Comparison of experimental magnetization and specific-heat data with Landau-Ginzburg theory results for high-temperature superconductors near Hc2

Abstract

We have recently studied the magnetization and specific heat for two- and three-dimensional superconductors, starting from Landau-Ginzburg theory. In this paper we compare the results of this study with available experimental data. All our results have been calculated for a strong magnetic field along the c axis in the region near the Hc2 line where the lowest-Landau-level approximation is valid. We show that the theoretical two-dimensional magnetization compares very well with that measured for the high-Tc superconductor Bi 2:2:2:3, which is a quasi-two-dimensional system. Our comparison leads to an estimate of κ, the Ginzburg-Landau parameter as κ≃140. In three dimensions a reasonable fit to the specific heat for a conventional superconductor (niobium) is obtained, but the anisotropic Landau-Ginzburg theory cannot be made to fit YBa2Cu3O7−δ over any sizable temperature range. It is only when the Lawrence-Doniach model is considered (which takes into account the layered structure of the system) that a fit becomes possible over any temperature range. At high temperatures the form of this function is the same as the two-dimensional Landau-Ginzburg theory and the fact that this fits the experimental data indicates that the layers are acting independently.

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