Photo-induced changes in charge-ordered state of Ti4O 7

Abstract

We have investigated photo-induced effects on the charge-ordered state of Ti4O7 with pump-probe spectroscopy. Reflectivity of the probe light changes after the pulsed pump excitation, and then recovers. The photo-induced effects are observed only when the pump power exceeds a threshold value, indicative of cooperative nature of the formation process, and the recovery rate shows thermally activated behaviour. We propose that the photo-induced state is a metastable charge localized state where charge disorder is induced by a photon-assisted charge transfer process from Ti 26+ dimers to the neighbouring Ti4+ions. Moreover, it is found that subsequent cw laser irradiation converts the photo-induced state into the charge-ordered state. We interpret this result in terms of formation of Ti26+ dimers via an inverse charge transfer process assisted by the cw optical excitation. © 2009 IOP Publishing Ltd.