An example of a voltage signal obtained from our simulation. Voltages are calculated by determining the velocities of vortices moving in a small region of the sample. In this case, the vortex motion is periodic.
Through large-scale computer simulations, we investigate the voltage noise that is observed experimentally in many superconductors when a current is applied to the superconductor in the presence of a magnetic field. Experiment and theory indicate that the small fluctuations in voltage are caused when discrete bundles of magnetic flux known as vortices move due to the Lorentz force generated by the current. However, the voltage noise is not identical for all samples and exhibits interesting properties which have not been fully explained, such as periodicity and changes in variance. We have developed a parallel molecular dynamics simulation in order to observe the interaction of magnetic vortices with sample impurities on time and length scales that are experimentally difficult to access. Using the detailed knowledge of vortex position and movement offered by our simulation, we examine vortex motion patterns and topological order in samples with different microscopic characteristics and identify relationships between voltage noise characteristics and vortex-pinning interactions. A detailed picture of the individual and collective behavior of vortices under well-controlled conditions is produced for a given signature of voltage noise. The observed vortex motion ranges from vortex plastic flow in systems with few strong pins, to elastic flow in weakly pinned systems.
C.J. Olson, C. Reichhardt, and F. Nori,
Phys. Rev. Lett. 80, 2197 (1998).
C.J. Olson, C. Reichhardt, and F. Nori,
Phys. Rev. Lett. 81, 3757 (1998).
Back to Home
Last Modified: 1/1/02