Self-field effects on flux flow in two-dimensional arrays of Nb Josephson junctions

Measurements and numerical studies of the self-induced magnetic field effects on flux flow in twodimensional arrays of niobium Josephson junctions have been performed. It was found that the flux-flow resistance becomes larger as the penetration depth of the array decreases. A phenomenological model, which agrees qualitatively with the experiments and simulations, is presented to explain the self-field effects on flux flow. Due to the smaller spatial extent of supercurrents around a vortex when self-fields are important, both the mass of the vortex and the array viscosity decrease. The decreased mass and viscosity lead to an increase in flux-flow resistance. The effects of spin-wave damping are also discussed for underdamped arrays. Measurements and simulations on the spatial dependence of flux flow indicate that more complex dynamics is involved in the flux-flow regime than a simple linear flow of the vortices. @S0163-1829~96!02933-5#