Photoinduced Changes in High Temperature Superconducting Films

Photoexcitation experiments performed in oxygen deficient but metallic YBa,Cu,O, c-axis oriented films revealed that the persistent photoinduced enhancement of conductivity and superconductivity are not restricted to the insulating side of the metal-insulator transition. A clear increase of the critical temperature T,, which is accompanied by a decrease of the resistivity in the normal state pab, is observed for all studied oxygen contents (6.4 < x < 6.6). In this oxygen content range, the persistent photoinduced changes in T, and pab have a strong dependence on the oxygen stoichiometry of the film. Several mechanisms which may explain the persistent photoinduced phenomena are discussed.