Quantum fluctuations in current-carrying thin films of YBa2Cu3O7-δ

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-δ microbridges are found to agree well with a model based on the quantum nucleation of vortices. Light ion irradiation drastically shifts the characteristics to lower currents. Within the model, the current scale associated with the onset of dissipation can be related to the superconducting carrier density. We compare the reduction in the superconducting carrier density deduced from the model with direct measurements employing infrared reflectance spectroscopy and find excellent agreement.