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Doping Dependence of Gap Inhomogeneities at Bi$_{2}$Sr$_{2}$CaCu$_{2}$O$_{8+δ}$ SurfacesOct 22 2011We study the inhomogeneity of the electronic pairing gap observed by STM near the surface of Bi$_{2}$Sr$_{2}$CaCu$_{2}$O$_{8+\delta}$ to be correlated with interstitial O defects. We treat the problem in a slave boson mean field theory of a disordered ... More

Order Parameter "Holes" and Theory of Microwave Conductivity in YBCOJul 09 1999We propose that the low temperature discrepancy between simple d-wave models of the microwave conductivity and existing experiments on single crystals of YBCO can be resolved by including the scattering of quasiparticles from "holes" of the order parameter ... More

The Kondo lattice model from strong-coupling viewpointNov 30 2001We present some preliminary results on the phase diagram of the 2D S=1/2 Kondo lattice model at finite doping. As a starting point the Hamiltonian is written in terms of local spin and charge excitations, and the interactions between these modes are subsequently ... More

Nonzero Fermi Level Density of States for a Disordered d-Wave SuperconductorApr 29 1996It has been known for some time that, in three dimensions, arbitrarily weak disorder in unconventional superconductors with line nodes gives rise to a nonzero residual density of zero-energy quasiparticle states N(0), leading to characteristic low-temperature ... More

Quasiparticle Interference and Symmetry of Superconducting Order Parameter in Strongly Electron-Doped Iron-based SuperconductorsMar 14 2019Motivated by recent experimental reports of significant spin-orbit coupling (SOC) and a sign-changing order-parameter in the Li$_{1-x}$Fe$_x$(OHFe)$_{1-y}$Zn$_y$Se superconductor with only electron pockets present, we study the possible Cooper-pairing ... More

Quasiparticle Transport in the Vortex State of Unconventional SuperconductorsSep 04 1998I consider the problem of the vortex contribution to quasiparticle transport in unconventional superconductors with line nodes, a nd argue that the magnetic field dependence of transport coefficients is fixed by the same scattering processes which limit ... More

Using Gap Symmetry and Structure to Reveal the Pairing Mechanism in Fe-based SuperconductorsOct 05 2015Jan 09 2016I 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 ... More

Nodes to the grindstone: viewpoint on ``Band- and momentum-dependent electron dynamics in superconducting Ba(Fe$_{1-x}$Co$_x$)$_2$As$_2$ as seen via electronic Raman scattering" [arXiv:0910.0898]Dec 18 2009Raman spectroscopy of a cobalt-doped iron-pnictide superconductor reveals the complex electronic structure of the superconducting state in this material. [Viewpoint on Phys. Rev. B 80, 180510 (2009), arXiv:0910.0898]

Superconducting phase diagram of the paramagnetic one-band Hubbard modelMay 23 2016Sep 06 2016We study spin-fluctuation-mediated superconductivity in the one-band Hubbard model. Higher order effective interactions in $U$ give rise to a superconducting instability which is very sensitive to changes in the Fermi surface topology arising as a function ... More

Magnetic field -induced phase transition in a $d_{x^2-y^2}$-wave superconductor at low temperaturesMar 23 1998Apr 16 1998We consider, within BCS weak coupling theory, the instability of a $d_{x^2-y^2}$-wave superconductor to a state of mixed symmetry $d+iq$, $q=d_{xy},s$. In zero magnetic field we show that there is a large and physically reasonable range of interaction ... More

Magnetic correlations on the full chains of Ortho-II YBa$_2$Cu$_3$O$_{6.5}$Nov 26 2008Nov 27 2008We propose that the NMR line shape on the chain Cu in the stoichiometric high-$T_c$ superconductor Ortho-II YBa$_2$Cu$_3$O$_{6.5}$ is determined by the magnetization induced on Cu near O vacancies, due to strong magnetic correlations in the chains. An ... More

Transport Properties of d-Wave Superconductors in the Vortex StateJan 12 1998We calculate the magnetic field dependence of quasiparticle transport properties in the vortex state of a d-wave superconductor arising solely from the quasiparticle's Doppler shift in the superflow field surrounding the vortex. Qualitative features agree ... More

Angle-dependent magnetothermal conductivity in d-wave superconductorsDec 14 1999We analyse the behavior of the thermal conductivity, $\kappa(H)$, in the vortex state of a quasi-two-dimensional d-wave superconductor when both the heat current and the applied magnetic field are in the basal plane. At low temperature the effect of the ... More

Thermal Conductivity Anisotropy in Superconducting $UPt_3$Oct 25 1994Recent thermal conductivity measurements on $UPt_3$ single crystals by Lussier et al. indicate the existence of a strong b--c anisotropy in the superconducting state. We calculate the thermal conductivity in various unconventional candidate states appropriate ... More

Quasiparticles in the Vortex State of Dirty d-Wave SuperconductorsFeb 25 1998We consider the problem of the vortex contribution to thermal properties of dirty d-wave superconductors. In the clean limit, Volovik has argued that the main contribution to the density of states in a d-wave superconductor arises from extended quasiparticle ... More

Collective modes in superconductors with competing s- and d-wave interactionsJul 27 2015Sep 17 2015We calculate the collective mode spectrum in models of superconductors with attractive interactions in s-and d channels as a function of their relative strength, across a phase diagram that includes transition between s, s+id, and d-wave ground states. ... More

Effect of disorder on the competition between nematic and superconducting order in FeSeJul 29 2016Oct 10 2016Crystalline FeSe is known to display strong nematic order below a weak tetragonal-orthorhombic structural transition around $T_s\sim 90$K, and a superconducting transition at $T_c\sim 9K$. Recently, it was shown that electron irradiation, which creates ... More

Vortex Contribution to Specific Heat of Dirty $d$-Wave Superconductors: Breakdown of ScalingAug 28 1997Feb 25 1998We consider the problem of the vortex contribution to thermal properties of dirty d-wave superconductors. In the clean limit, the main contribution to the density of states in a d-wave superconductor arises from extended quasiparticle states which may ... More

Orbital selective pairing and gap structures of iron-based superconductorsNov 08 2016May 08 2017We discuss the influence on spin-fluctuation pairing theory of orbital selective strong correlation effects in Fe-based superconductors, particularly Fe chalcogenide systems. We propose that a key ingredient for an improved itinerant pairing theory is ... More

Orbital selective pairing and gap structures of iron-based superconductorsNov 08 2016We discuss the influence on spin-fluctuation pairing theory of orbital selective strong correlation effects in Fe-based superconductors, particularly Fe chalcogenide systems. We propose that a key ingredient for an improved itinerant pairing theory is ... More

Imaging Orbital-selective Quasiparticles in the Hund's Metal State of FeSeFeb 06 2018Jul 22 2018Strong electronic correlations, emerging from the parent Mott insulator phase, are key to copper-based high temperature superconductivity (HTS). By contrast, the parent phase of iron-based HTS is never a correlated insulator. But this distinction may ... More

Discovery of Orbital-Selective Cooper Pairing in FeSeNov 07 2016FeSe is the focus of intense research interest because of its unusual non-magnetic nematic state and because it forms the basis for achieving the highest critical temperatures of any iron-based superconductor. However, its Cooper pairing mechanism has ... More

Visualizing Orbital-selective Quasiparticle Interference in the Hund's Metal State of FeSeFeb 06 2018High temperature superconductivity (HTS) in Cu-based materials is generated by strong electronic correlations due to proximity of the Mott insulator phase. By contrast, the undoped phase proximate to Fe-based HTS is never an insulator. But this striking ... More

Singular current response from isolated impurities in d-wave superconductorsMar 15 2002Oct 10 2002The current response of a d-wave superconductor containing a single impurity is calculated and shown to be singular in the low-temperature limit, leading in the case of strong scattering to a 1/T term in the penetration depth $\lambda(T)$ similar to that ... More

Discovery of Orbital-Selective Cooper Pairing in FeSeNov 07 2016May 22 2017The superconductor FeSe is of intense interest thanks to its unusual non-magnetic nematic state and potential for high temperature superconductivity. But its Cooper pairing mechanism has not been determined. Here we use Bogoliubov quasiparticle interference ... More

Optical and Thermal-Transport Properties of an Inhomogeneous d-Wave SuperconductorAug 30 2001Apr 15 2002We calculate transport properties of disordered 2D d-wave superconductors from solutions of the Bogoliubov-de Gennes equations, and show that weak localization effects give rise to a finite frequency peak in the optical conductivity similar to that observed ... More

Theory of Thermal Conductivity in YBa_2Cu_3O_{7-δ}Oct 21 1996We calculate the electronic thermal conductivity in a d-wave superconductor, including both the effect of impurity scattering and inelastic scattering by antiferromagnetic spin fluctuations. We analyze existing experiments, particularly with regard to ... More

Effective doping and suppression of Fermi surface reconstruction via Fe vacancy disorder in KxFe2-ySe2Apr 12 2012We investigate the effect of disordered vacancies on the normal-state electronic structure of the newly discovered alkali-intercalated iron selenide superconductors. To this end we use a recently developed Wannier function based method to calculate from ... More

Fe-based superconductors: seven years laterDec 22 2014Iron-based superconductors were discovered seven years ago, in 2008. This short review summarizes what we learned about these materials over the last seven years, what are open questions, and what new physics we expect to extract from studies of this ... More

Effect of dopant atoms on local superexchange in cuprate superconductors: a perturbative treatmentSep 17 2008Apr 21 2009Recent scanning tunneling spectroscopy experiments have provided evidence that dopant impurities in high- Tc superconductors can strongly modify the electronic structure of the CuO2 planes nearby, and possibly influence the pairing. To investigate this ... More

Scattering by impurity-induced order parameter ``holes'' in d-wave superconductorsSep 19 1998Nonmagnetic impurities in d-wave superconductors cause strong local suppressions of the order parameter. We investigate the observable effects of the scatterigng off such suppressions in bulk samples by treating the order parameter "hole" as a pointlike ... More

Renormalization of thermal conductivity of disordered d-wave superconductors by impurity-induced local momentsJul 26 2006Aug 01 2006The low-temperature thermal conductivity \kappa_0/T of d-wave superconductors is generally thought to attain a "universal" value independent of disorder at sufficiently low temperatures, providing an important measure of the magnitude of the gap slope ... More

Extinction of quasiparticle interference in underdoped cuprates with coexisting orderNov 23 2008Recent scanning tunnelling spectroscopy measurements [Y. Koksaka et al., Nature 454, 1072 (2008)] have shown that dispersing quasiparticle interference peaks in Fourier transformed conductance maps disappear as the bias voltage exceeds a certain threshold ... More

Heat Transport and the Nature of the Order Parameter in Superconducting $UPt_3$Sep 08 1995Recent thermal conductivity data on the heavy fermion superconductor $UPt_3$ have been interpreted as offering support for an $E_{2u}$ model of the order parameter as opposed to an $E_{1g}$ model. In this paper, we analyze this issue from a theoretical ... More

Microwave conductivity of d-wave superconductors with extended impuritiesNov 12 2004We investigate the influence of extended scatterers on the finite temperature and finite frequency microwave conductivity of d-wave superconductors. For this purpose we generalize a previous treatment by Durst and Lee, which is based on a nodal approximation ... More

Magnetic field dependence of the penetration depth of d-wave superconductors with strong isolated impuritiesAug 24 2003A d-wave superconductor with isolated strong non-magnetic impurities should exhibit an upturn in the penetration depth at low temperatures. Here we calculate how an external magnetic field supresses this effect.

Transport properties of 3D extended s-wave states in Fe-based superconductorsJan 29 2011Jul 29 2011The Fermi surfaces of Fe-pnictide superconductors are fairly two-dimensional (2D), and it has thus come as a surprise that recent penetration depth and thermal conductivity measurements on systems of the 122 type have reported c-axis transport coefficients ... More

Distinguishing d-wave from highly anisotropic s-wave superconductorsMar 05 1994Apr 02 2010Systematic impurity doping in the Cu-O plane of the hole-doped cuprate superconductors may allow one to decide between unconvention al ("d-wave") and anisotropic conventional ("s-wave") states as possible candidates for the order parameter in these materials. ... More

$Π$ à la node: disordered d-wave superconductors in two dimensions for the random massesAug 29 2001We review work on the problem of disorder in the 2D d-wave superconducting state, and show that the symmetries of the normal state and the disorder distribution are vital for understanding the low-energy behavior. Most previous theoretical results for ... More

Multichannel Kondo impurities in superconductorsJun 18 1994We discuss the effect of multichannel Kondo impurities on superconductivity. In the strong coupling regime such impurities are pairbreakers, in contrast to the ordinary Kondo effect. Measurements of $T_c$-suppression may help in identifying impurities ... More

Low Temperature Properties of Anisotropic Superconductors with Kondo ImpuritiesJan 26 1994Jan 27 1994We present a self-consistent theory of superconductors in the presence of Kondo impurities, using large-$N$ slave-boson methods to treat the impurity dynamics. The technique is tested on the s-wave case and shown to give good results compared to other ... More

Theory of quasiparticle vortex bound states in Fe-based superconductors: application to LiFeAsNov 01 2011Spectroscopy of vortex bound states can provide valuable information on the structure of the superconducting order parameter. Quasiparticle wavefunctions are expected to leak out in the directions of gap minima or nodes, if they exist, and scanning tunneling ... More

Breakdown of universal transport in correlated d-wave superconductorsNov 14 2007Dec 13 2007The prediction and observation of low-temperature universal thermal conductivity in cuprates has served as a keystone of theoretical approaches to the superconducting state, but recent measurements on underdoped samples show strong violations of this ... More

Effects of Fermi Surface Anisotropy on Unconventional Superconductivity in UPt_3Mar 11 1998We discuss the weak-coupling BCS theory of the heavy fermion superconductor UPt_3, accounting for that system's anisotropic, multisheeted Fermi surface by expanding the order parameter and pair potential in terms of appropriate basis functions of the ... More

Ultranodal pair states in iron-based superconductorsMar 01 2019We show that multiband superconductors with dominant spin singlet, intraband pairing of spin-1/2 electrons can undergo a transition to a state with Bogolibuov Fermi surfaces -- surfaces of zero energy excitations that are topologically protected in the ... More

Experimental Demonstration of the Sign Reversal of the Order Parameter in (Li1-xFex)OHFe1-yZnySeApr 20 2017Iron pnictides are the only known family of unconventional high-temperature superconductors besides cuprates. Until recently, it was widely accepted that superconductivity is spin-fluctuation driven and intimately related to their fermiology, specifically, ... More

Thermodynamics of d-wave superconductors in a magnetic fieldNov 06 2000We investigate the thermodynamic properties of a two-dimensional d-wave superconductor in the vortex state using a semiclassical approach, and argue that such an approach is valid for the analysis of the experimental data on high-temperature superconductors. ... More

Spin excitations in layered antiferromagnetic metals and superconductorsJul 16 2012The proximity of antiferromagnetic order in high-temperature superconducting materials is considered a possible clue to the electronic excitations which form superconducting pairs. Here we study the transverse and longitudinal spin excitation spectrum ... More

Infrared conductivity of a d_{x^2-y^2}-wave superconductor with impurity and spin-fluctuation scatteringOct 23 1995Calculations are presented of the in-plane far-infrared conductivity of a d_{x^2-y^2}-wave superconductor, incorporating elastic scattering due to impurities and inelastic scattering due to spin fluctuations. The impurity scattering is modeled by short-range ... More

d-Wave Model for Microwave Response of High-Tc SuperconductorsMar 06 1994Mar 11 1994We develop a simple theory of the electromagnetic response of a d- wave superconductor in the presence of potential scatterers of arbitrary s-wave scattering strength and inelastic scattering by antiferromagnetic spin fluctuations. In the clean London ... More

Defects in correlated metals and superconductorsNov 06 2007In materials with strong local Coulomb interactions, simple defects such as atomic substitutions strongly affect both macroscopic and local properties of the system. A nonmagnetic impurity, for instance, is seen to induce magnetism nearby. Even without ... More

Relating STM, ARPES, and Transport in the Cuprate Superconducting StateSep 08 2004We discuss a wealth of data from various types of experiments which together suggest that the superconducting state of optimally to overdoped BSCCO-2212 can be well-described by the BCS theory with a d-wave gap together with small-angle scattering from ... More

Local quasiparticle lifetimes in a d-wave superconductorDec 30 2007Scanning tunnelling spectroscopy (STS) measurements find that the surface of Bi-2212 is characterized by nanoscale sized regions, "gap patches," which have different magnitudes for the d-wave energy gap. Recent studies have shown that the tunnelling conductance ... More

c-Axis Infrared Conductivity of a d_{x^2-y^2}-Wave Superconductor with Impurity and Spin-Fluctuation ScatteringAug 09 1996Results of a calculation of the c-axis infrared conductivity sigma_c for a d_{x^2-y^2}-wave superconductor which include both elastic impurity and inelastic spin-fluctuation scattering are presented and compared with the ab-plane conductivity sigma_{ab} ... More

Anomaly at Delta_k in the ARPES spectrum of dirty superconductorsOct 27 2004Jan 28 2005Elastic forward scattering can lead to an anomaly in the ARPES spectrum of the cuprate superconductors. Here we discuss how this anomaly can be used to provide a measurement of the superconducting gap Delta_k for k values away from the Fermi surface.

Elastic forward scattering in the cuprate superconducting stateJun 13 2004We investigate the effect of elastic forward scattering on the ARPES spectrum of the cuprate superconductors. In the normal state, small angle scattering from out-of-plane impurities is thought to broaden the ARPES spectral response with minimal effect ... More

Origin of electronic dimers in the spin-density wave phase of Fe-based superconductorsJul 18 2013Oct 30 2013We investigate the emergent impurity-induced states arising from point-like scatterers in the spin-density wave phase of iron-based superconductors within a microscopic five-band model. Independent of the details of the band-structure and disorder potential, ... More

Lower Bound for the Fermi Level Density of States of a Disordered D-Wave Superconductor in Two DimensionsMar 05 1997We consider a disordered d--wave superconductor in two dimensions. Recently, we have shown in an exact calculation that for a lattice model with a Lorentzian distributed random chemical potential the quasiparticle density of states at the Fermi level ... More

Robust determination of superconducting gap sign changes via quasiparticle interferenceJul 29 2015Feb 21 2016Phase-sensitive measurements of the superconducting gap in Fe-based superconductors have proven more difficult than originally anticipated. While quasiparticle interference (QPI) measurements based on scanning tunneling spectroscopy are often proposed ... More

Relaxation of Hot Quasiparticles in a d-Wave SuperconductorJul 08 2003Jan 23 2004Motivated by recent pump-probe experiments we consider the processes by which "hot" quasiparticles produced near the antinodes of a d-wave superconductor can relax. We show that in a large region of momentum space processes which break Cooper pairs are ... More

Inhomogeneous order-parameter suppression in disordered d-wave superconductorsFeb 21 2000Jul 22 2000We report on a numerical study of disorder effects in 2D d-wave BCS superconductors. We compare exact numerical solutions of the Bogoliubov-deGennes (BdG) equations for the density of states $\rho(E)$ with the standard T-matrix approximation. Local suppression ... More

Sublattice model of atomic scale pairing inhomogeneity in a superconductorJun 30 2008Jul 05 2008We study a toy model for a superconductor on a bipartite lattice, where intrinsic pairing inhomogeneity is produced by two different coupling constants on the sublattices. The simplicity of the model allows for analytic solutions and tests of the consequences ... More

Theory of Resistivity Upturns in Metallic CupratesMay 10 2009We propose that the experimentally observed resistivity upturn of cuprates at low temperatures may be explained by properly accounting for the effects of disorder in a strongly correlated metallic host. Within a calculation of the DC conductivity using ... More

Comment on ``Density of States of Disordered Two-Dimensional Crystals with Half-Filled Band''Feb 12 2001In a recent letter (PRL 84, 3930 (2000)) Nakhmedov et al. claimed that the Van Hove singularity at $\epsilon=0$ in the density of states (DoS) of the two-dimensional crystal with half-filled tight-binding band survives the addition of substitutional impurities. ... More

Proximity of antiferromagnetism and superconductivity in LaO$_{1-x}$F$_x$FeAs: effective Hamiltonian from ab initio studiesMar 21 2008May 01 2008We report density functional theory calculations for the parent compound LaOFeAs of the newly discovered 26K Fe-based superconductor LaO$_{1-x}$F$_x$FeAs. We find that the ground state is an ordered antiferromagnet, with staggered moment about 2.3$\mu_B$, ... More

Density of states "width parity" effect in d-wave superconducting quantum wiresOct 31 2000Jun 08 2001We calculate the density of states (DOS) in a clean mesoscopic d-wave superconducting quantum wire, i.e. a sample of infinite length but finite width $N$. For open boundary conditions, the DOS at zero energy is found to be zero if $N$ is even, and nonzero ... More

Correlation and disorder-enhanced nematic spin response in superconductors with weakly broken rotational symmetryNov 08 2011Recent experimental and theoretical studies have highlighted the possible role of a electronic nematic liquid in underdoped cuprate superconductors. We calculate, within a model of d-wave superconductor with Hubbard correlations, the spin susceptibility ... More

Gap symmetry and structure of Fe-based superconductorsJun 19 2011Oct 24 2011The recently discovered Fe-pnictide and chalcogenide superconductors display low-temperature properties suggesting superconducting gap structures which appear to vary substantially from family to family, and even within families as a function of doping ... More

Electron pairing in the presence of incipient bands in iron-based superconductorsAug 19 2015Recent experiments on certain Fe-based superconductors have hinted at a role for paired electrons in "incipient" bands that are close to, but do not cross the Fermi level. Related theoretical works disagree on whether or not strong-coupling superconductivity ... More

Comment on ``$T$-dependence of the magnetic penetration depth in unconventional superconductors at low temperatures: Can it be linear?"Jun 05 1998Oct 31 1998We comment on a recent letter by Schopohl and Dolgov (SD) which raised the possibility that a d-wave superconductor might be thermodynamically unstable in the limit $T\to 0$. The point of our comment is that this instability can be inevitably prevented ... More

Neutron Scattering Resonance and the Fe-pnictide Superconducting GapFeb 28 2009The existence of a neutron scattering resonance at a wavevector q* implies a sign change of the gap between two Fermi surface regions separated by wavevector q* . For the Fe pnictides, a resonance has been observed for a wavevector q* which connects a ... More

Two impurities in a d-wave superconductor:local density of statesAug 01 2002Jan 31 2003We study the problem of two local potential scatterers in a d-wave superconductor, and show how quasiparticle bound state wave functions interfere. Each single-impurity electron and hole resonance energy is in general split in the presence of a second ... More

Power spectrum of many impurities in a d-wave superconductorJul 10 2003Recently the structure of the measured local density of states power spectrum of a small area of the \BSCCO (BSCCO) surface has been interpreted in terms of peaks at an "octet" of scattering wave vectors determined assuming weak, noninterfering scattering ... More

Quantum interference in nested d-wave superconductors: a real-space perspectiveJan 31 2003We study the local density of states around potential scatterers in d-wave superconductors, and show that quantum interference between impurity states is not negligible for experimentally relevant impurity concentrations. The two impurity model is used ... More

Two routes to magnetic order by disorder in underdoped cupratesSep 08 2011We study disorder-induced magnetism within the Gutzwiller approximation applied to the t-J model relevant for cuprate superconductors. In particular, we show how disorder generates magnetic phases by inducing local droplets of antiferromagnetic order ... More

Reply to the Comment by A.A. Nersesyan and A.M. Tsvelik on the "Non--Zero Fermi Level Density of States for a Disordered d-Wave Superconductor in Two Dimensions" (PRL 77, 3013 (1996)) by K. Ziegler, M.H. Hettler and P.J. HirschfeldMar 05 1997In a recent Comment (cond-mat/9701197) on our Letter (PRL 77, 3013 (1996), cond-mat/9604176) Nersesyan and Tsvelik questioned the relevance of our exact calculation of the density of states (DOS) of a 2D d-wave superconductor using a Lorentzian disorder ... More

Superconducting gap variations induced by structural supermodulation in BSCCOApr 27 2007We discuss the possibility that the strain field introduced by the structural supermodulation in Bi-2212 and certain other cuprate materials may modulate the superconducting pairing interaction. We calculate the amplitude of this effect, visible in scanning ... More

Ab Initio Calculation of Impurity Effects in Copper Oxide MaterialsMay 01 2005We describe a method for calculating, within density functional theory, the electronic structure associated with typical defects which substitute for Cu in the CuO2 planes of high-Tc superconducting materials. The focus is primarily on Bi2Sr2CaCu2O8, ... More

Spin-dependent quasiparticle reflection and bound states at interfaces with itinerant antiferromagnetsAug 02 2004We present a formulation of the quasiclassical theory of junctions between itinerant antiferromagnets (AF) and s-wave (sSC) and d-wave superconductors (dSC). For the simplest two-sublattice antiferromagnet on a bipartite lattice, we derive Andreev-type ... More

Cubic Curves, Finite Geometry and CryptographyJul 21 2011Some geometry on non-singular cubic curves, mainly over finite fields, is surveyed. Such a curve has 9,3,1 or 0 points of inflexion, and cubic curves are classified accordingly. The group structure and the possible numbers of rational points are also ... More

Model of Electronic Structure and Superconductivity in Orbitally Ordered FeSeFeb 11 2015May 08 2015We provide a band structure with low-energy properties consistent with recent photoemission and quantum oscillations measurements on FeSe, assuming mean-field like s and/or d-wave orbital ordering at the structural transition. We show how the resulting ... More

Vortex in a d-wave superconductor at low temperaturesMar 09 2000Aug 24 2000A systematic perturbation theory is developed to describe the magnetic field-induced subdominant $s$- and $d_{xy}$-wave order parameters in the mixed state of a $d_{x^2-y^2}$-wave superconductor, enabling us to obtain, within weak-coupling BCS theory, ... More

Free Energy and Magnetic Penetration Depth of a $d$-Wave Superconductor in the Meissner StateJul 13 1999Mar 09 2000We investigate the free energy and the penetration depth of a quasi-two-dimensional d-wave superconductor in the presence of a weak magnetic field by taking account of thermal, nonlocal and nonlinear effects. In an approximation in which the superfluid ... More

Is the nonlinear Meissner effect unobservable?Aug 23 1998Dec 09 1998We examine the effects of nonlocal electrodynamics for a d-wave superconductor on the field dependence of the magnetic penetration depth. The linear field dependence predicted in the local limit, commonly known as the nonlinear Meissner effect, is instead ... More

On plane maximal curvesFeb 23 1998The genus of a maximal curve over a finite field with r^2 elements is either g_0=r(r-1)/2 or less than or equal to g_1=(r-1)^2/4. Maximal curves with genus g_0 or g_1 have been characterized up to isomorphism. A natural genus to be studied is g_2=(r-1)(r-3)/8, ... More

Observability of quantum phase fluctuations in cuprate superconductorsJun 20 2000Jan 04 2001We study the order parameter phase fluctuation effects in cuprate superconductors near T=0, using a quasi-two-dimensional d-wave BCS model. An effective phason theory is obtained which is used to estimate the strength of the fluctuations, the fluctuation ... More

Itinerant approach to magnetic neutron scattering of FeSe: effect of orbital selectivityJul 25 2018Jan 07 2019Recent STM experiments and theoretical considerations have highlighted the role of interaction-driven orbital selectivity in FeSe, and its role in generating the extremely anisotropic superconducting gap structure in this material. We study the magnetic ... More

The effect of disorder on electronic Raman scattering in the superconducting state of iron pnictidesJun 27 2010Electronic Raman scattering measures a polarization-dependent scattering intensity which can provide information about the location of nodes in the energy gap of an unconventional superconductor as well as its overall symmetry. In this paper, we calculate ... More

Theory of thermal conductivity in extended-$s$ state superconductors: application to ferropnictidesJul 27 2009Jul 27 2009Within a two-band model for the recently discovered ferropnictide materials, we calculate the thermal conductivity assuming general superconducting states of $A_{1g}$ ("s-wave") symmetry, considering both currently popular isotropic "sign-changing" $s$ ... More

Effect of nonmagnetic impurities on $s_\pm$ superconductivity in the presence of incipient bandsJun 01 2016Several Fe chalcogenide superconductors without hole pockets at the Fermi level display high temperature superconductivity, in apparent contradiction to naive spin fluctuation pairing arguments. Recently, scanning tunneling microscopy measurements have ... More

Spin excitations in a model of FeSe with orbital orderingOct 08 2015Jan 02 2016We present a theoretical study of the dynamical spin susceptibility for the intriguing Fe-based superconductor FeSe, based on a tight-binding model developed to account for the temperature-dependent band structure in this system. The model allows for ... More

Transport Properties of "Extended-s" State SuperconductorsJun 09 1995Superconducting states with "extended s-wave" symmetry have been suggested in connection with recent ARPES experiments on BSCCO. In the presence of impurities, thermodynamic properties of such states reflect a residual density of states $N(0)$ for a range ... More

Extinction of impurity resonances in large-gap regions of inhomogeneous d-wave superconductorsAug 07 2008Impurity resonances observed by scanning tunneling spectroscopy in the superconducting state have been used to deduce properties of the underlying pure state. Here we study a longstanding puzzle associated with these measurements, the apparent extinction ... More

Disorder-induced freezing of dynamical spin fluctuations in underdoped cupratesMay 04 2010May 21 2010We study the dynamical spin susceptibility of a correlated d-wave superconductor (dSC) in the presence of disorder, using an unrestricted Hartree-Fock approach. This model provides a concrete realization of the notion that disorder slows down spin fluctuations, ... More

Effect of Order-Parameter Suppression on Scattering by Isolated Impurities in Asymmetric BandsDec 09 1999The single-impurity problem in d-wave superconductors with asymmetric bands is discussed. The effect of local order parameter suppression near the impurity is to shift the quasiparticle resonance. Contrary to previous work [A. Shnirman et al., Phys. Rev. ... More

Quasi-particle Lifetimes in a d_{x^2-y^2} SuperconductorJun 08 2001We consider the lifetime of quasi-particles in a d-wave superconductor due to scattering from antiferromagnetic spin-fluctuations, and explicitly separate the contribution from Umklapp processes which determines the electrical conductivity. Results for ... More

Evolution of the neutron resonances in AFe2Se2Jun 22 2012Recent experiments on the alkali-intercalated iron selenides have raised questions about the symmetry of the superconducting phase. Random phase approximation calculations of the leading pairing eigenstate for a tight- binding 5-orbital Hubbard-Hund model ... More

Interface-induced d-wave pairingAug 09 2011We discuss a scenario for interface-induced superconductivity involving pairing by dipolar excitations proximate to a two-dimensional electron system controlled by a transverse electric field. If the interface consists of transition metal oxide materials, ... More

Nodal Quasiparticle Lifetimes in Cuprate SuperconductorsJul 29 2005Dec 19 2005A new generation of angular-resolved photoemission spectroscopy (ARPES) measurements on the cuprate superconductors offer the promise of enhanced momentum and energy resolution. In particular, the energy and temperature dependence of the on-shell nodal ... More

Using controlled disorder to distinguish $s_\pm$ and $s_{++}$ gap structure in Fe-based superconductorsOct 28 2012Dec 05 2013We reconsider the effect of disorder on the properties of a superconductor characterized by a sign-changing order parameter appropriate for Fe-based materials. Within a simple two band model, we calculate simultaneously $T_c$, the change in residual resistivity ... More