Cedric Weber, David D. O'Regan, Nicholas D. M. Hine, Mike C. Payne, Gabriel Kotliar, Peter B. Littlewood
Vanadium dioxide undergoes a first order metal-insulator transition (MIT) at
340 K. At high temperature, the crystal structure is metallic with the rutile
structure (R), while it transforms to the monoclinic (M$_1$) phase and becomes
insulating below the transition temperature. Experimental evidence suggests
that the insulator is obtained due to strong correlations in this material,
however density functional theory (DFT) predicts the M$_1$ phase to be
metallic. In this work, we develop and carry out state of the art linear
scaling DFT calculations refined with non-local dynamical mean-field theory
(DMFT). We validate our approach by applying this cutting edge methodology to
the M$_1$ phase of VO$_2$. We find that a Peierls-Mott instability is
responsible for the insulating M$_1$ phase, which furthermore survives a large
degree of disorder accounting for the MIT observed when no long-range
crystallographic order is present. The Peierls-Mott instability involves two
electrons per vanadium atom in $t_{2g}$ orbitals and reconciles the Peierls
picture with recent soft x-ray absorption spectroscopy (XAS), which points
towards a breaking of the one electron per 3d orbital picture suggested early
by Goodenough. Finally, since fluctuations in VO$_2$ thin film deposition may
cause departure from the ideal stoichiometry, we discuss how the MIT is
affected by oxygen vacancies.
View original:
http://arxiv.org/abs/1202.1423
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