UV-LIGHT IRRADIATION EFFECTS ON OXIDE SUPERCONDUCTING THIN-FILMS

Bi2Sr2CaCu2O(x) thin films prepared on (100) MgO substrates by rf magnetron sputtering were irradiated with ultra-violet (UV) light in He gas of about 500 Pa using a low pressure mercury lamp. The zero-resistance temperature and the critical current density were gradually decreased with irradiation time. X-ray photoemission spectra showed that the mean Cu valence of the film was decreased approximately from +2 to +1 by the irradiation while the valence of Bi ions was not changed. These imply that the UV light irradiation selectively reduces Cu ions and the superconductivity strongly depends on the Cu valence.