Optical conductivity in commensurate spin-density-waves at quarter-filling

We examine the effects of the commensurability and charge ordering on the optical conductivity of spin-density-wave states using the extended Hubbard model with one-dimensional quarter-filled band. The conductivity obtained by both single particle and collective excitations is calculated within the random phase approximation. The mass enhancement due to inter-site repulsive interactions is estimated from the contribution of the collective mode.