Massless Dirac cones in graphene: experiments and theory

TL;DR

This paper combines experimental ARPES data and theoretical modeling to demonstrate the existence of a large, unconventional gap in modified graphene, described by a massless Dirac model, challenging traditional massive gap explanations.

Contribution

It provides experimental evidence and theoretical analysis for a massless Dirac gap in graphene, introducing a new perspective on gap formation mechanisms.

Findings

Large unconventional gap observed in modified graphene

Massless Dirac model effectively describes the gap

Conditions for spontaneous symmetry breaking discussed

Abstract

The opening of a gap in single-layer graphene is often ascribed to the breaking of the equivalence between the two carbon sublattices. We show by angle-resolved photoemission spectroscopy that Ir- and Na-modified graphene grown on the Ir(111) surface presents a very large unconventional gap that can be described in terms of a phenomenological "massless" Dirac model. We discuss the consequences and differences of this model in comparison of the standard massive gap model, and we investigate the conditions under which such anomalous gap can arise from a spontaneous symmetry breaking.