Effects of long-range disorder and electronic interactions on the optical properties of graphene quantum dots

TL;DR

This paper explores how long-range disorder and electron interactions influence the optical behavior of large graphene quantum dots, revealing the importance of many-body effects and size in optical responses.

Contribution

It introduces a combined theoretical approach to model disorder and interactions in large graphene quantum dots, highlighting their impact on optical properties.

Findings

Tight-binding models are insufficient for low-energy spectra in disordered dots.

Universal optical conductivity emerges as dot size increases.

Disorder causes absorption spectra to align with experimental graphene data.

Abstract

We theoretically investigate the effects of long-range disorder and electron-electron interactions on the optical properties of hexagonal armchair graphene quantum dots consisting of up to 10806 atoms. The numerical calculations are performed using a combination of tight-binding, mean-field Hubbard and configuration interaction methods. Imperfections in the graphene quantum dots are modelled as a long-range random potential landscape, giving rise to electron-hole puddles. We show that, when the electron-hole puddles are present, tight-binding method gives a poor description of the low-energy absorption spectra compared to meanfield and configuration interaction calculation results. As the size of the graphene quantum dot is increased, the universal optical conductivity limit can be observed in the absorption spectrum. When disorder is present, calculated absorption spectrum approaches the experimental results for isolated monolayer of graphene sheet.