Spin and orbital occupation and phase transitions in V2O3
2000
Polarization dependent x-ray-absorption measurements were performed on pure and Cr-doped ${\mathrm{V}}_{2}{\mathrm{O}}_{3}$ single crystals in the antiferromagnetic insulating, paramagnetic insulating, and metallic phases. The orbital occupation of the V ${3d}^{2}$ ion is found to depend appreciably on the phase, but always with the $S=1$ character, requiring an explanation which is beyond the elegant simplicity of the pure one-band Hubbard model or of models in which the ${a}_{1g}$ orbital is projected out by means of a simple dimerization. The results reveal the critical role of the spin and orbital dependence of the on-site $3d\ensuremath{-}3d$ Coulomb energy, and a mechanism is proposed to explain the closing or opening of the band gaps which are of much higher energy scale than the transition temperatures.
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