Andreev reflection versus Coulomb blockade in hybrid semiconductor nanowire devices

TL;DR

This paper explores how Coulomb blockade, Andreev reflection, and quantum interference compete in semiconductor nanowires with superconducting contacts, revealing different transport regimes based on coupling strength and charging energy.

Contribution

It provides a comparative analysis of transport phenomena in InAs and InP nanowires under various coupling and Coulomb interaction conditions, highlighting the interplay of these effects.

Findings

Negative differential conductance due to BCS density of states

Andreev reflection dominates at intermediate coupling

Universal conductance fluctuations enhanced by Andreev reflection

Abstract

Semiconductor nanowires provide promising low-dimensional systems for the study of quantum transport phenomena in combination with superconductivity. Here we investigate the competition between the Coulomb blockade effect, Andreev reflection, and quantum interference, in InAs and InP nanowires connected to aluminum-based superconducting electrodes. We compare three limiting cases depending on the tunnel coupling strength and the characteristic Coulomb interaction energy. For weak coupling and large charging energy, negative differential conductance is observed as a direct consequence of the BCS density of states in the leads. For intermediate coupling and charging energy smaller than the superconducting gap, the current-voltage characteristic is dominated by Andreev reflection and Coulomb blockade produces an effect only near zero bias. For almost ideal contact transparencies and negligible charging energy, we observe universal conductance fluctuations whose amplitude is enhanced due to Andreev reflection at the contacts.