In-plane and out-of-plane conductivity enhancement in oxygen-depleted YBa 2Cu 3O x thin films during long-term photoexcitation

Abstract

Long-term photoexcitation experiments were performed on oxygen depleted YBa 2Cu 3O x ( x≈6.6) thin films, prepared by pulsed laser ablation on tilted SrTiO 3 substrates. From the anisotropic resistivity of these films, the in-plane ( σ ab ) and out-of-plane ( σ c ) conductivities were calculated. White-light photoexcitation at various temperatures from 70 to 305 K yielded strongly temperature dependent increases of both σ ab and σ c . The photoinduced changes of the anisotropy σ ab / σ 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.