TRANSPORT IN NORMAL-SUPERCONDUCTOR-NORMAL STRUCTURES WITH LOCAL CONSERVATION OF CURRENT

We study the transport properties of an NSN structure with an insulati ng barrier at each NS interface. Coherent quasiparticle scattering is assumed and self-consistency is implemented exactly to guarantee local charge conservation. The presence of a finite condensate flow has a g reater influence on the transport properties than either the gap depre ssion near the interfaces or the coherent nature of scattering. We fin d that a nonzero phase gradient causes a shift towards lower voltages of the first peak in the differential conductance and a global enhance ment of current. At low currents, eve obtain gap profiles near the int erfaces that are consistent with the criteria for boundary conditions employed in macroscopic descriptions. At higher voltages, the gap prof ile can change qualitatively due to the presence of nonequilibrium qua siparticles. The structure of resonances due to multiple coherent scat tering is smoothed out for long superconductors. (C) 1998 Elsevier Sci ence B.V. All rights reserved.