Ab initio high-energy excitonic effects in graphite and graphene
Résumé
We present ab initio many-body calculations of the optical absorption in bulk graphite, graphene and bilayer of graphene. Electron-hole interaction is included solving the Bethe-Salpeter equation on top of a GW quasiparticle electronic structure. For all three systems, we observe strong excitonic effects at high energy, well beyond the continuum of $\pi \to \pi^*$ transitions. In graphite, these affect the onset of $\sigma \to \sigma^*$ transitions. In graphene, we predict an excitonic resonance at 9 eV arising from a background continuum of dipole forbidden transitions. In the graphene bilayer, the resonance is slightly shifted to 9.8 eV. Our results for graphite are in good agreement with experiments.
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