Andreev states, supercurrents and interface effects in clean SN multilayers

TL;DR

This paper investigates the local density of states and supercurrents in clean SN multilayers, highlighting the limitations of the Andreev approximation at critical transverse widths and emphasizing the importance of exact methods and interface effects.

Contribution

It extends previous models by analyzing critical transverse widths where the Andreev approximation fails, incorporating interface barriers and exact reflection effects.

Findings

Andreev approximation breaks down at critical widths

Exact treatment needed for accurate results at certain widths

Interface barriers influence supercurrent coupling

Abstract

We present results for the local density of states in the S and N layers of a SN multilayer, and the supercurrent, based on a Green's function formalism, as an extension of previous calculations on NS, SNS and SNSNS systems. The gap function is determined selfconsistently. Our systems are chosen to have a finite transverse width. We focus on phenomena which occur at so-called critical transverse widths, at which a new transverse mode is starting to contribute. It appears, that for an arbitrary width the Andreev approximation (AA), which takes into account only Andreev reflection at the SN interfaces, works well. We show that at a critical width the AA breaks down. An exact treatment is required, which considers also ordinary reflections. In addition, we study the influence of an interface barrier on the coupling between the S-layers.