▎ 摘　　要

In heavily n-doped graphene, when pushing the Fermi level to the vicinity of the Van Hove singularity, exotic electronic ground states are expected to occur driven by many-body interactions. These competing phases, such as chiral superconductivity, charge, or spin density waves, find their stability based on the amount of doping induced in the graphene layer. In this work we present a method for effectively tuning the doping level of graphene near the Van Hove singularity. Epitaxially grown buffer layer graphene on SiC(0001) is decoupled from the SiC substrate and strongly n doped up to its Van Hove singularity via ytterbium intercalation. Upon annealing the Yb/graphene system at increasing temperatures, a topological transition at the Fermi level and a continuous upshift of the Dirac point are observed, indicating a decrease in charge carrier density. The intercalated Yb atoms adopt an ordered pattern while their concentration is reduced with annealing temperature. These variations significantly affect the charge transfer to the graphene layer and allow the systematic control of the doping level in the vicinity of the Van Hove singularity via one single experimental parameter. As such, the Yb intercalation technique can provide a reliable and convenient way of accessing different ordered ground states predicted in highly doped graphene.