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

We report high-resolution angle-resolved photoemission spectroscopy on sodium tungsten bronzes, NaxWO3, which exhibit a metal-insulator transition as a function of x. We found that the near-EF states are localized in NaxWO3 (x0.25) due to the strong disorder caused by the random distribution of Na+ ions in the WO3 lattice, which makes the system insulating. In the metallic regime we found that the rigid shift of band structure can explain the metallic NaxWO3 band structure with respect to Na doping.