K-Dependent Spectrum and Optical Conductivity near Metal–Insulator Transition in Multi-Orbital Hubbard Bands

Abstract

We apply the dynamical mean field theory (DMFT) combined with the iterative perturbation theory (IPT) to the doubly degenerate e g and the triply degenerate t 2g bands on a simple cubic lattice and a body-centered cubic lattice and calculate the spectrum and optical conductivity in arbitrary electron occupation. The spectrum simultaneously shows the effects of multiplet structure together with the electron ionization and affinity levels of different electron occupations, coherent peaks at the Fermi energy in the metallic phase and an energy gap at an integer filling of electrons for sufficiently large Coulomb U . We also discuss the critical value of the Coulomb U for degenerate orbitals on a simple cubic lattice and a body-centered cubic lattice.