Transient Photoinduced Conductivity in Single-Crystals of YBa2Cu3O7-d: Photodoping to the Metallic State

Abstract

The temperature dependences of the transient photoinduced conductivity in YBa2Cu3O7-δ at different light intensities (IL) and of the doping-induced conductivity at different δ are similar, indicative of photodoping. For δ≊0.7, signatures of the photoinduced transition to metallic behavior are observed at IL>5×1015 photons/cm2; the deep resistivity minimum below 100 K, reminiscent of the onset of superconductivity in granular superconductors and in inhomogeneously doped samples, is interpreted in terms of phase separation and metallic-droplet formation. A longitudinal magnetic field (≤0.5 T) reduces both the resistivity minimum and the superlinear contribution to the transient photoconductance. For δ≊0.6, the lifetime of the photoexcited state is enhanced by nearly 3 orders of magnitude at high excitation levels, indicative of metastability.