Theory of ferromagnetic metal to paramagnetic insulator transition in R(1-x)A(x)MnO(3)

The double-exchange model for thr Mn oxides with orbital degeneracy is stud ied with including on-site Coulomb repulsion, Jahn-Teller (J-T) coupling, a nd doping-induced disorder. In the strong interaction limit, it is mapped o nto 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 less than or equal to x < 0.5 can be explained by further including the disorder effect of cation size mismatch. An insta bility against phase separation is also found in the paramagnetic phase in systems with large cation size mismatch.