Evidence for long-lived quasiparticles trapped in superconducting point contacts

TL;DR

This paper reports the observation of long-lived quasiparticles trapped in superconducting atomic contacts, significantly affecting supercurrent flow and revealing new insights into quasiparticle dynamics in superconductors.

Contribution

It provides experimental evidence for quasiparticle trapping in Andreev bound states with unprecedented long lifetimes exceeding 100 microseconds.

Findings

Supercurrent is suppressed near phase { extpi} in atomic contacts.

Quasiparticle trapping occurs when Andreev energy is below half the superconducting gap.

Trapped quasiparticles have lifetimes over 100 microseconds.

Abstract

We have observed that the supercurrent across phase-biased, highly transmitting atomic size contacts is strongly reduced within a broad phase interval around {\pi}. We attribute this effect to quasiparticle trapping in one of the discrete sub-gap Andreev bound states formed at the contact. Trapping occurs essentially when the Andreev energy is smaller than half the superconducting gap {\Delta}, a situation in which the lifetime of trapped quasiparticles is found to exceed 100 \mus. The origin of this sharp energy threshold is presently not understood.