INFLUENCE OF THE 3D-2D CROSSOVER ON THE CRITICAL-CURRENT OF NB CU MULTILAYERS/

We report the experimental observation of the Josephson critical curre nt across layers, I(c) perpendicular-to, for Nb/Cu multilayers. Unique samples with a small cross section (20 mum in diameter) consisting of ten Nb/Cu junctions were fabricated for such measurements. A strong i nfluence of the dimensional 3D-2D cross-over on the I(c)perpendicular- to was observed. Thus, as the temperature becomes smaller than T2D, hy steresis in the current-voltage characteristic appears and the behavio r of the temperature dependence of the I(c)perpendicular-to changes. F or T > T2D the diminishing of the hysteresis is caused by a sharp decr ease of the junction capacitance in the 3D regime when the sample beco mes uniform across layers. Calculation of the critical-current tempera ture dependence I(c)perpendicular-to (T) for our multilayers was made. An agreement between experimental and theoretical dependencies I(c)pe rpendicular-to (T) was found. From the theoretical simulations, we hav e obtained the dependence of the crossover and the critical temperatur es of multilayers on the layer thicknesses, the boundary transparency, and layer conductivity.