Direct observation of vortex dynamics in two-dimensional Josephson-junction arrays

Low-temperature scanning microscopy is used to obtain two-dimensional images of vortex dynamics in two-dimensional overdamped Josephson junction arrays at zero applied magnetic field. A vortex model is then employed to characterize the images. Results show that vortex-vortex interaction becomes for evident in the arrays as the bias current increases. Nucleation of current-induced vortices at the array boundaries also occurs at bias currents slightly above the critical current.