Nonequilibrium dynamics in charge transfer insulators
Photo-doping of Mott insulators provides a rather simple example of a pulse induced non-equilibrium phase transition, where a pulse with a frequency larger than the Mott gap produces doublon-holon pairs and results in a non-thermal conducting state. However for several transition metal oxides, like high-temperature superconductors and Ni oxides, the ionic interaction plays a crucial dynamical role. We study the photo-doping in the archetypical model for transition metal oxides as proposed by Emery , where the strongly correlated copper d orbital is hybridized with the oxygen p orbitals. We will study this model within the time-dependent non-local extension of the dynamics mean field theory in order to properly describe the charge screening after the photo-excitation. Within the Emery model we will classify the high energy excitations as the upper Hubbard band, identify the low energy structure corresponding to the Zhang-Rice singlet and emphasize the role of screening. We will present the modification of the charge transfer gap after the photo-excitation due to static effects and the change in the screening. At the end we will clarify the difference in the response between the single band Mott insulator and the multi-band charge transfer insulator.
 V. J. Emery, Phys. Rev. Lett. 58, 2794 (1987)