Direct temporal measurement of hot-electron relaxation in a phonon-cooled metal island

TL;DR

This study directly measures the relaxation rate of hot electrons in a micron-scale metal island using a fast superconductor-insulator-normal metal tunnel junction thermometer, confirming theoretical predictions of electron-phonon cooling.

Contribution

It introduces a novel experimental setup for real-time measurement of electron thermal relaxation in a small metal island, providing direct validation of electron-phonon cooling theory.

Findings

Measured electron-phonon relaxation rate matches theoretical predictions

Demonstrated fast (~20 MHz) temperature measurement capability

Controlled electron heating above phonon temperature

Abstract

We report temporal measurements of the electronic temperature and the electron-phonon thermal relaxation rate in a micron-scale metal island, with a heat capacity of order 1 fJ/K . We employed a superconductor-insulator-normal metal tunnel junction, embedded in a radio-frequency resonator, as a fast (~ 20 MHz) thermometer. A resistive heater coupled to the island allowed us to drive the electronic temperature well above the phonon temperature. Using this device, we have directly measured the thermal relaxation of the hot electron population, with a measured rate consistent with the theory for dynamic electron-phonon cooling.