X-ray Irradiation Effects on the Superconductive Properties of YBa2Cu3Oy and GdBa2Cu3Oz

We observed a metastable change in the superconducting properties of YBa2Cu3Oy (YBCO) and GdBa2Cu3Oz (GdBCO) induced by X-ray irradiation. T-c0, which is defined as the temperature below which the electric resistance is zero within the measurement accuracy, was increased by up to 1.9 K in YBCO and GdBCO. The irradiation effect was more pronounced for the YBCO sample with lower T-c0. These observations are consistent with those of light irradiation, and are attributable to hole doping in the CuO2 plane via the generation of electron-hole pairs by the X-ray and subsequent trapping of the electrons at oxygen vacancies. The relaxation of the irradiation effect was observed to be within 100 h from the viewpoint of conductivity and Raman spectra, and is explained as the detrapping of the electrons and recombination with holes, similarly to the case of light irradiation.