Electronic and magnetic properties of graphene quantum dots with two charged vacancies

Abstract

Electronic and magnetic properties of a system of two charged vacancies in hexagonal shaped graphene quantum dots are investigated using a mean-field Hubbard model as a function of the Coulomb potential strength β of the charge impurities and the distance R between them. For β=0, the magnetic properties of the vacancies are dictated by Lieb’s rules where the opposite (same) sublattice vacancies are coupled antiferromagnetically (ferromagnetically) and exhibit Fermi oscillations. Here, we demonstrate the emergence of a non-magnetic regime within the subcritical region: as the Coulomb potential strength is increased to β∼0.1, before reaching the frustrated atomic collapse regime, the magnetization is strongly suppressed and the ground state total spin projection is given by Sz=0 both for opposite and same sublattice vacancy configurations. When long-range electron–electron interactions are included within extended mean-field Hubbard model, the critical value for the frustrated collapse increases from βcf∼0.28 to βcf∼0.36 for R<27Å.