Clarifying the apparent flattening of the graphene band near the van Hove singularity

Graphene band renormalization at the proximity of van Hove singularity (VHS) has been investigated by angle-resolved photoemission spectroscopy (ARPES) on Li-doped quasi-freestanding graphene cobalt (0001) surface. The absence hybridization with substrate, doping contribution well represented a rigid energy shift and excellent electron-electron interaction screening ensured metallic substrate offer privileged point view for such investigation. A clear ARPES signal is detected along M Brillouin zone, giving rise to an apparent flattened band. By simulating spectral function from density functional theory calculated bands, we demonstrate that originates "shadow" unoccupied above Fermi level. Such interpretation put forward any additional strong correlation effects VHS proximity, reconciling mean field description structure even in highly doped scenario.