Coexistence of spin-glass and type-II ceramic superconductivity

Abstract

Abstract The new magnetic phase which has been observed recently in La2-x Ba x CuO4 at low temperatures for small concentrations of Ba, is studied in a phenomenological approach in which the superconducting (SC) and spin-glass (SG) phases are assumed to coexit. We construct the free energy in terms of two order parameters under the following assumptions: it must be a scalar; the theory must be gauge invariant; and simplicity (i.e. the standard assumptions in a Lagrangian formalism). We are thus induced from recent experiments to the conclusion that the SG ordering enhances the SC ordering and vice versa.