Effects of 300 MeV Au+24 ion irradiation on superconductivity in YBa2Cu3O7 epitaxial films

We report the effects of 300 MeV gold ion irradiation on the transition temperature (Tc) and critical current density (Jc) of YBa2Cu3O7 epitaxial films. The radiation at a dose as low as 5.6×1010 ions/cm2 decreases the zero field Tc and Jc. However, the response of the mixed state in 1–8 T field remains relatively unchanged up to a dose of ∼9×1010 ions/cm2. We argue that the stiffness of the flux lines in a film geometry and the pinning sites distributed at a length scale much smaller than that of the ion-induced defects are responsible for this null result.