Electronic structure of metallicK0.3MoO3and insulatingMoO3from high-energy spectroscopy

Abstract

We present high-energy spectroscopy results on the occupied and unoccupied electronic structures of the strongly anisotropic compounds ${\mathrm{MoO}}_{3}$ and ${\mathrm{K}}_{0.3}{\mathrm{MoO}}_{3}$ near the Fermi level. X-ray photoemission reveals a close similarity of the valence-band spectra in both materials. The metal ${\mathrm{K}}_{0.3}{\mathrm{MoO}}_{3}$ 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 ${\mathrm{MoO}}_{3}$ 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 ${\mathrm{K}}_{0.3}{\mathrm{MoO}}_{3},$ strong local Mo $4d\ensuremath{-}\mathrm{O}$ $2p$ 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.