Scholarly Articles and Publications

Quantum Dynamics of Triplet Superconducting Circuits

Fri, 1 Mar 2013 22:29:14 -0600

Abstract: We generalize the formalism of circuit quantum electrodynamics to include spin-triplet superconducting elements. This generalization introduces the spin dynamics of Cooper pairs in addition to the phase and charge dynamics. For triplet superconductors the dynamics of spin is encoded in the D vector for the spin-projections of the Cooper pairs, and the conduction electronic spin polarization S. At frequencies below the superconducting gap h̵ω < ∆ the coupling of D and S - described by Leggett’s equations – leads to frequency shifts of the normal-state electron spin resonance. Quantization of a spin-triplet superconducting circuits is achieved by including the Hamiltonian that generates Leggett’s equations. Analytical and numerical results for the excitation frequencies of various elementary circuits are reported, the observation of which would allow the determination of key properties of the triplet superconducting pairing such as the “spin-orbit” energy.

Authors: David G. Ferguson, Jens Koch and J. A. Sauls
Publication: submitted to Phys. Rev. Lett. (2013).
Preprint: [PDF]

Chiral Phases of Superfluid 3He in an Anisotropic Medium

Thu, 21 Feb 2013 22:03:21 -0600

Abstract: Recent advances in the fabrication and characterization anisotropic of silica aerogels with exceptional homogeneity provide new insight into the nature of unconventional pairing in disordered anisotropic media. I report theoretical analysis and predictions for the equilibrium phases of superfluid 3He infused into a low-density, homogeneous uniaxial aerogel. Ginzburg-Landau (GL) theory for a class of equal-spin-pairing (ESP) states in a medium with uniaxial anisotropy is developed and used to analyze recent experiments on uniaxially strained aerogels. For 3He in an axially “stretched” aerogel GL theory predicts a transition from normal liquid into a chiral ABM phase at Tc1 in which the chirality axis, ˆl, is aligned along the strain axis. This orbitally aligned state, is protected from random fluctuations in the anisotropy direction, has a positive NMR frequency shift, a sharp NMR resonance line and is identified with the high-temperature ESP-1 phase of superfluid 3He in axially stretched aerogel. A second transition into a biaxial phase is predicted to onset at a slightly lower temperature, Tc2 < Tc1. This phase is an ESP state,breakst ime-reversal symmetry, and is defined by an orbital order parameter that spontaneously breaks axial rotation symmetry. This transition is driven by the coupling of an axially aligned 1D “polar” order parameter to the two time-reversed 2D axial ABM states. The biaxial phase has a continuous degeneracy associated with the projection of its chiral axis in the plane normal to the anisotropy axis. Theoretical predictions for the NMR frequency shifts of the biaxial phase provide an identification of the ESP-2 as the biaxial state, partially disordered by random anisotropy (Larkin-Imry-Ma effect). The “width” of the jump in the NMR frequency shift at Tc2 provides an estimate of the orbital domain size, ξLIM ≃ 5 μm at 18 bar. I show that the random anisotropy results from mesoscopic structures in silica aerogels. This model for the random anisotropy field is coarse-grained on the atomic scale, and is formulated in terms of local anisotropy in the scattering of quasiparticles in an aerogel with orientational correlations. Long-range order of locally anisotropic scattering centers is related to the splitting of the two ESP phases.

Author: J. A. Sauls
Publication: submitted to Physical Review B
Preprint: [PDF]

Eprint: ArXiv

Majorana Excitations, Spin- and Mass Currents on the Surface of the Topological Superfluid 3He-B

Sun, 10 Feb 2013 22:46:21 -0600

Abstract: The surface excitation spectrum and spin current of 3He-B with specular reflection is discussed. We report theoretical results for the surface the Andreev bound state and continuum spectrum, and present the results for spin current density on the surface of 3He-B. Surface states with momentum pf are spin polarized transverse to pf. A non-vanishing ground-state spin current is confined on the surface within a few coherence lengths. The temperature dependence of the spin current originates from the Majorana branches of excitations, and exhibits power law, T3, behavior for T ≪ Tc in the fully gapped B-phase.

Authors: Hao Wu and J. A. Sauls
Publication: submitted to Physical Review B
Preprint: [PDF]

Eprint: ArXiv

Surface states, Edge currents, and the Angular Momentum of Chiral P-wave Superfluids

Wed, 7 Dec 2011 08:12:47 -0600

Abstract: The spectra of fermionic excitations, pairing correlations and edge currents confined near the boundary of a chiral p-wave superfluid are calculated to leading order in ℏ/pf ξ . Results for the energy- and momentum-resolved spectral functions, including the spectral current density, of a chiral p-wave superfluid near a confining boundary are reported. The spectral functions reveal the subtle role of the chiral edge states (Weyl Fermion branch) in relation to the edge current and the angular momentum of a chiral p-wave superfluid, including the power law suppression of Lz(T) ≈ (N /2) ℏ [1 - β T2 ] for 0 ≲ T ≪ Tc in the fully gapped 2D chiral superfluid. The edge current and ground-state angular momentum are also shown to be sensitive to boundary conditions, and as a consequence the topology and geometry of the confining boundaries. For perfect specular boundaries the edge current accounts for the ground-state angular momentum, Lz = (N /2) ℏ, of a cylindrical disk of chiral superfluid with N /2 fermion pairs. Non-specular scattering can dramatically suppress the edge current. In the limit of perfect retro-reflection the edge states form a flat band of zero modes that are non-chiral and generate no edge current. For a chiral superfluid film confined in a cylindrical toroidal geometry the ground-state angular momentum is, in general, non-extensive, and can have a value ranging from Lz > (N/2) ℏ to Lz < −(N/2) ℏ depending on the ratio of the inner and outer radii and the degree of back scattering on the inner and outer surfaces. Non-extensive scaling of Lz, and the reversal of the ground-state angular momentum for a toroidal geometry, would provide a unique signature of broken time-reversal symmetry of the ground state of superfluid 3He-A, as well as direct observation of chiral edge currents.

Authors: J. A. Sauls
Publication: Phys. Rev. B. 84, 214509 (2011).
Local: [PDF]

Effects of Fractal Scaling and Lévy Flights on Transport of Liquid 3He in Aerogel

Fri, 28 Jan 2011 09:57:36 -0600

Abstract: The transport of heat by liquid 3He impregnated into silica aerogel is limited at low temperatures by elastic scattering of quasiparticles by the aerogel. The gossamer structure of silica aerogel is a realization of a random fractal - a solid with no long-range order, but power-law scaling of the density correlation function. Complementary to fractal scaling of the particle-particle correlation function is the appearance of a power law distribution of free flight paths. The open structure shown in the DLCA simulations of low-density aerogel leads to a distribution of exceedingly long flight paths governed by a Lévy distribution. I describe a theory for anomalous diffusion of quasiparticles in which the Lévy distribution of long free paths is interrupted by inelastic collisions between quasiparticles. These rare events lead to finite temperature corrections to the thermal diffusion coefficient of the form, κ/T = K0 − K1 (T /T*)β , where T* is the temperature at which the elastic and inelastic mean free paths are equal and β is related to the fractal dimension of the Lévy distribution.
Authors: J. A. Sauls
Publication: in preparation for Phys. Rev. B
Seminar: March APS Meeting & KettersonFest (Northwestern)

Impurity Effects on Vortex States in S-wave and D-wave superconductors

Sat, 22 Jan 2011 18:27:31 -0600

Abstract: The effects of impurity scattering on the equilibrium vortex lattice states in s- and d-wave superconductors are investigated quantitatively within quasiclassical theory of inhomogeneous superconductivity. Quantitative calculations of the pair potential, supercurrent, internal fields and local electronic states are reported in both the Born and unitarity limits. Striking differences in the electronic structure of vortex lattice states for s- and d-wave pairing are found for Born and unitary scattering. The zero-energy density of states at the vortex core is larger in unitarity limit than in Born limit for s-wave pairing, but the opposite is the case for d-wave pairing. Impurity scattering is also shown to suppress the Kramer-Pesch effect of vortex core shrinking in the T➝ 0 limit. Impurity effects on the magnetic field dependence of density of states, the paramagnetic susceptibility and flux line lattice form factor amplitude are reported. The theoretical results provide the basis for a quantitative comparison with experimental results for vortex lattice states for conventional and unconventional superconductors with impurity disorder.

Authors: M. Ichioka, K. Machida and J. A. Sauls
Publication: in preparation for Phys. Rev. B

Thermodynamic Potential for Superfluid 3He in Aerogel

Thu, 1 Jul 2010 14:34:11 -0500

Abstract: We present a free energy functional for superfluid 3He in the presence of homogeneously distributed impurity disorder which extends the Ginzburg-Landau free energy functional to all temperatures. We use the new free energy functional to calculate the thermodynamic potential, entropy, heat capacity and density of states for the B-phase of superfluid 3He in homogeneous, isotropic aerogel.

Authors: Sarosh Ali, Liangsheng Zhang and J. A. Sauls
Publication: Journal of Low Temperature Physics (Online First), December 10, 2010.
Local: [PDF]

Eprint: arXiv:1011.2513

Theory of Heat Transport of Normal Liquid 3He in Aerogel

Fri, 30 Oct 2009 14:48:57 -0500

Abstract: The introduction of liquid 3He into silica aerogel provides us a with model system in which to study the effects of disorder on the properties of a strongly correlated Fermi liquid. The transport of heat, mass and spin exhibits cross-over behavior from a high temperature regime, where inelastic scattering dominates, to a low temperature regime dominated by elastic scattering off the aerogel. We report exact and approximate solutions to the Boltzmann-Landau transport equation for the thermal conductivity of liquid 3He, including elastic scattering of quasiparticles by the aerogel and inelastic quasiparticle collisions. These results provide quantitative predictions for the transport properties of liquid 3He in aerogel over a wide range of pressure, temperature and aerogel density. In particular, we obtain a scaling function, F(T/T*), for the normalized thermal conductivity, K/Kel, in terms of a reduced temperature, T/T*, where T* is a cross-over temperature defined by the elastic and inelastic collision rates. Theoretical results are compared with the available experimental data for the thermal conductivity.

Authors: J. A. Sauls and P. Sharma
Publication: New J. Phys. 12, 083056 (2010)

Local: reprint
Eprint: arXiv:1003.1748

Charge Dynamics of Vortex Cores in Layered Chiral Triplet Superconductors

Sat, 11 Apr 2009 16:42:57 -0500

Abstract: In an accompanying paper [New J. Phys. 11 075008 (2009)] we have studied the equilibrium properties of vortices in a chiral quasi-two dimensional triplet superfluid/superconductor. Here we extend our studies to include the dynamical response of a vortex core in a chiral triplet superconductor to an external a.c. electromagnetic field. We consider in particular the response of a doubly quantized vortex with a homogeneous core in the time-reversed phase. The external frequencies are assumed to be comparable in magnitude to the superconducting gap frequency, such that the vortex motion is non-stationary but can be treated by linear response theory. We include broadening of the vortex core bound states due to impurity scattering and consider the intermediate clean regime, with a broadening comparable to or larger than the quantized energy level spacing. The response of the order parameter, impurity self energy, induced fields and currents are obtained by a self-consistent calculation of the distribution functions and the excitation spectrum. Using these results we obtain the self-consistent dynamically induced charge distribution in the vicinity of the core. This charge density is related to the nonequilibrium response of the bound states and order parameter collective mode, and dominates the electromagnetic response of the vortex core.

Authors: Matthias Eschrig and J. A. Sauls
Publication: New J. Phys. 11 075009 (2009). Part of Focus on Superconductors with Exotic Symmetries.
Local: [reprint]
Eprint: arXiv:0904.1819

Vortices in Chiral P-wave Spin-Triplet Superconductors and Superfluids

Fri, 27 Feb 2009 16:52:53 -0600

Abstract: Superconductors exhibit unconventional electronic and magnetic properties if the Cooper pair wave function breaks additional symmetries of the normal phase. Rotational symmetries in spin- and orbital spaces, as well as discrete symmetries such as space and time inversion, may be spontaneously broken. When this occurs in conjunction with broken U(1) gauge symmetry, new physical phenomena are exhibited below the superconducting transition that are characteristic of the broken symmetries of the pair condensate. This is particularly true of vortices and related defects. Superconductors with a multi-component order parameter exhibit a variety of different vortex structures and closely related defects that are not possible in condensates belonging to a one-dimensional representation. In this article we discuss the structure of vortices in Fermionic superfluids and superconductors which break chiral symmetry, i.e. combined broken time-inversion and 2D parity. In particular, we consider the structure of vortices and defects that might be realized in thin films of 3He-A and the layered superconductor Sr2RuO4, and identify some of the characteristic signatures of broken chiral symmetry that should be revealed by these defects.

Authors: J. A. Sauls and Matthias Eschrig
Publication: New J. Phys. 11 075008 (2009). Part of Focus on Superconductors with Exotic Symmetries.
Local: [reprint]
Eprint: arXiv:0903.0011

Theory of Spin-Transport and Spin-Transfer Torque in Superconducting-Magnetic Nanostructures

Thu, 4 Sep 2008 16:59:35 -0500

Abstract: Spin transport currents and the spin-transfer torques in voltage-biased superconducting-ferromagnetic nanopillars (SFNFS point contacts) are computed. We develop and implement an algorithm based on the Ricatti formulation of the quasiclassical theory of superconductivity to solve the time-dependent boundary conditions for the nonequilibrium Green's functions for spin transport through the ferromagnetic interfaces. A signature of the nonequilibrium torque is a component perpendicular to the plane spanned by the two ferromagnetic moments. The perpendicular component is absent in normal-metal-ferromagnetic nanopillar contacts but is shown to have the same order of magnitude as the in-plane torque for nonequilibrium SFNFS contacts. The out-of-plane torque is due to the rotation of quasiparticle spin by the exchange fields of the ferromagnetic layers. In the ballistic limit the equilibrium torque is related to the spectrum of spin-polarized Andreev bound states, while the ac component, for small bias voltages, is determined by the nearly adiabatic dynamics of the Andreev bound states. The nonlinear voltage dependence of the nonequilibrium torque, including the subharmonic gap structure and the high-voltage asymptotics, is attributed to the interplay between multiple Andreev reflections, spin filtering, and spin mixing. These properties of spin angular momentum transport may be exploited to control the state of nanomagnets.

Authors: Erhai Zhao and J. A. Sauls
Publication: Physical Review B 78, 174511 (2008). Editors’ recommended reading [reprint]
Vir. J. Appl. Supercond. 15, 10 (2009)
Vir. J. Nano. Sci. Tech. 18, 21 (2009)

Eprint: cond-mat/0702371

Anomalous Attenuation of Transverse Sound in Superfluid 3He

Tue, 17 Jun 2008 17:29:57 -0500

Abstract: We present the first measurements of the attenuation of transverse sound in superfluid 3He-B. We use fixed path length interferometry combined with the magneto-acoustic Faraday effect to vary the effective path length by a factor of 2, resulting in absolute values of the attenuation. We find that attenuation is significantly larger than expected from the theoretical dispersion relation, in contrast with the phase velocity of transverse sound. We suggest that the anomalous attenuation can be explained by surface Andreev bound states.

Authors: J.P. Davis, J. Pollanen, H. Choi, J.A. Sauls, W.P. Halperin, A.B. Vorontsov
Publication: Phys. Rev. Lett. 101, 085301 (2008). [reprint]
Eprint: arXiv:0807.2221

Discovery of an Excited Pair State in Superfluid 3He

Sun, 27 Apr 2008 17:57:11 -0500

Abstract: Collective modes are the fingerprint of a condensed phase. The spectroscopy of these modes in superfluid 3He and unconventional superconductors can provide key information on the symmetry of the condensate as well as the microscopic pairing mechanism responsible for the ground state and excitation energies. Here, we use interferometry within an acoustic cavity—which is very sensitive to changes in the velocity of transverse sound—to reveal a new collective mode in the B phase of superfluid 3He (3He-B). We identify the mode as an excited bound state of Cooper pairs, which is weakly bound with an excitation energy within 1% of the pair-breaking edge. On the basis of the selection rules for coupling of transverse sound to a collective mode in 3He-B, combined with the observation of acoustic birefringence near the collective mode frequency, we infer that the new mode is most likely a spin-triplet (S=1), f-wave pair exciton (orbital momentum L=3) with total angular momentum, J=4. The existence of a pair exciton with J=4 suggests an attractive, subdominant, f-wave pairing interaction in liquid 3He.

Authors: J.P. Davis, J. Pollanen, H. Choi, J.A. Sauls, and W.P. Halperin
Publication: Nature Physics 4, 571 - 575 (2008) [reprint]
Eprint: arXiv:0801.1497

Dynamics of Spin Transport in Voltage-Biased Josephson Junctions

Wed, 16 May 2007 18:30:20 -0500

Abstract: We investigate spin transport in voltage-biased spin-active Josephson junctions. The interplay of spin filtering, spin mixing, and multiple Andreev reflection leads to nonlinear voltage dependence of the dc and ac spin current. We compute the voltage characteristics of the spin current (IS) for superconductor-ferromagnet-superconductor Josephson junctions. The subharmonic gap structure of IS(V) is shown to be sensitive to the degree of spin mixing generated by the ferromagnetic interface, and exhibits a pronounced even-odd effect associated with spin transport during multiple Andreev reflection processes. For strong spin mixing both the magnitude and the direction of the dc spin current can be sensitively controlled by the bias voltage.

Authors: Erhai Zhao and J. A. Sauls
Publication: Phys. Rev. Lett. 98, 206601 (2007). [reprint]

Eprint: cond-mat/0603610

Crystalline Order in Superfluid 3He Films

Mon, 22 Jan 2007 18:09:52 -0600

Abstract: We predict an inhomogeneous phase of superfluid 3He films in which translational symmetry is spontaneously broken in the plane of the film. This phase is energetically favored over a range of film thicknesses, Dc2(T) < D < Dc1(T), separating distinct homogeneous superfluid phases. The instability at the critical film thickness, Dc2 ~ 9 , is a single- mode instability generating striped phase order in the film. Numerical calculations of the order parameter and free energy indicate a second-order instability to a periodic lattice of degenerate B-like phases separated by domain walls at Dc1 ~ 13

Authors: Anton Vorontsov and J. A. Sauls
Publication: Phys. Rev. Lett. 98, 045301 (2007). Editors’ recommended reading [reprint]

Eprint: cond-mat/0601565

Nonequlibrium Spin-Transfer Torque in SFNFS Junctions

Thu, 7 Sep 2006 13:39:51 -0500

Abstract: We report theoretical results for the nonequilibrium spin current and spin-transfer torque in voltage-biased SFNFS Josephson structures. The subharmonic gap structures and high voltage asymptotic behaviors of the dc and ac components of the spin current are analyzed and related to the spin-dependent inelastic scattering of quasiparticles at both F layers.

Authors: Erhai Zhao and J. A. Sauls
Publication: AIP Conf. Proc., Vol. 850 (1) pp. 893-894 (2006). [reprint]

Eprint: cond-mat/0507449

Phase Diagram and Spectroscopy of FFLO States of Two-dimensional d-wave Superconductors

Wed, 2 Nov 2005 13:53:11 -0600

Abstract: Experimental evidence suggests that the Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) state may be realized in the unconventional, heavy-fermion superconductor CeCoIn5. We present a self-consistent calculation of the field versus temperature phase diagram and order parameter structures for the FFLO states of quasi-two-dimensional d-wave superconductors. We calculate the spatially nonuniform order parameter, free energy density, and local density of states for magnetic fields parallel to the superconducting planes. We predict that the lower critical magnetic field transition between the spatially uniform and nonuniform FFLO state is second order. We discuss the signatures of the nonuniform FFLO state which should be observable in scanning tunneling microscopy measurements of the local density of states.

Authors: A. B. Vorontsov, J. A. Sauls and M. J. Graf
Publication: Physical Review B 72, 184501 (2005). [reprint]

Eprint: cond-mat/0506257

Magnetization and Spin Diffusion of Liquid 3He in Aerogel

Thu, 7 Jul 2005 14:37:29 -0500

Abstract: We report theoretical calculations and experimental measurements of the normal-state spin diffusion coefficient of 3He in aerogel, including both elastic and inelastic scattering of 3He quasiparticles, and compare these results with data for 3He in 98% porous silica aerogel. This analysis provides a determination of the elastic mean free path within the aerogel. Measurements of the magnetization of the superfluid phase in the same aerogel samples provide a test of the theory of pairbreaking and magnetic response of low-energy excitations in the “dirty” B phase of 3He in aerogel. A consistent interpretation of the data for the spin-diffusion coefficient, magnetization, and superfluid transition temperature is obtained by including correlation effects in the aerogel density.

Authors: J. A. Sauls, Y. M. Bunkov, E. Collin, H. Godfrin, and P. Sharma
Publication: Physical Review B 72, 024507 (2005). [reprint]

Eprint: cond-mat/0408492

Domain Walls in Superfluid 3He-B

Tue, 8 Feb 2005 14:51:59 -0600

Abstract: We consider domain walls between regions of superfluid 3He-B in which one component of the order parameter has the opposite sign in the two regions far from one another. We report calculations of the order parameter profile and the free energy for two types of domain wall, and discuss how these structures are relevant to superfluid 3He confined between two surfaces.

Authors: A. B. Vorontsov and J. A. Sauls
Publication: J. Low Temp. Phys. 138, 283 (2005). [reprint]
Eprint: arXiv:cond-mat/0408465

Nonequilibrium Superconductivity Near Spin-Active Interfaces

Fri, 22 Oct 2004 15:00:26 -0500

Abstract: The Riccati formulation of the quasiclassical theory of nonequilibrium superconductors is developed for spin-dependent scattering near magnetic interfaces. We derive boundary conditions for the Riccati distribution functions at a spin-active interface. The boundary conditions are formulated in terms of an interface S-matrix describing the reflection and transmission of the normal-state conduction electrons by the interface. The S-matrix describes the effects of spin-filtering and spin-mixing (spin-rotation) by a ferromagnetic interface. The boundary conditions for the Riccati equations are applicable to a wide range of nonequilibrium transport properties of hybrid systems of superconducting and magnetic materials. As an application we calculate the spin and charge conductance of a normal metal-ferromagnet superconductor (NFS) point contact; the spin-mixing angle that parameterizes the S-matrix is determined from experimental measurements of the peak in the sub-gap differential conductance of the NFS point contact. We also use the new boundary conditions to derive the effects of spin-mixing on the phase-modulated thermal conductance of a superconducting-ferromagnetic-superconducting (SFS) point contact. For high-transparency (metallic ferromagnet) ``π'' junctions, the phase modulation of the thermal conductance is dramatically different from that of non-magnetic, ``0'' junctions. For low-transparency (insulating ferromagnet) SFS tunnel junctions with weak spin mixing resonant transmission of quasiparticles with energies just above the gap edge leads to an increase of the thermal conductance, compared to the normal-state conductance at Tc, over a broad temperature range when the superconducting phase bias is ϕ ≥ π/2.

Authors: Erhai Zhao Tomas Löfwander and J. A. Sauls
Publication: Physical Review B 70, 134510 (2004). [reprint]
Virtual J. Appl. Supercond. v. 7, i. 9 (2004)
arXiv: cond-mat/0404074

Helium-Three in Aerogel

Thu, 26 Aug 2004 14:19:24 -0500

Abstract: Liquid 3He confined in silica aerogel provides us with a unique system to study the effects of quenched disorder on the properties of a strongly correlated quantum liquid. The superfluid phases display interplay between disorder and complex symmetry-breaking.

Authors: W.P. Halperin and J. A. Sauls
Publication: [reprint]
Eprint: arXiv:cond-mat/0408593

Nonlinear magnetic field dependence of the conductance in d-wave NIS tunnel junctions

Fri, 23 Jul 2004 15:17:25 -0500

Abstract: The ab -plane normal-metal/insulator/superconductor-tunnelling conductance in d-wave superconductors shows a zero-bias conductance peak which is predicted to split in a magnetic field. In a pure d -wave superconductor the splitting is linear for fields small on the scale of the thermodynamic critical field. The field dependence is shown to be nonlinear, even at low fields, in the vicinity of a surface phase transition into a local time-reversal symmetry breaking state. The field evolution of the conductance is sensitive to temperature, doping, and the symmetry of the subdominant pairing channel.

Authors: M. Fogelström, D. Rainer and J. A. Sauls
Publication: Physical Review B 70, 012503 (2004). [reprint]
Virtual J. Appl. Supercond. v. 7, i. 3 (2004)
Eprint: cond-mat/0302197

Specific Heat of Disordered Superfluid 3He

Sun, 23 May 2004 14:29:45 -0500

Abstract: The specific heat of superfluid 3He, disordered by a silica aerogel, is found to have a sharp discontinuity marking the thermodynamic transition to superfluidity at a temperature reduced from that of bulk 3He. The magnitude of the discontinuity is also suppressed. This disorder effect can be understood from the Ginzburg-Landau theory which takes into account elastic quasiparticle scattering suppressing both the transition temperature and the amplitude of the order parameter. We infer that the limiting temperature dependence of the specific heat is linear at low temperatures in the disordered superfluid state, consistent with predictions of gapless excitations everywhere on the Fermi surface.

Authors: H. Choi, K. Yawata, T. M. Haard, J. P. Davis, G. Gervais, N. Mulders, P. Sharma, J. A. Sauls, and W. P. Halperin
Publication: Physical Review Letters, 93, 145301 (2004). [reprint]

Eprint: cond-mat/0408493

Heat Transport through Josephson Point Contacts

Thu, 8 Apr 2004 17:07:15 -0500

Abstract: We present a comprehensive study of heat transport through small superconducting point contacts. The heat current for a temperature biased weak link is computed as a function of temperature and barrier transparency of the junction. The transport of thermal energy is controlled by the quasiparticle transmission probability for the point contact that couples the superconducting leads. We derive this transmission probability and results for the heat current starting from nonequilibrium transport equations and interface boundary conditions for the Keldysh propagators in quasiclassical approximation. We discuss the thermal conductance for both clean and dirty superconducting leads, as well as aspects of the nonlinear current response. We show that the transmission probability for continuum quasiparticle states is both energy- and phase-dependent, and controlled by an interface Andreev bound state below the continuum. For high transparency barriers the formation of a low-energy bound state, when the phase is tuned to Φ=π, leads to a reduction of the heat current relative to that for Φ=0. For low-transparency barriers, a shallow Andreev bound state just below the continuum edge is connected with resonant transmission of quasiparticles for energies just above the gap edge, and leads to enhanced heat conductance as the temperature is lowered below the superconducting transition.

Authors: Erhai Zhao, Tomas Löfwander and J. A. Sauls
Publication: Phys. Rev. B 69, 134503 (2004). [reprint]
Virtual J. Appl. Supercond. v. 6, i. 8 (2004)
Eprint: cond-mat/0308041

Spectrum of Third Sound Cavity Modes on Superﬂuid 3He Films

Sun, 15 Feb 2004 16:55:36 -0600

Abstract: We report theoretical calculations of the spectrum of third sound modes for a cylindrically symmetric film of superfluid 3He, and compare these results with experimental data for the mode frequencies and amplitude spectrum of surface waves of superfluid 3He films.

Authors: A. B. Vorontsov and J. A. Sauls
Publication: J. Low Temp. Phys. 134, 101 (2004). [reprint]
Eprint: arXiv:cond-mat/0309599

Impurity Effects on the A1-A2 Splitting of Superﬂuid 3He in Aerogel

Fri, 5 Dec 2003 18:49:58 -0600

Abstract: When liquid 3He is impregnated into silica aerogel a solid-like layer of 3He atoms coats the silica structure. The surface 3He is in fast exchange with the liquid on NMR timescales. The exchange coupling of liquid 3He quasiparticles with the localized 3He spins modifies the scattering of 3He quasiparticles by the aerogel structure. In a magnetic field the polarization of the solid spins gives rise to a splitting of the scattering cross-section of for ``up’’ vs. ``down’' spin quasiparticles, relative to the polarization of the solid 3He. We discuss this effect, as well as the effects of non-magnetic scattering, in the context of a possible splitting of the superfluid transition for ↑↑ vs. ↓↓ Cooper pairs for superfluid 3He in aerogel, analogous to the A1-A2 splitting in bulk 3He. Comparison with the existing measurements of Tc for B < 5 kG, which show no evidence of an A1-A2 splitting, suggests a liquid-solid exchange coupling of order J = 0.1 mK. Measurements at higher fields, B > 20 kG, should saturate the polarization of the solid 3He and reveal the A1-A2 splitting.

Authors: J. A. Sauls and Priya Sharma
Publication: Phys. Rev. B 68, 224502 (2003). [reprint]

Eprint: cond-mat/0306099

Thermodynamic Properties of Thin Films of Superﬂuid 3He-A

Fri, 22 Aug 2003 17:22:03 -0500

Abstract: The pairing correlations in superfluid 3He are strongly modified by quasiparticle scattering off a surface or an interface. We present theoretical results and predictions for the order parameter, the quasiparticle excitation spectrum, and the free energy for thin films of superfluid 3He. Both specular and diffuse scatterings by a substrate are considered, while the free surface is assumed to be a perfectly reflecting specular boundary. The results are based on self-consistent calculations of the order parameter and quasiparticle excitation spectrum at zero pressure. We obtain results for the phase diagram, free energy, entropy, and specific heat of thin films of superfluid 3He.

Authors: A. B. Vorontsov and J. A. Sauls
Publication: Phys. Rev. B 68, 064508 (2003). [reprint]

Eprint: cond-mat/0304054

Phase Modulated Thermal Conductance of Josephson Weak Links

Thu, 14 Aug 2003 18:32:20 -0500

Abstract: We present a theory for quasiparticle heat transport through superconducting weak links. The thermal conductance depends on the phase difference ($\phi$) of the superconducting leads. Branch conversion processes, low-energy Andreev bound states near the contact and the suppression of the local density of states near the gap edge are related to phase-sensitive transport processes. Theoretical results for the influence of junction transparency, temperature and disorder, on the phase modulation of the conductance are reported. For high-transmission weak links, D → 1, the formation of an Andreev bound state at εb = Δ cos(φ/2) leads to suppression of the density of states for the continuum excitations that transport heat, and thus, to a reduction in the conductance for φ ≅ π. For low-transmission (D << 1) barriers resonant scattering at energies ε ≅(1+D/2) Δ leads to an increase in the thermal conductance as T drops below Tc (for phase differences near φ = π).

Authors: Erhai Zhao, Tomas Löfwander and J. A. Sauls
Publication: Phys. Rev. Lett. 91, 077003 (2003). [reprint]
Virtual J. Appl. Supercond. v. 5, i. 4 (2003)
Eprint: cond-mat/0302346

Shot Noise in Normal Metal/d-wave Superconductor Junctions

Wed, 6 Aug 2003 17:39:47 -0500

Abstract: We present theoretical calculations and predictions for the shot noise in voltage-biased junctions of dx2-y2 superconductors and normal metal counterelectrodes. In the clean limit for the d-wave superconductor the shot noise vanishes at zero voltage because of resonant Andreev reflection by zero-energy surface bound states. We examine the sensitivity of this resonance to impurity scattering. We report theoretical results for the magnetic field dependence of the shot noise, as well as the fingerprints of subdominant s- and dxy pairing channels.

Authors: Tomas Löfwander, M. Fogelström and J. A. Sauls
Publication: Phys. Rev. B 68, 054504 (2003). [reprint]
Virtual J. Appl. Supercond. v. 5, i. 4 (2003)
Eprint: cond-mat/0304588

Thermal Conductivity of Superfluid 3He in Aerogel

Sat, 8 Mar 2003 09:50:46 -0600

Abstract: When 3He is impregnated into high-porosity aerogel, a new scattering channel is available to 3He quasiparticles, viz., elastic scattering off the aerogel strands. We examine the effects of elastic and inelastic scattering on the transport properties of 3He in aerogel, and report new results for the thermal conductivity of superfluid 3He in aerogel within the framework of homogeneous and isotropic scattering. This model predicts significant variations in the temperature dependence of the thermal conductivity as a function of pressure, scattering cross-section and aerogel density. Measurements of the thermal conductivity of 3He in 98% aerogel at p=7.4 bar [1] are in good agreement with theoretical calculations based on either the BW or the ABM phase order parameters. At higher pressures, where pairbreaking effects are weaker, significant differences in the thermal conductivity for these two phases are predicted.

Authors: Priya Sharma and J. A. Sauls
Publication: Physica B, 329-333, 313 (2003). [reprint]
Proceedings of the 23rd International Conference on Low Temperature Physics
Eprint: cond-mat/0212208

Comment on ‘‘Magnetic ﬁeld effects on neutron diffraction in the antiferromagnetic phase of UPt3’’

Fri, 27 Dec 2002 19:08:27 -0600

Abstract: Fåk, van Dijk, and Wills (FDW) question our analysis of elastic neutron-scattering experiments in the antiferromagnetic phase of UPt3. They state that our analysis is incorrect because we average over magnetic structures that are disallowed by symmetry. We disagree with FDW and reply to their criticism below. FDW also point out that we have mistaken the magnetic-field direction in the experiment reported in N. H. van Dijk, B. Fåk, L. P. Regnault, A. Huxley, and M-T. Fernández-Díaz, Phys. Rev. B 58, 3186 (1998). We correct this error and note that our previous conclusion is also valid for the correct field orientation.

Authors: J. Moreno and J. A. Sauls
Publication: Physical Review B 66, 216402 (2002). [reprint]

Eprint: cond-mat/0202504

Vortex Structure & Dynamics in Layered Superconductors

Mon, 1 Oct 2001 12:18:17 -0500

Abstract: We investigate the equilibrium and nonequilibrium properties of the core region of vortices in layered superconductors. We discuss the electronic structure of singly and doubly quantized vortices for both s-wave and d-wave pairing symmetry. We consider the intermediate clean regime, where the vortex-core bound states are broadened into resonances with a width comparable to or larger than the quantized energy level spacing, and calculate the response of a vortex core to an \em a.c. electromagnetic field for vortices that are pinned to a metallic defect. We concentrate on the case where the vortex motion is nonstationary and can be treated by linear response theory. The response of the order parameter, impurity self energy, induced fields and currents are obtained by a self-consistent calculation of the distribution functions and the excitation spectrum. We then obtain the dynamical conductivity, spatially resolved in the region of the core, for external frequencies in the range, 0.1Δ < ħω < 3Δ. We also calculate the dynamically induced charge distribution in the vicinity of the core. This charge density is related to the nonequilibrium response of the bound states and collective mode, and dominates the electromagnetic response of the vortex core.

Authors: M. Eschrig, D. Rainer and J. A. Sauls
Publication: Proceedings of the Workshop on "Vortex Dynamics in Unconventional Superconductors" (2001)
pp. 175-203, Springer-Verlag, eds. R. Huebener, N. Schopohl and G. E. Volovik (Dresden). [reprint]
Eprint: arXiv:0903.0011

Magnetic Susceptibility of the Balian-Werthamer Phase of 3He in Aerogel

Thu, 16 Aug 2001 10:00:23 -0500

Abstract: The equilibrium superfluid phase of 3He impregnated into high-porosity (98%) silica aerogels appears to be a non-equal-spin-pairing state in zero field at all pressures, which is generally assumed to be the Balian–Werthamer (BW) phase modified by the depairing effects of the aerogel structure. The nuclear magnetic susceptibility played a key role in identifying the B-phase of pure 3He with the BW state. We report theoretical calculations of the nuclear magnetic susceptibility for the BW model of superfluid 3He in aerogel within the framework of the Fermi-liquid theory of superfluid 3He. Scattering of quasiparticles by the aerogel, in addition to Fermi-liquid exchange corrections, leads to substantial changes in the susceptibility of the BW phase. The increase in the magnetic susceptibility of 3He-aerogel compared to pure 3He-B is related to the polarizability of the gapless excitations and the impurity-induced local field. The limited data that is available is in rough agreement with theoretical predictions. Future measurements could prove important for a more definitive identification of the ordered phase, as well as for refining the theoretical model for the effects of disorder and scattering on the properties of superfluid 3He.

Authors: Priya Sharma and J. A. Sauls
Publication: J. Low Temp. Phys., 125, 115–142 (2001). [reprint]

Eprint: cond-mat/0107446

Magnetic Field Effects on Neutron Diffraction in the Antiferromagnetic phase of UPt3

Tue, 19 Dec 2000 12:37:25 -0600

Abstract: We discuss possible magnetic structures in UPt3 based on our analysis of elastic neutron-scattering experiments in high magnetic fields at temperatures T < TN. The existing experimental data are compatible with a true antiferromagnetic order displaying a single-q antiferromagnetic structure with three independent domains. For modest in-plane spin-orbit interactions, the Zeeman coupling between the antiferromagnetic order parameter and the magnetic field induces a rotation of the magnetic moments, but not an adjustment of the propagation vector of the magnetic order. A triple-q magnetic structure is also consistent with neutron experiments, but in general leads to a nonuniform magnetization in the crystal. New experiments involving higher fields and polarized neutrons could decide between these structures.

Authors: J. Moreno and J. A. Sauls
Publication: Physical Review B 63, 024419 (2000). [reprint]

Eprint: cond-mat/0004253

Transport Properties of Normal Liquid 3He in Aerogel

Mon, 2 Oct 2000 19:10:07 -0500

Abstract: The impregnation of aerogel by 3He provides a new opportunity to study the effects of disorder on the properties of liquid 3He. The transport coefficients exhibit cross-over behaviour from the high-temperature regime, where inelastic 3He-3He scattering dominates, to a low-temperature regime dominated by elastic scattering of 3He off the aerogel. Within the homogenous scattering model, analytical expressions for the thermal conductivity and viscosity can be derived and are shown in graphical form for 3He in aerogel.

Authors: Priya Venkataramani and J. A. Sauls
Publication: Physica B: Condensed Matter, 284-288, pp. 297-298 (2000).

Local: [reprint]

Tunneling into Disordered d-wave Superconductors

Mon, 2 Oct 2000 12:39:48 -0500

Abstract: We present model calculations of the effects of disorder on the ab-plane tunneling conductance in d-wave superconductors. Surface disorder is included by a layer of non-magnetic impurities and by a nano-faceted surface. The surface model is put to a test by performing a fit to conductance measurements on Pr-doped YBCO.

Authors: A. Poenicke, M. Fogelström and J. A. Sauls
Publication: Physica B: Condensed Matter, 284-288, pp. 589-590 (2000).

Local: [reprint]

Magneto-acoustic rotation of transverse waves in 3He-B

Wed, 2 Aug 2000 15:55:29 -0500

Abstract: In superfluid 3He-B, the off-resonant coupling of the J = 2(-), M = ± 1 order parameter collective modes to transverse current excitations stabilizes propagating transverse waves with low damping for frequencies above that of the J = 2(-) modes. Right- (RCP) and left circularly polarized (LCP) transverse modes are degenerate in zero field; however, a magnetic field with H parallel to q lifts this degeneracy giving rise to the acoustic analog of circular birefringence and an acoustic Faraday effect for linearly polarized transverse sound waves (Moores and Sauls, J. Low Temp. Phys. 91, 13 (1993)). We present theoretical results for the temperature, pressure and field dependence of the Faraday rotation angle, and compare the theory with recent measurements (Lee et al., Nature 400, 431 (1999)). The analysis provides a direct measurement of the Lande g-factor for the J = 2(-) modes, and new information on the magnitude of f-wave pairing correlations in 3He-B.

Authors: J. A. Sauls, Y. Lee, T. Haard, and W. Halperin.
Publication: Physica B: Condensed Matter, 284-288, pp. 267-268 (2000) [reprint]
Eprint: cond-mat/9910262

Identification of the Orbital Pairing Symmetry of UPt3

Mon, 12 Jun 2000 15:45:54 -0500

Abstract: This paper summarizes the results of a comprehensive analysis of the thermodynamic and transport data for the superconducting phases of UPt3. Calculations of the transverse sound attenuation as a function of temperature, frequency, polarization, and disorder are presented for the leading models of the superconducting order parameter. Measurements of the specific heat, thermal conductivity, and transverse sound attenuation place strong constraints on the orbital symmetry of the superconducting order parameter. We show that the superconducting A and B phases are in excellent agreement with pairing states belonging to the odd-parity E2u orbital representation.

Authors: M. J. Graf, S.-K. Yip, and J. A. Sauls
Publication: Physical Review B 62,14393 (2000). [reprint]

Eprint: cond-mat/0006180

Acoustic Faraday Effect in Superfluid 3He-B

Wed, 5 Apr 2000 16:28:57 -0500

Abstract: We have observed that the direction of linearly polarized transverse sound in superfluid 3He-B rotates in a magnetic field. This acoustic Faraday effect proves the existence of a propagating transverse sound mode in 3He and provides clear evidence for spontaneously broken relative spin–orbit symmetry.

Authors: Y. Lee, T. Haard, J. A. Sauls and W. Halperin.
Publication: Physica B: Condensed Matter, 280, pp. 106-107 (2000)
Local: [reprint]

Transport in the Heavy-Fermion Superconductor UPt3

Wed, 5 Apr 2000 10:35:21 -0500

Abstract: We report new theoretical results and analysis for the transport properties of superconducting UPt3 based on the leading models for the pairing symmetry. We use Fermi surface data and the measured inelastic scattering rate to show that the low-temperature thermal conductivity and transverse sound attenuation in the A and B phase of UPt3 are in excellent agreement with pairing states belonging to the two-dimensional orbital E2u representation.

Authors: M. J. Graf, S.-K. Yip, and J. A. Sauls
Publication: Physica B 280, 176-177 (2000). [reprint]

Eprint: cond-mat/9907285

Observation of Paramagnetic Meissner Currents - Evidence for Surface Andreev Bound States

Thu, 20 Jan 2000 19:21:35 -0600

Abstract: We report the observation of anomalous Meissner currents (AMCs) in thin films of superconducting YBCO with oriented internal surfaces introduced by heavy-ion bombardment. High-precision measurements of the penetration depth λ(T) reveal an upturn in the temperature dependence of λ(T) below T≈15 K, which is strongly dependent on the orientation and density of the surfaces. The magnitude of the observed effect, its onset temperature and its dependence on the orientation of the surfaces are in quantitative agreement with the theory of surface effects in d-wave superconductors. The anomaly is interpreted as a consequence of surface-induced Andreev bound states (ABSs) carrying paramagnetic currents.

Authors: W. Prusseit, H. Walter, R. Semerad, H. Kinder, W. Assmann, H. Huber, B. Kabius, H. Burkhardt, D. Rainer, and J. A. Sauls
Publication: Physica C: Superconductivity, 317-318, pp. 396-402 (1999).

Local: [reprint]

Broken Symmetry and Non-Equilibrium Superfluid 3He

Sat, 15 Jan 2000 19:15:40 -0600

Abstract: These lecture notes provide an introduction to non-equilibrium superfluid 3He, with applications to high-frequency excitations, including aspects of symmetry breaking in 3He and its effects on collective mode dynamics. In 1957 Landau predicted that liquid 3He would support propagating shear waves at low temperatures, i.e. a transverse sound mode. Such waves have recently been observed at low temperatures in the superfluid B-phase of liquid 3He. These observations provide a beautiful example of the effect of spontaneous symmetry breaking in condensed matter. I discuss the theory of transverse wave propagation in 3He and the recent detection of these waves by magneto-acoustic rotation of the 3He polarization in a magnetic field.

Authors: J. A. Sauls
Publication: Lecture Notes for the 1999 Les Houches Winter School, published in ``Topological Defects and Non-Equilibrium Symmetry Breaking Phase Transitions’’ (H. Godfrin and Y. Bunkov, eds.), pp. 239–265 Elsievier Science Publishers, Amsterdam, (2000). ISBN 0792362047, 9780792362043.
Local: reprint
Eprint: cond-mat/9910260

Local Time-Reversal Symmetry Breaking in d(x2 - y2) Superconductors

Tue, 28 Sep 1999 12:27:29 -0500

Abstract: We show that an isolated impurity in a spin singlet dx2-y2 superconductor generates a dxy order parameter with locally broken time-reversal symmetry. The origin of this effect is a coupling between the dx2-y2 and the dxy order parameter induced by spin-orbit scattering off the impurity. The signature of locally broken time-reversal symmetry is an induced orbital charge current near the impurity, which generates a localized magnetic field in the vicinity of the impurity. We present a microscopic theory for the impurity-induced dxy component, discuss its spatial structure as well as the pattern of induced current and local magnetic field near the localized impurity spin.

Authors: M. J. Graf, A. V. Balatsky and J. A. Sauls
Publication: Physical Review, B 61, pp. 3255–3258 (2000).

Local: [reprint]
arXiv: cond-mat/9907300

Spin-Orbit Scattering in d(x2 - y2) Superconductors

Thu, 22 Jul 1999 12:13:13 -0500

Abstract: We show that spin-orbit scattering off an isolated magnetic impurity in a singlet dx2-y2 superconductor generates a dxy order parameter with locally broken time-reversal symmetry. A consequence of the induced dxy component are orbital charge currents and a magnetic field in the vicinity of the magnetic impurity.

Authors: M. J. Graf, A. V. Balatsky and J. A. Sauls
Publication: Intl. Journ. Mod. Phys. B, 13, pp. 3513 - 3515 (1999).

Local: [reprint]

Discovery of the Acoustic Faraday Effect in Superfluid 3He-B

Thu, 10 Jun 1999 15:32:03 -0500

Abstract: Acoustic waves provide a powerful tool for studying the structure of matter. For example, the speed, attenuation and dispersion of acoustic waves can give useful information on molecular forces and the microscopic mechanisms of absorption and scattering of acoustic energy. In solids, both compression and shear waves occur—longitudinal and transverse sound, respectively. But normal liquids do not support shear forces and consequently transverse waves do not propagate in liquids, with one notable exception. In 1957 Landau predicted that the quantum-liquid phase of 3He might support transverse sound waves at sufficiently low temperatures, the restoring forces for shear waves being supplied by the collective quantum behaviour of the particles in the fluid. Such shear waves will involve displacements of the fluid transverse to the direction of propagation, and so define a polarization direction similar to that of electromagnetic waves. Here we confirm experimentally the existence of transverse sound waves in superfluid 3He-B by observing the rotation of the polarization of these waves in the presence of a magnetic field. This phenomenon is the acoustic analogue of the magneto-optic Faraday effect, whereby the polarization direction of an electromagnetic wave is rotated by a magnetic field applied along the propagation direction.

Authors: Y. Lee, T. Haard, W. P. Halperin, and J. A. Sauls.
Publication: Nature 400, 431-433 (29 July 1999) [reprint]
Eprint: cond-mat/9902129

Electromagnetic Response of a Vortex in Layered Superconductors

Mon, 10 May 1999 18:18:33 -0500

Abstract: We calculate the response of a vortex core in a layered superconductor to an ac electromagnetic field. In particular we investigate the intermediate clean regime, where the broadening of the vortex core bound states is comparable to or larger than the level spacing. The response of the order parameter, impurity self-energy, and currents are obtained by a self-consistent determination of the distribution functions and the excitation spectrum. The response is dominated by order parameter collective modes coupled to the fermion excitations of the vortex core. At low frequencies this coupling leads to substantially enhanced absorption in the vortex core.

Authors: M. Eschrig, D. Rainer and J. A. Sauls
Publication: Physical Review B 60, 10447-10454 (1999).

Local: [reprint]
arXiv: cond-mat/9805299

Fermi Liquid Superconductivity: Concepts, Equations, Applications

Thu, 18 Mar 1999 15:47:44 -0600

Abstract: The modern theory of superconductivity started in 1957 with the publication by Bardeen, Cooper and Schrieﬀer on the Theory of Superconductivity, wildly known as the BCS theory. Theorists on both the ‘east’ and ‘west’ established within a few years basically a complete “standard theory of superconductivity” which was ﬁnally comprehensively reviewed by leading western experts in Superconductivity edited by Parks in 1969. At about the time Parks’ books were edited two papers by Eilenberger and Larkin & Ovchinnikov were published, which demonstrated, independently, that the complete standard theory of (equilibrium) superconductivity can be formulated in terms of a quasiclassical transport equation. Somewhat later this result was generalized to non-equilibrium conditions by Eliashberg and Larkin & Ovchinnikov. We consider this theory the generalization of Landau’s theory of normal Fermi liquids to the superconducting states of metals or superﬂuid states of liquid 3He. It combines Landau’s semiclassical transport equations for quasiparticles with the concepts of pairing and particle-hole coherence that are the basis of the Bardeen, Cooper and Schrieﬀer theory. We will call this theory alternatively the ”quasiclassical theory”, as it was coined by Larkin and Ovchinnikov, or the ”Fermi liquid theory of superconductivity”.

Authors: M. Eschrig, J. A. Sauls, H. Burkhardt, and D. Rainer
Publication: Lecture Notes for the 1998 NATO Advanced Study Institute on Superconductivity, Albena, Bulgaria, published in ``High-Tc Superconductors and Related Materials: Materials Science, Fundamental Properties, and Some Future Electronic Applications’ (S. L. Dreschsler and T. Mishonov, eds.), vol. 86, pp. 33, Published by Springer, 2001. ISBN 0792368738, 9780792368731
Reprint

Superconducting Fluctuations Effects on the Electron Spin Susceptibility in YBa2Cu3O6.95

Wed, 10 Feb 1999 13:03:04 -0600

Abstract: The electronic spin susceptibility of YBa2Cu3O6.95 has been measured with high precision up to 24 T with 17O nuclear magnetic resonance. Its temperature dependence can be accounted for by superconducting fluctuations that result in a smooth crossover from the normal to the vortex liquid state. A magnetic-field-temperature phase diagram for this crossover has been established having strong upward curvature.

Authors: H. N. Bachman, V. F. Mitrović, A. P. Reyes, W. P. Halperin, M. Eschrig, J. A. Sauls, A. Kleinhammes, P. Kuhns, and W. G. Moulton
Publication: Physical Review B 60, pp. 7591–7594 (1999).

Local: [reprint]
arXiv: cond-mat/9901231

Effects of Strong Magnetic Fields on the Pairing Fluctuations in High Temperature Superconductors

Tue, 15 Dec 1998 13:14:36 -0600

Abstract: We present the theory for the effects of superconducting pairing fluctuations on the nuclear spin-lattice relaxation rate 1/T1 and the NMR Knight shift for layered superconductors in high magnetic fields. These results can be used to clarify the origin of the pseudogap in high-Tc cuprates, which has been attributed to spin fluctuations as well as pairing fluctuations. We present theoretical results for s-wave and d-wave pairing fluctuations and show that recent experiments in optimally doped YBa2Cu3O7-δ are described by d-wave pairing fluctuations [V. F. Mitrović et al., Phys. Rev. Lett. 82, 2784 (1999); H. N. Bachman et al., Phys. Rev. B 60, 7591 (1999)]. In addition, we show that the orthorhombic distortion in YBa2Cu3O7-δ accounts for an experimentally observed discrepancy between 1/T1 obtained by nuclear quadrupole resonance and nuclear magnetic resonance at low field. We propose an NMR experiment to distinguish a fluctuating s-wave order parameter from a fluctuating strongly anisotropic order parameter, which may be applied to the system NdCdxCuO4-δ and possibly other layered superconductors.

Authors: M. Eschrig, D. Rainer and J. A. Sauls
Publication: Physical Review B 59, pp. 12095-12113 (1999).

Local: [reprint]
arXiv: cond-mat/9901233

Andreev Bound States, Surfaces and Subdominant Pairing in High Tc Superconductors

Sun, 11 Oct 1998 18:43:28 -0500

Abstract: A characteristic feature of the BCS theory of superconductivity is the quantum-mechanical coherence of particle and hole states. Direct observation of particle-hole coherence in unusual superconducting materials is a strong indication of traditional superconductivity. We use the Fermi liquid theory of superconductivity to study the implications of particle-hole coherence on properties of d-wave superconductors near surfaces. Typical surface phenomena are the suppression of the superconducting order parameter, surface bound states associated with Andreev reflection, anomalous screening currents, and spontaneous breaking of time-reversal symmetry. We review these phenomena and present new results for the effects of surface roughness.

Authors: D. Rainer, H. Burkhardt, M. Fogelström and J. A. Sauls
Publication: J. Phys. Chem. Solids 59, pp. 2040-2044 (1998). Proceedings of SNS97, Woods Hole, MA.

Local: [reprint]
arXiv: cond-mat/0302197