Persistent photoconductivity in YBa2Cu3Ox by visible and UV excitation below Tc

We studied the persistent photoconductivity in underdoped metallic YBa2Cu3Ox (x∼6.6) by visible and UV excitation above and below Tc. The results show that the photodoping effect exists also when the sample is in the superconducting state and that its efficiency is approximately the same as at low temperatures above Tc. The dependence of the effect on the temperature where the photodoping is performed is essentially the same for visible light and UV radiation, i.e., a relatively small effect at low temperatures but a significantly larger effect near room temperature. We also observed that the efficiency is somewhat smaller with UV radiation, in contrast to previous results in semiconducting samples