Electron–phonon interaction in thin copper and gold films

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 T4 temperature dependence in both metals. The result is in accordance with the theory of e–p scattering in disordered films with vibrating boundaries and impurities, in contrast to the T3-law expected for pure samples, and T2-law for static disorder. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)