The Edge Magnetization and Strip Phase of Graphene Quantum Dots with Long-Range Coulomb Interaction

We investigate the magnetism and optical absorption properties of charge neutral hexagonal graphene quantum dots (GQDs) terminated with zigzag edges by using a tight-binding Hubbard type model for the π electrons. Within the Hartree—Fock approximation and taking into account the long-range Coulomb interaction, our calculation yields a ferromagnetic ground state with magnetic moments localized on the edges for GQDs, and also gives an antiferromagnetism state with the energy very close to the ferromagnetism ground state. We find that both the ferromagnetic and the antiferromagnetic states have stripe patterned charge density distributions as a result of the long-range Coulomb interaction. The optical conductivity for GQDs has an energy gap in the low frequency regime in contrast to the bulk neutral graphene sheet where a universal constant is approached.