Superconducting proximity effect in semiconductor nanowires

TL;DR

This paper investigates the proximity effect in semiconductor-superconductor nanostructures, revealing that increasing semiconductor thickness unexpectedly suppresses the induced superconducting gap due to interband coupling, affecting the design of Majorana fermion systems.

Contribution

It introduces the novel insight that semiconductor thickness critically influences the proximity-induced gap, a factor previously neglected in theoretical models.

Findings

Thicker semiconductors lead to suppressed superconducting gaps.

Interband coupling causes the suppression of the proximity effect.

The induced gap becomes weakly dependent on interface transparency.

Abstract

We theoretically consider the proximity effect in semiconductor-superconductor hybrid nanostructures, which are being extensively studied in the context of the ongoing search for non-Abelian Majorana fermions in solid state systems. Specifically, we consider the dependence on the thickness of the semiconductor in the direction normal to the interface, a physical effect that has been uncritically neglected in all prior work on the subject. Quite surprisingly, we find the completely unanticipated result that increasing the semiconductor thickness leads to a drastic suppression of the induced superconducting gap due to proximity-induced interband coupling. As a result, in the limit of strong semiconductor-superconductor coupling, the proximity-induced gap becomes much smaller than the bulk superconductor gap and depends weakly on the interface transparency.