Photodoping effect in Y-Ba-Cu-O Josephson junctions and thin films
We report our studies on the photo doping effect in YBa/sub 2/Cu/sub 3/O/sub x/ (YBCO) grain-boundary weak links and partially oxygen-depleted (T/sub c,mid/ /spl ap/52 K) thin films, We focus our attention on the erasable process, in which persistent photoconductivity (PPC) introduced by light at low temperatures relaxes back above 260 K. In the tested 2-/spl mu/m-wide step-edge grain-boundary junctions, PPC manifested itself as above 30% increase of the critical current, while the illuminated films exhibited up to 2.5 K enhancement of T/sub c/'s. In the case of films, we also observed upon illumination a continuous decrease (no saturation effect) of both the longitudinal and transversal (Hall) resistivities. In-situ Hall effect band model, PPC at low temperatures results in the increase of both the hole mobility and concentration, while at temperatures above 250 K, the mobility is reduced after prolonged illumination, whereas the carrier concentration is enhanced even more than allow temperatures. We have also demonstrated that the T/sub c/ enhancement due to photodoping is a function of the carrier concentration rather than the mobility, Our experimental results indicate that the physical origin of PPC is same in both YBCO grain-boundary junctions and partially oxygen-depleted films, and can be understood as the coexistence of photoassisted oxygen ordering and photoinduced charge transfer.