  Vortices in topological superconductors are predicted to host Majorana bound
states (MBSs) as exotic quasiparticles. In recent experiments, the spatially
non-split zero-energy vortex bound state in topological superconductors has
been regarded as an essential spectroscopic signature for the observation of
MBSs. Here, we report the observation of anisotropic non-split zero-energy
vortex bound states in a conventional elemental superconductor with a
topologically trivial band structure using scanning tunneling microscopy and
spectroscopy. The experimental results, corroborated by quasi-classical
theoretical calculations, indicate that the non-split states directly reflect
the quasiparticle trajectories governed by the surface electronic structure.
Our study implies that non-split zero-energy states are not a conclusive
signature of MBSs in vortex cores, stimulating a revision of the current
understanding of such states.
