The crossing indicates subtle dissipation effects of columnar defects in both the liquid and solid vortex phases. We are examining these effects for evidence of vortex entanglement, a promising new effect with important implications for basic science and technology. Initiated a new set of experiments on vortex dynamics in a periodic pinning environment. We have exploited a novel technique for producing perfect periodic structures using the interference patterns of two coherent laser beams developed by Prof. Steve Brueck of the Center for High Technology Materials, University of New Mexico. This method allows the production of films of conventional and copper oxide superconductors containing a periodic lattice of holes with spacing in the micron range.
Initial results show strong dynamic effects at the matching field.
Developed a phenomenological theory of aging of the vortex system at zero driving current. Aging allows the vortices to find the most energetically favorable pinning configuration, and causes an abrupt onset of motion under increasing driving current. We have developed both shielding methods, which characterize the local pinning strength by examining the field penetration, and transport methods, which directly image the path and magnitude of transport currents within the superconductor. Both techniques have been applied to commercially produced superconducting wires. We have developed a non-destructive technique for observing cracks in commercial superconducting wires which interrupt the supercurrent flow and degrade performance.