Metal-insulator transition in the half-filling two-orbital Hubbard model on the triangular lattice

We have investigated the half-filled two-orbital Hubbard model on a triangular lattice by means of the dynamical mean-field theory. The local squared moments of charge, spin, and orbital and the optical conductivity clearly show that the metal-insulator transition (MIT) occurs at U-c, U-c = 18.2, 16.8, 6.12, and 5.85 for Hund's coupling J= 0, 0.01U, U/4, and U/3, respectively. The distinct continuities of the double occupation of electrons, the local squared moments, and the local susceptibility of charge, spin, and orbital suggest that for J > 0, the MIT is first-order; however, at J = 0, the MIT is second order. We attribute the first-order nature of the MIT to the symmetry lowering of the systems with finite Hund's coupling.