Quasiparticle spectrum around a vortex line in ad-wave superconductor

Abstract
We study the quasiparticle spectrum around a single vortex line in a superconductor with dx2-y2 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.