New method to study the proximity effect at the normal-metal–superconductor interface

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Abstract
The excess current of a point contact on a Ag-Pb bilayer has been measured for several thicknesses of the Ag film. The excess current is due to Andreev reflection and contains information about the position dependence of the superconducting order parameter near the interface. If the Ag film is very thin, the excess current is that of a normal-metal–superconductor point contact, though slightly changed because of the depression of the order parameter at the surface of the bilayer. For larger thicknesses, the combination of the proximity effect and the limited mean free path of the electrons yields very different current-voltage characteristics.