Frustrated Dipole Order Induces Noncollinear Proper Ferrielectricity in Two Dimensions

Achieving novel physical properties in two-dimensional (2D) materials should enable numerous functionalities in nanoscale devices. In recent years, interest in high-performance 2D ferroelectric materials has also grown rapidly across multiple scientific and engineering disciplines. Here, dioxydihalides MO₂X₂ materials (where M= Mo and W; X= Cl and Br) are studied based on density functional theory calculations. For dioxydihalides MO₂X₂ monolayers, we predict that they should display noncollinear ferrielectricity, induced by competing ferroelectric and antiferroelectric softmodes [1]. More importantly, this intrinsic noncollinearity of dipoles generates unique physical properties, such as Z2xZ2 topological domains, atomic-scale dipole vortices/anti-vortices, and negative piezoelectricity. Our investigations should open the door to a new branch of 2D materials in the pursuit of intrinsically strong noncollinear ferrielectricity.

[1] Ling-Fang Lin, Yang Zhang, Adriana Moreo, Elbio Dagotto, and Shuai Dong, Phys. Rev. Lett. 123, 067601 (2019).