SELF-CONSISTENT CURRENT-VOLTAGE CHARACTERISTICS OF NORMAL-SUPERCONDUCTOR INTERFACES

We study the nonlinear transport properties of NS (normal-superconduct or) and NSN structures by means of a self-consistent microscopic descr iption. A nonzero superfluid velocity causes the various quasiparticle channels within the S to open at different voltages. The gap reductio n is very sensitive to the details of quasiparticle scattering. At low temperatures, superconductivity, sometimes in a peculiar gapless form , may survive up to voltages much higher that k(B)T(c)/e. The minimum voltage for quasiparticle transmission is shown to decrease strongly w ith temperature and with the transmittivity of the barrier.