Recombination limited energy relaxation in a BCS superconductor

TL;DR

This study investigates how quasiparticles relax energy in a superconductor at very low temperatures, revealing a significant reduction in energy flux in the superconducting state and suggesting additional relaxation mechanisms beyond current theories.

Contribution

It provides experimental measurements of quasiparticle energy relaxation in aluminium superconductors and compares them with existing quasiclassical theory, highlighting discrepancies and potential new relaxation processes.

Findings

Strong reduction of energy flux in superconducting state at low temperatures

Quantitative flux exceeds theoretical predictions in both states

Possible indication of enhanced or additional relaxation mechanisms

Abstract

We study quasiparticle energy relaxation at sub-kelvin temperatures by injecting hot electrons into an aluminium island and measuring the energy flux from electrons into phonons both in the superconducting and in the normal state. The data show strong reduction of the flux at low temperatures in the superconducting state, in qualitative agreement with the presented quasiclassical theory for clean superconductors. Quantitatively, the energy flux exceeds that from the theory both in the superconducting and in the normal state, possibly suggesting an enhanced or additional relaxation process.