MAGNETIC-FIELD DECOUPLING AND 3D-2D CROSSOVER IN NB CU MULTILAYERS/

Transport properties of Nb/Cu multilayers were measured along and acro ss layers. Ir is shown that not only the temperature but also the magn etic field parallel to layers can effectively decouple layers and caus e the three-to-two-dimensional (3D-2D) crossover. As a consequence of the 3D-2D crossover, sharpening of the resistive transition with curre nt along layers occurs due to the appearance of a strong intrinsic pin ning in the 2D state. Evidence for the intrinsic Josephson effect in t he 2D state is provided both by the pei-iodic modulation of the dynami c resistance across layers versus the parallel magnetic field and by t he multiply branched I-V curves caused by flux-flow of Josephson vorti ces in the stacked superconductor-normal-metal-superconductor junction s composing the multilayer. By measurements across layers the ''breaki ng field'' at which the proximity induced superconductivity in the nor mal layers of superconductor-normal-metal (Nb/Cu) multilayers is destr oyed was observed directly. A dimensionality diagram in the (H-T) plan e was deduced from our data. Reasons for complication of the ''Fraunho fer pattern,'' I-c(H), in ''long'' multilayers are discussed.