BALLISTIC CHARGE-TRANSPORT IN SUPERCONDUCTING WEAK LINKS

Ballistic charge transport through mesoscopic superconductor-normal-me tal-superconductor (SNS) microbridges is investigated within the frame work of the Keldysh technique. At low voltages we find a peak in the c onductance G approximately (l(in)/2a)(1/R0), where lin is the inelasti c mean free path, 2a is the normal layer thickness, and R0 is the Shar vin resistance. In this limit the dissipative current is carried by qu asiparticles which are trapped in the pair potential well of height DE LTA, suffering multiple Andreev reflections and relaxing inside the N layer. For larger voltages eV greater than or similar to (2a/l(in))DEL TA quasiparticle are accelerated out of the N layer and relax in super conducting banks. The current-voltage characteristic of the system in this regime is calculated both analytically and numerically. In the in termediate voltage range V approximately DELTA/e we analyze the subhar monic gap structure on the I-V curve and show that this structure is m ost pronounced in the temperature range T approximately DELTA/k(B) and vanishes for both T --> 0 and T --> T(C). We explain this behavior ta king into account the contribution of thermally excited quasiparticles with momenta opposite to the direction of total current flow.