Direct observation of the lowest indirect exciton state in the bulk of hexagonal boron nitride

R. Schuster, C. Habenicht, M. Ahmad, M. Knupfer, B. Büchner
2018 Physical review B  
We combine electron energy-loss spectroscopy and first-principles calculations based on density-functional theory (DFT) to identify the lowest indirect exciton state in the in-plane charge response of hexagonal boron nitride (h-BN) single crystals. This remarkably sharp mode forms a narrow pocket with a dispersion bandwidth of ∼ 100 meV and, as we argue based on a comparison to our DFT calculations, is predominantly polarized along the ΓK-direction of the hexagonal Brillouin zone. Our data
more » ... rt the recent report by Cassabois et al. (Nat. Photon. 10, 262) who indirectly inferred the existence of this mode from the photoluminescence signal, thereby establishing h-BN as an indirect semiconductor.
doi:10.1103/physrevb.97.041201 fatcat:azyyjv2rtzbqrhv73yhpu5ve6y