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

Abstract

I review theoretical ideas and implications of experiments for the gap structure and symmetry of the Fe-based superconductors. Unlike any other class of unconventional superconductors, one has in these systems the possibility to tune the interactions by small changes in pressure, doping or disorder. Thus, measurements of order parameter evolution with these parameters should enable a deeper understanding of the underlying interactions. I briefly review the "standard paradigm" for $s$-wave pairing in these systems, and then focus on developments in the past several years which have challenged this picture. I discuss the reasons for the apparent close competition between pairing in s- and d-wave channels, particularly in those systems where one type of Fermi surface pocket -- hole or electron -- is missing. Observation of a transition between $s$- and $d$-wave symmetry, possibly via a time reversal symmetry breaking "$s+id$" state, would provide an importantconfirmation of these ideas. Several proposals for detecting these novel phases are discussed, including the appearance of order parameter collective modes in Raman and optical conductivities. Transitions between two different types of $s$-wave states, involving various combinations of signs on Fermi surface pockets, can also proceed through a $\mathcal{T}$-breaking "$s+is$" state. I discuss recent work that suggests pairing may take place away from the Fermi level over a surprisingly large energy range, as well as the effect of glide plane symmetry of the Fe-based systems on the superconductivity, including various exotic, time and translational invariance breaking pair states that have been proposed. Finally, I address disorder issues, and the various ways systematic introduction of disorder can (and cannot) be used to extract information on gap symmetry and structure.

41 pp., Published in special focus issue of Comptes Rendus Physique (Paris) on recent progress in Fe-based Superconductivity. Full issue with 10 review articles available at http://www.sciencedirect.com/science/journal/16310705/17/1-2

References in corpus (100)

• Unconventional pairing originating from disconnected Fermi surfaces in superconducting LaFeAsO${}_{1-x}$F${}_x$}
• Superconductivity at 36 K in beta-Fe1.01Se with the compression of the interlayer separation under pressure
• Near-degeneracy of several pairing channels in multiorbital models for the Fe-pnictides
• Antiferromagnetic order and spin dynamics in iron-based superconductors
• Magnetism, superconductivity, and pairing symmetry in Fe-based superconductors
• Strong Correlations and Magnetic Frustration in the High Tc Iron Pnictides
• Theory of Electron Nematic Order in LaOFeAs
• Effect of Structural Parameters on Superconductivity in Fluorine-Free LnFeAsO1-y (Ln=La,Nd)
• Magnetism and its microscopic origin in iron-based high-temperature superconductors
• Correlated electronic structure of LaOFeAs
• A minimal two-band model for the superconducting Fe-pnictides
• Ising and Spin orders in Iron-based Superconductors
• Heavily electron-doped electronic structure and isotropic superconducting gap in AxFe2Se2 (A=K,Cs)
• Electronic Structure and Doping in BaFe${}_2$As${}_2$ and LiFeAs: Density Functional Calculations
• Why Does Undoped FeSe Become A High Tc Superconductor Under Pressure?
• Structure determination and coexistence of superconductivity and antiferromagnetic order in (Li0.8Fe0.2)OHFeSe
• Pairing Symmetry in a Two-Orbital Exchange Coupling Model of Oxypnictides
• Orbital-driven nematicity in FeSe
• Field-induced superconducting phase of FeSe in the BCS-BEC cross-over
• Emergence of the nematic electronic state in FeSe
• The challenge of unravelling magnetic properties in LaFeAsO
• Spin-orbital frustrations and anomalous metallic state in iron-pnictide superconductors
• Effect of magnetic frustration on nematicity and superconductivity in Fe chalcogenides
• Theory of magnetic excitations in iron-based layered superconductors
• Reconstruction of Band Structure Induced by Electronic Nematicity in an FeSe Superconductor
• ${}^{75}$As NMR studies of superconducting LaO${}_{0.9}$F${}_{0.1}$FeAs
• Proximity of antiferromagnetism and superconductivity in LaO${}_{1-x}$F${}_x$FeAs: effective Hamiltonian from ab initio studies
• Origin of the tetragonal-to-orthorhombic (nematic) phase transition in FeSe: a combined thermodynamic and NMR study
• Two-dimensional resonant magnetic excitation in BaFe1.84Co0.16As2
• Observation of a Robust Zero-energy Bound State in Iron-based Superconductor Fe(Te,Se)
• Lifting of xz/yz orbital degeneracy at the structural transition in detwinned FeSe
• Spin Gap and Resonance at the Nesting Wavevector in Superconducting FeSe0.4Te0.6
• Iron-based layered superconductor LaO${}_{1-x}$F${}_x$FeAs: an antiferromagnetic semimetal
• Spin-singlet superconductivity with multiple gaps in PrO0.89F0.11FeAs
• Spin fluctuations and superconductivity in a 3D tight-binding model for BaFe2As2
• Self-Consistent Vertex Correction Analysis for Iron-Based Superconductors: Mechanism of Coulomb-Interaction-Driven Orbital Fluctuations
• Spin-triplet p-wave pairing in a 3-orbital model for iron pnictide superconductors
• Anomalous Fermi surface in FeSe seen by Shubnikov-de Haas oscillation measurements
• Anisotropic Energy Gaps of Iron-based Superconductivity from Intra-band Quasiparticle Interference in LiFeAs
• Three-dimensional Resonance in superconducting BaFe${}_{1.9}$Ni${}_{0.1}$As${}_2$
• Pairing State with a time-reversal symmetry breaking in FeAs based superconductors
• NMR relaxation rate in superconducting pnictides: extended $s_{\pm }$ scenario
• Observation of two distinct $d_{xz}/d_{yz}$ band splittings in FeSe
• Superfluid density of the $\pm$s-wave state for the iron-based superconductors
• Strong nodeless pairing on separate electron Fermi surface sheets in (Tl, K)Fe${}_{1.78}$Se${}_2$ probed by ARPES
• Origin of Gap Anisotropy in Spin Fluctuation Models of the Fe-pnictides
• Inter-pocket pairing and gap symmetry in Fe-based superconductors with only electron pockets
• Fe-based superconductors: seven years later
• Lifting of nodes by disorder in extended-$s$ state superconductors: application to ferropnictides
• On the multi-orbital band structure and itinerant magnetism of iron-based superconductors
• Symmetry of spin excitation spectra in the tetragonal paramagnetic and superconducting phases of 122-ferropnictides
• Even Parity, Orbital Singlet and Spin Triplet Pairing for Superconducting $La(O_{1-x}{F}_x)FeAs$
• Neutron Scattering Resonance and the Fe-pnictide Superconducting Gap
• The origin of nematic order in FeSe
• Pairing symmetry in a two-orbital Hubbard model on a square lattice
• Synthesis of a new alkali metal-organic solvent intercalated iron selenide superconductor with Tc{\approx}45K
• Orbital Fluctuation Theory in Iron Pnictides: Effects of As-Fe-As Bond Angle, Isotope Substitution, and $Z^2$-Orbital Pocket on the Superconductivity
• Electronic nematic susceptibility of iron-based superconductors
• Spin fluctuations in LiFeAs observed by neutron scattering
• Disorder-induced topological change of the superconducting gap structure in iron pnictides
• A Generic Two-band Model for Unconventional Superconductivity and Spin-Density-Wave Order in Electron and Hole Doped Iron-Based Superconductors
• Strong-coupling Spin-singlet Superconductivity with Multiple Full Gaps in Hole-doped Ba${}_{0.6}$K${}_{0.4}$Fe${}_2$As${}_2$ Probed by Fe-NMR
• 59-Co and 75-As NMR Investigation of Electron-Doped High Tc Superconductor BaFe(1.8)Co(0.2)As(2) (Tc = 22K)
• Antiferromagnetic ordering in the absence of a structural distortion in Ba(Fe{1-x}Mn{x})2As2
• Coulomb repulsion and correlation strength in LaFeAsO from Density Functional and Dynamical Mean-Field Theories
• Superconductivity at Tc = 44 K in LixFe2Se2(NH3)y
• Interplay between magnetic properties and Fermi surface nesting in iron pnictides
• Spin fluctuations in iron pnictides and chalcogenides: From antiferromagnetism to superconductivity
• Fourier transform spectroscopy of d-wave quasiparticles in the presence of atomic scale pairing disorder
• Disorder-Induced Static Antiferromagnetism in Cuprate Superconductors
• Synthesis and post-annealing effects of alkaline-metal-ethylenediamine-intercalated superconductors Ax(C2H8N2)yFe2-zSe2 (A = Li, Na) with Tc = 45 K
• Interpretation of scanning tunneling quasiparticle interference and impurity states in cuprates
• Angle-resolved photoemission evidence of s-wave superconducting gap in KxFe2-ySe2 superconductor
• Observation of strong electron pairing on bands without Fermi surfaces in LiFe1-xCoxAs
• ${}^{75}$As NQR and NMR studies of superconductivity and electron correlations in iron arsenide Li${}_x$FeAs
• Nodes in the Gap Function of LaFePO, the Gap Function of the Fe(Se,Te) Systems, and the STM Signature of the s${}_{\pm }$ Pairing
• Magnetic interactions in iron superconductors: A review
• Model of Electronic Structure and Superconductivity in Orbitally Ordered FeSe
• Impurity Effects in Sign Reversing Fully-Gapped Superconductors: Analysis of FeAs Superconductors
• Theory for Magnetism and Triplet Superconductivity in LiFeAs
• Antiferromagnetic Correlation and the Pairing Mechanism of the Cuprates and Iron Pnictides : a View From the Functional Renormalization Group Studies
• Unified picture of the doping dependence of superconducting transition temperatures in alkali metal/ammonia intercalated FeSe
• Unfolding of the electronic structure through the induced representations of space groups: Application to Fe-based superconductors
• Pinpointing Gap Minima in Ba(Fe${}_{0.94}$Co${}_{0.06}{)}_2$As${}_2$ \textit{via} Band Structure Calculations and Electronic Raman Scattering
• Effects of cobalt doping and three-dimensionality in $BaF{e}_{2}A{s}_2$
• Determining gap nodal structures in Fe-based superconductors: angle-dependence of the low temperature specific heat in an applied magnetic field
• The role of striction at magnetic and structural transitions in iron-pnictides
• Theory of Raman response in a superconductor with extended s-wave symmetry: Application to Fe-pnictides
• Enhancing magnetic stripe order in iron pnictides by RKKY exchange interactions
• Model for nodal quasiparticle scattering in a disordered vortex lattice
• Single Impurity Problem in Iron-Pnictide Superconductors
• Unexpected impact of magnetic disorder on multiband superconductivity
• Spectral properties of transition metal pnictides and chalcogenides: angle-resolved photoemission spectroscopy and dynamical mean field theory
• Sudden reversal in the pressure dependence of Tc in the iron-based superconductor CsFe2As2: A possible link between inelastic scattering and pairing symmetry
• Magnetic field evolution of the quasiparticle interference in a d-wave superconductor
• Magnetic excitations of Fe_{1+y}Se_xTe_{1-x} in magnetic and superconductive phases
• Manipulation of gap nodes by uniaxial strain in iron-based superconductors
• Orbital Degeneracy and the Microscopic Model of the FeAs Plane in the Iron-Based Superconductors
• Glide-Plane Symmetry and Superconducting Gap Structure of Iron-Based Superconductors
• Single nonmagnetic impurity resonance in FeSe-based 122-type superconductors as a probe for pairing symmetry

Cited by in corpus (116)

• Electronic structure of quantum materials studied by angle-resolved photoemission spectroscopy
• Discovery of Orbital-Selective Cooper Pairing in FeSe
• Unconventional Superconductivity
• Orbital selective pairing and gap structures of iron-based superconductors
• On the Remarkable Superconductivity of FeSe and its Close Cousins
• Anisotropic spin fluctuations in detwinned FeSe
• Orbital selective pairing and superconductivity in iron selenides
• Orbital selectivity and emergent superconducting state from quasi-degenerate $s-$ and $d-$wave pairing channels in iron-based superconductors
• Ultra-high critical current densities, the vortex phase diagram and the effect of granularity of the stoichiometric high-Tc superconductor, CaKFe${}_4$As${}_4$
• Strong Correlations, Strong Coupling and s-wave Superconductivity in Hole-doped BaFe2As2 Single Crystals
• Energy Gap Evolution Across the Superconductivity Dome in Single Crystals of (Ba${}_{1-x}$K${}_x$)Fe${}_2$As${}_2$
• Superconductivity in nickel based 112 systems
• Superconducting Properties of the $s^{\pm }$-wave state: Fe-based superconductors
• High Tc via spin fluctuations from incipient bands: application to monolayers and intercalates of FeSe
• Enhancement of Tc by point-like disorder and anisotropic gap in FeSe
• Nodeless multiband superconductivity in stoichiometric single crystalline CaKFe${}_4$As${}_4$
• Influence of the multiband sign changing superconductivity on the vortex cores and on vortex pinning in the new stoichiometric high Tc CaKFe4As4
• Nodeless superconductivity in kagome metal CsV${}_3$Sb${}_5$ with and without time reversal symmetry breaking
• Nematic Pairing from Orbital Selective Spin Fluctuations in FeSe
• Signature of the Leggett mode in the A1g Raman response: from MgB2 to iron-based superconductors
• Superconducting gap structure of FeSe
• Topological Ultranodal pair states in iron-based superconductors
• Hund's induced Fermi-liquid instabilities and enhanced quasiparticle interactions
• Superconductivity from repulsive interactions on the kagome lattice
• Orbital selectivity enhanced by nematic order in FeSe
• Orbital-selective Mott phase in multiorbital models for iron pnictides and chalcogenides
• Impurities in multiband superconductors
• High-field transport properties of a P-doped BaFe2As2 film on technical substrate
• Orbital selectivity in electron correlations and superconducting pairing of iron-based superconductors
• Iron-based superconductivity extended to the novel silicide LaFeSiH
• Role of vertex corrections in the matrix formulation of the random phase approximation for the multiorbital Hubbard model
• Influence of Spin Orbit Coupling in the Iron-Based Superconductors
• Nodal gaps in the nematic superconductor FeSe from heat capacity
• Electronic properties, low-energy Hamiltonian and superconducting instabilities in CaKFe${}_4$As${}_4$
• Probing the pairing interaction and multiple Bardasis-Schrieffer modes using Raman spectroscopy
• Tracing the $s_{\pm }$-symmetry in iron pnictides by controlled disorder
• Superfluid density and microwave conductivity of FeSe superconductor: ultra-long-lived quasiparticles and extended s-wave energy gap
• Unconventional superconductivity protected from disorder on the kagome lattice
• Electron irradiation effects on superconductivity in PdTe${}_2$: an application of a generalized Anderson theorem
• Novel three-dimensional Fermi surface and electron-correlation-induced charge density wave in FeGe
• Evidence for d-wave superconductivity in single layer FeSe/SrTiO3 probed by quasiparticle scattering off step edges
• Hubbard interactions in iron-based pnictides and chalcogenides: Slater parametrization, screening channels and frequency dependence
• Conservation laws, vertex corrections, and screening in Raman spectroscopy
• Multiorbital singlet pairing and $d+d$ superconductivity
• Spin resonance in the superconducting state of Li${}_{1-x}$Fe${}_x$ODFe${}_{1-y}$Se observed by neutron spectroscopy
• The electron-phonon interaction with forward scattering peak is a relevant approach to high Tc superconductivity in FeSe films on SrTiO3 and TiO2
• Impact of Iron-site defects on Superconductivity in LiFeAs
• Towards a quantitative description of tunneling conductance of superconductors: application to LiFeAs
• Analytical slave-spin mean-field approach to orbital selective Mott insulators
• Chiral Majorana Hinge Modes in Superconducting Dirac Materials
• High Tc superconductivity in CaKFe${}_4$As${}_4$ in absence of nematic fluctuations
• Interplay between superconductivity and itinerant magnetism in underdoped Ba${}_{1-x}$K${}_x$Fe${}_2$As${}_2$ ($x=$ 0.2) probed by the response to controlled point-like disorder
• Impurity-induced bound states inside the superconducting gap of FeSe
• Effect of gap anisotropy on the spin resonance peak in the superconducting state of iron-based materials
• Orbital-dependent self-energy effects and consequences for the superconducting gap structure in multi-orbital correlated electron systems
• Robustness of Quasiparticle Interference Test for Sign-changing Gaps in Multiband Superconductors
• Broken mirror symmetry, incommensurate spin correlations, and $B_{2g}$ nematic order in iron pnictides
• Subdominant $d$-wave interaction in superconducting CaKFe${}_4$As${}_2$?
• Impact of topology on the impurity effects in extended $s$-wave superconductors with spin-orbit coupling
• Crossover from impurity-controlled to granular superconductivity in (TMTSF)2ClO4
• Electron and Superconducting Properties of the AFeAs (A= Li, Na) Family Alkali-Metal Pnictides: Current Stage of the Research (mini-review)
• Spin fluctuation anisotropy as a probe of orbital-selective hole-electron quasiparticle excitations in detwinned Ba(Fe1-xCox)2As2
• Iron-based superconductors: tales from the nuclei
• Effect of nonmagnetic impurities on $s_{\pm }$ superconductivity in the presence of incipient bands
• Synthesis, phase stability, structural and physical properties of 11-type iron chalcogenides
• Zero-bias anomaly in nano-scale hole-doped Mott insulators on a triangular silicon surface
• Superconductivity in 2D electron gas induced by high energy optical phonon mode and large polarization of the STO substrate
• Electronic vortex structure of Fe-based superconductors: application to LiFeAs
• Identifying Topological Superconductivity in 2D Transition-Metal Dichalcogenides
• The Coulomb problem in iron based superconductors
• Fluctuations and pairing in Fe-based superconductors: Light scattering experiments
• Structure of the pairing gap from orbital nematic fluctuations
• Cooper pairs without 'glue' in high-$T_c$ superconductors
• Effects of momentum-dependent quasiparticle renormalization on the gap structure of iron-based superconductors
• Evidence of nodal superconductivity in LaFeSiH
• Local characterization of a heavy-fermion superconductor via sub-Kelvin magnetic force microscopy
• Details of the disorder-induced transition between $s_{\pm }$ and $s_{++}$ states in two-band model for Fe-based superconductors
• Effect of disorder on the competition between nematic and superconducting order in FeSe
• Superconducting Order Parameter and Bosonic Mode in Hydrogen-Substituted NdFeAsO${}_{0.6}$H${}_{0.36}$ Revealed by Multiple Andreev Reflection Spectroscopy
• Quasiparticle Interference and Symmetry of Superconducting Order Parameter in Strongly Electron-Doped Iron-based Superconductors
• Anomalous magneto-elastic coupling in Au-doped BaFe2As2
• Constraints on the total coupling strength to bosons in iron based superconductors
• Accurate modeling of FeSe with screened Fock exchange and Hund's metal correlations
• Linear mapping between magnetic susceptibility and entanglement in conventional and exotic one-dimensional superfluids
• Multi-Atom Quasiparticle Scattering Interference for Superconductor Energy-Gap Symmetry Determination
• Anisotropic magnetic excitations of a frustrated bilinear-biquadratic spin model -- Implications for spin waves of detwinned iron pnictides
• Orbital-selective correlations and renormalized electronic structure in LiFeAs
• Friedel oscillations and chiral superconductivity in monolayer NbSe${}_2$
• Superconducting Order Parameters in overdoped BaFe${}_{1.86}$Ni${}_{0.14}$As${}_2$ Revealed by Multiple Andreev Reflection Spectroscopy of Planar Break-Junctions
• Iron-based superconductors: Foreword
• Stabilization of $s$-wave superconductivity through arsenic $p$-orbital hybridization in electron-doped BaFe${}_2$As${}_2$
• In-plane p-wave coherence length in iron-based superconductors
• Unconventional pairing in Ising superconductors: Application to monolayer NbSe${}_2$
• Doping evolution of the gap structure and spin-fluctuation pairing in $Ba(F{e}_{1-x}C{o}_x{)}_{2}A{s}_2$ superconductors
• Quasiparticle interference in multiband superconductors with strong coupling
• Spin and charge susceptibilities of the two-orbital model within the cluster perturbation theory for Fe-based materials
• Exploring multichannel superconductivity in ThFeAsN
• Theory of potential impurity scattering in pressurized superconducting La${}_3$Ni${}_2$O${}_7$
• Effect of nonsymmorphic space group on correlation functions in iron-based superconductors
• Evidence of a multiple boson emission in Sm${}_{1-x}$Th${}_x$OFeAs
• Superconductivity and phonon self-energy effects in Fe${}_{1+y}$Te${}_{0.6}$Se${}_{0.4}$
• Nonlocal electrodynamics and the penetration depth of superconducting Sr${}_2$RuO${}_4$
• Magnetic disorder and gap symmetry in optimally electron doped Sr(Fe, Co)${}_2$As${}_2$ superconductor
• Charge correlations suppress unconventional pairing in the Holstein model
• Decisive proofs of the $s_{\pm }\to s_{++}$ transition in the temperature dependence of the magnetic penetration depth
• Re-entrant topological order in strongly correlated nanowire due to Rashba spin-orbit coupling
• Thermodynamics of $s_{\pm }-to-s_{++}$ transition in iron pnictides in the vicinity of the Born limit
• Putative quantum critical point in the itinerant magnet ZrFe${}_4$Si${}_2$ with a frustrated quasi-one-dimensional structure
• The role of orbital nesting in the superconductivity of Iron-based Superconductors
• Critical point of the transition between $s_{\pm }$ and $s_{++}$ states of a two-band superconductor with nonmagnetic impurities
• Three-dimensional spin susceptibility in Ba${}_{0.75}$K${}_{0.25}$Fe${}_2$As${}_2$: Out-of-plane modulation revealed by neutron spectroscopy and theoretical modeling
• "Universal" ${\Delta }_{max}/T_c$ in Fe Based Superconductors
• Particular type of gap in the spectrum of multiband superconductors
• Proximity-induced hidden order transition in a correlated heterostructure Sr${}_2$VO${}_3$FeAs
• PhD Thesis: Electronic correlations in multiorbital systems
• Specific Heat and the gap structure of a Nematic Superconductor, application to FeSe