Phonon-drag induced suppression of the Andreev hole current in superconducting niobium contacts

TL;DR

This study reveals that high bias voltages generate non-equilibrium phonons in superconducting niobium contacts, which suppress the Andreev hole current by scattering low-energy holes and disrupting electron-hole coherence.

Contribution

It demonstrates the impact of phonon wind on Andreev reflection in superconducting contacts, highlighting a phonon-induced suppression mechanism.

Findings

Strong suppression of Andreev hole current at high bias voltages

Phonon wind causes scattering lengths of low-energy holes to decrease to 100 nm

Disruption of electron-hole retracing due to phonon interactions

Abstract

We have investigated how the Andreev-reflection hole current at ballistic point contacts responds to a large bias voltage. Its strong suppression could be explained by the drag excerted by the non-equilibrium phonon wind generated by high-energy electrons flowing through the contact. The hole - phonon interaction leads to scattering lengths of the low-energetic holes down to 100\,nm, thereby destroying the coherent retracing of the electron path by the Andreev-reflected holes.