Quasiparticle relaxation in optically excited high-Q superconducting resonators

TL;DR

This paper measures quasiparticle relaxation times in superconducting films, revealing a saturation at low temperatures indicating an additional relaxation mechanism beyond electron-phonon interactions.

Contribution

It provides experimental data on quasiparticle relaxation in tantalum and aluminium, highlighting a second relaxation channel at low temperatures.

Findings

Relaxation time increases with decreasing temperature at high T

Saturation of relaxation time occurs at low T

Evidence of a second relaxation mechanism

Abstract

The quasiparticle relaxation time in superconducting films has been measured as a function of temperature using the response of the complex conductivity to photon flux. For tantalum and aluminium, chosen for their difference in electron-phonon coupling strength, we find that at high temperatures the relaxation time increases with decreasing temperature, as expected for electron-phonon interaction. At low temperatures we find in both superconducting materials a saturation of the relaxation time, suggesting the presence of a second relaxation channel not due to electron-phonon interaction.