Ultraviolet absorption spectrum of the half-filled bilayer graphene

TL;DR

This paper investigates the optical properties of half-filled AB-stacked bilayer graphene considering excitonic pairing, Coulomb interactions, and temperature effects, providing detailed theoretical insights and comparisons with existing data.

Contribution

It introduces a comprehensive four-band model to analyze excitonic effects on optical responses in bilayer graphene, aligning well with prior experimental and theoretical results.

Findings

Excitonic pairing significantly alters the optical spectra.

Interlayer Coulomb interactions modify plasmon excitations.

The model accurately predicts optical properties across various regimes.

Abstract

We consider the optical properties of the half-filled AB-stacked bilayer graphene with the excitonic pairing and condensation between the layers. Both intra and interlayer local Coulomb interaction effects have been taken into account and the role of the exact Fermi energy has been discussed in details. We have calculated the absorption coefficient, refractive index, dielectric response functions and the electron energy loss spectrum for different interlayer Coulomb interaction regimes and for different temperatures. Considering the full four-band model for the interacting AB bilayer graphene, a good agreement is achieved with other theoretical and experimental works on the subject, in particular, limiting cases of the theory. The calculations, presented here, permit to estimate accurately the effects of excitonic pairing and condensation on the optical properties of the bilayer graphene. The modifications of the plasmon excitation spectrum are discussed in details for a very large interval of the interlayer interaction parameter.