Temperature-dependent electronic structure of VO2 in the insulating phase

We have studied the temperature-dependent electronic structure of VO2 in the insulating phase. The V 3d and O 2p bands become broader and their band edges are shifted toward the Fermi level (E-F) with increasing temperature. The V 2p and O is core-Level spectra also show a similar temperature dependence. These observations combined with optical spectra indicate that the position of E-F relative to the conduction-band minimum is fixed and that the band gap changes mainly below E-F. We also point out the possibility that electron-phonon interaction plays an important role in the temperature dependence of spectra in the insulating phase and may drive the metal-insulator transition.