Microscopic theory of the optical properties of colloidal graphene quantum dots

Isil Ozfidan, Marek Korkusinski, A. Devrim Güçlü, John A. McGuire, and Pawel Hawrylak
Phys. Rev. B 89, 085310 – Published 21 February 2014

Abstract

We 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.

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  • Received 28 October 2013
  • Revised 15 January 2014

DOI:https://doi.org/10.1103/PhysRevB.89.085310

©2014 American Physical Society

Authors & Affiliations

Isil Ozfidan1,2, Marek Korkusinski1, A. Devrim Güçlü3, John A. McGuire4, and Pawel Hawrylak1,2

  • 1Quantum Theory Group, Security and Disruptive Technologies, Emerging Technologies Division, National Research Council of Canada, Ottawa, Canada K1A OR6
  • 2Physics Department, University of Ottawa, Ottawa, Canada
  • 3Department of Physics, Izmir Institute of Technology IZTECH, Izmir, Turkey
  • 4Department of Physics and Astronomy, Michigan State University, East Lansing, Michigan 48824, USA

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Issue

Vol. 89, Iss. 8 — 15 February 2014

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