Microscopic theory of the optical properties of colloidal graphene quantum dots

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DOIResolve DOI: http://doi.org/10.1103/PhysRevB.89.085310
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TypeArticle
Journal titlePhysical Review B - Condensed Matter and Materials Physics
ISSN1098-0121
Volume89
Issue8
Article number85310
AbstractWe present a microscopic theory of electronic and optical properties of colloidal graphene quantum dots (CGQDs). The single-particle properties are described in the tight-binding model based on the pz carbon orbitals. Electron-electron screened Coulomb direct, exchange, and scattering matrix elements are calculated using Slater pz orbitals. The many-body ground state and excited states are constructed as a linear combination of a finite number of excitations from the Hartree-Fock (HF) ground state (GS) by exact diagonalization techniques. HF ground states corresponding to semiconductor, Mott-insulator, and spin-polarized phases are obtained as a function of the strength of the screened interaction versus the tunneling matrix element. In the semiconducting phase of a triangular CGQD, the top of the valence band and the bottom of the conduction band are found to be degenerate due to rotational symmetry. The singlet and triplet exciton spectra from the HF GS are obtained by solving the Bethe-Salpeter equation. The low-energy exciton spectrum is predicted to consist of two bright-singlet exciton states corresponding to two circular polarizations of light and a lower-energy band of two dark singlets and 12 dark triplets. The robustness of the bright degenerate singlet pair against correlations in the many-body state is demonstrated as well as the breaking of the degeneracy by the lowering of symmetry of the CGQD. The band-gap renormalization, electron-hole attraction, fine structure, oscillator strength, and polarization of the exciton are analyzed as a function of the size, shape, screening, and symmetry of the CGQD. The theoretical results are compared with experimental absorption spectra.
Publication date
PublisherAmerican Physical Society
LanguageEnglish
AffiliationNational Research Council Canada; Security and Disruptive Technologies
Peer reviewedYes
NPARC number21272627
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Record identifierfabc734d-e2fd-4fc8-814e-12c60e2a476e
Record created2014-12-03
Record modified2016-05-09
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