Title: Doping a bad metal: Origin of suppression of the metal-insulator transition in nonstoichiometric ${\mathrm{VO}}_2$

Abstract

Rutile ( $R$) phase ${\mathrm{VO}}_2$ 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 ( $M_1$) phase below $T_{\text{MIT}}~340\text{K}$. It has been experimentally illustrated that one can control this transition by doping ${\mathrm{VO}}_2$. In particular, doping with oxygen vacancies ( $V_{\text{O}}$) has been shown to completely suppress this MIT without any structural transition. We explain this suppression by elucidating the influence of oxygen vacancies on the electronic structure of the metallic $R$ phase ${\mathrm{VO}}_2$, 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. DMC calculations show a gap closure in the $M_1$ phase when vacancies are present, suggesting that when vacancies are introduced in the high-temperature rutile phase, the dimerized insulating phase cannot be reached when temperature is lowered. Both DMFT and DMC calculations of nonstoichiometric metallic rutile phase shows that this tendency not to dimerize in the presence of vacancies is because $V_{\text{O}}$'s tend to change the $\mathrm{V}\text{-}3d$ 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 research further suggests that the MIT is predominantly driven by a correlation-induced CDW instability along the V-V dimerization direction.

Authors:

Ganesh, P. ^[1]; Lechermann, Frank ^[2]; Kylanpaa, Ilkka ^[3]; Krogel, Jaron ^[4]; Kent, Paul R. C. ^[5]; Heinonen, Olle ^[6]

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+ Show Author Affiliations

1. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States). Center for Nanophase Materials Science (CNMS)
2. Univ. of Hamburg (Germany). Inst. for Theoretical Physics
3. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States). Materials Science & Technology Division; Tampere Univ. of Technology (Finland)
4. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States). Materials Science & Technology Division
5. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States). Center for Nanophase Materials Science (CNMS) and Computational Sciences and Engineering Division
6. Argonne National Lab. (ANL), Argonne, IL (United States). Materials Science Division

Publication Date:

2020-04-23

Research Org.:

Argonne National Lab. (ANL), Argonne, IL (United States); Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States); Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)

Sponsoring Org.:

USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22). Materials Sciences & Engineering Division

OSTI Identifier:

1617648

Alternate Identifier(s):

OSTI ID: 1615954

Grant/Contract Number:  

AC02-06CH11357; AC05-00OR22725; AC02-05CH11231

Resource Type:

Accepted Manuscript

Journal Name:

Physical Review B

Additional Journal Information:

Journal Volume: 101; Journal Issue: 15; Journal ID: ISSN 2469-9950

Publisher:

American Physical Society (APS)

Country of Publication:

United States

Language:

English

Subject:

36 MATERIALS SCIENCE; 75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND SUPERFLUIDITY