Incoherent charge dynamics in perovskite manganese oxides

A minimal model is proposed for the perovskite manganese oxides showing strongly incoherent charge dynamics with a suppressed Drude weight in the ferromagnetic and metallic phase near the insulator. We investigate a generalized double-exchange model which includes three elements; the orbital degeneracy of e_g conduction bands, the Coulomb interaction and fluctuating Jahn-Teller distortions. We demonstrate that Lanczös diagonalization calculations combined with Monte Carlo sampling of the largely fluctuating lattice distortions result in the optical conductivity which quantitatively accounts for the experimental indications. It is found that all three elements are indispensable for understanding the charge dynamics in these compounds.