Zur Kontaktwirkung in supraleitenden Doppelschichten aus Cu/Pb
The transition temperatures of superimposed films of copper and lead are measured at very low temperatures by means of a helium3-cryostat. The double films are condensed in situ inside the cryostat at 200 °K, and have never been warmed up or brought to air before measuring. Careful measurements of the residual resistivities, film thicknesses and the choice of ln<ls enable us to compare the experimental results with the various theories of the proximity effect. The non-homogeneous structure of the films and the surface scattering of the electrons have been considered in a first approximation by the use of an effective resistivity. A fitting of the theoretical curves to the measured temperatures indicates either the existence of barrier layers between the two metals (in contradiction to the experiments of the proximity effect between two known superconductors) or copper being a superconductor itself with a low transition temperature. This paper indicates that many experimental and theoretical problems are left unsolved in this field in contradiction to the more optimistic judgement of other authors. ⋆ Für eine kritische Diskussion der Experimente und ein vollständiges Literaturverzeichnis wird auf den zusammenfassenden Vortrag in dem Internationalen Colloquium über Grundprobleme der Physik Dünner Schichten, Clausthal (1965) und auf den Bericht der Sommerschule für Supraleitung, Steibis/Allgäu (1965) verwiesen.
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