Electron-phonon interaction in ultrathin Nb films

The heating of electrons in the normal and resistive states of thin Nb superconducting films is studied. The electron-phonon interaction times τeph are determined by direct measurements of the relaxation time of the sample resistance and also on the basis of the magnitude of the electron heating. The dependence of τeph on the electron mean free path, τeph∞l-1, shows that, in accordance with the theoretical conclusions, at low temperatures the contribution of nonelastic electron scattering by impurities to the energy relaxation cancels, whwreas the temperature dependence τeph∞T-2 observed is due to the modification of the phonon spectrum in thin films