DOCSLIB.ORG

Unconventional Superconductivity

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Unconventional Superconductivity Unconventional Superconductivity G. R. Stewart Department of Physics, University of Florida, Gainesville, FL USA 32611 Gregory Randall Stewart Department of Physics 2001 Museum Road University of Florida Gainesville, FL 32611 USA *Email: [email protected] 001 352 3929263 Acknowledgements: This work was supported by the United States Department of Energy, Office of Basic Energy Sciences, under contract number DE-FG02-86ER45268. Abstract: “Conventional” superconductivity, as used in this review, refers to electron-phonon coupled superconducting electron pairs described by BCS theory. Unconventional superconductivity refers to superconductors where the Cooper pairs are not bound together by phonon-exchange but instead by exchange of some other kind, e. g. spin fluctuations in a superconductor with magnetic order either coexistent or nearby in the phase diagram. Such unconventional superconductivity has been known experimentally since heavy fermion CeCu2Si2, with its strongly correlated 4f electrons, was discovered to superconduct below 0.6 K in 1979. Since the discovery of unconventional superconductivity in the layered cuprates in 1986, the study of these materials saw Tc jump to 164 K by 1994. Further progess in high temperature superconductivity would be aided by understanding the cause of such unconventional pairing. This review compares the fundamental properties of 9 unconventional superconducting classes of materials - from 4f-electron heavy fermions to organic superconductors to classes where only three known members exist to the cuprates with over 200 examples – with the hope that common features will emerge to help theory explain (and predict!) these phenomena. In addition, three new emerging classes of superconductors (topological, interfacial – e. g. FeSe on SrTiO3, and H2S under high pressure) are briefly covered, even though their “conventionality” is not yet fully determined. Keywords: superconductivity; unconventional; symmetry; heavy fermion; cuprate PACS index categories: 74.20.Mn Nonconventional mechanisms 74.25.-q Properties of superconductors 74.70.-b Superconducting materials other than cuprates 74.72.-h Cuprate superconductors 1. Introduction Superconductivity, the phenomenon where the resistivity falls to zero below a certain critical temperature Tc (discovered in Hg at 4.2 K in 1911) and the magnetic flux is expelled from the bulk of the superconductor (a phenomenon discovered in 1933), was explained as due to electron-phonon coupling by Bardeen, Cooper, and Schrieffer (BCS) in 1957. The BCS weak- coupled theory describes the condensation into the superconducting state as due to the exchange of phonons between electrons of opposite spins, an s=0 singlet ground state. Thus the average phonon frequency, <>, or equivalently the characteristic Debye temperature, D, (a phenomenological cutoff of the phonon frequencies) plays an important role in the BCS expression for Tc BCS Tc <>exp(-1/N(0)V) eq. 1 where N(0) is the electronic density of states at the Fermi energy and V is an average electron- phonon coupling strength parameter. The BCS weak coupling theory has N(0)V<1. Many superconductors (e. g. the over 25 superconducting elements [1] and various classes including A15 superconductors [2] - useful for high field magnets), are generally believed to be described by the BCS model, as extended by various improvements (called Eliashberg theory) that encompass stronger coupling. Defining “Unconventional Superconductor” (UcS) as a material where the Cooper pairing deviates from the BCS description, where the attraction between pairs and driving mechanism for condensation into the superconducting state might come from, e. g., exchange of spin fluctuations, is not a definition new to this review. This is consistent, e. g., with the definition of UcS in the phenomenological theory review of UcS by Sigrist and Ueda [3] from 1991. There are several other ways (as discussed thoroughly in section 2) to define an UcS. Based on a discussion of symmetry [4] by Tsuei and Kirtley, any long range ordering transition is accompanied by a lowering of symmetry. In a BCS superconductor the only symmetry broken is the one dimensional global gauge symmetry, U(1), caused by the macroscopic phase coherence that occurs below Tc. In an UcS, one or more additional symmetries (e. g. time reversal symmetry or reflection symmetry) are broken. p-, d-, and f-wave as well as s± (theorized for iron based superconductors [IBS]) pairing symmetries all break reflection symmetry. Thus, another definition of UcS could be a superconductor in which at least two symmetries are broken at Tc. As we will see, although a majority of the 9 superconducting UcS classes discussed herein exhibit such additional symmetry breaking (e. g. time reversal and reflection symmetry breaking in the hole-doped cuprates), others (including recently discovered classes or classes with only a few members) do not. Thus, we will remain with the “non-BCS” definition of UcS as being the best representation of the fundamental theme of this review. Here, in the Introduction, a short overview discussion will help the reader follow the discussion of the nine classes of UcS, and the three additional classes. As can be inferred from the short discussion above, it is not at present possible to state the cause of UcS, if indeed (as seems unlikely) there is only one such cause. The present review aims to summarize the properties of the various classes of UcS in a way that points to fundamental similarities. One of the questions important for understanding UcS is: what characteristics of materials are causes of, or at least consistent with, UcS? 1.) As we will see in this review, most UcS have strong electron correlations through their d-electrons (cuprates, IBS, Sr2RuO4, cobalt oxide hydrates, layered nitrides) or f-electrons (heavy Fermions and coexistent superconductivity and ferromagnetism). Only the organic UcS rely on pairing between p-electrons. 2.) The main instability found in UcS is antiferromagnetism (as will be seen herein in phase diagrams and discussions for the heavy Fermion 115 structure, CeCu2Si2, U(Pd,Ni)2Al3, for both electron- and hole-doped cuprates, for the majority (but not all) of the IBS, the non- centrosymmetric superconductors like CePt3Si that are strongly correlated, organics, and cobalt oxide hydrates.) In addition there are coexistent superconducting and ferromagnetic compounds like UGe2. Another instability found in some UcS is charge density waves (hole-doped cuprates, theorized in some heavy Fermion superconductors, and cobalt oxide hydrates.) 3.) Two dimensional behavior based on the crystalline structure plays an important role and is widespread in many of the UcS: cuprates (where the ratio of resistivities along the c-axis vs the ab-plane can be larger than 1000), IBS (c/ab ~ 100), Sr2RuO4, layered metal nitride halides, cobalt oxide hydrates, and the 115 structure heavy Fermion superconductors, while there is quasi-1d behavior in some of the organics. This d<3 behavior can play an important role in creating UcS since according to the Mermin Wagner theorem fluctuation effects for d<3 become more important. Such fluctuation effects are predicted (as discussed below) to be a possible superconducting pairing mechanism (superconducting ‘glue’) in these same aforementioned superconductors. 2d antiferromagnetic fluctuations are repulsive, so a Fermi surface with a sign change in the order parameter where the repulsive interaction is large can cause (see the s± model discussed below for the IBS) attraction and condensation into a superconducting state. Put another way, this sign change in the order parameter under translation by the magnetic ordering vector of the parent phase “tends to remove the detrimental effects of the on-site Coulomb repulsion between the electrons.” (Norman [5]). Thus, details of the Fermi surface topology are important and 2d crystalline structures are indeed widespread in UcS. Of course, there are obvious counterexamples, for instance the indisputably 3d nature of the cubic unconventional heavy Fermion superconductor UBe13. With all of these named properties being ‘consistent’ with UcS, there still remains no ability to a priori predict unconventional superconductivity. Put another way, there is no ‘microscopic’ theory of UcS, like the BCS theory for conventional superconductivity, since - due to the strong correlations - solving the pairing in UcS is a non-perturbative problem. As Norman has put it [5] “developing a rigorous theory for any of these classes of materials [in the UcS] has proven to be a difficult challenge, and will continue to be one of the major problems in physics in the decades to come.” It is the goal of this review to provide a comprehensive overview of UcS in one place to aid in this challenge. Fig. 1 (color online): Time line of the discovery of some unconventional superconductors The first superconductor identified as unconventional was CeCu2Si2, Tc=0.6 K, reported [6] by Steglich et al. in 1979. Rather than electron-phonon coupling, the pairing in CeCu2Si2 has been described as due to some sort of fluctuations (either quantum critical and/or antiferromagnetic.) Steglich et al.’s discovery led to the discovery of other unconventional superconductors of the same class as shown in Fig. 1 (UBe13 in 1983, UPt3 in 1984, . ), where this class is known as heavy fermion superconductors (HFS) due to the large (sometimes > 100 rest mass of the electron) effective mass m* of the conduction electrons, where these
Load more

Recommended publications
  • Comparing the Superconductivity of Mgb2 and Sr2ruo4
    Comparing the superconductivity of MgB2 and Sr2RuO4 Etienne Palosa) (PHYS 232: Electronic Materials) The physical properties of two superconducting materials are compared in their normal and superconducting states. Their similarities and differences are reviewed in a systematic manner, beginning with a description of the unit cell. Structural, thermodynamic, electronic and magnetic properties are compared. In the super- conducting state, re compare the superconducting parameters of the materials and the effect on TC induced by physical or chemical changes to the systems. The sim- ilarities and differences between the conventional superconductor MgB2 and the unconventional superconductor Sr2RuO4 are discussed mainly within the context of experimental evidence reported in the literature. I. INTRODUCTION Some of the most important unresolved questions in condensed matter physics are re- lated to superconductivity. While the phenomena was observed over one-hundred years ago and an theory that explains conventional superconductivity has been established for the better half of a century, there is no unified theory of conventional and unconventional su- perconductivity. Or is there? However, through continuous theoretical, experimental and collaborative efforts, much has been learned about the physics of superconducting materi- als. The two main categories of superconductors are (i) conventional: those explained by the Bardeen{Cooper{Schrieffer (BCS) theory, and (ii) unconventional: materials whose su- perconducting mechanisms do not satisfy the conditions in BCS theory. In these materials, the superconducting mechanism is not phonon-mediated. In this work, a comparison of the physical properties of one conventional and one uncon- ventional superconductors is presented. On one hand, we have magnesium diboride, MgB2, a material whose superconductivity was discovered in 20011, decades after it's synthesis and crystal structure was first reported.
    [Show full text]
  • High Pressure Study of High-Temperature Superconductors
    High Pressure Study of High-Temperature Superconductors Von der Fakultät Mathematik und Physik der Universität Stuttgart zur Erlangung der Würde eines Doktors der Naturwissenschaften (Dr. rer. nat.) genehmigte Abhandlung Vorgelegt von Sofia-Michaela Souliou aus Thessaloniki (Griechenland) Hauptberichter: Prof. Dr. Bernhard Keimer Mitberichter: Prof. Dr. Martin Dressel Tag der mündlichen Prüfung: 29 September 2014 Max-Planck-Institut für Festkörperforschung Stuttgart 2014 Contents Zusammenfassung in deutscher Sprache9 Introduction 13 1 High-Temperature Superconductors 17 1.1 Cuprate superconductors . 17 1.1.1 Crystal Structure and Carrier Doping . 17 1.1.2 Electronic Structure . 20 1.1.3 Phase diagram . 24 1.1.4 The YBa2Cu3O6+x and YBa2Cu4O8 systems . 37 1.1.5 High Pressure Effects . 43 1.2 Iron-based Superconductors . 47 1.2.1 Crystal Structure and Superconductivity . 47 1.2.2 Electronic Structure . 49 1.2.3 Phase Diagram . 52 1.2.4 The REFeAsO "1111" family . 57 1.2.5 High Pressure Effects . 59 2 Raman scattering 63 2.1 Overview of Inelastic Light Scattering . 63 2.2 Phononic Raman scattering . 65 2.2.1 Classical description of phononic Raman scattering . 65 2.2.2 Quantum mechanical description of phononic Raman scattering . 68 2.2.3 Phonon Interactions . 71 2.3 Phononic Raman scattering under high pressure . 75 2.4 The Raman spectrum of high-Tc cuprate and iron-based superconductors . 77 2.4.1 Raman modes of YBa2Cu3O6+x .................. 77 2.4.2 Raman modes of YBa2Cu4O8 ................... 84 2.4.3 Raman modes of REFeAsO1−xFx .................. 86 2.5 Analysis of the phononic Raman data . 89 5 Contents 3 Experimental Techniques 93 3.1 High Pressures and Low Temperatures .
    [Show full text]
  • Scanning Tunneling Microscopy Study on Strongly Correlated Materials
    Scanning Tunneling Microscopy Study on Strongly Correlated Materials The Harvard community has made this article openly available. Please share how this access benefits you. Your story matters Citation He, Yang. 2016. Scanning Tunneling Microscopy Study on Strongly Correlated Materials. Doctoral dissertation, Harvard University, Graduate School of Arts & Sciences. Citable link http://nrs.harvard.edu/urn-3:HUL.InstRepos:26718719 Terms of Use This article was downloaded from Harvard University’s DASH repository, and is made available under the terms and conditions applicable to Other Posted Material, as set forth at http:// nrs.harvard.edu/urn-3:HUL.InstRepos:dash.current.terms-of- use#LAA Scanning Tunneling Microscopy Study on Strongly Correlated Materials a dissertation presented by Yang He to The Department of Physics in partial fulfillment of the requirements for the degree of Doctor of Philosophy in the subject of Physics Harvard University Cambridge, Massachusetts June 2015 ©2014 – Yang He all rights reserved. Thesis advisor: Professor Jennifer E. Hoffman Yang He Scanning Tunneling Microscopy Study on Strongly Correlated Materials Abstract Strongly correlated electrons and spin-orbit interaction have been the two major research direc- tions of condensed matter physics in recent years. The discovery of high temperature superconduc- tors in 1986 not only brought excitement into the field but also challenged our theory on quantum materials. After almost three decades of extensive study, the underlying mechanism of high temper- ature superconductivity is still not fully understood, the reason for which is mainly a poor under- standing of strongly correlated systems. The phase diagram of cuprate superconductors has become more complicated throughout the years as multiple novel electronic phases have been discovered, while few of them are fully understood.
    [Show full text]
  • A Quantum Critical Point at the Heart of High Temperature Superconductivity
    View metadata, citation and similar papers at core.ac.uk brought to you by CORE provided by Apollo A quantum critical point at the heart of high temperature superconductivity B. J. Ramshaw,1 S. E. Sebastian,2 R. D. McDonald,1 James Day,3 B. Tan,2 Z. Zhu,1 J.B. Betts,1 Ruixing Liang,3, 4 D. A. Bonn,3, 4 W. N. Hardy,3, 4 and N. Harrison1 1Mail Stop E536, Los Alamos National Labs, Los Alamos, NM 87545∗ 2Cavendish Laboratory, Cambridge University, JJ Thomson Avenue, Cambridge CB3 OHE, U.K 3Department of Physics and Astronomy, University of British Columbia, Vancouver V6T 1Z4, Canada 4Canadian Institute for Advanced Research, Toronto M5G 1Z8, Canada (Dated: April 27, 2014) 1 In the quest for superconductors with high transition temperatures (Tc s), one emerging motif is that unconventional superconductivity is enhanced by fluc- tuations of a broken-symmetry phase near a quantum-critical point. While re- cent experiments have suggested the existence of the requisite broken symmetry phase in the high-Tc cuprates, the signature of quantum-critical fluctuations in the electronic structure has thus far remained elusive, leaving their importance for high-Tc superconductivity in question. We use magnetic fields exceeding 90 tesla to access the underlying metallic state of the cuprate YBa2Cu3O6+δ over an unprecedented range of doping, and magnetic quantum oscillations reveal a strong enhancement in the quasiparticle effective mass toward optimal doping. This mass enhancement is a characteristic signature of quantum criticality, and identifies a quantum-critical point at pcrit ≈ 0:18. This point also represents the juncture of the vanishing pseudogap energy scale and the disappearance of Kerr rotation, the negative Hall coefficient, and the recently observed charge order, suggesting a mechanism of high-Tc that is strongest when these definitive exper- imental signatures of the underdoped cuprates converge at a quantum critical point.
    [Show full text]
  • Probing Phase Separation and Local Lattice Distortions in Cuprates by Raman Spectroscopy
    Review Probing Phase Separation and Local Lattice Distortions in Cuprates by Raman Spectroscopy Efthymios Liarokapis Department of Physics, National Technical University of Athens, 15780 Athens, Greece; [email protected]; Tel.: +30-210-7722930 Received: 25 September 2019; Accepted: 27 October 2019; Published: 1 November 2019 Abstract: It is generally accepted that high temperature superconductors emerge when extra carriers are introduced in the parent state, which looks like a Mott insulator. Competition of the order parameters drives the system into a poorly defined pseudogap state before acquiring the normal Fermi liquid behavior with further doping. Within the low doping level, the system has the tendency for mesoscopic phase separation, which seems to be a general characteristic in all high Tc compounds, but also in the materials of colossal magnetoresistance or the relaxor ferroelectrics. In all these systems, metastable phases can be created by tuning physical variables, such as doping or pressure, and the competing order parameters can drive the compound to various states. Structural instabilities are expected at critical points and Raman spectroscopy is ideal for detecting them, since it is a very sensitive technique for detecting small lattice modifications and instabilities. In this article, phase separation and lattice distortions are examined on the most characteristic family of high temperature superconductors, the cuprates. The effect of doping or atomic substitutions on cuprates is examined concerning the induced phase
    [Show full text]
  • Hole-Doped Cuprate High Temperature Superconductors
    Hole-Doped Cuprate High Temperature Superconductors C. W. Chu, L. Z. Deng and B. Lv Department of Physics and Texas Center for Superconductivity University of Houston Abstract Hole-doped cuprate high temperature superconductors have ushered in the modern era of high temperature superconductivity (HTS) and have continued to be at center stage in the field. Extensive studies have been made, many compounds discovered, voluminous data compiled, numerous models proposed, many review articles written, and various prototype devices made and tested with better performance than their nonsuperconducting counterparts. The field is indeed vast. We have therefore decided to focus on the major cuprate materials systems that have laid the foundation of HTS science and technology and present several simple scaling laws that show the systematic and universal simplicity amid the complexity of these material systems, while referring readers interested in the HTS physics and devices to the review articles. Developments in the field are mostly presented in chronological order, sometimes with anecdotes, in an attempt to share some of the moments of excitement and despair in the history of HTS with readers, especially the younger ones. 1. Introduction Hole-doped cuprate superconductors have played an indispensable role in the exciting development of high temperature superconductivity (HTS) science and technology over the last 28 years. They ushered in the era of cuprate high temperature superconductivity and helped create a subfield of physics, namely, “high temperature superconductivity” as we know it today. It all began with the observation of superconductivity up to 35 K in the Ba-doped La2CuO4 ternary compound by Alex Mueller and George Bednorz of IBM Zurich Laboratory in 1986 [1], followed immediately by the discovery of superconductivity at 93 K in the new self-doped YBa2Cu3O7 quaternary compound by C.
    [Show full text]
  • Direct Observation of Orbital Hybridisation in a Cuprate
    Direct Observation of Orbital Hybridisation in a Cuprate Superconductor C. E. Matt,1, 2 D. Sutter,1 A. M. Cook,1 Y. Sassa,3 M. M˚ansson,4 O. Tjernberg,4 L. Das,1 M. Horio,1 D. Destraz,1 C. G. Fatuzzo,5 K. Hauser,1 M. Shi,2 M. Kobayashi,2 V. N. Strocov,2 T. Schmitt,2 P. Dudin,6 M. Hoesch,6 S. Pyon,7 T. Takayama,7 H. Takagi,7 O. J. Lipscombe,8 S. M. Hayden,8 T. Kurosawa,9 N. Momono,9, 10 M. Oda,9 T. Neupert,1 and J. Chang1 1Physik-Institut, Universit¨at Z¨urich, Winterthurerstrasse 190, CH-8057 Z¨urich, Switzerland 2Swiss Light Source, Paul Scherrer Institut, CH-5232 Villigen PSI, Switzerland 3Department of Physics and Astronomy, Uppsala University, SE-75121 Uppsala, Sweden 4KTH Royal Institute of Technology, Materials Physics, SE-164 40 Kista, Stockholm, Sweden 5Institute of Physics, Ecole´ Polytechnique Fed´erale de Lausanne (EPFL), Lausanne CH-1015, Switzerland 6Diamond Light Source, Harwell Campus, Didcot OX11 0DE, UK. 7Department of Advanced Materials, University of Tokyo, Kashiwa 277-8561, Japan 8H. H. Wills Physics Laboratory, University of Bristol, Bristol BS8 1TL, United Kingdom 9Department of Physics, Hokkaido University - Sapporo 060-0810, Japan 10Department of Applied Sciences, Muroran Institute of Technology, Muroran 050-8585, Japan The minimal ingredients to explain the es- which, in turn, suppresses superconductivity5,9. Second, sential physics of layered copper-oxide (cuprates) Fermi level dz2 -hybridisation, depending on dA, reduces materials remains heavily debated. Effective low- the pairing strength6,10. Experimental evidence, how- energy single-band models of the copper-oxygen ever, points in opposite directions.
    [Show full text]
  • Superstripes and Complexity in High-Temperature Superconductors
    J. Supercon. Nov. Mag. 2012 DOI :10.1007/s10948-012-1670-6 Superstripes and complexity in high-temperature superconductors Antonio Bianconi 1,2 and Nicola Poccia 1 1Department of Physics, Sapienza University of Rome, P. le A. Moro 2, 00185 Roma, Italy 2Rome International Center for Materials Science (RoCMat) Superstripes, Via dei Sabelli 119A, 00186 Roma, Italy Abstract: While for many years the lattice, electronic and magnetic complexity of high- temperature superconductors (HTS) has been considered responsible for hindering the search of the mechanism of HTS now the complexity of HTS is proposed to be essential for the quantum mechanism raising the superconducting critical temperature. The complexity is shown by the lattice heterogeneous architecture: a) heterostructures at atomic limit; b) electronic heterogeneity: multiple components in the normal phase; c) superconducting heterogeneity: multiple superconducting gaps in different points of the real space and of the momentum space. The complex phase separation forms an unconventional granular superconductor in a landscape of nanoscale superconducting striped droplets which is called the “superstripes” scenario. The interplay and competition between magnetic orbital charge and lattice fluctuations seems to be essential for the quantum mechanism that suppresses thermal decoherence effects at an optimum inhomogeneity. Keywords: Complexity, superconductivity, multi-component, multi-gaps, superlattice, superstripes. *web site : www.rocmat.eu E-mail: [email protected] 1. Introduction. The search for new materials with a higher superconducting critical temperature has been carried out during the last 100 years. In the early period, the material research was focusing on pure and simple pure metals made by a single element. At ambient pressure niobium has the highest superconducting critical temperature 9.3 K.
    [Show full text]
  • Direct Observation of Orbital Hybridisation in a Cuprate Superconductor
    Zurich Open Repository and Archive University of Zurich Main Library Strickhofstrasse 39 CH-8057 Zurich www.zora.uzh.ch Year: 2018 Direct observation of orbital hybridisation in a cuprate superconductor Matt, C E ; Sutter, D ; Cook, A M ; et al Abstract: The minimal ingredients to explain the essential physics of layered copper-oxide (cuprates) materials remains heavily debated. Effective low-energy single-band models of the copper–oxygen orbitals are widely used because there exists no strong experimental evidence supporting multi-band structures. Here, we report angle-resolved photoelectron spectroscopy experiments on La-based cuprates that provide direct observation of a two-band structure. This electronic structure, qualitatively consistent with density functional theory, is parametrised by a two-orbital (dx2−y2 and dz2) tight-binding model. We quantify the orbital hybridisation which provides an explanation for the Fermi surface topology and the proximity of the van-Hove singularity to the Fermi level. Our analysis leads to a unification of electronic hopping parameters for single-layer cuprates and we conclude that hybridisation, restraining d-wave pairing, is an important optimisation element for superconductivity. DOI: https://doi.org/10.1038/s41467-018-03266-0 Posted at the Zurich Open Repository and Archive, University of Zurich ZORA URL: https://doi.org/10.5167/uzh-157585 Journal Article Published Version The following work is licensed under a Creative Commons: Attribution 4.0 International (CC BY 4.0) License. Originally published at: Matt, C E; Sutter, D; Cook, A M; et al (2018). Direct observation of orbital hybridisation in a cuprate superconductor. Nature Communications, 9:972.
    [Show full text]
  • Microstructure and Properties of High-Temperature Superconductors
    Microstructure and Properties of High-Temperature Superconductors Bearbeitet von Ivan Parinov 1. Auflage 2013. Buch. xxi, 779 S. Hardcover ISBN 978 3 642 34440 4 Format (B x L): 15,5 x 23,5 cm Gewicht: 1364 g Weitere Fachgebiete > Physik, Astronomie > Elektrodynakmik, Optik > Halbleiter- und Supraleiterphysik Zu Inhaltsverzeichnis schnell und portofrei erhältlich bei Die Online-Fachbuchhandlung beck-shop.de ist spezialisiert auf Fachbücher, insbesondere Recht, Steuern und Wirtschaft. Im Sortiment finden Sie alle Medien (Bücher, Zeitschriften, CDs, eBooks, etc.) aller Verlage. Ergänzt wird das Programm durch Services wie Neuerscheinungsdienst oder Zusammenstellungen von Büchern zu Sonderpreisen. Der Shop führt mehr als 8 Millionen Produkte. Chapter 2 High-Temperature Superconductors. Overview 2.1 General Remarks on Type-II Superconductors High-temperature superconductors placed in the center of our research are the type-II superconductors. Therefore, their properties and superconductivity mech- anisms are considered in more detail. The term type-II superconductors was first introduced by Abrikosov in his classical paper [4], where he assumed a detailed phenomenological theory of these materials’ behavior, based on the Ginzburg– Landau theory, and explained their magnetic properties. Initially, Abrikosov’s theory was greeted with certain skepticism: so much out of the ordinary was in its predictions. However, at the next development of physics of superconductors this theory obtained numerous experimental supports. Finally, several years later it was accepted in total, when it consequently explained the complex behavior of superconducting alloys and compounds, in particular the very high critical fields of some materials. As it has been noted for type-II superconductors, the energy of an interface between a normal and a superconducting region rns \ 0.
    [Show full text]
  • Thermodynamic Critical Field and Superconducting Fluctuation of Vortices for High Temperature Cuprate Superconductor: La-214 " (2001)
    Iowa State University Capstones, Theses and Retrospective Theses and Dissertations Dissertations 2001 Thermodynamic critical field nda superconducting fluctuation of vortices for high temperature cuprate superconductor: La-214 Yung Moo Huh Iowa State University Follow this and additional works at: https://lib.dr.iastate.edu/rtd Part of the Condensed Matter Physics Commons Recommended Citation Huh, Yung Moo, "Thermodynamic critical field and superconducting fluctuation of vortices for high temperature cuprate superconductor: La-214 " (2001). Retrospective Theses and Dissertations. 1047. https://lib.dr.iastate.edu/rtd/1047 This Dissertation is brought to you for free and open access by the Iowa State University Capstones, Theses and Dissertations at Iowa State University Digital Repository. It has been accepted for inclusion in Retrospective Theses and Dissertations by an authorized administrator of Iowa State University Digital Repository. For more information, please contact [email protected]. INFORMATION TO USERS This manuscript has been reproduced from the microfilm master. UMI films the text directly from the original or copy submitted. Thus, some thesis and dissertation copies are in typewriter face, while others may be from any type of computer printer. The quality of this reproduction is dependent upon the quality of the copy submitted. Broken or indistinct print, colored or poor quality illustrations and photographs, print bleedthrough, substandard margins, and improper alignment can adversely affect reproduction.. In the unlikely event that the author did not send UMI a complete manuscript and there are missing pages, these will be noted. Also, if unauthorized copyright material had to be removed, a note will indicate the deletion. Oversize materials (e.g., maps, drawings, charts) are reproduced by sectioning the original, beginning at the upper left-hand corner and continuing from left to right in equal sections with small overlaps.
    [Show full text]
  • Mechanism of High-Temperature Superconductivity in Correlated-Electron Systems
    Article Mechanism of High-Temperature Superconductivity in Correlated-Electron Systems Takashi Yanagisawa National Institute of Advanced Industrial Science and Technology 1-1-1 Umezono, Tsukuba, Ibaraki 305-8568, Japan; [email protected] Received: 25 April 2019; Accepted: 15 June 2019; Published: 19 June 2019 Abstract: It is very important to elucidate the mechanism of superconductivity for achieving room temperature superconductivity. In the first half of this paper, we give a brief review on mechanisms of superconductivity in many-electron systems. We believe that high-temperature superconductivity may occur in a system with interaction of large-energy scale. Empirically, this is true for superconductors that have been found so far. In the second half of this paper, we discuss cuprate high-temperature superconductors. We argue that superconductivity of high temperature cuprates is induced by the strong on-site Coulomb interaction, that is, the origin of high-temperature superconductivity is the strong electron correlation. We show the results on the ground state of electronic models for high temperature cuprates on the basis of the optimization variational Monte Carlo method. A high-temperature superconducting phase will exist in the strongly correlated region. Keywords: strongly correlated electron systems; mechanisms of superconductivity; high-temperature superconductivity; kinetic driven superconductivity; optimization variational Monte Carlo method; Hubbard model; three-band d-p model 1. Introduction It is a challenging research subject to clarify the mechanism of high temperature superconductivity, and indeed it has been studied intensively for more than 30 years [1–3]. For this purpose, it is important to clarify the ground state and phase diagram of electronic models with strong correlation because high temperature cuprates are strongly correlated electron systems.
    [Show full text]