Fabrication and properties of very thin proximity Josephson junctions

We report on Josephson current measurements in Nb-NbxOy-Cu/Pb tunnel junctions where the Cu/Pb electrode is a very thin proximity sandwich. The Cu and Pb film thicknesses are of the order of 100 Å, which is much smaller than the coherence length, so that the superconducting order is uniform across the sandwich and the influence of the Cu-Pb interface barrier can be neglected (Cooper limit). Although the Pb layer is electrically discontinuous, the junctions exhibit current-voltage characteristics and Josephson effects similar to the behaviour of a classical Nb-NbxOy-Pb junction.