CORRELATIONS BETWEEN CRITICAL-CURRENT DENSITY AND PENETRATION DEPTH IN ION-IRRADIATED YBA2CU3O7 THIN-FILMS

Point defects have been introduced into YBa2Cu3O7 through low energy h elium ion irradiation in order to probe the origin of dissipation in a current-carrying superconductor, Resistivity, infrared reflectance an d x-ray diffraction measurements indicate that the films are not chemi cally altered and that the induced point defects act as scattering cen tres. Measured electric field-current density characteristics are foun d to be well described by a model based on quantum current fluctuation s. This description is used to extract the change in the superconducti ng carrier density with ion damage which agrees well with direct measu rements of the same quantity by infrared reflectance. The implications of the relation between dissipation and the superconducting carrier d ensity, or alternatively the magnetic penetration depth, are discussed .