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Single-particle excitation spectra of C60 molecules and monolayers

Fei Lin, Erik S. Sørensen, Catherine Kallin, and A. John Berlinsky
Phys. Rev. B 75, 075112 – Published 21 February 2007
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  • INTRODUCTION
  • MODEL
  • RESULTS
  • CONCLUSION
  • ACKNOWLEDGEMENTS
    • References

    Abstract

    In this paper, we present calculations of single-particle excitation spectra of neutral and three-electron-doped Hubbard C60 molecules and monolayers from large-scale quantum Monte Carlo simulations and cluster perturbation theory. By a comparison with experimental photoemission, inverse photoemission, and angle-resolved photoemission data, we estimate the intermolecular hopping integrals and the C60 molecular orientation angle, finding agreement with recent x-ray photoelectron diffraction experiments. Our results demonstrate that a simple effective Hubbard model, with intermediate coupling U=4t, provides a reasonable basis for modeling the properties of C60 compounds.

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    • Received 30 October 2006

    DOI:https://doi.org/10.1103/PhysRevB.75.075112

    ©2007 American Physical Society

    Authors & Affiliations

    Fei Lin1, Erik S. Sørensen2, Catherine Kallin2, and A. John Berlinsky2

    • 1Department of Physics, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801, USA
    • 2Department of Physics and Astronomy, McMaster University, Hamilton, Ontario, Canada L8S 4M1

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    Vol. 75, Iss. 7 — 15 February 2007

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    • Figure 1
      Figure 1
      (Color online) 2D hexagonal monolayer of identically oriented C60 molecules [lattice constant a=10.02Å for the superlattice (Ref. 11)] and its corresponding first Brillouin zone. The definition of the molecular rotation angle θ is the same as in the caption of Fig. 4 of Ref. 11, which is defined by two lines, both projected onto the plane of the layer, one from a molecular center to a NN molecular center, as shown, and the other from a molecular center through a pentagon face center. θ=0° when these two lines coincide. Counterclockwise rotation of the molecule corresponds to a positive rotation angle. For K3C60, the black squares represent two K+ ions, one above the other, while gray ones denote a single K+ ion (Ref. 11).Reuse & Permissions
    • Figure 2
      Figure 2
      (Color online) DOS of (a) C60 and (b) C603− single molecules from QMC and MEM for U=4t and βt=10. A total of 465 and 620 bins of space-time Green’s functions are collected for C60 and C603−, respectively, for MEM analysis. Each bin is an average over 100 space-time Green’s functions, which are collected after each QMC sweep over the whole space-time lattice.Reuse & Permissions
    • Figure 3
      Figure 3
      Single-particle spectral functions of a 2D Hubbard model from (a) QMCPT and (b) EDCPT with open boundary conditions. The cluster is of 3×4 dimension. The two methods predict very similar single-particle excitation energies and energy gaps. Note that special k points Γ, M, and X are for a 2D square lattice, different from those in Fig. 1.Reuse & Permissions
    • Figure 4
      Figure 4
      (Color online) DOS of hexagonal (a) C60 monolayer with U=0, (b) C60 monolayer with U=4t, and (c) K3C60 monolayer with U=4t from QMCPT calculations for t′=−0.3t and T=0.1t. Shaded areas are occupied by electrons.Reuse & Permissions
    • Figure 5
      Figure 5
      Determination of NN molecular hopping integral t′ and molecular orientation angle θ by comparing the experimental ARPES result (Ref. 11) (upper panel) with the theoretical one (lower panel), which has t′=−0.3t and molecular rotation angle θ=64°. The energy unit has been converted to eV using t=2.72eV. The momentum unit is Å−1.Reuse & Permissions
    • Figure 6
      Figure 6
      (Color online) Comparison of DOS from QMCPT calculations and experimental PES data (Ref. 11) for C60 (upper panel) and K3C60 (lower panel) hexagonal monolayers. The QMCPT energy scale has been converted to eV by setting t=2.72eV.Reuse & Permissions
    • Figure 7
      Figure 7
      Band dispersions along ΓM direction with different rotation angles θ for a 2D hexagonal K3C60 superlattice from QMCPT calculations. The other parameters are fixed: U=4t, t′=−0.3t, and T=0.1t. The momentum unit is Å−1.Reuse & Permissions
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