Photoinduced transient thermoelectric effect in a perovskite manganitePr0.67Sr0.33MnO3film

Pulsed laser-induced transient thermoelectric effect (TTE) for perovskite manganite ${\mathrm{Pr}}_{0.67}{\mathrm{Sr}}_{0.33}{\mathrm{MnO}}_3$ thin films has been measured under dc electric and magnetic fields. Without any external fields, a photoinduced TTE voltage is small (∼0.5 mV). When an electric field is applied, its magnitude enhances appreciably and decays exponentially with two relaxation times, but its sign is changed by varying temperature. The TTE voltage and its sign are also varied by applying magnetic field, from which the Curie temperature is determined. Based on the available band model of this material, we have discussed a possible mechanism for the observed TTE signals. The TTE phenomenon is primarily due to the formation of a bipolar state of photogenerated electrons and holes, which reflect strongly on the characteristic band structure in the paramagnetic and ferromagnetic phases. Its decay process is a recombination of the electron-hole pairs through some recombination centers, in which the Jahn-Teller or polaron effect is found to be appreciable near the Curie temperature.