Excitonic Effects on the Optical Response of Graphene and Bilayer Graphene

TL;DR

This paper uses first-principles calculations to study how many-electron effects, especially excitons, influence the optical properties of graphene, bilayer graphene, and graphite, revealing prominent excitonic peaks and consistent infrared absorbance with experiments.

Contribution

It provides the first detailed ab initio analysis of excitonic effects on the optical response of these materials, highlighting the formation of resonant excitons and their spectral signatures.

Findings

Resonant excitons cause a prominent absorption peak near 4.5 eV.

Infrared absorbance per graphene layer is approximately 2.4%, matching experiments.

Additional low-frequency features are observed in bilayer graphene due to band structure effects.

Abstract

We present first-principles calculations of many-electron effects on the optical response of graphene, bilayer graphene, and graphite employing the GW-Bethe Salpeter equation approach. We find that resonant excitons are formed in these two-dimensional semimetals. The resonant excitons give rise to a prominent peak in the absorption spectrum near 4.5 eV with a different line shape and significantly redshifted peak position from those of an absorption peak arising from interband transitions in an independent quasiparticle picture. In the infrared regime, our calculated optical absorbance per graphene layer is approximately a constant, 2.4%, in agreement with recent experiments; additional low frequency features are found for bilayer graphene because of band structure effects.