Voltage steps in the current-induced resistive state of thin-film type-I superconductors

We report the observation of voltage steps in the current-induced resistive state in superconducting strips of lead and indium. The strips were 1.7-6 mm long, 0.1-8.0 μm thick, and 100-300 μm wide. The voltage steps are attributed to the nucleation of trains of flux tubes moving rapidly from the edge to the center of the strip. In the center, opposite tubes arriving from opposite edges annihilate each other. The moving flux-tube trains are, obviously, the outgrowth to the case of a three-dimensional type-I superconductor of the dynamic behavior of the weak-link Josephson junction, and, in particular, of the Anderson-Dayem bridge. From a simple eddy-current-damping model we have estimated the number of flux tubes existing simultaneously in a single flux-tube train.