Metal-insulator transition in the double perovskites

We construct an effective Hamiltonian for the motion of electrons among the transition-metal ions of ordered double perovskites like Sr2FeMoO6, in which strong intra-atomic Coulomb repulsion U is present in only one of the inequivalent transition metal sites. Using a slave-boson formalism, we construct a phase diagram that describes a charge-transfer transition between insulating and metallic behavior as the parameters of the model are changed. The parameters for Sr2FeMoO6 are estimated from first-principles calculations and a transition to the insulating state with negative pressure is obtained.