Optical responses of photoexcited states in the one-dimensional ionic Hubbard model

Abstract

Photoinduced optical responses are studied in the one-dimensional ionic Hubbard model with the nearest-neighbor repulsion V. For V = 0, carriers introduced by photoirradiation move freely both in the Mott insulator phase and in the band insulator phase, giving rise to a Drude peak in the optical conductivity spectrum. The carriers in the Mott insulator phase remain conducting for 0 < V < 2t because their kinetic energy overcomes the binding energy. By contrast, the electrons and the holes in the band insulator phase are bound to form excitons for V > 0, which do not contribute to the charge transport unless the excitation energy allows them to be separated. The dependence of the Drude weight in the lowest-energy photoexcited state on V and the system size is investigated for both phases. Implications to experimental studies of halogen-bridged metal-complex chains are discussed.