Sliding Flexoelectricity in Two-Dimensional van der Waals Systems

TL;DR

This paper explores how bending deformation in two-dimensional sliding ferroelectric bilayers induces a novel flexoelectric effect through interlayer sliding and kink formation, revealing new ways to manipulate polarization.

Contribution

It introduces the concept of sliding flexoelectricity in 2D ferroelectric bilayers and demonstrates the formation of polarization-reversing kinks due to bending.

Findings

Bending causes irreversible kink formation beyond a critical angle.

Kinks originate from competition between bending and van der Waals energies.

Kinks contain ferroelectric domain walls that reverse polarization.

Abstract

Two-dimensional sliding ferroelectrics, with their unique stacking degrees of freedom, offer a different approach to manipulate polarization by interlayer sliding. Bending sliding ferroelectrics inevitably leads to interlayer sliding motion, thus altering stacking orders and polarization properties. Here, by using machine-learning force field, we investigate the effects of bending deformation on geometries, stackings, energies, and polarizations in sliding ferroelectric bilayer h-BN and 3R-MoS2. We predict that bent ferroelectric bilayer forms irreversible kinks instead of arc when the bending angle exceeds a critical value. We demonstrate that the kinks originate from the competition between bending energy and interlayer van der Waals energy. The kink contains a ferroelectric domain wall that reverses the polarization, effectively inducing a flexoelectric effect. We term this phenomenon "sliding flexoelectricity" to distinguish it from conventional strain-gradient-induced flexoelectricity.