Upper Critical Field in Layered Superconductors

Abstract

The theoretical statements about a restoration of a superconductivity at magnetic fields higher than the quasiclassical upper critical field and a reentrance of superconductivity at temperatures T_c(H)≈ T_c(0) in the superconductors with open Fermi surfaces are reinvestigated taking into account a scattering of quasiparticles on the impurities. The system of integral equations for determination of the upper critical field parallel to the conducting planes in a layered conventional and unconventional superconductors with impurities are derived. The H_c2(T) values for the ``clean'' case in the Ginzburg-Landau regime and at any temperature in the ``dirty'' case are found analytically. The upper limit of the superconductor purity when the upper critical field definately has a finite value is established.