A theory of the upper critical field in antiferromagnetic superconductors

Abstract

A generalized Ginzburg-Landau approach is used to study the nonmonotonic temperature dependence of the upper critical field H_c2(T) in antiferromagnetic superconductors RE(M_o)₆S₈; RE = Dy, Tb, Gd. It is found that electrodynamic effects incorporated through screening and indirect coupling between the staggered magnetization M_Q (T) and superconducting order parameter ψ cannot explain the observed nonmonotonicity. This suggests that the direct coupling between the two order parameters should be considered to understand the experimental results, a finding which is consistent with recent microscopic calculations.