Magnetic-field penetration depth and material parameters of V-Ag multilayered superconductors

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Abstract
We have made measurements of the magnetic field penetration depth λ of V-Ag proximity-coupled multilayers for the first time. The layer-thickness dependence of λ exhibits a nonmonotonic behavior (existence of a minimum λ). This is interpreted as a crossover from a single superconductor to a composite one. When the Ag layer becomes thicker, the temperature dependence of λ begins to deviate from that of usual superconductors, showing that the proximity effect is involved. In addition, from λ and our previously found upper-critical-field parameters, the Ginzburg-Landau parameter, the thermodynamic critical field at 0 K, and the electronic coefficient of the normal-state specific heat are obtained. The variation of these parameters with layer thickness is also discussed.