Photoinduced Changes of the Electrical Anisotropy in Oxygen-Depleted YBa2Cu3O x

Long-term photoexcitation experiments were performed on Y Ba ₂ Cu ₃ O _x (x6.6) thin films, prepared by pulsed-laser deposition on tilted SrTiO₃ substrates. From the anisotropic resistance of the samples, the in-plane and the out-of-plane resistivities were calculated. Photoexcitation was carried out with a He-Ne laser at various temperatures from 70 K to 305 K. We observed that the electrical anisotropy _c/_ab increased at low temperatures, but decreased at high temperatures. This unusual behavior resembles that of the in-plane Hall mobility in a previous study. Possible interpretations according to the models for the photodoping effect in YBa ₂ Cu ₃ O _x are discussed.