HIGH-ENERGY-RESOLUTION PHOTOEMISSION INVESTIGATION OF MONOPHOSPHATE TUNGSTEN BRONZES

High-energy-resolution angle resolved photoemission measurements have been carried out on monophosphate tungsten bronzes with pentagonal tun nels (PO2)(4)(WO3)(2m) for different values of m (6 less than or equal to m less than or equal to 12). A broad angle independent feature is observed near the Fermi level whose position exhibits a systematic tre nd: the peak shifts to higher binding energy with increasing m. These experimental data are not corroborated by band calculations which pred ict a narrow band whose energy position moves towards the Fermi level with increasing m. Therefore the spectroscopic properties cannot be de scribed within a one-electron band formalism. Finally, the temperature dependence of the spectra only shows the usual Fermi level broadening and a small shift of the main feature. No evidence of spectral modifi cations induced by Peierls transition for low m values is observed. (C ) 1997 Elsevier Science Ltd.