Two-dimensional (2D) ferroelectrics with robust polarization down to atomic thicknesses provide building blocks for functional heterostructures. Experimental realization remains challenging because of the requirement of a layered polar crystal. Here, we demonstrate a rational design approach to engineering 2D ferroelectrics from a nonferroelectric parent compound by using van der Waals assembly. Parallel-stacked bilayer boron nitride exhibits out-of-plane electric polarization that reverses depending on the stacking order. The polarization switching is probed through the resistance of an adjacently stacked graphene sheet. Twisting the boron nitride sheets by a small angle changes the dynamics of switching because of the formation of moiré ferroelectricity with staggered polarization. The ferroelectricity persists to room temperature while keeping the high mobility of graphene, paving the way for potential ultrathin nonvolatile memory applications.

具有低至原子厚度的稳健极化的二维 (2D) 铁电体为功能异质结构提供了构建模块。由于需要分层极性晶体，实验实现仍然具有挑战性。在这里，我们展示了一种合理的设计方法，通过使用范德瓦尔斯组装从非铁电母体化合物设计 2D 铁电体。平行堆叠的双层氮化硼表现出面外电极化，其反转取决于堆叠顺序。通过相邻堆叠的石墨烯片的电阻来探测极化切换。由于形成具有交错极化的莫尔铁电，将氮化硼片以小角度扭转会改变开关的动力学。