Prediction of two-dimensional van der Waals ferroelectric materials

Based on density functional theory calculations, we discover a class of two-dimensional van der Waals ferroelectric materials with spontaneous out-of-plane electric polarization, and the orientation of the electric polarization can be reversed by a seemly lateral shift of a single atomic layer. We further find that the electronic structures of a bilayer of such two-dimensional ferroelectric materials can be switched to be either semiconducting or metallic, depending on their relative orientations of the electric polarization. This finding expand the family of the two-dimensional materials with ferroelectricity and offers new opportunities to tune the properties of van der Waals heterstructures for practical device applications.