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Journal ArticleDOI

Using Gap Symmetry and Structure to Reveal the Pairing Mechanism in Fe-based Superconductors

01 Jan 2016-Comptes Rendus Physique (Elsevier Masson)-Vol. 17, Iss: 1, pp 197-231
About: This article is published in Comptes Rendus Physique.The article was published on 2016-01-01 and is currently open access. It has received 169 citations till now. The article focuses on the topics: Explicit symmetry breaking & Spontaneous symmetry breaking.
Citations
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TL;DR: In this paper, the symmetry and the structure of the superconducting gap in Fe-based superconductors and the underlying pairing mechanism in these systems were reviewed and it was shown that all pairing states obtained so far can be understood within the same universal pairing scenario and are well described by the effective low energy model with a small number of input parameters.
Abstract: I review recent works on the symmetry and the structure of the superconducting gap in Fe-based superconductors and on the underlying pairing mechanism in these systems. The experimental data on superconductivity show very rich behavior, with potentially different symmetry of a superconducting state for different compositions of the same material. The variety of different pairing states raised the issue whether the physics of Fe-based superconductors is model-dependent or is universal, governed by a single underlying pairing mechanism. I argue that the physics is universal and that all pairing states obtained so far can be understood within the same universal pairing scenario and are well described by the effective low-energy model with a small number of input parameters.

288 citations

Journal ArticleDOI
07 Jul 2017-Science
TL;DR: In this paper, the authors used Bogoliubov quasiparticle interference imaging to determine the Fermi surface geometry of the electronic bands surrounding the Γ = (0, 0) and X = (π/ a Fe, 0) points of FeSe and to measure the corresponding superconducting energy gaps.
Abstract: The superconductor iron selenide (FeSe) is of intense interest owing to its unusual nonmagnetic nematic state and potential for high-temperature superconductivity. But its Cooper pairing mechanism has not been determined. We used Bogoliubov quasiparticle interference imaging to determine the Fermi surface geometry of the electronic bands surrounding the Γ = (0, 0) and X = (π/ a Fe , 0) points of FeSe and to measure the corresponding superconducting energy gaps. We show that both gaps are extremely anisotropic but nodeless and that they exhibit gap maxima oriented orthogonally in momentum space. Moreover, by implementing a novel technique, we demonstrate that these gaps have opposite sign with respect to each other. This complex gap configuration reveals the existence of orbital-selective Cooper pairing that, in FeSe, is based preferentially on electrons from the d yz orbitals of the iron atoms.

260 citations

Journal ArticleDOI
TL;DR: Angle-resolved photoemission spectroscopy (ARPES) has emerged as a leading experimental probe for studying the complex phenomena in quantum materials, a subject of increasing importance as mentioned in this paper.
Abstract: Angle-resolved photoemission spectroscopy (ARPES) has emerged as a leading experimental probe for studying the complex phenomena in quantum materials, a subject of increasing importance The power of this technique stems from the directness and the richness of the momentum-resolved information it can provide, such as band dispersion, Fermi surface topology, and electron self-energy Over the past decade, the significantly improved energy and momentum resolution and carefully matched experiments have turned this technique into a sophisticated tool in characterizing the electronic structure of complex materials This revolution is mostly evident in the study of cuprate high-temperature superconductors More recently, this technique has played a critical role in advancing our understanding of the newly discovered iron-based superconductors and topological insulators In this paper we review some of the recent ARPES results and discuss the future perspective in this rapidly developing field

255 citations

Journal Article
TL;DR: In this article, the pairing symmetry of a two-orbital J1-J2 model for FeAs layers in oxypnictides was studied, and it was shown that the mixture of an intraorbital unconventional s-x;{2}y,{2}} approximately cos(k_{x})cos(k-y}) pairing symmetry was favored for J2>J1.
Abstract: We study the pairing symmetry of a two-orbital J1-J2 model for FeAs layers in oxypnictides. We show that the mixture of an intraorbital unconventional s_{x;{2}y;{2}} approximately cos(k_{x})cos(k_{y}) pairing symmetry, which changes sign between the electron and hole Fermi surfaces, and a very small d_{x;{2}-y;{2}} approximately cos(k_{x})-cos(k_{y}) component is favored in a large part of the J1-J2 phase diagram. A pure s_{x;{2}y;{2}} pairing state is favored for J2>J1. The signs of the d_{x;{2}-y;{2}} order parameters in the two different orbitals are opposite. While a small d_{xy} approximately sin(k_{x})sin(k_{y}) interorbital pairing coexists in the above phases, the intraorbital d_{xy} pairing is not favored even for large J2.

186 citations

Journal ArticleDOI
TL;DR: In this article, the authors compared 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.
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 06 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 progress 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

132 citations

References
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Book
01 Jan 1975
TL;DR: In this article, a revised version of the book has been published to incorporate the many new developments in superconductivity, including new topics on high temperature superconductors and nonequilibrium superconductivities.
Abstract: Appropriate for intermediate or advanced courses in superconductivity, this edition has been revised to incorporate the many new developments in superconductivity. Expanded topic coverage includes new chapters on high temperature superconductors and nonequilibrium superconductivity.

7,800 citations

Journal ArticleDOI
TL;DR: It is reported that a layered iron-based compound LaOFeAs undergoes superconducting transition under doping with F- ions at the O2- site and exhibits a trapezoid shape dependence on the F- content.
Abstract: We report that a layered iron-based compound LaOFeAs undergoes superconducting transition under doping with F- ions at the O2- site. The transition temperature (Tc) exhibits a trapezoid shape dependence on the F- content, with the highest Tc of ∼26 K at ∼11 atom %.

6,643 citations

Journal ArticleDOI
TL;DR: It is argued that the newly discovered superconductivity in a nearly magnetic, Fe-based layered compound is unconventional and mediated by antiferromagnetic spin fluctuations, though different from the usual superexchange and specific to this compound.
Abstract: We argue that the newly discovered superconductivity in a nearly magnetic, Fe-based layered compound is unconventional and mediated by antiferromagnetic spin fluctuations, though different from the usual superexchange and specific to this compound. This resulting state is an example of extended s-wave pairing with a sign reversal of the order parameter between different Fermi surface sheets. The main role of doping in this scenario is to lower the density of states and suppress the pair-breaking ferromagnetic fluctuations.

1,952 citations

Journal ArticleDOI
TL;DR: In this paper, a review of recent developments in the phenomenological description of unconventional superconductivity is presented, starting with the BCS theory of superconductivities with anisotropic Cooper pairing, and the group-theoretical derivation of the generalized Ginzburg-Landau theory for unconventional supercondivity.
Abstract: This article is a review of recent developments in the phenomenological description of unconventional superconductivity. Starting with the BCS theory of superconductivity with anisotropic Cooper pairing, the authors explain the group-theoretical derivation of the generalized Ginzburg-Landau theory for unconventional superconductivity. This is used to classify the possible superconducting states in a system with given crystal symmetry, including strong-coupling effects and spin-orbit interaction. On the basis of the BCS theory the unusual low-temperature properties and the (resonant) impurity scattering effects are discussed for superconductors with anisotropic pairing. Using the Ginzburg-Landau theory, the authors study several bulk properties of such superconductors: spontaneous lattice distortion, upper critical magnetic field, splitting of a phase transition due to uniaxial stress. Two possible mechanisms for ultrasound absorption are discussed: collective modes and damping by domain-wall motion. The boundary conditions for the Ginzburg-Landau theory are derived from a correlation function formulation and by group-theoretical methods. They are applied to a study of the Josephson and proximity effects if unconventional superconductors are involved there. The magnetic properties of superconductors that break time-reversal symmetry are analyzed. Examples of current and magnetic-field distributions close to inhomogeneities of the superconducting order parameter are given and their physical origin is discussed. Vortices in a superconductor with a multicomponent order parameter can exhibit various topological structures. As examples the authors show fractional vortices on domain walls and nonaxial vortices in the bulk. Furthermore, the problem of the possible coexistence of a superconducting and a magnetically ordered phase in an unconventional superconductor is analyzed. The combination of two order parameters that are almost degenerate in their critical temperature is considered with respect to the phase-transition behavior and effects on the lower and upper critical fields. Because heavy-fermion superconductors---which are possible realizations of unconventional superconductivity---have been the main motivation for the phenomenological studies presented here, the authors compare the theoretical results with the experimental facts and data. In particular, they emphasize the intriguing features of the compound U${\mathrm{Pt}}_{3}$ and consider in detail the alloy ${\mathrm{U}}_{1\ensuremath{-}x}{\mathrm{Th}}_{x}{\mathrm{Be}}_{13}$.

1,577 citations

Journal ArticleDOI
C. C. Tsuei1, John R. Kirtley1
TL;DR: The recent development of phase-sensitive tests, combined with the refinement of several other symmetry-sensitive techniques, has for the most part settled this controversy in favor of predominantly $d$-wave symmetry for a number of optimally hole-and electron-doped cuprates as mentioned in this paper.
Abstract: Pairing symmetry in the cuprate superconductors is an important and controversial topic. The recent development of phase-sensitive tests, combined with the refinement of several other symmetry-sensitive techniques, has for the most part settled this controversy in favor of predominantly $d$-wave symmetry for a number of optimally hole- and electron-doped cuprates. This paper begins by reviewing the concepts of the order parameter, symmetry breaking, and symmetry classification in the context of the cuprates. After a brief survey of some of the key non-phase-sensitive tests of pairing symmetry, the authors extensively review the phase-sensitive methods, which use the half-integer flux-quantum effect as an unambiguous signature for $d$-wave pairing symmetry. A number of related symmetry-sensitive experiments are described. The paper concludes with a brief discussion of the implications, both fundamental and applied, of the predominantly $d$-wave pairing symmetry in the cuprates.

1,486 citations