X-ray Absorption and Inverse Photoemission Study of Y1-xCaxTiO3

We have performed the O 1s x-ray absorption (XAS) and resonant inverse photoemission spectroscopy (RIPES) in Mott insulator YTiO₃, band insulator CaTiO₃ and Y_0.61Ca_0.39TiO₃ with a metal-insulator transition. In CaTiO₃, the spectrum has strong π^* and σ^* peaks derived from the Ti 3d-O 2 p hybridization bands near the Fermi level. On the other hand the peaks almost disappear in the XAS spectrum of YTiO₃. In Y_0.61Ca_0.39TiO₃, the intensities of the π^* and σ^* structures increase with decreasing temperature, showing that degree of the p-d hybridization increases from the insulator to metal phases.