Can the "shadow" of graphene band clarify its flatness?

TL;DR

This study uses ARPES to investigate graphene's band structure near the van Hove singularity, revealing that the observed flatness is due to a spectral 'shadow' effect rather than strong correlations.

Contribution

It demonstrates that the apparent band flattening near the VHS in doped graphene is caused by a spectral shadow, not additional correlation effects, reconciling experimental observations with mean field theory.

Findings

ARPES detects a flattened band near the M point.

Simulation shows the signal originates from a spectral shadow.

No evidence of strong correlation effects at VHS proximity.

Abstract

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