Anisotropic Upper Critical Fields of Disordered Nb(0.53)Ti(0.47)-Ge Multilayers

摘要

We report studies of the upper critical fields of Nb/sub 0.53/Ti/sub 0.47/-Ge multilayers consisting of thick Ge layers and varying thickness Nb/sub 0.53/T/sub 0.47/ layers. Both the angular dependence and the temperature dependence of the upper critical fields indicate a dimensional crossover at a Nb/sub 0.53/Ti/sub 0.47/ layer thickness near 200/angstrom/. All the 2D samples display a cusp-like upper critical field angular dependence with a sharper cusp for thinner Nb/sub 0.53/Ti/sub 0.47/ layers. The parallel upper critical fields are tentatively fitted with an expression combining the 2D field dependence of Rickayzen, the paramagnetic limiting behavior of Maki and the disorder-related Coulomb interaction effects of Maekawa and Fukuyama. The perpendicular fields are fitted with the Maekawa, Ebisawa and Fukuyama theory; better agreement is obtained for thinner Nb/sub 0.53/Ti/sub 0.47/ sublayers when the paramagnetic limiting effect is included. 24 refs., 7 figs.