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

Electronic structure of pulsed laser deposited epitaxial LaVO3 (LVO) thin film grown on LaAlO3 (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 V 3d - O 2p hybridized region, is observed in valence band spectrum (VBS) of LVO film at 130 K. Resonant photoemission study at 130 K confirms the presence of charge transfer screened 3dnL (L: hole in the O 2p) final state along with the dominant 3dn-1 final state at 1.5 eV binding energy in the valence band. On the contrary, in the room temperature VBS dominant V 3d sates with only 3dn-1 kind final state is accentuated. To understand this difference, density functional theory (DFT) calculations are employed. The changes in crystal structure from room temperature orthorhombic (O-LVO) to low temperature monoclinic (M-LVO) symmetry leads to remarkable change in the electronic structure around the Fermi level, including transition from direct to indirect nature of band gap. Our calculations also confirm an enhanced O 2p character in the valence band edge of M-LVO that is hybridized with V 3d. These results are further corroborated with octahedral distortions associated with the structural transition.