Current-induced flux motion in type-I superconducting films studied at 100-ns time resolution

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Abstract
The motion of magnetic flux tubes in the current-induced resistive state of superconducting Pb films several microns thick has been studied with magnetooptical flux detection in conjunction with a high-speed stroboscope, permitting the time-resolved observation of rapid flux-tube dynamics. A computer model of flux-tube motion has been developed which, when suitably modified, is in reasonable agreement with the experimental results. By measuring the flux-tube velocity directly, it has been determined that the phenomenological expression for the viscous drag coefficient is inadequate and can account for only about 20% of the observed drag force. A recalculation of the viscous drag including quasiparticle diffusion and relaxation effects is offered as an explanation of this disparity.