ANISOTROPY OF THE LOWER CRITICAL-FIELD IN A NB CU MULTILAYER THE EVIDENCE FOR 3D-2D CROSSOVER/

The critical fields, H(c1) and H(c2), of the superconducting Nb(200 an gstrom)/Cu(150 angstrom) multilayer were measured in the temperature r ange from T(c) (7.2 K) down to 2 K. The anisotropy of the lower critic al field for the S/N multilayer was obtained for the first time. The a nisotropy of H(c1) exhibited a sharp upturn at T almost-equal-to 5.5 K. This temperature was found to coincide with the temperature of the 3D-2D crossover obtained from the measurements of the upper critical f ield. A qualitative description of the behavior of H(c1)parallel-to (T ) regarding the core structure of the vortex in S/N multilayers was ma de.