Metal–insulator transition in sodium tungsten bronzes, NaxWO3, studied by angle-resolved photoemission spectroscopy

Abstract We report high-resolution angle-resolved photoemission spectroscopy on sodium tungsten bronzes, Na x WO 3 , which exhibit a metal–insulator transition as a function of x . We found that the near- E F states are localized in Na x WO 3 ( x ⩽ 0.25 ) due to the strong disorder caused by the random distribution of Na + ions in the WO 3 lattice, which makes the system insulating. In the metallic regime we found that the rigid shift of band structure can explain the metallic Na x WO 3 band structure with respect to Na doping.