Density of bound states in a vortex core

The local density of states as derived from Kramer and Pesch's theory of bound states in a vortex core is compared with recent scanning-tunneling experiments. Effects of impurities and finite flux-line distance are approximately taken into account. In the isolated vortex regime one finds qualitative, but not quantitative, agreement with all experimental data reported so far. The results depend sensitively on impurity content. A nonmonotonic behavior of the density of states as a function of the distance from the flux-line center is predicted. The unexpected properties of the density of states are discussed in terms of the direction-dependent single-particle excitations bound to the core