Quasiparticle Spectra around a Single Vortex in a {ital d} -Wave Superconductor

Using the Bogoliubov{emdash}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 {ital pure} d wave. It, however, exhibits a fourfold symmetry when the mixing of an s -wave component occurs. A peak with a {ital 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 YBa{sub 2}Cu {sub 3}O{sub 7-{delta}} monocrystal. {copyright} {ital 1997} {ital The American Physical Society}