Zero-bias tunneling anomaly at a vortex core

The sharp peak in the tunneling conductance at a vortex core, reported by Hess et al. in NbSe2, is attributed to self-energy corrections of the normal electrons (in the core) caused by their coupling to excitations of the superconducting region (outside the core). The shape of the zero-bias anomaly is reproduced without benefit from adjustable parameters, though the predicted size is a little too large. If the critical currents in the superconducting region (outside the core) are recognized by letting the excitation density (at zero energy) be finite, then a perfect fit can be obtained.