Study on the high spectral intensity at the Dirac energy of single-layer graphene on an SiC substrate

TL;DR

This study investigates the origin of high spectral intensity at the Dirac energy in single-layer graphene on SiC, attributing it to buffer layer-induced in-gap states rather than plasmaron bands, based on ARPES measurements.

Contribution

It provides experimental evidence linking high spectral intensity in single-layer graphene to buffer layer states, clarifying the origin of this phenomenon.

Findings

High spectral intensity observed at Dirac energy in single-layer graphene.

Double-layer graphene does not show this high spectral intensity.

Buffer layer states are responsible for the in-gap states causing the high spectral intensity.

Abstract

We have investigated electron band structure of epitaxially grown graphene on an SiC(0001) substrate using angle-resolved photoemission spectroscopy. In single-layer graphene, abnormal high spectral intensity is observed at the Dirac energy whose origin has been questioned between in-gap states induced by the buffer layer and plasmaron bands induced by electron-plasmon interactions. With the formation of double-layer graphene, the Dirac energy does not show the high spectral intensity any longer different from the single-layer case. The inconsistency between the two systems suggests that the main ingredient of the high spectral intensity at the Dirac energy of single-layer graphene is the electronic states originating from the coupling of the graphene $\pi$ bands to the localized $\pi$ states of the buffer layer, consistent with the theoretical prediction on the presence of in-gap states.