Electronic structure of metallic K0.3MoO3 and insulating MoO3 from high-energy spectroscopy

We present high-energy spectroscopy results on the occupied and unoccupied electronic structures of the strongly anisotropic compounds MoO₃ and K_0.3MoO₃ near the Fermi level. X-ray photoemission reveals a close similarity of the valence-band spectra in both materials. The metal K_0.3MoO₃ shows an additional Mo 4d-derived conduction band whose population is achieved by electron transfer from K to Mo. This is concluded from studies on intentional surface doping of insulating MoO₃ which leads to the occurrence of Mo 4d-like defect states near the Fermi level. Information on the unoccupied states and their orbital symmetries was obtained by polarization-dependent x-ray absorption spectroscopy. These experiments confirm previous descriptions of the electronic structure in terms of a molecular-orbital picture. For K_0.3MoO₃, strong local Mo 4d-O 2p bonding is not only found along the chain direction but also perpendicular to it. This finding is reminiscent of earlier band calculations, which found the chains to form pairs by pronounced transverse hybridization, with the overall bandwidth remaining one dimensionally anisotropic. This adds an important aspect to the discussion on possible Luttinger-liquid physics in the low-dimensional Mo bronzes.