3, J. A. Krieger6,7,8, I. Vobornik9, J. Fujii9, T. Okuda10, V. N. Strocov6, M. B. H. Breese1,11, F. Parmigiani3,5, G. Rossi4,9, S. Picozzi12, R. Thomale2, G. Sangiovanni2, R. J. Cava13, and G. Panaccione9,* 1Singapore Synchrotron Light Source, National University of Singapore, 5 Research Link, 117603, Singapore 2Institut für Theoretische Physik und Astrophysik, Universität Würzburg, Am Hubland Campus Süd, Würzburg 97074, Germany 3Elettra - Sincrotrone Trieste S.C.p.A., Strada Statale 14, km 163.5, Trieste 34149, Italy 4Dipartimento di Fisica, Universitá di Milano, Via Celoria 16, I-20133 Milano, Italy 5Universitá degli Studi di Trieste - Via A. Valerio 2, Trieste 34127, Italy 6Paul Scherrer Institute, Swiss Light Source, CH-5232 Villigen, Switzerland 7Laboratory for Muon Spin Spectroscopy, Paul Scherrer Institute, CH-5232 Villigen PSI, Switzerland 8Laboratorium für Festkörperphysik, ETH Zürich, CH-8093 Zürich, Switzerland 9Istituto Officina dei Materiali (IOM)-CNR, Laboratorio TASC, in Area Science Park, S.S.14, Km 163.5, I- 34149 Trieste, Italy 10Hiroshima Synchrotron Radiation Center (HSRC), Hiroshima University, 2-313 Kagamiyama, Higashi- Hiroshima 739-0046, Japan. 11Department of Physics, National University of Singapore, 117576, Singapore 12Consiglio Nazionale delle Ricerche (CNR-SPIN), c/o Univ. Chieti-Pescara "G. D'Annunzio", 66100 Chieti, Italy 13Department of Chemistry, Princeton University, Princeton, New Jersey 08544, USA * Corresponding author: [email protected] Currently, there is a flurry of research interest on materials with an unconventional electronic structure, and we have already seen significant progress in their understanding and engineering towards real-life applications.
  • Towards Three-Dimensional Weyl-Surfacesemimetals in Graphene Networks

    Towards Three-Dimensional Weyl-Surfacesemimetals in Graphene Networks

    See discussions, stats, and author profiles for this publication at: https://www.researchgate.net/publication/289587680 Towards Three-Dimensional Weyl-SurfaceSemimetals in Graphene Networks Article in Nanoscale · January 2016 DOI: 10.1039/C6NR00882H · Source: arXiv CITATIONS READS 130 175 6 authors, including: Chengyong Zhong Yuan Ping Chen Chengdu University Jiangsu University 36 PUBLICATIONS 856 CITATIONS 120 PUBLICATIONS 2,599 CITATIONS SEE PROFILE SEE PROFILE Yuee Xie Shengyuan Yang Xiangtan University Singapore University of Technology and Design 69 PUBLICATIONS 1,781 CITATIONS 280 PUBLICATIONS 7,389 CITATIONS SEE PROFILE SEE PROFILE Some of the authors of this publication are also working on these related projects: phase change materials View project A class of topological nodal rings and its realization in carbon networks View project All content following this page was uploaded by Chengyong Zhong on 19 December 2017. The user has requested enhancement of the downloaded file. Nanoscale View Article Online PAPER View Journal | View Issue Towards three-dimensional Weyl-surface semimetals in graphene networks† Cite this: Nanoscale, 2016, 8, 7232 Chengyong Zhong,a Yuanping Chen,*a Yuee Xie,*a Shengyuan A. Yang,b Marvin L. Cohenc and S. B. Zhang*d Graphene as a two-dimensional topological semimetal has attracted much attention for its outstanding properties. In contrast, three-dimensional (3D) topological semimetals of carbon are still rare. Searching for such materials with salient physics has become a new direction in carbon research. Here, using first- principles calculations and tight-binding modeling, we propose a new class of Weyl semimetals based on three types of 3D graphene networks. In the band structures of these materials, two flat Weyl surfaces appear in the Brillouin zone, which straddle the Fermi level and are robust against external strain.