PROXIMITY EFFECT UNDER NONEQUILIBRIUM CONDITIONS IN DOUBLE-BARRIER SUPERCONDUCTING JUNCTIONS

A microscopic theory is developed for structures S-N-N' (S is a superconductor, N, N' are normal metals) with potential barriers at the interfaces. The length of the N layer is supposed to be shorter than the energy relaxation length but longer than the mean free path l, and the dirty case is considered (l is shorter than the coherence length in the N-layer). The differential conductance is calculated for different values of the barrier resistances compared to the resistance of the middle layer. The conductance has an anomaly (a peak) at voltages V <DELTA due to an enhancement of the proximity effect at low energies (voltages). The anomaly is suppressed by pairbreaking mechanisms. It is shown that the magnetoconductance can be negative or positive depending on the ratio of the barrier resistances and on the voltage. The AC conductance (admittance) has a peak at a frequency omega <DELTA. At high voltages V much greater than DELTA a transition from an excess current at high barrier transparencies to a deficit current at low barrier transparencies is found in S-N-N' (S) structures.