2D spontaneous valley polarization from inversion symmetric single-layer lattices

Abstract 2D spontaneous valley polarization attracts great interest both for its fundamental physics and potential applications in advanced information technology, but it can only be obtained from inversion asymmetric single-layer crystals, while the possibility to create symmetric lattices remains unknown. Here, starting lattices, a general design principle realizing based on van der Waals interaction is mapped out. Using first-principles calculations, we further demonstrate feasibility of this real material T-FeCl 2 . More remarkably, such exhibits additional exotic out-of-plane ferroelectricity, which could manifest many distinctive properties, example, ferroelectricity-valley coupling magnetoelectric coupling. The explored design-guideline phenomena are applicable vast family materials. Our work not opens up platform valleytronic research also promises lattices.