Existence of a metallic ferromagnetic phase in models for undoped manganites

Hotta, Takashi

The existence of a novel metal-insulator transition in the ferromagnetic state of models for undoped manganites is here discussed using numerical techniques applied to the -orbital degenerate Hubbard model tightly coupled with Jahn-Teller distortions. The ground-state phase diagram is presented in the plane defined by the electron-phonon coupling and Coulomb interaction . In contrast to the standard one-band Hubbard model for cuprates, the metallic phase is found to exist for finite values of both and in the present -orbital Hubbard model even at half-filling, due to the Fermi-surface topology which is incompatible with the staggered orbital ordering concomitant to the insulating phase. Based on the present results, a possible scenario for Colossal Magneto-Resistive effect is discussed in undoped manganites.