PERSISTENT PHOTOCONDUCTIVITY IN HIGH T-C GRAIN-BOUNDARY JOSEPHSON-JUNCTIONS

We observed persistent photoconductivity in YBa2Cu3Ox bicrystal grain boundary Josephson junctions. Upon illumination of these grain boundar y Josephson junctions, the normal state resistance decreases and the c ritical current increases. This strongly suggests that the grain bound ary in these films consists of oxygen depleted YBa2Cu3Ox. A comparison with the persistent photoconductivity in oxygen depleted YBa2Cu3Ox th in films implies an average oxygen content of x = 6.6 +/- 0.1 for the grain boundary. The spectral dependence has a lower threshold for pers istent photoconductivity in the junctions (approximate to 1.2 eV) than in thin films. (C) 1997 American Institute of Physics.