Extended regime of metastable metallic and insulating phases in a two-orbital electronic system

We investigate the metal-to-insulator phase transition driven by the density-density electronic interaction in the quarter-filled model on a cubic lattice with two orbitals split by a crystal field. We show that a systematic consideration of the nonlocal collective electronic fluctuations strongly affects the picture of the phase transition provided by the dynamical mean-field theory. Our calculations reveal the appearance of metallic and Mott insulating states characterized by the same density but different values of the chemical potential, which is missing in the local approximation to electronic correlations. We find that the region of concomitant metastability of these two solutions is remarkably broad in terms of the interaction strength. It starts at a critical value of the interaction slightly larger than the bandwidth and extends to more than twice the bandwidth, where the two solutions merge into a Mott insulating phase. Our results illustrate that nonlocal correlations can have crucial consequences on the electronic properties in the strongly correlated regime of the simplest multiorbital systems.