Quasiparticle spectra around a single vortex in a d-wave superconductor

Using the Bogoliubov-de Gennes equation, we study the quasiparticle spectra around a single vortex in a d-wave superconductor. In the temperature region where the Ginzburg-Landau theory is valid, we find that the local density of states preserves a circular symmetry when the symmetry of the superconducting order parameter is pure d wave. It, however, exhibits a fourfold symmetry when the mixing of an s-wave component occurs. A peak with a large energy gap is found in the local density of states at the center of the vortex, which corresponds to the lowest bound state. Our results are consistent with a recent scanning tunneling microscopy experiment in a YBa2Cu3O7-delta monocrystal.