Vortex dynamics in two-dimensional underdamped, classical Josephson-junction arrays

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Abstract
We present a systematic experimental study on vortex dynamics in two-dimensional Josephson-junction arrays built of underdamped single junctions in which charging effects can be neglected. Arrays in both square and triangular geometries are measured in small magnetic fields at low temperatures. We find that the whole picture of the spatial dynamics of vortices in two-dimensional arrays is analogous to the dynamics of the phase in a single junction. We study in detail the depinning current, the flux-flow resistance, and the maximum velocity of propagating vortices. Our data show that vortices in underdamped arrays, when driven with a current, experience more damping than can be explained by Ohmic-dissipation alone. A simple semiquantitative model, in which the energy lost to junctions in the wake of the moving vortices is taken into account, explains our data very well. The model shows that vortices will always experience damping no matter how underdamped the single junctions are.