Interfacial ferroelectricity in stacking-engineered van der Waals materials

Ultrathin ferroelectrics have great potential in the creation of non-volatile memory devices with compact volume and low energy consumption. Different from the conventional top-down approach of thinning down bulk polar materials, the bottom-up approach based on van der Waals assembly can engineer 2D ferroelectrics out of non-ferroelectric parent compounds. 

By cutting one monolayer boron nitride (BN) in half and stacking them in parallel, we engineer an inversion-symmetry broken bilayer BN that hosts out-of-plane polarization. This polarization can be switched by an out-of-plane electric field through the in-plane sliding motion between the BN layers[1]. We further generalize this interfacial ferroelectricity concept to bilayer transition metal dichalcogenides[2]. We probe the polarization switching in these stacking-engineered ferroelectrics by an adjacent graphene sensor layer and visualize the switching using piezoelectric force microscopy. Besides real space ferroelectricity engineering, we demonstrate the ability to engineer material band structures in the reciprocal space. When a small twist angle is introduced to the ferroelectric BN bilayer, the staggered out-of-plane polarizations in twisted BN constitute a moiré ferroelectric substrate that can modify band structures of the target material which senses the moiré potential.

[1] K. Yasuda et al., Science 372, 1458–1462 (2021).

[2] X. Wang et al., Nat. Nano. 17, 367–371 (2022).