Scanning-Tunneling-Microscope Observation of the Abrikosov Flux Lattice and the Density of States near and inside a Fluxoid

The Abrikosov flux lattice is imaged in Nb${\mathrm{Se}}_2$ by tunneling into the superconducting gap edge with a low-temperature scanning-tunneling microscope. The tunneling conductance into a single vortex core is strongly peaked at the Fermi energy, suggesting the existence of core states or core excitations. As one moves away from the core, this feature evolves into a density of states which is consistent with a BCS superconducting gap.