Localization of Quasiparticles in an NS Structure

TL;DR

This paper investigates how quasiparticles localize in a normal-superconductor (NS) structure due to Andreev reflection, highlighting the role of disorder correlation length in the localization phenomenon.

Contribution

It provides criteria for quasiparticle localization in NS structures and clarifies the impact of disorder type on this effect, combining semiclassical and quantum perspectives.

Findings

Localization occurs with smooth disorder of large correlation length.

Short-range disorder destroys quasiparticle localization.

Localized states produce resonance peaks in tunneling density of states.

Abstract

We discuss localization of quasiparticles in an extended NS structure in the situation when the reflection from the NS interface is mostly of Andreev kind. The localization of quasiparticle states arises due to trajectory retracing caused by Andreev reflection. This effect is semiclassical in the sense that in the classical limit the states become fully localized, while quantum effects destroy localization behaviour. We derive the criteria for this localization and show that it takes place only for sufficiently smooth disorder with large correlation length, whereas short-range disorder destroys the effect. Localization of quasiparticle states gives rise to resonance peaks in the local tunneling density of states.