Reproduced out-of-plane ferroelectricity in monolayer SnTe van der Waals heterostructures.

Due to the shrinking in size of nonvolatile memory devices, the two-dimensional ferroelectric van der Waals (vdW) heterostructures have received huge attention. However, it is still difficult to maintain the out-of-plane (OOP) ferroelectricity. In this work, we have theoretically investigated the relationship between the ferroelectricity and the strain of bulk and few-layer SnTe by first-principles calculations. The results indicate that the-SnTe can exist stably within the strain between -6% and 6%, and the complete OOP polarization occurs within the strain between -4% and -2%. Unfortunately, the OOP polarization disappears while the bulk-SnTe is thinned to a few layers. However, the complete OOP polarization recurs in monolayer SnTe/PbSe vdW heterostructures, which is due to the strong interface coupling. Our findings provide an effective way to enhance ferroelectric performance, which is beneficial for the design of ultra-thin ferroelectric devices.