Superconducting vortex avalanches, voltage bursts, and vortex plastic flow: Effect of the microscopic pinning landscape on the macroscopic properties

Abstract

Using large-scale simulations on parallel processors, we analyze in detail the dynamical behavior of superconducting vortices undergoing avalanches. In particular, we quantify the effect of the pinning landscape on the macroscopic properties of vortex avalanches and vortex plastic flow. These dynamical instabilities are triggered when the external magnetic field is increased slightly, and are thus driven by a flux gradient rather than by thermal effects. The flux profiles, composed of rigid flux lines that interact with 100 or more vortices, are maintained in the Bean critical state and do not decay away from it. By directly determining vortex positions during avalanches in the plastically moving lattice, we find that experimentally observable voltage bursts correspond to the pulsing movement of vortices along branched channels or winding chains in a manner reminiscent of lightning strikes. This kind of motion cannot be described by elastic theories. We relate the velocity field and cumulative patterns of vortex flow channels with statistical quantities, such as distributions of avalanche sizes. Samples with a high density of strong pinning sites produce very broad avalanche distributions. Easy-flow vortex channels appear in samples with a low pinning density, and typical avalanche sizes emerge in an otherwise broad distribution of sizes. We observe a crossover from interstitial motion in narrow channels to pin-to-pin motion in broad channels as pin density is increased. Videos available at http://www-personal.engin.umich.edu/~nori