Experimental Study of the Effects of Disorder in Weakly Disordered Superconducting Aluminum Films.

We have studied the effects of disorder on superconductivity in weakly disordered aluminum films by a nonequilibrium technique. We observed for the first time thermal phase fluctuations and the predicted strong temperature dependence of electron-electron scattering rate below T_ {rm c}. The pair-breaking rates from both of these processes increase approximately linearly in the resistance per square of Al film, R_square, and phase fluctuation term has a weak temperature dependence. We measured low-voltage resistance of high-resitance and low-resistance Al-A lO_{rm x} -Cu tunnel junctions as a function of both temperature and supercurrents, either directly applied or induced by parallel magnetic fields. Al films were weakly disordered with resistance per square of the film, R_square, ranging from 1.7Omega to 22Omega and measurements were done in the temperature range of 0.4T_{rm c} ~ 7T_{rm c}. Data agree with our model calculations including both electron-electron scattering and thermal phase fluctuations. From measurements on high-resistance junctions, we demonstrate our understanding of the pair-breaking effect of supercurrents. From the results on low-resistance junctions, we observed both thermal phase fluctuations and the strong temperature dependence of electron-electron scattering.