Many-body effects on the optical conductivity of the correlated band insulators

Abstract

The two-band Hubbard model with the density of states obtained from the band calculation for FeSi is investigated. The temperature dependence of the density of states and the optical conductivity are calculated with self-consistent second-order perturbation theory. It is found that the calculated optical conductivity reproduces the experimental result that the gap in the optical conductivity is filled up at a lower temperature than the gap size. It is also found that the peak at the gap edge shifts to the lower-frequency region due to the correlation effect, as is seen in the experiments.