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 YBa 2Cu3Ox (x approximate to 6.6) thin films, prepared by pulsed laser ablation on tilted SrTiO3 substrates. From the anisotropic resistivity of these fil ms, the in-plane (sigma(ab)) and out-of-plane (sigma(c)) conductivities wer e 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 performe d. At 70 K, the anisotropy increased monotonically during 24 h of illuminat ion, whereas, at higher temperatures, a short increase at the very beginnin g of the illumination was followed by a long-term decrease. Additionally, s pectroscopic investigations at the above temperatures were performed to det ermine the influence of different excitation energies. (C) 1999 Elsevier Sc ience B.V. All rights reserved.