Magneto-optic imaging of proton-irradiated high T-c superconducting thin films: A revisit of J(c)(T) functional and flux pinning enhancement

We have performed systematic quantitative measurements of the critical curr ent density J(c)(B,T) for YBCO thin films proton-irradiated to various dosa ges using the MOI technique. Results for external magnetic fields up to 400 Oe and temperature ranging from 5 to 80 K are T resented for a 600 nm thick YBCO film irradiated by proton up to a dosage of 10(16) cm(-2) at 500 keV. While no significant differences were observed for T > 50K, the J(c) value s consistently increased with the increasing external field for T < 50 K.