A MICROSCOPIC MODEL FOR THE NONEQUILIBRIUM PROXIMITY EFFECT IN SUPERCONDUCTOR-NORMAL METAL JUNCTIONS

The current-voltage characteristics of a superconductor-normal metal j unction are affected by the proximity superconductivity induced on the normal side. We study this effect using the quasiclassical theory. We first present a unified derivation of the previous results obtained b y time-dependent Ginzburg-Landau (TDGL) theories. In order to study th e effect beyond the scope of the TDGL theory, we approximate the induc ed order parameter by a step function. The amplitude and the phase of the induced order parameter as well as the width of the step are deter mined self-consistently. The calculation is made in the pure limit, bu t no restrictions are set on the temperature or on the transmission co efficient of the junction besides the ones implicit in the step approx imation. A time-dependent solution for the order parameter is found at all currents or voltages. It is found that the results in the TDGL re gion and outside are relatively similar, although different mechanisms are responsible for the conversion from the normal to supercurrent in each case.