In-plane and out-of-plane conductivity enhancement in oxygen-depleted YBa2Cu3Ox thin films during long-term photoexcitation

Long-term photoexcitation experiments were performed on oxygen depleted YBa2Cu3Ox (x approximate to 6.6) thin films, prepared by pulsed laser ablation on tilted SrTiO3 substrates. From the anisotropic resistivity of these films, the in-plane (sigma(ab)) and out-of-plane (sigma(c)) conductivities were calculated. White-light photoexcitation at. various temperatures from 70 to 305 K yielded strongly temperature dependent increases of both sigma(ab) and sigma(c). The photoinduced changes of the anisotropy sigma(ab)/sigma(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. (C) 1999 Elsevier Science B.V. All rights reserved.