Effects of Orbital Degeneracy and Electron Correlation on Charge Dynamics in Perovskite Manganese Oxides

Taking the orbital degeneracy of e_g conduction bands and the Coulomb interaction into account in a double-exchange model, we investigate the charge dynamics of perovskite Mn oxides by the Lanczös diagonalization method. In the metallic phase near the Mott insulator, it is found that the optical conductivity for a spin-polarized two-dimensional system exhibits a weight transfer to a broad and incoherent structure within the lower-Hubbard band together with a suppressed Drude weight. It reproduces a qualitative feature of the experimental results. As an orbital effect, we find that an anomalous charge correlation at quarter filling suppresses the coherent charge dynamics and signals precursor to the charge ordering.