Physica c-superconductivity and its applications vol:341 pages:981-984
(H)igh resolution scanning Hall probe microscopy has been used to study flux structures in various nanostructured superconducting samples. Five micron square YBCO disks exhibit rotationally symmetric flux structures at high temperatures and after field-cooling to low temperatures. We find that their magnetic response can be almost perfectly compensated by tuning the applied magnetic field. High temperature measurements of the 'local magnetisation' above the disks as a function of applied field display pronounced sawtooth structures with very sharp jumps. In contrast asymmetric flux structures are observed after cooling in H=0 and the application of a field at low temperatures. We speculate that we may possibly be observing the formation of Giant Vortex states at high temperatures and multi-vortex states at low temperatures.