Enhanced charge-transfer character in the monoclinic phase of Mott insulator LaVO3 thin films

The electronic structure of a pulsed laser deposited epitaxial $\mathrm{La}\mathrm{V}{\mathrm{O}}_{3}$ (LVO) thin film grown on a $\mathrm{LaAl}{\mathrm{O}}_{3}$ (001) (LAO) substrate has been studied at room temperature and at 130 K, which is below the structural (141 K) and magnetic transition temperatures (143 K) of single-crystal LVO. Significant modification in spectral intensity, largely around the $\mathrm{V}\phantom{\rule{0.16em}{0ex}}3d\text{\ensuremath{-}}\mathrm{O}\phantom{\rule{0.16em}{0ex}}2p$ hybridized region, is observed in the valence band spectrum (VBS) of a LVO film at 130 K. Resonant photoemission study at 130 K confirms the presence of a charge-transfer screened $3{d}^{n}\underline{\mathrm{L}}$ ($\underline{\mathrm{L}}$: hole in the $\mathrm{O}\phantom{\rule{0.16em}{0ex}}2p$) final state along with the dominant $3{d}^{n\ensuremath{-}1}$ final state at 1.5 eV binding energy in the valence band. On the contrary, in the room temperature VBS, dominant $\mathrm{V}\phantom{\rule{0.16em}{0ex}}3d$ states with only the $3{d}^{n\ensuremath{-}1}$ kind of final state are accentuated. To understand this difference, density functional theory calculations are employed. The changes in crystal structure from room temperature orthorhombic to low temperature monoclinic ($M$ LVO) symmetry leads to remarkable change in the electronic structure around the Fermi level, including transition from the direct to the indirect nature of the band gap. Our calculations also confirm an enhanced $\mathrm{O}\phantom{\rule{0.16em}{0ex}}2p$ character in the valence band edge of $M$ LVO that is hybridized with $\mathrm{V}\phantom{\rule{0.16em}{0ex}}3d$. These results are further corroborated with octahedral distortions associated with the structural transition.