  We present an experimental study of the diffusive transport in a normal metal
near a superconducting interface, showing the re-entrance 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.
This re-entrance 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.
