Observation of Dynamic Interaction of Vortices with Pinning Centers by Lorentz Microscopy

When a magnetic field penetrates a superconductor, it forms lattices of thin filaments called magnetic vortices. If a current is applied, these vortices move if not pinned down, destroying the superconductivity. The spatiotemporal behavior of the vortices was observed in a niobium film with a square lattice of defects made by ion irradiation. The vortices formed a domain of lattices. When the intensity of the applied magnetic field was decreased, the vortices were driven out of the film across its edges; when the intensity was increased, the vortices were driven into the film. The lattice exhibited brief and intermittent flow in “rivers” along domain boundaries. The rivers did not always flow along the same paths because new lattice domain configurations emerged whenever the flow stopped.