REENTRANCE OF THE METALLIC CONDUCTANCE IN A MESOSCOPIC PROXIMITY SUPERCONDUCTOR

We present an experimental study of the diffusive transport in a norma l metal near a superconducting interface, showing the reentrance of th e metallic conductance at very low temperature. This new mesoscopic re gime comes in when the thermal coherence length of the electron pairs exceeds the sample size; The reentrance is suppressed by a bias voltag e given by the Thouless energy and can be strongly enhanced by an Ahar onov-Bohm flux. Experimental results are well described by the lineari zed quasiclassical theory.