Optical spectra and exciton Mott transition in correlated electron–hole systems

Optical properties in the insulating states of three-dimensional electron–hole systems are studied using a two-band Hubbard model with both repulsion U and attraction image. For two types of insulators, the Mott–Hubbard type and the biexciton type at half-filling, in particular, interband absorption spectra are calculated analytically within the two-site dynamical mean-field theory and ladder approximation. We show that an excitonic peak structure appears due to an “exciton” in the sea of correlated fermions when image is larger than a certain critical value.