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A New Scenario on the Metal-Insulator Transition in VO2
The metal-insulator transition in VO2 was investigated using the three-band
Hubbard model, in which the degeneracy of the 3d orbitals, the on-site Coulomb
and exchange interactions, and the effects of lattice distortion were
considered. A new scenario on the phase transition is proposed, where the
increase in energy level separation among the t_2g orbitals caused by the
lattice distortion triggers an abrupt change in the electronic configuration in
doubly occupied sites from an S=1 Hund's coupling state to a spin S=0 state
with much larger energy, and this strongly suppresses the charge fluctuation.
Although the material is expected to be a Mott-Hubbard insulator in the
insulating phase, the metal-to-insulator transition is not caused by an
increase in relative strength of the Coulomb interaction against the electron
hopping as in the usual Mott transition, but by the level splitting among the
t_2g orbitals against the on-site exchange interaction. The metal-insulator
transition in Ti2O3 can also be explained by the same scenario. Such a large
change in the 3d orbital occupation at the phase transition can be detected by
linear dichroic V 2p x-ray absorption measurements.Comment: 5 pages, 5 figures, to be published in J. Phys. Soc. Jpn. Vol. 72 No.
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