Electronic Structure of the Bond Disproportionated Bismuthate AgBiO
arXiv:2106.09075 · doi:10.1103/PhysRevMaterials.5.064202
Abstract
We present a comprehensive study on the silver bismuthate AgBiO, synthesized under high-pressure high-temperature conditions, which has been the subject of recent theoretical work on topologically complex electronic states. We present X-ray photoelectron spectroscopy results showing two different bismuth states, and X-ray absorption spectroscopy results on the oxygen -edge showing holes in the oxygen bands. These results support a bond disproportionated state with holes on the oxygen atoms for AgBiO. We estimate a band gap of 1.25~eV for AgBiO from optical conductivity measurements, which matches the band gap in density functional calculations of the electronic band structure in the non-symmorphic space group , which supports two inequivalent Bi sites. In our band structure calculations the disproportionated AgBiO is expected to host Weyl nodal chains, one of which is located 0.5~eV below the Fermi level. Furthermore, we highlight similarities between AgBiO and the well-known disproportionated bismuthate BaBiO, including breathing phonon modes with similar energy. In both compounds hybridization of Bi- and O- atomic orbitals is important in shaping the band structure, but in contrast to the Ba- in BaBiO, the Ag- bands in AgBiO extend up to the Fermi level.