Three-dimensional band structure of highly metallic Na0.8WO3 by angle-resolved photoemission spectroscopy

Three-dimensional electronic structure of highly metallic sodium tungsten bronze, Na0.8WO3, is investigated by high-resolution angle-resolved photoemission spectroscopy. The experimentally determined valence-band structure along the momentum directions both parallel and perpendicular to the surface has been compared with the results of ab initio band-structure calculation. The angle-resolved photoemission spectroscopy spectra for different photon energies reveal that possibly the oxygen vacancies in the system are responsible for the evolution of density of states at the top of Gamma point in experimental valence band. The band dispersion around Gamma(X) point leading to an electronlike Fermi surface is well predicted by the band calculation. As we move from bulk-sensitive to more-surface-sensitive photon energy, we found emergence of Fermi surfaces at X(M) and M(R) points similar to the one at Gamma(X) point, suggesting the reconstruction of surface due to rotation/deformation of WO6 octahedra.