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Optical gap between dangling-bond states of a single-domain diamond C(111)-2 × 1 by reflectance anisotropy spectroscopy

The optical gap between dangling-bond states has been measured on a single-domain diamond C(111)-2×1 surface. The experimental result is 1.47 eV. Such a large surface gap (even larger if excitonic effects are considered) so far has not been obtained by state-of-the-art band calculations and its physical origin is still not elucidated. The experimental result suggests a strong electron-phonon interaction in this surface. The renormalization of the bare electronic transition energy by electron-phonon interaction provides a clue to solve the apparent disagreement between theory and experiment.