Persistent photoconductivity in high Tc grain boundary Josephson junctions

We observed persistent photoconductivity in YBa2Cu3Ox bicrystal grain boundary Josephson junctions. Upon illumination of these grain boundary Josephson junctions, the normal state resistance decreases and the critical current increases. This strongly suggests that the grain boundary in these films consists of oxygen depleted YBa2Cu3Ox. A comparison with the persistent photoconductivity in oxygen depleted YBa2Cu3Ox thin films implies an average oxygen content of x=6.6±0.1 for the grain boundary. The spectral dependence has a lower threshold for persistent photoconductivity in the junctions (≈1.2 eV) than in thin films.