Characterization of magnetic states of graphene quantum dots of different shapes by application of electric field

Abstract

In this work, we have demonstrated that the optical properties of magnetic states of graphene quantum dots (GQDs) is significantly influenced by their shape and application of external electric field. Our computations at the restricted Hartree-Fock and unrestricted Hartree-Fock level employing the Pariser-Parr-Pople (PPP) model based Hamiltonian have illustrated that the optical band-gap of the nonmagnetic (NM) state changes much more drastically than the antiferromagnetic (AFM) and ferromagnetic (FM) configurations as the shape of the GQD is altered. Further, the geometric configuration of GQDs and external electric field govern the energetic ordering of their magnetic states and consequently, nature of phase transition exhibited by these quantum dots. In addition, the optical spectra of AFM state of diamond shaped graphene quantum dot exhibits a spin-dependent splitting on application of external electric field while no such splitting is observed for the AFM phase of hexagonal shaped graphene quantum dot. This splitting was attributed to the type of spin-density distribution in GQDs. Further, the electro-absorption (EA) spectra exhibits distinct variations for the different magnetic phases of GQDs. Hence, our results have indicated that EA spectra is an efficient method to characterize the different magnetic states of GQDs of varied shapes.