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

摘要

We theoretically investigate the effects of long-range disorder andelectron-electron interactions on the optical properties of hexagonal armchairgraphene quantum dots consisting of up to 10806 atoms. The numericalcalculations are performed using a combination of tight-binding, mean-fieldHubbard and configuration interaction methods. Imperfections in the graphenequantum dots are modelled as a long-range random potential landscape, givingrise to electron-hole puddles. We show that, when the electron-hole puddles arepresent, tight-binding method gives a poor description of the low-energyabsorption spectra compared to meanfield and configuration interactioncalculation results. As the size of the graphene quantum dot is increased, theuniversal optical conductivity limit can be observed in the absorptionspectrum. When disorder is present, calculated absorption spectrum approachesthe experimental results for isolated monolayer of graphene sheet.