Evidence for absence of metallic surface states in BiO2-terminated BaBiO3 thin films

We investigated the atomic configuration and the electronic structure of a BaBiO3 (BBO) thin film and its (001) surface. It was theoretically predicted that two-dimensional electron gases would be formed when the film is BiO2-terminated. We deduced depth-profile information for a BBO thin film using angle-dependent X-ray photoemission spectroscopy. Analysis of the spectral weights of the Ba 3d and Bi 4f core levels confirmed that the BBO film should have a BiO2-terminated topmost layer. We used in-situ angle-resolved photoemission spectroscopy to experimentally determine the electronic structure of a BBO thin film and found no metallic surface state. We distinguished surface states from bulk states by evaporating potassium atoms in-situ on the surface. A surface state near the bottom of the topmost bulk valence band, which was predicted by the DFT calculations, was identified. However, other surface states well separated from the bulk states were not observed. Our results provided evidence that descriptions of the BBO electronic structure require more detailed and elaborate approaches. •An atomic configuration and a surface state of a BiO2-terminated BaBiO3 thin film were studied.•The depth-profile information of our BaBiO3 film was investigated and it had a BiO2 termination layer.•Contrary to the theoretical proposal for a 2DEG on a BiO2-terminated BaBiO3, no surface metallic state was observed.•The absence of the metallic surface state may be attributed to misprediction on the band gap size.