The modified Ginzburg-Landau theory for anisotropic high temperature superconductors

The modified Ginzburg-Landau theory, MGL, for strongly anisotropic high temperature superconductors (HTSC's) is reviewed and the MGL equations are re-derived to be used in solving two important fundamental problems. The first one concerns the evaluation of the domain-wall energy problem by a complete solution of the derived equations. The modified free energy functional is used to calculate the maximum supercurrents in both HTSC's and the conventional superconductors. Our calculations show that the surface energy vanishes at the critical value of the GL parameter κc=1/√2{(1-M)(1+M/3)}1/2, where 0 ≤ M < 1. Therefore, the transformation from type II to type I superconductivity is possible at temperatures very close to the transition critical one, at which κ(T) becomes zero. The generalized formulas of the superconducting current allowed us to calculate the maximum supercurrents for both the HTSC's and the conventional ones. The possible maximum currents are anisotropic and have higher values for HTSC's. Our results are in good agreement with the related theoretical works as well as with the experimental data. (author). 25 refs, 3 figs