Absorption and optical selection rules of tunable excitons in biased bilayer graphene

TL;DR

This paper investigates the excitonic optical properties of biased bilayer graphene with tunable band gaps, using a semi-analytical approach to derive optical selection rules and absorption spectra, matching recent experimental results.

Contribution

It introduces a semi-analytical method combining tight binding and Bethe-Salpeter equations to analyze excitonic effects in biased bilayer graphene, providing clear optical selection rules.

Findings

Derived analytical optical selection rules.

Calculated absorption spectra matching experiments.

Validated the model with recent experimental data.

Abstract

Biased bilayer graphene, with its easily tunable band gap, presents itself as the ideal system to explore the excitonic effect in graphene based systems. In this paper we study the excitonic optical response of such a system by combining a tight binding model with the solution of the Bethe-Salpeter equation, the latter being solved in a semi-analytical manner, requiring a single numerical quadrature, thus allowing for a transparent calculation. With our approach we start by analytically obtaining the optical selection rules, followed by the computation of the absorption spectrum for the case of a biased bilayer encapsulated in hexagonal boron nitride, a system which has been the subject of a recent experimental study. An excellent agreement is seen when we compare our theoretical prediction with the experimental data.