Three-dimensional band structure of highly metallic Na(0.8)WO(3) 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 ? point in experimental valence band. The band dispersion around ?(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 ?(X) point, suggesting the reconstruction of surface due to rotation/deformation of WO6 octahedra.