Theory of ferromagnetic metal to paramagnetic insulator transition inR1−xAxMnO3

Abstract

The double-exchange model for the Mn oxides with orbital degeneracy is studied with including on-site Coulomb repulsion, Jahn-Teller (J-T) coupling, and doping-induced disorder. In the strong interaction limit, it is mapped onto a single-band Anderson model, in which all scattering mechanisms can be treated on an equal footing. We show that the spin and J-T disorders lead to a metal-insulator transition (MIT) only at low carrier density. The MIT observed in samples with $0.2<~x<0.5$ can be explained by further including the disorder effect of cation size mismatch. An instability against phase separation is also found in the paramagnetic phase in systems with large cation size mismatch.