We report the experimental observation of the Josephson critical current 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 influence of the dimensional 3D-2D cross-over on the I(c)perpendicular-to was observed. Thus, as the temperature becomes smaller than T2D, hysteresis in the current-voltage characteristic appears and the behavior of the temperature dependence of the I(c)perpendicular-to changes. For T > T2D the diminishing of the hysteresis is caused by a sharp decrease of the junction capacitance in the 3D regime when the sample becomes uniform across layers. Calculation of the critical-current temperature dependence I(c)perpendicular-to (T) for our multilayers was made. An agreement between experimental and theoretical dependencies I(c)perpendicular-to (T) was found. From the theoretical simulations, we have obtained the dependence of the crossover and the critical temperatures of multilayers on the layer thicknesses, the boundary transparency, and layer conductivity.
Bibliographical noteCopyright (1994) by the American Physical Society.
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