Experimental indication for supercurrents carried by opened transport channels

Electrical-transport properties of mesoscopic junctions consisting of a ballistic two-dimensional electron gas coupled at two sides to overlaying superconducting contacts are presented. The properties suggest that, despite the presence of transport limiting barriers in the sample, supercurrents are carried by a few modes that have near-unity transmission probability. We can qualitatively account for the presence of these resonances by the theory of disorder-induced opening of tunnel channels. {copyright} {ital 1996 The American Physical Society.}