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

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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 mK. By Joule heating the electron gas and measuring the electron temperature, we show that the electron-phonon (e-p) scattering rate in the simplest noble metal disordered thin films (Cu,Au) follows a T⁴ temperature dependence, leading to a stronger decoupling of the electron gas from the lattice at the lowest temperatures. This power law is indicative e-p coupling mediated by vibrating disorder, in contrast to the previously observed T³ and T² laws.