Photoconductivity in Manganites

We report two types of photoconductivity effects observed by illumination of oxygen deficient manganites thin films with UV or visible light. One is the persistent photoconductivity effect observed at low temperature (T < 30 K) when the thin film is in the metallic state. This effect is analog to the persistent photoconductivity observed in the high T_c superconductors particularly in oxygen deficient YBaCuO thin films. The other type of effect is a photo-induced transition to metallic state at temperatures T < 100 K observed in Pr_2/3Sr_1/3MnO₃ thin film which stays always in the semiconducting state in the darkness. This photo induced metallic transition from a semiconducting state leads to a non persistent colossal photoconductivity (several orders of magnitude of decrease of the resistivity).