Stabilizing Phosphorene-Like Group IV-VI Compounds via van der Waals Imprinting for Multistate Ferroelectricity and Tunable Spin Transport

Layered group IV-VI compounds (i.e., SnSe, SnS, GeSe, and GeS) in the puckered structure resembling black-phosphorene (BlackP) have attracted increasing interest because of their intriguing ferroic orders and outstanding thermoelectric properties. By invoking the guiding principles of isovalency and isomorphism for promoting van der Waals epitaxy, and based on comprehensive first-principles calculations, here it is shown that the typically metastable BlackP-like GeTe can be readily stabilized on the (001) surface of isostructural SnSe. Importantly, the ferroelectricity of such a BlackP-like GeTe monolayer can be substantially enhanced compared to the freestanding state, due to the substrate enlarged in-plane polar displacements. The GeTe/SnSe heterobilayer exhibits multiple ferroelectric/ferrielectric polarization states, which can be exploited for high-density memory devices. These mutually switchable polarization states are also shown to be internally locked with the spin polarization of the valence/conduction bands with pronounced Rashba spin-orbit splitting and Berry curvature dipole. These findings highlight the intuitive yet enabling power of van der Waals imprinting in growing novel 2D materials for enriched functionalities. The enabling power of van der Waals imprinting is invoked to stabilize metastable group IV-VI compounds, as exemplified by the Black-phosphorene-like puckered GeTe on the (001) surface of the isostructural ground-state phase of SnSe. Remarkably, the as-grown IV-VI heterostructures harbor significantly enhanced spontaneous polarization and multistate ferro-/ferri-electricity compelling for next-generation memory devices, as well as polarization-tunable persistent spin helix state and Berry curvature dipole promising for achieving coherent spin transport and nonlinear Hall effect. image