The effects of heavy-ion irradiation on superconductivity in YBa₂Cu₃O₇ epitaxial films

Abstract

The authors report a comparative study of superconducting behavior of YBa₂Cu₃O₇ epitaxial films irradiated with Ag and Au ions of several hundred megaelectronvolt energy. The irradiation results in columnar defects of average diameter ~55 Å and ~110 Å 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. The results also show that in these films, which have intrinsically strong pinning, a marginal enhancement in the critical current density (J_c) occurs when the defect density is < 5×10¹⁰ cm² and the defect diameter is on 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 J_c.