Upper critical field of V-Ag multilayered superconductors

Abstract

We report investigations of the upper critical field (Hc2⊥ and Hc2?) of V-Ag proximity-coupled superconducting multilayer structures, prepared by ultrahigh-vacuum electron-beam evaporation. By means of x-ray diffraction analysis, successful formation of an artificial superstructure is confirmed. From resistivity measurement parallel to the layers, the electron mean free paths in the V and Ag layers are determined. With reference to these transport properties, characterization of Hc2 has been made. For three-dimensional multilayer structures, Hc2 is analyzed in terms of the temperature dependence of Hc2⊥, the zero-temperature coherence length, and the anisotropy Hc2?/Hc2⊥. Our results are in quantitative agreement with the relevant theories. For quasi-two-dimensional multilayer structures, a peculiar temperature dependence has been revealed in both Hc2⊥ and Hc2?. Hc2⊥ exhibits positive curvature near Tc, and it is continuously enhanced with the increase of multilayer period, as predicted theoretically. In contrast with the monotonic variation in Hc2⊥, a drastic upturn at a certain temperature (dimensional crossover) and an upward inflection at a higher temperature have been observed in Hc2?. These two types of anomalies in Hc2? are discussed in the context of the commensurability between the multilayer structure and the vortex lattice.

Source-reported materials — not catalogue approval

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