Dimensional effects in V/Cu superconducting superlattices.

Abstract

The superconductor-normal-metal phase transitions in V/Cu superlattices have been studied in parallel and perpendicular magnetic fields. Two crossovers from three-dimensional to two-dimensional and from two-dimensional to three-dimensional have been observed in magnetoresistance R(H,T) and in dependencies of the fluctuating conductivity \ensuremath{\sigma}'(T) in a parallel magnetic field. The crossover in low magnetic field is caused by the fact that the superconducting coherence length ${\ensuremath{\xi}}_{\mathit{S}}$(T) becomes of the order of the superstructure period \ensuremath{\Lambda}. The crossover in high magnetic field is due to the competition of the normal-metal coherence length ${\ensuremath{\xi}}_{\mathit{N}}$ and magnetic length ${\mathit{L}}_{\mathit{H}}$. The experimental results are in good agreement with numerical solution of the Ginzburg-Landau equation for superconductor-normal-metal-superconductor (SNS) superlattices.