Theory of optical properties of graphene quantum dots

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Journal titlePhysica Status Solidi - Rapid Research Letters
Pages102110; # of pages: 9
SubjectEnergy gap; Excited states; Excitons; Graphene; Ground state; Magnetic moments; Nanocrystals; Semiconductor quantum dots; Characteristic bands; Conduction band edge; Configuration interactions; Linear combinations; Mean field; Optical spectra; Transient absorption spectra; Tunable optical properties; Optical properties
AbstractWe present here a theory of the optical properties of graphene quantum dots (GQDs) with tunable band gaps by lateral size confinement, from UV to THz. Starting from the Hartree-Fock ground state, we construct the correlated many-body ground and excited states of GQDs as a linear combination of a finite number of electron-hole pair excitations. We discuss the evolution of the band gap with size and its renormalization by self-energy and excitonic effects. We calculate and analyze the dipole moments of graphene quantum dots that possess a degenerate valence and conduction band edge, and construct a characteristic exciton and biexciton spectrum. We find an exciton band consisting of a pair of robust, spin singlet bright exciton states and a band of dark, spin singlet and spin triplet, exciton states at lower energies. We predict a characteristic band of biexciton levels at the band edge, discuss the Auger processes and identify a biexciton-exciton cascade. Our theoretical results are compared with experimental linear absorption and non-linear transient absorption spectra of colloidal GQDs. We next discuss the optical properties of triangular GQDs with zigzag edges whose magnetic moment can be controlled by gates. The control over the magnetic moment through carrier density manipulation results in optical spin blockade and gate tunable optical properties over a wide range of photon energies.
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AffiliationNational Research Council Canada; Security and Disruptive Technologies
Peer reviewedYes
NPARC number21277490
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Record identifiere6402735-dee3-48a5-91b2-83a3d3fa1b41
Record created2016-03-09
Record modified2016-05-09
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