Photoemission evidence for a Mott-Hubbard metal-insulator transition inVO2

Abstract

The temperature $(T)$-dependent metal-insulator transition (MIT) in ${\text{VO}}_{2}$ is investigated using bulk sensitive hard-x-ray $(\ensuremath{\sim}8\text{ }\text{keV})$ valence-band, core-level, and $\text{V}\text{ }2p\ensuremath{-}3d$ resonant photoemission spectroscopies (PESs). The valence-band and core-level spectra are compared with full-multiplet cluster model calculations including a coherent screening channel. Across the MIT, $\text{V}\text{ }3d$ spectral weight transfer from the coherent ($3{d}^{1}\underset{̱}{C}$ final) states at Fermi level to the incoherent ($3{d}^{0}+3{d}^{1}\underset{̱}{L}$ final) states, corresponding to the lower Hubbard band, leads to gap formation. The spectral shape changes in $\text{V}\text{ }1s$ and $\text{V}\text{ }2p$ core levels as well as the valence band are nicely reproduced from cluster model calculations, providing electronic structure parameters. Resonant PES finds that the $3{d}^{1}\underset{̱}{L}$ states resonate across the $\text{V}\text{ }2p\ensuremath{-}3d$ threshold in addition to the $3{d}^{0}$ and $3{d}^{1}\underset{̱}{C}$ states. The results support a Mott-Hubbard transition picture for the first-order MIT in ${\text{VO}}_{2}$.