Domain walls in superconductors: Andreev bound states and tunneling features

TL;DR

This paper investigates domain walls in tetragonal superconductors with broken time-reversal symmetry, revealing that they support subgap Andreev bound states with unique tunneling signatures.

Contribution

It provides a comprehensive analysis of domain walls in various superconducting states within D_{4h} symmetry, highlighting their bound states and tunneling features.

Findings

Domain walls support subgap Andreev bound states.

Bound state energies depend on propagation direction.

Tunneling experiments can detect these bound states.

Abstract

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.