The role of impurities on the optical properties of rectangular graphene flakes

TL;DR

This study explores how impurities, especially at zigzag edges, significantly alter the optical properties of rectangular graphene flakes, revealing edge-specific impurity effects on electronic excitations.

Contribution

It introduces a detailed analysis of impurity effects on graphene flakes' optical properties using configuration interaction calculations beyond mean field approximations.

Findings

Impurities at zigzag edges dramatically affect optical responses.

Edge-specific impurity effects depend on impurity location and potential strength.

Charge localization occurs on zigzag edges during optical transitions.

Abstract

We study rectangular graphene flakes using mean field states as the basis for a configuration interaction calculation, which allows us to analyze the low lying electronic excited states including electron correlations beyond the mean field level. We find that the lowest energy transition is polarized along the long axis of the flake, but the charge distributions involved in these transitions are invariably localized on the zigzag edges. We also investigate the impact of both short and long range impurity potentials on the optical properties of these systems. We predict that even a weak impurity localized at a zigzag edge of the flake can have a significant -- and often dramatic -- effect on its optical properties. This is in contrast to impurities localized at armchair edges or central regions of the flake, for which we predict almost no change to the optical properties of the flake even with strong impurity potentials.