Study of the Superconducting Proximity Effects by Josephson Tunneling

We have studied Josephson tunneling in lead – lead oxide – copper – lead junctions with the intent of investigating the proximity effects between normal (Cu) and superconducting (Pb) metals. Zero-voltage tunneling currents of the order of milliamps have been observed in junctions with varying copper thicknesses and electron mean free paths. We have interpreted our measurements of the temperature dependence of the maximum Josephson current in terms of a model based on the de Gennes – Werthamer theory of the proximity effects. As a result of our work we conclude that the de Gennes – Werthamer theory has considerable usefulness outside the strict limits of validity in which it was derived.