Density of states in the vortex state of type-II superconductors

The local, direction resolved density of states in the vortex state of clean type-II superconductors is calculated for arbitrary energies and inductions. It is obtained by solving numerically the quasi- classical equations of superconductivity, using parameters corresponding to Nb or V. The excitation spectrum is discussed for arbitrary inductions and, for the special case of large vortex distance, compared with previous theories. Tunneling states of quasiparticles are calculated explicitly for the first time and a shift of continuum states to energies higher than ${\psi }_{\mathrm{BCS}}$ is found. Some conclusions specific to the important materials Nb and V are drawn. The energy dependence of the local density of states near the vortex axis is found to be in qualitative agreement with recent scanning-tunneling-microscope measurements.