Phonon relaxation of subgap levels in superconducting quantum point contacts

TL;DR

This paper calculates the phonon-induced relaxation rates of subgap states in superconducting quantum point contacts, revealing conditions under which relaxation times can significantly exceed bulk quasiparticle lifetimes.

Contribution

It provides a theoretical computation of the relaxation rate of subgap states in superconducting quantum point contacts, highlighting the impact of contact reflection on relaxation times.

Findings

Relaxation time can be much longer than bulk quasiparticle lifetime with low reflection.

Phonon emission governs the relaxation process.

Relaxation rates depend on contact reflection and subgap state properties.

Abstract

Superconducting quantum point contacts are known to possess two subgap states per each propagating mode. In this note we compute the low-temperature relaxation rate of the upper subgap state into the lower one with the emission of an acoustic phonon. If the reflection in the contact is small, the relaxation time may become much longer than the characteristic lifetime of a bulk quasiparticle.