Direct observation of vortex lattice transitions in mesoscopic superconducting single crystals using STM

Superconductors containing mesoscopic artificially-engineered defects are orders of magnitude more resistant to the destructive effect of the magnetic field. We present scanning tunnelling microscopy study of the vortex lattice configurations in a mesoscopic single crystal superconductor—normal metal heterostructure. We observe co-existence of a strongly interacting multiquanta vortex lattice and interstitial Abrikosov vortices that form a composite magnetic flux distribution which undergoes a series of transitions between different topological configuration states. The vortex configuration states are strongly dependent on the nanoscale architecture of the superconductor and applied magnetic field. Scanning tunnelling spectroscopy images show the evolution of vortex topological states when the number of flux quanta in the system changes.