Fermionic boundary modes in two-dimensional noncentrosymmetric superconductors

TL;DR

This paper investigates the spectrum of Andreev boundary modes in two-dimensional noncentrosymmetric superconductors, revealing how boundary states depend on pairing symmetry and spin-orbit coupling.

Contribution

It provides a detailed analysis of boundary modes in 2D noncentrosymmetric superconductors with various pairing symmetries, highlighting the influence of spin-orbit coupling.

Findings

Existence of subgap Andreev boundary states in all cases.

Zero-energy modes' properties depend on gap symmetry and spin-orbit strength.

Boundary states vary with time-reversal symmetry breaking and pairing type.

Abstract

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.