Overdoping graphene beyond the van Hove singularity

TL;DR

This study successfully doped graphene beyond the van Hove singularity, revealing a Lifshitz transition and opening pathways to explore exotic many-body phases in two-dimensional materials.

Contribution

It demonstrates a method to achieve extreme doping levels in graphene, surpassing the van Hove singularity and observing the associated electronic structure changes.

Findings

Lifshitz transition from electron to hole Fermi surface topology

Doping level reached 5.5×10^{14} cm^{-2}

Electronic structure renormalizations confirmed by spectroscopy

Abstract

At very high doping levels the van Hove singularity in the $\pi^*$ band of graphene becomes occupied and exotic ground states possibly emerge, driven by many-body interactions. Employing a combination of ytterbium intercalation and potassium adsorption, we $n$ dope epitaxial graphene on silicon carbide past the $\pi^*$ van Hove singularity, up to a charge carrier density of 5.5$\times$10$^{14}$ cm$^{-2}$. This regime marks the unambiguous completion of a Lifshitz transition in which the Fermi surface topology has evolved from two electron pockets into a giant hole pocket. Angle-resolved photoelectron spectroscopy confirms these changes to be driven by electronic structure renormalizations rather than a rigid band shift. Our results open up the previously unreachable beyond-van-Hove regime in the phase diagram of epitaxial graphene, thereby accessing an unexplored landscape of potential exotic phases in this prototype two-dimensional material.