Observation of disorder-induced weakening of electron-phonon interaction in thin noble-metal films

Abstract

We have used symmetric normal metal-insulator-superconductor (NIS) tunnel junction pairs, known as SINIS structures, for ultrasensitive thermometry in the temperature range $50--700\phantom{\rule{0.3em}{0ex}}\mathrm{mK}$. By Joule heating the electron gas and measuring the electron temperature, we show that the electron-phonon $(e\text{\ensuremath{-}}p)$ scattering rate in the simplest noble-metal disordered thin films (Cu,Au) follows a ${T}^{4}$ temperature dependence, leading to a stronger decoupling of the electron gas from the lattice at the lowest temperatures. This power law is indicative $e\text{\ensuremath{-}}p$ coupling mediated by vibrating disorder, in contrast to the previously observed ${T}^{3}$ and ${T}^{2}$ laws.