Doping a Bad Metal: Origin of Suppression of Metal-Insulator Transition in Non-Stoichiometric VO${}_2$

Abstract

Rutile ($R$) phase VO${}_2$ is a quintessential example of a strongly correlated bad-metal, which undergoes a metal-insulator transition (MIT) concomitant with a structural transition to a V-V dimerized monoclinic phase below T${}_{MIT}\sim 340K$. It has been experimentally shown that one can control this transition by doping VO${}_2$. In particular, doping with oxygen vacancies ($V_O$) has been shown to completely suppress this MIT {\em without} any structural transition. We explain this suppression by elucidating the influence of oxygen-vacancies on the electronic-structure of the metallic $R$ phase VO${}_2$, explicitly treating strong electron-electron correlations using dynamical mean-field theory (DMFT) as well as diffusion Monte Carlo (DMC) flavor of quantum Monte Carlo (QMC) techniques. We show that $V_O$'s tend to change the V-3$d$ filling away from its nominal half-filled value, with the $e_g^{\pi }$ orbitals competing with the otherwise dominant $a_{1g}$ orbital. Loss of this near orbital polarization of the $a_{1g}$ orbital is associated with a weakening of electron correlations, especially along the V-V dimerization direction. This removes a charge-density wave (CDW) instability along this direction above a critical doping concentration, which further suppresses the metal-insulator transition. Our study also suggests that the MIT is predominantly driven by a correlation-induced CDW instability along the V-V dimerization direction.

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• Electronic structure and optical properties of quantum crystals from first principles calculations in the Born-Oppenheimer approximation
• Lattice and Electronic properties of VO${}_2$ with the SCAN(+$U$) approach
• Correlation induced emergent charge order in metallic vanadium dioxide