A Superconducting “Dripping Faucet”
Stuart Field, Ghe. Stan
Colorado State University
A well-known system exhibiting complex dynamics is that of a dripping faucet. Here, a drop grows until it reaches a threshold size. It then detaches and falls under the influence of gravity. Analysis of the times between successive drops reveals regions of periodic, multiply-periodic, and chaotic behavior as system parameters are varied. Current-driven flux tubes in type-I superconductors share many characteristics of this growth-and-break off mechanism. Individual tubes nucleate and grow at the sample edge, until they reach a threshold size and break off; they are then driven across the sample width by the applied current. The similarities with the dripping faucet are clear, and similarly complex dynamics might be expected. We have thus developed a novel high-bandwidth Hall probe to detect the nucleation and subsequent motion of magnetic flux tubes along a fabricated constriction in a lead sample. The probe system has a bandwidth of 4 MHz, and sufficient field resolution to detect in real time the passage of individual flux tubes beneath the probe. In this way, many thousands of flux drop events can be recorded, with sub-microsecond time resolution. Nonlinear time series analysis applied to our data reveals rich and complicated features of driven flux tube dynamics.