COHERENT PHENOMENA IN MESOSCOPIC CYLINDERS OF CU AND AG IN PROXIMITY WITH A SUPERCONDUCTOR

Copper and silver cylinders driven to superconductivity by the proximity effect show a novel form of quantum coherence. Below a characteristic temperature T(min), the induced diamagnetic currents in Cu and Ag decrease as the temperature is reduced. The diamagnetic current is restored by the application of a small magnetic field H < 10 Oe. For T < T(min) the condition K(N)-1 greater-than-or-equal-to L is fulfilled and the magnetic response can be described by DELTA(chi) = A exp(K(N)-1/L). Here K(N)-1 is the decay length of the induced pair amplitude and L the perimeter of the cylinder. We interpret this reentrant behaviour as resulting from a paramagnetic persistent current which opposes the diamagnetic Meissner current. Strong similarities between this novel magnetic response and persistent currents in mesoscopic normal metal rings are found.