Abstract

Vortices in superconductors are often regarded as a distinct state of matter, representing an ensemble of interacting particles whose density can be varied simply by changing the externally applied magnetic field. When, in addition, vortices are confined in a small (mesoscopic) superconductor, their number and spatial arrangement correspond to a series of discrete superconducting states characterized by vorticity L. A number of new and exotic states have been reported or predicted for such mesoscopic superconductors: paramagnetic Meissner effect, fractional and negative vortices, giant vortices and distinct multivortex states. We have studied multi-vortex configurations in mesoscopic superconductors directly, by using the Bitter decoration technique and the results will be reviewed in this talk. Two different types of mesoscopic samples have been studied: thin-film based and single-crystal-based. In both cases, confinement was found to have a profound effect on vortex arrangements, e.g., concentric shells of vortices were found for circular geometry, with well defined shell-filling rules and magic numbers for vorticities corresponding to complete vortex shells. The observed behaviour will be compared with that for some other confined systems of interacting particles.