High- Tc superconductivity induced by ferromagnetic clustering

Abstract

We propose a theoretical model which allows to explain high- T c superconductivity in perovskites. It starts from a Hubbard-type Hamiltonian and from a description of the antiferromagnetic state. We show that when doping with holes immobile ferromagnetic clusters are formed which at higher hole concentrations percolate to metallic lines. The superconductivity occurring along these one-dimensional lines is caused by deformation coupling to Jahn-Teller active optical vibrations. Only a small isotope effect is predicted. The model also explains the spin-glass behaviour for intermediate concentrations and the destruction of superconductivity at high concentrations.