Peak effect at microwave frequencies in swift heavy ion irradiated YBa2Cu3O7−δ thin films

The vortex dynamics at microwave frequencies in YBa2Cu3O7−δ (YBCO) films have been studied. We observe a peak in the microwave (4.88 and 9.55 GHz) surface resistance in some films in magnetic fields up to 0.8 T. This is associated with the ‘peak-effect’ phenomenon and reflects the order–disorder transformation of the flux line lattice near the transition temperature. Introduction of artificial pinning centers like columnar defects created as a result of irradiation with 200 MeV Ag ion (at a fluence of 4 × 10^10 ions/cm2) leads to the suppression of the peak in films previously exhibiting ‘peak effect’