QUANTUM FLUCTUATIONS IN CURRENT-CARRYING THIN-FILMS OF YBA2CU3O7-DELTA

Light ion irradiation is used to gain insight into nonlinear transport in the absence of an applied magnetic field. Detailed measurements of the electric-field-current-density characteristics of YBa2Cu3O7-delta microbridges are found to agree well with a model based on the quantu m nucleation of vortices. Light ion irradiation drastically shifts the characteristics to lower currents. Within the model, the current scal e associated with the onset of dissipation can be related to the super conducting carrier density. We compare the reduction in the supercondu cting carrier density deduced from the model with direct measurements employing infrared reflectance spectroscopy and find excellent agreeme nt.