Anomalous spectral-weight transfers unraveling oxygen screening and electronic correlations in the insulator-metal transition of VO2

Vanadium dioxide (VO2) undergoes an unusual insulator-metal transition (IMT), and after decades of study, the origin of the IMT remains hotly debated. Here, by analyzing spectral-weight transfers (SWTs) of x-ray absorption spectroscopy at the VL3,2 and O K edges on specially designed VO2 films, we observe d||(dx2-y2) band splitting at the VL3,2 edges across the IMT, accompanied by anomalous SWTs as high as ∼12eV at the OK edge, indicating strong electronic correlations. Surprisingly, a few oxygen vacancies induce dramatic SWTs at the OK edge, but the sample remains conducting. Supported by theoretical calculations, we find that in the metallic state, direct V(3d)-V(3d) and O(2p)-V(3d) hybridized orbital correlations are screened by O(2p)-V(3dπ) hybridized orbitals, while in the insulating state they are strongly correlated due to changes in the oxygen orbital occupancy. Our result shows the importance of screenings and electronic correlations for IMTs in VO2.