Electron-phonon interaction in thin copper and gold films

TL;DR

This study investigates the electron-phonon interaction in thin copper and gold films at very low temperatures, revealing a $T^{4}$ dependence consistent with disordered film theory, using tunnel junction thermometry.

Contribution

It provides experimental evidence for the $T^{4}$ temperature dependence of electron-phonon scattering in disordered thin metal films at sub-Kelvin temperatures.

Findings

Electron-phonon scattering rate follows a $T^{4}$ law.

Results align with theories for disordered films with vibrating boundaries.

Contrasts with $T^{3}$ and $T^{2}$ laws for pure and static disorder samples.

Abstract

We have studied the electron-phonon (e-p) interaction in thin Cu and Au films at sub-Kelvin temperatures with the help of the hot electron effect, using symmetric normal metal-insulator-superconductor tunnel junction pairs as thermometers. By Joule heating the electron gas and measuring the electron and the lattice temperatures simultaneously, we show that the electron-phonon scattering rate follows a $T^{4}$ temperature dependence in both metals. The result is in accordance with the theory of e-p scattering in disordered films with vibrating boudaries and impurities, in contrast to the $T^{3}$-law expected for pure samples, and $T^{2}$-law for static disorder.