Superconducting Properties of Compositionally Modulated Pb/Ge Thin Films

摘要

Finely layered superconducting Pb/Ge multilayers have been made on liquid nitrogen cooled sapphire substrates with use of a mass spectrometer rate controlled electron beam evaporation scheme. Individual layer thicknesses range from 1 to 10 nm, each sample containing 50 to 100 Pb/Ge layer pairs with different Pb-to-Ge thickness ratio. An x-ray analysis showed that the samples have a superlattice structure consisting of amorphous Ge layers and (III) textured polycrystalline Pb layers. Transport studies reveal that the relationship between Tc and Pb-layers resistance is influenced by the layer thickness and the evaporation conditions. Measurements of the upper critical field versus temperature clearly show the dimensional crossover effects present in Josephson coupled two-dimensional superconductors. The maximum observed in the critical current versus field curve is related to the individual layer thickness. (ERA citation 12:018510)