Mott transition in multi-orbital systems

Metal insulator transitions driven by local Coulomb interactions are among the most fascinating phenomena in condensed matter physics. They occur in a large variety of transition metal compounds. Most of these strongly correlated materials consist of valence bands derived from electronic d shells where intra- and inter-orbital Coulomb interactions are equally important and where the crystal structure splits the valence bands into narrow and wide subbands. A fundamental question is whether these systems exhibit a common Mott transition, implying all subbands to be either metallic or insulating, or successive orbital dependent transitions, implying a coexistence region with metallic and insulating behavior present in different subbands. Using the dynamical mean field theory we show that inter-orbital Coulomb interactions lead to a single Mott transition. Nevertheless, the subbands exhibit more or less strongly correlated excitation spectra in the metallic phase and different band gaps in the insulating phase.