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

The Nb/NbZr multilayer is a typical one composed of two materials with the same bulk transition temperature and different electron diffusion constants and exhibits an anomalous upturn at T+ in the temperature dependence of parallel upper critical field H-c2 parallel to(T) For all samples which show the upturn behavior in H-c2 parallel to(T), we have found the anomalous minimum and maximum at a tilt of angle theta = theta* and a perpendicular direction theta = 0, respectively. Of particular interest is the existence of a different tendency in the variation of theta* and H-c2 perpendicular to-peak as a function of T below and above T+. From our experimental results, we suggest the dimensional crossover of the localization of Delta(r) for a tilt of angle. The angular dependence of H-c2(T) has been in a good agreement with the numerical calculations.