Electro-absorption spectra of magnetic states of diamond shaped graphene quantum dots

Abstract

In this work, employing restricted Hartree-Fock (RHF) as well as unrestricted Hartree-Fock (UHF) mean-field theory and incorporating long-range coulomb interactions within the Pariser-Parr-Pople (PPP) model based Hamiltonian, the effect of size and electric field on the optical properties of various magnetic states of diamond shaped graphene quantum dots (DQDs) has been elucidated. Our calculations have demonstrated that the energetic ordering of excited states and consequently the sequence of electric-field induced phase transition exhibited by the different magnetic phases changes with varying size of DQDs. The optical band-gap for the AF state decreases very gradually as compared to that of the FM and NM configurations, with increase in size of DQD. It is observed that the optical spectrum of the antiferromagnetic (AF) state exhibits a spin-sensitive splitting, while no such splitting is observed for the ferromagnetic (FM) configuration, under the application of electric field. In addition, our computations have established that the magnitude of optical band-gap splitting and the shifting trends (red-shift or blue-shift) of the optical spectrum of spin-up orbitals with respect to that of spin-down orbitals of the AF phase, with the application of electric field, can be tuned by changing the size of DQD.