Photodoping and relaxation of persistent photoconductivity in YBa₂Cu₃O_x studied by in-situ transport measurements

We report on in-situ resistivity and Hall-effect studies of partially oxygen-depleted YBa2Cu3Ox thin films during white light illumination. The measurements were performed at various temperatures between the superconducting transition and room temperature. At all temperatures the resistivity and the Hall coefficient decreased as a function of the illumination time. The Hall number pH and the Hall mobility mu(H), calculated within a simple one-band model, showed an increase of p(H) during the illumination without a saturation. At low temperatures, mu(H) behaved similarly to p(H) At 200 K, however, mu(H) became constant after several hours of illumination, while at 260 K and 290 K, we observed a short increase of mu(H) followed by a long-term decrease. From the different time dependences of mu(H) and p(H), we conclude that two mechanisms contribute to the photodoping effect. Additionally, we observed that after termination of the illumination at 290 K the photodoped values of p(H) and mu(H) relaxed with substantially different time constants.