Research Highlights

Sliding Ferroelectrcity and Moiré Ferroelectricity

The symmetry of the materials can be different from that of the constituent layer in van der Waals heterostructures. For example, we can introduce inversion symmetry breaking in a centrosymmetric crystal, which leads to exotic electromagnetic responses in the material. In this work, we demonstrated that we can artificially create ferroelectrics by controlling the stacking angle of non-ferroelectric bilayer boron nitride and transition metal dichalcogenides. 

Ferroelectricity is a property where a material possesses spontaneous electric polarization that can be switched by the application of an electric field. Using the van der Waals heterostructure, we realized one of the world's thinnest (less than one nanometer!) ferroelectric materials stable at room temperature. This holds promise for future applications as energy-efficient nonvolatile memory devices. 

In addition to the importance from the application standpoint, these novel ferroelectric materials possess several unique features. The out-of-plane electric polarization is switched through in-plane sliding motion between the layers, hence the name "sliding ferroelectricity." Furthermore, by twisting the two layers of 2D materials, they exhibit unprecedented moiré ferroelectricity, where up and down polarization is periodically arranged on the nanoscale.

See also:
K. Yasuda et al., Science 372, 1458–1462 (2021).
X. Wang*, K. Yasuda* et al., Nature Nanotechnology 17, 367–371 (2022).