Enhancement of superconducting transition temperature in YBa2Cu3O7 thin films after proton irradiation

The influence of 3,9 MeV-proton irradiation on superconducting transition temperature of YBa2Cu3O7-δ thin films was investigated. The irradiation was carried out at temperatures controlled 25 and 120 deg C in oxygen atmosphere. At high fluences (Φt>2,8.1017 p/cm) the Tc degradation rate exceeds (ΔTc/ΔΦt)vac considerably. At medium fluences (1,5.1017 < Φt < 2,6.1017 p/cm2) the variation of superconducting properties acquires a very unstable character. Substantial increasing of superconducting transition temperature resulting either from the rise of the χ''(T) peak position or from appearance of a diamagnetic signal are observed. The observed enhancement of Tc can be attributed to the penetration of additional amount of oxygen from outer gaseous medium into the YBCO film and to subsequent redistribution of the oxygen atoms among vacant positions in the crystal. The last process can be reinforced by the radiation enhanced diffusion