CPM Seminar

Electronic, magnetic and optical properties of graphene quantum dots

Pawel Hawrylak

NRC Institute for Microstructural Sciences
National Research Council of Canada

We present a theory of electronic, magnetic and optical properties of gate controlled graphene quantum dots. The dependence of the energy gap on shape, size and edge for graphene quantum dots with up to a million atoms is predicted. Using a combination of density functional, tight-binding, Hartree-Fock and configuration interaction methods, we show that triangular graphene quantum dots with zigzag edges exhibit a shell of degenerate states at the Fermi level. The electronic, magnetic and optical properties are determined by the shell filling, with half-filled shell fully spin polarized. The presence of the shell leads to optical transitions simultaneously in the THz, visible and UV spectral ranges, determined by strong electron-electron and excitonic interactions. The relationship between optical properties and finite magnetic moment and charge density controlled by an external gate is discussed. When two quantum dots are stacked vertically in a bilayer quantum dot the total spins couple ferromagnetically. An application of vertical electric field allows to turn the magnetic moment off or isolate a single electron spin in a charge neutral structure free of nuclear spins. Potential applications of graphene in spintronics, energy and quantum information are discussed.