arXiv subjects

K. V. Samokhin

Publications and source records attributed to K. V. Samokhin.

At least 37 records · Page 2Linked to original sources

arXiv2016

Noncentrosymmetric superconductors in one dimension

We study the fermionic boundary modes (Andreev bound states) in a time-reversal invariant one-dimensional superconductor. In the presence of a substrate, spatial inversion symmetry is broken and the electronic properties are strongly affected by an antisymmetric spin-orbit coupling. We assume an arbitrary even number of nondegenerate bands crossing the Fermi level. We show that there is only one possible pairing symmetry in one dimension, an analog of s-wave pairing. The zero-energy Andreev bound states are present if the sign of the gap function in an odd number of bands is different from all other bands.

cond-mat.supr-con↗

arXiv2016

Fermionic boundary modes in two-dimensional noncentrosymmetric superconductors

We calculate the spectrum of the Andreev boundary modes in a two-dimensional superconductor formed at an interface between two different non-superconducting materials, e.g. insulating oxides. Inversion symmetry is absent in this system, and both the electron band structure and the superconducting pairing are strongly affected by the spin-orbit coupling of the Rashba type. We consider isotropic s-wave pairing states, both with and without time-reversal symmetry breaking, as well as various d-wave states. In all cases, there exist subgap Andreev boundary states, whose properties, in particular, the number and location of the zero-energy modes, qualitatively depend on the gap symmetry and the spin-orbit coupling strength.

cond-mat.supr-con↗

arXiv2016

Quasiparticles near domain walls in hexagonal superconductors

We calculate the energy spectrum of quasiparticles trapped by a domain wall separating different time reversal symmetry-breaking ground states in a hexagonal superconductor, such as UPt$_3$. The bound state energy is found to be strongly dependent on the gap symmetry, the domain wall orientation, the quasiparticle's direction of semiclassical propagation, and the phase difference between the domains. We calculate the corresponding density of states and show how one can use its prominent features, in particular, the zero-energy singularity, to distinguish between different pairing symmetries.

cond-mat.supr-con↗

arXiv2015

Symmetry and topology of two-dimensional noncentrosymmetric superconductors

We present a detailed study of the gap symmetry and the quasiparticle wave function topology in two-dimensional superconductors without inversion center. The strong spin-orbit coupling of electrons with the crystal lattice makes it necessary to describe superconductivity in terms of one or more nondegenerate bands characterized by helicity. We develop a topological classification of the superconducting states using the integer-valued Maurer-Cartan invariants and the Bogoliubov Wilson loops, and also calculate the spectrum of fermionic boundary modes.

cond-mat.supr-con↗

arXiv2015

Domain walls in superconductors: Andreev bound states and tunneling features

Domain walls can be formed in superconductors with a discrete degeneracy of the ground state, for instance, due to the breaking of time reversal symmetry. We study all cases where the formation of domain walls is possible in a tetragonal superconductor with the point group $D_{4h}$. We discuss both triplet and mixed singlet order parameters. It is found that in all cases the domain walls support subgap Andreev bound states, whose energies strongly depend on the direction of semiclassical propagation. The bound state contribution to the density of quasiparticle states exhibits peculiar features, which can be observed in tunneling experiments.

cond-mat.supr-con↗

arXiv2014

Helical states and solitons in noncentrosymmetric superconductors

We show how the two-band nature of superconductivity in noncentrosymmetric compounds leads to a variety of novel nonuniform superconducting states induced by a magnetic field. At low fields, a two-band helical state is realized, with a distinctly non-BCS quasiparticle spectrum. At high fields, the superconducting state becomes unstable towards the formation of a lattice of topological phase solitons.

cond-mat.supr-con↗

arXiv2013

Interaction between domain walls in chiral p-wave superconductors

We calculate microscopically the interaction energy of domain walls separating degenerate ground states in a chiral p-wave superconductor. The interaction is mediated by the quasiparticles experiencing Andreev scattering at the domain walls. As a by-product, we derive a useful general expression for the free energy of an arbitrary nonuniform texture of the order parameter in terms of the quasiparticle scattering matrix.

cond-mat.supr-con↗

arXiv2012

Phase solitons and subgap excitations in two-band superconductors

A phase soliton is a topological defect peculiar to two-band superconductors, which is associated with a $2π$ winding of the relative phase of the two superconducting condensates. We study the quasiparticle spectrum in the presence of a single planar phase soliton. We show that the order parameter phase variation in each of the bands leads to the existence of subgap states bound to the soliton. Calculation of the soliton energy valid at all temperatures is presented, with the exact analytical results obtained for a simple soliton model.

cond-mat.supr-con↗

arXiv2011

Domain walls in chiral p-wave superconductors: Quasiparticle spectrum and dynamics

We calculate microscopically the viscous friction coefficient and the effective mass of domain walls separating regions of opposite chirality in p-wave superconductors with k_x\pm ik_y order parameter. The domain wall viscosity and inertia are determined by the transitions between different Bogoliubov quasiparticle states induced by the domain wall motion. As a by-product, we present a detailed analysis of the quasiparticle spectrum, both bound and scattering, in the presence of a general domain wall with an arbitrary phase difference between the domains.

cond-mat.supr-con↗

arXiv2010

Tunneling into d-wave superconductors: Effects of interface spin-orbit coupling

Tunneling conductance of a clean normal metal/d-wave superconductor junction is studied by using the extended Blonder-Tinkham-Klapwijk formalism. We show that the conductance is significantly affected by the interface spin-orbit coupling of the Rashba type, which is inevitably present due to the asymmetry of the junction.

cond-mat.supr-con↗

arXiv2010

Effects of interface spin-orbit coupling on tunneling between normal metal and chiral p-wave superconductor

We study the tunneling conductance of a clean normal metal/chiral p-wave superconductor junction using the extended Blonder-Tinkham-Klapwijk formalism. It is shown that the spin-orbit coupling of the Rashba type that is present near the interface causes the subgap conductance peaks associated with the Andreev surface bound states to shift to a nonzero bias. We also investigate the effect of the Fermi wavevector mismatch between the normal metal and the superconductor.

cond-mat.supr-con↗

arXiv2010

Goldstone modes in Larkin-Ovchinnikov-Fulde-Ferrell superconductors

In nonuniform Larkin-Ovchinnikov-Fulde-Ferrell (LOFF) superconductors, both the gauge symmetry and the continuous translational symmetry of the normal state are spontaneously broken. This leads to additional bosonic excitations, or Goldstone modes, corresponding to the deformations of the order parameter amplitude modulation in real space. We derive general expressions for the energy of the phase and elastic Goldstone modes. As an example, the superfluid density and the elastic modulus of a one-dimensional LOFF superconductor are calculated at low temperatures.

cond-mat.supr-con↗

arXiv2010

Effects of impurities in noncentrosymmetric superconductors

Effects of disorder on superconducting properties of noncentrosymmetric compounds are discussed. Elastic impurity scattering, even for scalar impurities, leads to a strongly anisotropic mixing of the electron states in the bands split by the spin-orbit coupling. We focus on the calculation of the critical temperature, the upper critical field, and the spin susceptibility. It is shown that the impurity effects on the critical temperature are similar to those in multi-band centrosymmetric superconductors, in particular, Anderson's theorem holds for isotropic singlet pairing. In contrast, scalar impurities affect the spin susceptibility in the same way as spin-orbit impurities do in centrosymmetric superconductors. Another peculiar feature is that in the absence of inversion symmetry scalar disorder can mix singlet and triplet pairing channels. This leads to significant deviations of the upper critical field from the predictions of the Werthamer-Helfand-Hohenberg theory in the conventional centrosymmetric case.

cond-mat.supr-con↗

arXiv2009

Spin-orbit coupling and semiclassical electron dynamics in noncentrosymmetric metals

Spin-orbit coupling of electrons with the crystal lattice plays a crucial role in materials without inversion symmetry, lifting spin degeneracy of the Bloch states and endowing the resulting nondegenerate bands with complex spin textures and topologically nontrivial wavefunctions. We present a detailed symmetry-based analysis of the spin-orbit coupling and the band degeneracies in noncentrosymmetric metals. We systematically derive the semiclassical equations of motion for fermionic quasiparticles near the Fermi surface, taking into account both the spin-orbit coupling and the Zeeman interaction with an applied magnetic field. Some of the lowest-order quantum corrections to the equations of motions can be expressed in terms of a fictitious "magnetic field" in the momentum space, which is related to the Berry curvature of the band wavefunctions. The band degeneracy points or lines serve as sources of a topologically nontrivial Berry curvature. We discuss the observable effects of the wavefunction topology, focusing, in particular, on the modifications to the Lifshitz-Onsager semiclassical quantization condition and the de Haas-van Alphen effect in noncentrosymmetric metals.

cond-mat.other↗

arXiv2009

Tunneling conductance of ferromagnet/noncentrosymmetric superconductor junctions

Based on the extended Blonder-Tinkham-Klapwijk formalism, the tunneling conductance characteristics of a planar junction between a ferromagnet and a noncentrosymmetric superconductor are studied. The effects of the Rashba spin-orbit coupling (RSOC), the exchange energy, and the Fermi wave-vector mismatch (FWM) on the conductance are all taken into account. In the absence of the FWM, it is found that far away from the gap edge the conductance is suppressed by the RSOC, while around the gap edge it is almost independent of RSOC. The interplay of the RSOC and the exchange energy causes an enhancement of the subgap conductance, which is more pronounced when the RSOC is small. When the FWM is introduced, it is shown that the conductance is monotonically enhanced as the FWM parameter decreases.

cond-mat.supr-con↗

arXiv2008

Effects of impurities on Hc2(T) in superconductors without inversion symmetry

We calculate the upper critical field, Hc2(T), due to the orbital pair breaking in disordered superconductors without inversion symmetry. Differences from the usual centrosymmetric case are highlighted. The linearized gap equations in magnetic field, with the singlet and triplet pairing channels mixed by impurity scattering, are solved exactly for a cubic crystal.

cond-mat.supr-con↗

arXiv2008

Upper critical field in noncentrosymmetric superconductors

We calculate the upper critical field in superconductors without inversion symmetry at arbitrary temperatures, in the presence of scalar impurities. Both orbital and spin (paramagnetic) mechanisms of pair breaking are considered. The superconducting phase transition at nonzero field occurs into a helical vortex state, in which the order parameter is modulated along the applied field (in a cubic crystal). The helical state is stable with respect to disorder. However, if the difference between the densities of states in the electron bands split by spin-orbit coupling is neglected, then the order parameter modulation is present only at low temperatures, and only if the system is sufficiently clean and paramagnetically limited. This state resembles the Larkin-Ovchinnikov-Fulde-Ferrell state in centrosymmetric superconductors.

cond-mat.supr-con↗

arXiv2008

Nonuniform states in noncentrosymmetric superconductors

In noncentrosymmetric crystals, nonuniform superconducting states are possible even in the absence of any external magnetic field. The origin of these states can be traced to the Lifshitz invariants in the free energy, which are linear in spatial gradients. We show how various types of the Lifshitz invariants in noncentrosymmetric superconductors can be derived from microscopic theory.

cond-mat.supr-con↗