Zur Theorie der Übergangstemperaturen von supraleitenden Doppelschichten (Proximity-Effekt)

A theory of the transition temperature of superconducting, superposed films is given by generalizing the methods ofde Gennes andWerthamer. It is shown that the transition temperature of nonhomogeneous superconductors obeys a general rule, which is formally of the same kind as the corresponding formula for homogeneous superconductors and is valid for all mean free paths. The results ofWerthamer follow analytically in the dirty limit if the transition temperatures of the superposed films are nearly equal, but there is numerical agreement for almost all superconductor-superconductor films. In the thin film limit and for normalconductor-superconductor films there are essential deviations. The theory is in good accord with the experimental data. By calculating the unknown interaction constant of copper from the experimental transition temperatures of superposed Cu-Pb films one gets for copper a transition temperature of the order of 10^?2°K.