We analyze the fractal dimension, density, tortuosity, and size distribution of microscopic vortex channels in a variety of samples, as well as the voltage noise spectrum. Weaker pinning produces relatively straight channels while stronger pinning results in the formation of one or more winding channels that carry all flow, with each case producing a different voltage noise signature. A remarkable drop in tortuosity and noise power appears as a function of increasing disorder strength when a transition in the channel behavior occurs and the vortex-vortex interactions become less important. These figures show the paths followed through the sample by the vortices during a certain time interval.
Vortices enter on the left side of each figure and move towards the right.
White areas of the sample contain vortices that were never depinned. Pale blue areas of the sample indicate regions through which only a few vortices moved. Dark blue areas of the sample were heavily traveled by the vortices. Tortuosity and noise are low in these samples. View Java movie of moderately low pinning strength At moderately low pinning strengths, the channels become more well defined, but still braid significantly.