Boundary effects in two-band superconductors

TL;DR

This paper investigates how boundaries affect the superconducting properties of two-band materials, revealing surface states and complex gap variations influenced by interband coupling.

Contribution

It provides a microscopic analysis of boundary effects in two-band superconductors using the BCS model, highlighting the role of interband coupling.

Findings

Superconducting surface states are identified.

The difference between bulk and surface critical temperatures depends on interband coupling.

Boundaries induce multiple length scale variations in the superconducting gaps.

Abstract

We present a microscopic study of the behavior of the order parameters near boundaries of a two-band superconducting material, described by the standard tight-binding Bardeen-Cooper-Schrieffer model. We find superconducting surface states. The relative difference between bulk and surface critical temperatures is a nontrivial function of the interband coupling strength. For superconductors with weak interband coupling, boundaries induce variations of the gaps with the presence of multiple length scales, despite non-zero interband Josephson coupling.