THE EFFECTS OF HEAVY-ION IRRADIATION ON SUPERCONDUCTIVITY IN YBa2Cu3O7 EPITAXIAL FILMS

We report a comparative study of the superconducting behavior in YBa2Cu3O7 epitaxial films irradiated with Ag and Au ions of several hundred MeV energy. The irradiation results in columnar defects of average diameter similar to 55 and similar to 110 angstrom for Ag+21 and Au+24 ions respectively. A universal linear scaling is observed between the fractional areal damage vs the superconducting transition temperature and normal state resistivity. Our results also show that in these films with intrinsically strong pinning, a marginal enhancement in the critical current density (J(C)) occurs when the defect density is <= 5 x 10(10)/cm(2) and the defect diameter is of the order of coherence length. This criterion is satisfied by the silver ions. The damage due to Au+24 ions is much too severe to improve the J(C).