9510464 Lobb Vortices in type-II superconductors move in response to external forces, causing a measurable electric field in the superconductor. In spite of significant research on conventional superconductors the advent of high- temperature superconductors has shown that vortex motion is not very well understood. The initial evidence for this was provided by measurements of the Hall effect in the vortex state, which showed motion opposite to the direction predicted by conventional theory. Subsequent measurements have shown anomalies in the Nernst effect, as well as surprising non-linear effects. The proposed work will extend our earlier work in this field, studying Hall and longitudinal conductivity, the dynamics of strongly-driven vortices, vortex motion in ultra-thin superconducting films, vortex motion induced by temperature gradients, a modified Giaever flux transformer experiment, and the effect of order-parameter symmetry on vortexdynamics. . %%% When a magnetic field is applied to type-II superconductors such as high-temperature superconductors, it penetrates the material in the form of vortices containing a quantum of magnetic flux. Motion of these vortices creates an electric filed in the superconductor, which leads, for example, to non-zero resistivity when current is present. Since most applications of superconductors rely on zero resistivity, understanding of vortex motion is important. The research proposed here is aimed toward understanding vortex motion resulting from a number of different driving forces. The resistance and Hall resistance of superconductors will be measured, with emphasis on nonlinear effects as the current is varied, to understand the effect of pinning, vortex-vortex interactions, quantum states in vortex core, and possible effects of order-parameter symmetry. The motion of vo rtices in response to temperature gradients will also be measured, which provides an alternative area for testing theories of vortex motion, as well as providing a unique probe for studying the internal structure of vortices. . ***
