Calculation of the Superconducting Transition Temperature of Superimposed Films in the Diffusion Approximation

Abstract

The de Gennes-Guyon-Werthamer theory of the proximity effect in the diffusion approximation has been extended by the use of coupled integral equations for the order parameters in the two metals. The two theories are in excellent agreement for Pb-Al superimposed films, but there are significant differences for Pb-Cu films. Several experiments have indicated that copper may be a superconductor ($T_c\approx 0.010°$K); in view of various theoretical and experimental uncertainties, it is concluded that most of this evidence for superconductivity in copper must be considered doubtful. It is shown that different methods of cutting off divergent sums occurring in the theory can give significantly different results, introducing a further theoretical uncertainty.