Doping a bad metal: Origin of suppression of the metal-insulator transition in nonstoichiometric VO2

Abstract

Rutile (R) phase VO2 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 TMIT ∼ 340K. It has been experimentally shown that one can control this transition by doping VO2. In particular, doping with oxygen vacancies (VO) 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 VO2, 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 VO's tend to change the V-3d filling away from its nominal half-filled value, with the e π g orbitals competing with the otherwise dominant a1g orbital. Loss of this near orbital polarization of the a1g 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. arXiv:1811.01145v1 [cond-mat.mtrl-sci]

Geometrical‐, Electronic‐ and Optical Properties of Vanadium Dioxide: A Theoretical Perspective from Meta‐GGA SCAN

“…For example, several Exchange Correlation (XC) DFT functionals wrongly have suggested a ferromagnetic ground state for the system. [10] These functionals have also failed to reproduce the experimentally measured latent heat of transition, [10] the preferential phase stability of the low-temperature monoclinic M1-geometry over the high-temperature Rutile R-geometry, [4,10] the semiconducting bandgap of 0.6-0.7 eV, [1][2]4,[11][12][13] and the optical absorption features of monoclinic VO 2 in the infrared region. [14] In particular, the LDA, GGA and sometimes the meta-GGA functionals have incorrectly described the semiconducting and insulating behavior of VO 2 (M1), [4,15] thus incorrectly produced a magnetic ground state, either ferromagnetic (FM) or antiferromagnetic (AFM).…”

Metal–insulator transition tuned by oxygen vacancy migration across TiO2/VO2 interface

“…In correlated oxide systems, changes in oxygen content can profoundly alter electronic structure and even trigger a metal–insulator transition (MIT). VO 2-δ ( δ denotes oxygen non-stoichiometry) is such a material system, wherein a small change in composition can lead to a large modulation in correlation effects 16 – 20 . Near-stoichiometric VO 2 has 3 d 1 electron configuration and shows a MIT with a transition temperature T c ≈ 340 K, accompanied by a structural transition from low-temperature M1 (monoclinic) phase to high-temperature R (rutile) phase.…”

Local manifestations of thickness-dependent topology and edge states in the topological magnet MnBi2Te4

“…From a theoretical point of view, the improved agreement of our calculations with experiments, by variation of the exact exchange for different thicknesses, suggests a complicated interplay between electronic correlations, magnetism, and hybridization. This makes MBT an interesting benchmark system to validate a variety of theoretical methods beyond the conventional DFT approach such as the dynamic mean field theory and quantum Monte Carlo methods [39]. Furthermore, while plane-wave DFT-methods do not allow explicit simulations of step-edges, we demonstrate that DFT methods using multi-resolution real-space grids are suitable for largescale simulations [31][32][33], which agree well with plane-wave codes and enable calculations of edge states for arbitrary film thicknesses in future studies.…”