Vortex-core structure observed with a scanning tunneling microscope

The superconducting-vortex-core spectra show a zero-bias peak which splits within a coherence length of the core. Further away from the core these split peaks merge gradually with the gap edge and give a direct local measure of the superfluid velocity. The vortex-core states are imaged both at the Fermi energy and just below the gap to reveal two different sixfold star-shaped structures. The anisotropy and size of these images may be a consequence of the crystalline band structure with its charge-density-wave gap as well as the interaction of the neighboring vortices of the Abrikosov flux lattice.