Preferential position of order parameter and angular dependence of upper critical fields in Nb/NbZr multilayers

The Nb/NbZr multilayer, which is composed of two superconductors with the same critical temperature and the different electron diffusion constant, is a typical system to exhibit the anomalous upturn in T-dependence of upper critical field H-c2 parallel to parallel to the film surface. For the angular dependence of H-c2 we have observed a minimum on the tilt of theta is approximately equal to30 degrees=theta* (as theta=0 degrees for H perpendicular to film). This is interpreted as the dimensional crossover of the localized order parameter at theta*. This mechanism has been also confirmed in the variation of I-V characteristics with H-direction to the film, where the samples were located at the specific configuration in the field.