THE UPPER CRITICAL-FIELD OF SUPERCONDUCTORS WITH A CYLINDER-SYMMETRICAL FERMI-SURFACE

This paper presents a theory of the upper critical field Bc2(T) for a cylinder-symmetrical Fermi surface based on the theory of Werthamer, Helfand and Hohenberg (WHH-theory). Effects coming from impurity scattering are included. This special Fermi surface geometry requires the development of a model for the impurity scattering which goes beyond the usual Drude-like approach. Technical problems like inconsistencies between the Bc2-equations at Tc and the Tc-equations due to different approximations are analysed. The results of these calculations are discussed in detail and compared to equivalent calculations for a spherical Fermi surface. Finally, possible implications for the interpretation of experimental Bc2 data in high temperature super-conductors are pointed out. Most important, the theory predicts bigger in-plane Ginzburg-Landau coherence lengths and smaller Fermi velocities than the "classical" WHH-theory. © 1990.