Thickness dependence of the maximum DC Josephson current in superconducting proximity junctions

We investigated the maximum dc Josephson current I_M in NbNb_xO_yCu/Pb junctions as a function of normal layer thickness d_Cu. Theoretical calculations based on the McMillan proximity effect model are in good agreement with the experimental data. The monotonous decrease of RI_M (R is the normal tunneling resistance) indicates the absence of any oscillatory behaviour or anomaly in the pair amplitude F_Cu(d_Cu) of the Cu/Pb sandwich, in contradiction with theoretical prediction.