In-plane and out-of-plane conductivity enhancement in oxygen-depleted YBa₂Cu₃O_x thin films during long-term photoexcitation

Long-term photoexcitation experiments were performed on oxygen depleted YBa/sub 2/Cu/sub 3/O/sub x/ (x approximately=6.6) thin films, prepared by pulsed laser ablation on tilted SrTiO/sub 3/ substrates. From the anisotropic resistivity of these films, the in-plane ( sigma /sub ab/) and out-of-plane ( sigma /sub c/) conductivities were calculated. White-light photoexcitation at various temperatures from 70 to 305 K yielded strongly temperature dependent increases of both sigma /sub ab/ and sigma /sub c/. The photoinduced changes of the anisotropy sigma /sub ab// sigma /sub c/ strongly depended on the temperature at which the experiment was performed. At 70 K, the anisotropy increased monotonically during 24 h of illumination, whereas, at higher temperatures, a short increase at the very beginning of the illumination was followed by a long-term decrease. Additionally, spectroscopic investigations at the above temperatures were performed to determine the influence of different excitation energies.