Current-pulse effect in the intermediate state of superconducting lead films

The enhancement of the resistive voltage in the intermediate state of superconducting lead films due to a high current pulse has been studied at 4.2 degrees K as a function of the width of the pulse tau, the magnetic field H, and the film thickness. The film thickness ranged between 1 and 7 mu m. The resistive voltage increment after the current pulse, plotted versus tau, yields S-shaped curves which saturate at high values of tau. The half-time tau* decreases strongly with increasing H. Assuming that the voltage increment is caused by the formation of a laminar flux structure perpendicular to the current during the pulse, the product of tau* and the flux-flow velocity v(phi) during the pulse can be expected to be of the order of the periodicity length of the laminar flux structure. Estimating v(phi) at the pulse current from the flux-flow resistivity at small currents, the product tau* x v(phi) increases with increasing film thickness and is in reasonable agreement with the value expected from Landau's model of the intermediate state. The current-pulse effect disappears below a film thickness between 1 and 2 mu m. This can be understood from the experiments of Cody and Miller, which suggest that below a film thickness of about 1.5 mu m lead films behave like type-II material.