Effects of Proton Irradiation on the Microwave Surface Resistance of ${\rm YBa}_{2}{\rm Cu}_{3}{\rm O}_{7-\delta}$ 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 of proton-irradiated (YBCO) films grown on (LAO) substrates. The intrinsic was measured at 8.5 GHz at temperatures of 7-90 K with the effects of the finite film thickness taken into account. Significant reduction in the 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 with the value of 100 of the proton-irradiated one at 60 K appearing significantly lower than the corresponding one of 140 before irradiation. However, at temperatures below 20 K, the of the irradiated YBCO films was higher than that of the YBCO film before irradiation with the residual of the former appearing higher than that of the latter. No significant changes in the of YBCO films were observed when the films were irradiated with 20 MeV proton for 30-120 minutes to the fluences of to . The reduction in the of proton-irradiated YBCO films at 40-70 K was attributed to enhanced impurity scattering rate of compared to a value of for unirradiated YBCO.