Evidence for a single-layer van der Waals multiferroic
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2106.07661.pdf
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Author(s)
Song, Qian
Occhialini, Connor A
Ergeçen, Emre
Ilyas, Batyr
Amoroso, Danila
Barone, Paolo
Kapeghian, Jesse
Watanabe, Kenji
Taniguchi, Takashi
Botana, Antia S
Date Issued
February 24, 2022
Journal
Nature
Publisher
Springer Science and Business Media LLC
Citation
Song, Qian, Occhialini, Connor A, Ergeçen, Emre, Ilyas, Batyr, Amoroso, Danila et al. 2022. "Evidence for a single-layer van der Waals multiferroic." Nature, 602 (7898).
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Author's final manuscript
Abstract
Multiferroic materials have attracted wide interest because of their exceptional static1-3 and dynamical4-6 magnetoelectric properties. In particular, type-II multiferroics exhibit an inversion-symmetry-breaking magnetic order that directly induces ferroelectric polarization through various mechanisms, such as the spin-current or the inverse Dzyaloshinskii-Moriya effect3,7. This intrinsic coupling between the magnetic and dipolar order parameters results in high-strength magnetoelectric effects3,8. Two-dimensional materials possessing such intrinsic multiferroic properties have been long sought for to enable the harnessing of magnetoelectric coupling in nanoelectronic devices1,9,10. Here we report the discovery of type-II multiferroic order in a single atomic layer of the transition-metal-based van der Waals material NiI2. The multiferroic state of NiI2 is characterized by a proper-screw spin helix with given handedness, which couples to the charge degrees of freedom to produce a chirality-controlled electrical polarization. We use circular dichroic Raman measurements to directly probe the magneto-chiral ground state and its electromagnon modes originating from dynamic magnetoelectric coupling. Combining birefringence and second-harmonic-generation measurements with theoretical modelling and simulations, we detect a highly anisotropic electronic state that simultaneously breaks three-fold rotational and inversion symmetry, and supports polar order. The evolution of the optical signatures as a function of temperature and layer number surprisingly reveals an ordered magnetic polar state that persists down to the ultrathin limit of monolayer NiI2. These observations establish NiI2 and transition metal dihalides as a new platform for studying emergent multiferroic phenomena, chiral magnetic textures and ferroelectricity in the two-dimensional limit.
MIT Department
Massachusetts Institute of Technology. Department of Physics
Massachusetts Institute of Technology. Department of Materials Science and Engineering
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DOI of Published Version
https://doi.org/10.1038/s41586-021-04337-x
