Electronic structure of 3d1 configuration vanadium oxides studied by soft X-ray and hard X-ray photoemission spectroscopy

We investigate the electronic structure of 3d1 configuration vanadium oxides (VO2, SrVO3 and CaVO3) using soft X-ray (SX) and hard X-ray (HX) photoemission spectroscopy (PES). The valence band spectra of VO2 in SX- and HX-PES clearly show the opening of a gap at EF across the metal-insulator transition. Spectral changes in the V 2p and O 1s core levels were also observed. In addition, 3d1 configuration correlated metals SrVO3 and CaVO3 are typical materials whose valence band spectra are compared with dynamical mean-field theory. The V 2p and V 1s core level HX-PES of SrVO3 and CaVO3 show clear additional well-screened features. These features originate from bulk screening by a coherent band at EF. These spectra are nicely reproduced by a cluster model calculation, indicating a difference of the parameter V∗ for the interaction strength between the central V 3d orbitals and the coherent band.