Origins of anomalous electronic structures of epitaxial graphene on silicon carbide

TL;DR

This study uses first-principles calculations to reveal a new atomic interface structure in epitaxial graphene on silicon carbide that explains observed electronic anomalies, including a significant energy gap at the Dirac point.

Contribution

It uncovers a novel interfacial atomic structure causing electronic anomalies in epitaxial graphene, resolving experimental controversies and suggesting ways to engineer graphene's electronic properties.

Findings

Identification of a quasi-periodic $6\times 6$ domain pattern.

Theoretical energy spectrum matches experimental photoemission data.

Discovery of a substantial energy gap at the Dirac point.

Abstract

On the basis of first-principles calculations, we report that a novel interfacial atomic structure occurs between graphene and the surface of silicon carbide, destroying the Dirac point of graphene and opening a substantial energy gap there. In the calculated atomic structures, a quasi-periodic $6\times 6$ domain pattern emerges out of a larger commensurate $6\sqrt{3}\times6\sqrt{3}R30^\circ$ periodic interfacial reconstruction, resolving a long standing experimental controversy on the periodicity of the interfacial superstructures. Our theoretical energy spectrum shows a gap and midgap states at the Dirac point of graphene, which are in excellent agreement with the recently-observed anomalous angle-resolved photoemission spectra. Beyond solving unexplained issues of epitaxial graphene, our atomistic study may provide a way to engineer the energy gaps of graphene on substrates.