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Until a decade ago, people believed that ferroelectricity should not exist on materials below a certain critical thickness (of a few nanometers) due to depolarization fields induced at exposed faces. Furthermore, most known ferroelectrics were insulators. Nevertheless, members of a family of binary orthorhombic (layered) materials were known to be antipolar (i.e., they have intrinsic electric dipoles changing orientation among consecutive layers). The ground state of a single monolayer of those materials is degenerate. Structural degeneracies give rise to domains and structural transformations at finite temperature [1,2] and those materials are 2D ferroelectrics [3]. This field became further invigorated by the observation that intrinsic electric dipoles can be created by rotating successive monolayers, and also by the observation of ferroelectricity in elemental materials [4]. Currently, the field is gearing toward (i) the creation of multiferroic 2D materials by the adequate stacking of 2D magnets [5], (ii) the discovery of novel ferroic orders and their intercouplings, (iii) and toward coupling ferroic orders to other orders such as superconductivity.

[1] M. Mehboudi, et al., Nano Letters 16, 1704 (2016)
[2] M. Mehboudi, et al., Physical Review Letters 117, 246802 (2016)
[3] S. Barraza-Lopez, et al., Reviews of Modern Physics 93, 011001 (2021)
[4] G. G. Naumis, S. A. Herrera, S. P. Poudel, H. Nakamura, S. Barraza-Lopez.
Reports on Progress in Physics 87, 016502 (2024)
[5] S. P. Poudel, et al., Physical Review B 107, 195128 (2023)

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