Effects of proton irradiation on the microwave surface resistance of YBa2Cu3O7-δ films

Proton irradiations on superconducting bulk materials and thin films have enabled to enhance the critical current density and the upper critical field in the mixed state due to increased vortex pinning. We investigated the microwave surface resistance (R-s) of proton-irradiated YBa2Cu3O7-delta (YBCO)films grown on LaAlO3 (LAO) substrates. The intrinsic R. was measured at similar to 8.5 GHz at temperatures of 7-90 K with the effects of the finite film thickness taken into account. Significant reduction in the R-s of YBCO films were observed at temperatures of 40 K to 70 K when the films were irradiated with 20 MeV proton for 10 minutes to the fluence of 0.47 X 10(15) ions/cm(2) with the value of 100 mu Omega of the proton-irradiated one at 60 K appearing significantly lower than the corresponding one of 140 mu Omega before irradiation. However, at temperatures below 20 K, the Rs of the irradiated YBCO films was higher than that of the YBCO film before irradiation with the residual Rs of the former appearing higher than that of the latter. No significant changes in the R. of YBCO films were observed when the films were irradiated with 20 MeV proton for 30-120 minutes to the fluences of 1.4 x 10(15) to 5.7 x 10(15) ions/cm The reduction in the R-S of proton-irradiated YBCO films at 40-70 K was attributed to enhanced impurity scattering rate of similar to 2 X 10(12) Is compared to a value of similar to 7.6 x 10(11) Is for unirradiated YBCO.