Impurity-induced states in superconducting heterostructures

TL;DR

This paper investigates how a single impurity affects the electronic states in superconductor-semiconductor heterostructures, revealing impurity-induced bound states influenced by the coupling between layers, with implications for realizing Majorana modes.

Contribution

It provides a detailed analysis of impurity effects in superconductor/semiconductor heterostructures, highlighting how coupling modifies impurity-induced states and conditions for low-energy bound states.

Findings

Coupling can induce additional subgap bound states.

Impurity states are strongly affected by heterostructure coupling.

Conditions for low-energy impurity-bound states are identified.

Abstract

Heterostructures allow the realization of electronic states that are difficult to obtain in isolated systems. Exemplary is the case of quasi-one-dimensional heterostructures formed by a superconductor and a semiconductor with spin-orbit coupling in which Majorana zero-energy modes can be realized. We study the effect of a single impurity on the spectrum of superconducting heterostructures. We find that the coupling between the superconductor and the semiconductor can strongly affect the impurity-induced states and may induce additional subgap bound states that are not present in isolated uniform superconductors. For the case of quasi-one-dimensional superconductor/semiconductor heterostructures, we obtain the conditions for which the low-energy impurity-induced bound states appear.