Unraveling the Mott-Peierls intrigue in vanadium dioxide

Abstract

Vanadium dioxide is one of the most studied strongly correlated materials. Nonetheless, the intertwining between electronic correlation and lattice effects has precluded a comprehensive description of the rutile metal to monoclinic insulator transition, in turn triggering a longstanding "the chicken or the egg" debate about which comes first, the Mott localisation or the Peierls distortion. Here, we show that this problem is in fact ill-posed: the electronic correlations and the lattice vibrations conspire to stabilise the monoclinic insulator, and so they must be treated on equal footing not to miss relevant pieces of the VO2 physics. Specifically, we design a minimal model for VO2 that includes all the important physical ingredients: the electronic correlations, the multi-orbital character, and the two components antiferrodistortive mode that condenses in the monoclinic insulator. We solve this model by dynamical mean-field theory within the adiabatic Born-Oppenheimer approximation. Consistently with the first-order character of the metal-insulator transition, the Born-Oppenheimer potential has a rich landscape, with minima corresponding to the undistorted phase and to the four equivalent distorted ones, and which translates into an equally rich thermodynamics that we uncover by the Monte Carlo method. Remarkably, we find that a distorted metal phase intrudes between the low-temperature distorted insulator and high-temperature undistorted metal, which sheds new light on the debated experimental evidence of a monoclinic metallic phase.

Mott and pseudogap localization in pressurized NbO2

“…To advance our understanding of strongly correlated Mott-Peierls systems [6][7][8], we focus on the baddeleyite-type structural phase of NbO 2 [11]. In spite of earlier studies [13,14], the question we tackle here is how the electronic structure of NbO 2 [15] is dynamically reshaped by the interplay between MO dynamic electronic correlations and sizable lattice distortions under pressure, showing an emergent pseudogap regime as the precursor of the Mott localized state [16] in undoped NbO 2 at high pressure conditions. Along this line, we uncover a universal behavior of electronic reconstruction, extending beyond the compound of interest.…”

Magnetic-field-induced insulator–metal transition in W-doped VO2 at 500 T

“…On the other hand, the Zeeman energy corresponding to 500 T is~60 meV, which is less than the eV-order binding energy for a local isolated V-V dimer by more than two orders of magnitude. Therefore, it is likely that the electron correlation must also be included to obtain a quantitative understanding of the MFI-IM transition 4,10,25 . From the perspective of material science, because a singlet spin state with the formation of a cluster of magnetic atoms is exhibited by various other strongly correlated insulators, such as Ti 2 O 3 29,30 , AlV 2 O 4 31 and CuIr 2 S 4 32 , investigation of the effect of a magnetic field on their electronic states is an intriguing and important research problem.…”

“…Because this energy scale corresponds to 30,000 K, which is more than two orders of magnitude larger than the Zeeman energy, the observed magnetic-field-induced metallisation cannot be explained by considering only an isolated single dimer. Some many-body interactions through the electron correlation 4 , 10 , 25 might be necessary to understand the mechanism of dissociation of the dimers by controlling the electron spins.

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“…On the other hand, the Zeeman energy corresponding to 500 T is ~60 meV, which is less than the eV-order binding energy for a local isolated V–V dimer by more than two orders of magnitude. Therefore, it is likely that the electron correlation must also be included to obtain a quantitative understanding of the MFI–IM transition 4 , 10 , 25 .…”

Metallic Diluted Dimerization in VO2 Tweeds

“…The observation of weakened Coulomb correlations preceding the structural change, [ 10 ] in tune with numerous experimental and theoretical evidences for the coexistence of VV dimers with metallicity in monoclinic states, has led to numerous speculations about the Peierls/Mott character of the transition. [ 11–21 ] A key aspect to understanding the MIT is the way this decoupling manifests in real‐space patterns. Observations of metal/insulator phase coexistence reported so far can be classified into two types: i) spectroscopic imaging revealing transient nanoscale electronic phase separation within low‐symmetry (monoclinic) phases in strained films, [ 17–20 ] and ii) martensitic‐like (mesoscopic) domain patterns in freestanding beams and in epitaxial films, [ 19,22–24 ] combining phases related by the thermodynamic P–T triple point.…”