Star-Shaped Local Density of States around Vortices in a Type-II Superconductor

The electronic structure of vortices in a type II superconductor is analyzed within the quasiclassical Eilenberger framework. The possible origin of a sixfold “star” shape of the local density of states, observed by scanning tunneling microscope (STM) experiments on ${\mathrm{NbSe}}_2$, is examined in the light of the three effects: the anisotropic pairing, the vortex lattice, and the anisotropic density of states at the Fermi surface. Outstanding features of split parallel rays of this star are well explained in terms of an anisotropic $s$-wave pairing. This reveals not only a rich internal electronic structure associated with a vortex core, but also unique ability of the STM spectroscopy.