Microscopic origin of multiferroic behavior in monolayer NiI₂

A wide variety of two-dimensional (2D) materials displaying different electronic orders have been isolated, providing the basic building blocks for artificial van der Waals heterostructures. Remarkably, purely 2D ferroelectrics [1] and 2D ferromagnets [2] have been successfully isolated in 2018 and 2017, respectively. However, the discovery of a 2D multiferroic had remained elusive until 2021 [3,4]. These recent experiments demonstrate that NiI₂ displays a multiferroic behavior, opening up a whole new direction in van der Waals materials. Here I will present a systematic theoretical analysis of the multiferroicity in NiI₂ combining ab initio calculations and low-energy models. In particular, I will address the microscopic origin of the multiferroicity in NiI₂, and reveal its fine relation with non-collinearity and spin-orbit effects. This analysis will allow us to determine the main ingredients behind the multiferroic behavior of NiI₂, providing a starting point to design new 2D multiferroics.

References

[1] Chaojie Cui et al. Nano Letters, 18:1253, 2018.

[2] Bevin Huang et al. Nature, 546:270, 2017.

[3] Hwiin Ju et al. Nano Letters, 21:5126, 2021.

[4] Qian Song et al. ArXiv, 2106.07661, 2021.