Analyses of the Pinning Mechanism for the Superconductor/Normal-Metal and Superconductor/Superconductor Multilayers

摘要

The vortex pinning force of superconductor(S)ormal-metal(N) multilayers, Nb/Ti and Nb{sub}(100-x)Ti{sub}x/Ti, and superconductor(S)/superconductor (S') multilayers, Nb{sub}(100-x)Ti{sub}x/Nb and Nb{sub}28Ti{sub}72/Nb{sub}65Ti{sub}35, has been studied as a function of the layer thickness d for various compositions of x. The transverse pinning force density F{sub}(p⊥) acting perpendicular to the layer planes makes a peak around d ～ 2ξ{sub}(GL) (ξ{sub}(GL): the GL coherence length) for both the S/N and S/S' multilayers, where they exhibit the quasi-two-dimensional superconductivity. In contrast, the longitudinal pinning force density F{sub}(p||) acting parallel to the layer plane hardly depends on d. The pinning mechanism inherent in the layered structure has been analyzed based on the GL free energy, which clarified that the effective pinning force due to the multilayer structure originates from the difference in the potential energy for the S/N multilayer and from the difference in the kinetic energy for the S/S' multilayer between the constituent layers. The d dependence of the F{sub}(p⊥), however, has been found to be qualitatively similar for the S/N and S/S' multilayers.