Size dependence of the Superconducting critical temperature and fields of Nb/Al multilayers

Abstract

The critical temperatureTc of Nb/Al multilayers decreases as the total sample thickness dT is decreased while the thickness of each Nb and Al layer is kept constant. To understand this behavior, models based on the proximity effect and on weak two-dimensional (2D) localization are employed. The latter uses a characteristic length, the thermal diffusion length, in relation to dT to obtain 2D behavior and leads to a reasonable explanation of Tc(dT). It is also found that the slope atTc(dT) of the critical magnetic field perpendicular to the layers is independent of dT when the Nb and Al layer thicknesses are kept constant. The angular dependence of the critical field is also measured.