Non-Magnetic Impurity induced in-gap bound states in two band $s_{\pm}$ superconductors

TL;DR

This paper investigates how non-magnetic impurities induce in-gap bound states in two-band s-wave superconductors with a phase difference of π, highlighting the topological origin of these states.

Contribution

It demonstrates that non-magnetic impurities always induce in-gap bound states in s_{ ext{±}}-wave superconductors with a phase difference of π, linking the phenomenon to the topological properties of the system.

Findings

In-gap bound states are always induced by non-magnetic impurities when the phase difference is π.

The bound states are topologically protected due to the nature of the Bogoliubov-de Gennes equation.

The effect is specific to the s_{ ext{±}}-wave pairing symmetry with a phase difference of π.

Abstract

In this paper we study the effect of single non-magnetic impurity in two-band s-wave superconductors where the two s-wave order parameters have relative phase $\delta\neq0$ between them. We show that in-gap bound states are always induced by non-magnetic impurities when $\delta=\pi$ ($s_{\pm}$-wave superconductors). The bound state is a consequence of the topological nature of the corresponding Bogoliubov-de Gennes equation.