CHARGE-TRANSPORT IN PROXIMITY-EFFECT SNCNS CONSTRICTIONS

Josephson and quasiparticle currents in SNcNS contacts are calculated for the regimes of ballistic constriction ''c''. The relation between the current and electronic densities of states in NS proximity bilayer is found. The effect of the proximity N laver on the Andreev and norm al reflections of electrons at the constriction is studied. Excess cur rent at large voltages and subharmonic structure at low bias are analy zed as a function of material parameters of N and S and transparency o f the NS interface. The appearance of new series of subharmonic peaks due to two-gap structure in the density of states of proximity NS elec trodes is demonstrated. The relation between excess and critical curre nts is analyzed. The model is relevant for SNS junctions of constricte d geometry which is realized in S-2DEG-S and step-edge high T-c SNS co ntacts.