Anomalous upper critical fields of superconducting N b/ N bo.5 Z ro.5 multilayers

Abstract

Abstract Upper critical fields have been studied for N b/ N bo.5 Z ro.5 multilayers grown onto the substrates of 300°C by magnetron sputtering. The multilayers are constituted from two superconducting materials with different electronic diffusion constants and nearly equal critical temperatures. For the samples with period of 360-, 400- and 500-A, the upturn features at lower temperature in addition to dimensional crossover were observed in parallel upper critical field Hc2. Noticeable changes were also found in the transition width ΔHc2I (T) and the angular dependence of HC2 in the region of temperature which the upturn took place. The positive curvatures of H... had a tendency to depend upon N b layer thicknesses.