Peierls transition, ferroelectricity, and spin-singlet formation in the monolayer VOI${}_2$

Abstract

Using {\it ab initio} density functional theory and single-orbital Hubbard model calculations via the density matrix renormalization group method, we systematically studied the monolayer VOI${}_2$ with a $3d^1$ electronic configuration. Our phonon calculations indicate that the orthorhombic $Pmm2$ FE-II phase is the most likely ground state, involving a ferroelectric distortion along the $a$-axis and V-V dimerization along the $b$-axis. Specifically, the "pseudo Jahn-Teller" effect caused by the coupling between empty V ($d_{xz/yz}$ and $d_{3z^2-r^2}$) and O $2p$ states is proposed as the mechanism that stabilizes the ferroelectric distortion from the paraelectric phase. Moreover, the half-filled metallic $d_{xy}$ band displays a Peierls instability along the $b$-axis, inducing a V-V dimerization. We also found very short-range antiferromagnetic coupling along the V-V chain due to the formation of nearly-decoupled spin singlets in the ground state.

7 pages 5 figures

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• Non-$d^0$ Mn-driven ferroelectricity in antiferromagnetic BaMnO${}_3$
• Two-dimensional ferromagnetic-ferroelectric multiferroics in violation of the d0 rule
• Sequential structural and antiferromagnetic transitions in BaFe${}_2$Se${}_3$ under pressure
• Quasi-one-dimensional ferroelectricity and piezoelectricity in WO$X_4$ halogens

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