SUPERCONDUCTIVITY OF NB/CR MULTILAYERS

Multilayers of Nb/Cr have been fabricated by a UHV e-beam evaporation system with the nominal Cr layer thickness of 30 Å and the Nb layers varying from 30 to 1000 Å. The structural properties have been studied by computer modeling of the measured large angle x-ray spectra. It was found that the Nb/Cr films have symmetric interfaces. The resistivity temperature variation was measured using the dc four-probe method. For ML with bilayer thickness, Λ less than 250 Å, it varied inversely as Λ-1 indicating that the resistivity is dominated by electron scattering from the interfaces at low temperature. The Tc of Nb/Cr films varies from 9.1 K for dNb=1000 Å to below 4.2 K for dNb=26 Å. This can be explained by the de Gennes-Werthamer theory with corrections for the interface thicknesses. It was also found that the resistivity drop occurs in two steps for samples with dNb<1000 Å. The areas under the second steps increased almost linearly with the number of the interfaces. The parallel critical fields were measured for several of the multilayers.