Doppler Shift in Andreev Reflection from a Moving Superconducting Condensate in Nb/InAs Josephson Junctions

TL;DR

This paper investigates how magnetic fields affect Andreev reflection in Nb/InAs Josephson junctions, revealing a Doppler shift caused by screening currents that impacts the junction's electronic properties.

Contribution

It provides experimental evidence of Doppler shift effects in Andreev levels due to diamagnetic screening currents in hybrid superconductor-semiconductor junctions.

Findings

Magnetic-field suppresses Andreev reflection amplitude.

Doppler shift observed in Andreev energy levels.

Results explained by sample geometry and interface transparency.

Abstract

We study narrow ballistic Josephson weak links in a InAs quantum wells contacted by Nb electrodes and find a dramatic magnetic-field suppression of the Andreev reflection amplitude, which occurs even for in-plane field orientation with essentially no magnetic flux through the junction. Our observations demonstrate the presence of a Doppler shift in the energy of the Andreev levels, which results from diamagnetic screening currents in the hybrid Nb/InAs-banks. The data for conductance, excess and critical currents can be consistently explained in terms of the sample geometry and the McMillan energy, characterizing the transparency of the Nb/InAs-interface.