Reentrance of the metallic conductance in a mesoscopic proximity superconductor

We present an experimental study of the diffusive transport in a normal metal near a superconducting interface, showing the reentrance of the metallic conductance at very low temperature. This new mesoscopic regime comes in when the thermal coherence length of the electron pairs exceeds the sample size; The reentrance is suppressed by a bias voltage given by the Thouless energy and can be strongly enhanced by an Aharonov-Bohm flux. Experimental results are well described by the linearized quasiclassical theory.