Quasiparticle spectrum around a vortex line in a d-wave superconductor

We study the quasiparticle spectrum around a single vortex line in a superconductor with ${\mathit{d}}_{\mathit{x}}^2$-${\mathit{y}}^2$ symmetry. For E<Δ(T), the density of states around a vortex exhibits a fourfold symmetry, in sharp constrast to a superconductor with s-wave symmetry. This should be readily seen in scanning tunneling microscopy experiments.