PHOTODOPING EFFECT IN Y-BA-CU-O JOSEPHSON-JUNCTIONS AND THIN-FILMS

We report our studies on the photo doping effect in YBa2Cu3Ox(YBCO) gr ain-boundary weak links and partially oxygen-depleted (T-c,T-mid appro ximate to 52 K) thin films. We focus our attention on the erasable pro cess, in which persistent photoconductivity (PPC) introduced by light at low temperatures relaxes back above 260 K, In the tested 2-mu m-wid e step-edge grain-boundary junctions, PPC manifested itself as above 3 0% increase of the critical current, while the illuminated films exhib ited up to 2.5 K enhancement of their T-c's, In the case of films, we also observed upon illumination a continuous decrease (no saturation e ffect) of both the longitudinal and transversal (Hall) resistivities, In-situ Hall effect measurements showed that, within aspherical one-ba nd model, PPC at low temperatures results in the band model, PPC at lo w temperatures results in the increase of both the hole mobility and c oncentration, while at temperatures above 250 K, the mobility is reduc ed after prolonged illumination, whereas the carrier concentration is enhanced even more than at low temperatures, We have also demonstrated that the T-c enhancement due to photodoping is a function of the carr ier concentration rather than the mobility. Our experimental results i ndicate that the physical origin of PPC is the same in both YBCO grain boundary junctions and partially oxygen-depleted films, and can be un derstood as the coexistence of photoassisted oxygen ordering and photo induced charge transfer.