Electron energy relaxation in disordered superconducting NbN films

Abstract

We report onthe energy relaxation of electrons studied by means of magnetoconductance and photoresponse in a series of superconducting NbN film with thickness in the range from 3 to 33 nm. The inelastic scattering rate of electrons on phonons obeys Tntemperature dependence where the exponent is in the range ????≈3.2÷3.8and shows no systematically dependence on the degree of disorder. At 11K electron-phonon scattering times are in the range11.9 -17.5 ps.We show that in the studied NbN films the Debye temperature and the densityof phononstatesare both reduced with respect to bulk material. In the thinnest studied films reduced density of states along with the phonon trapping slowsdown the energy relaxationofelectrons by afactor of 4 as compared to the prediction of the tree dimensional phonon mode