Ferroelectricity in parallel-stacked transition metal dichalcogenides

2D ferroelectrics have great potential for dense and low-consumption nonvolatile memory applications. Recent reports have shown robust out-of-plane polarization in parallel-stacked bilayer hBN and small-angle-twisted bilayer hBN, which is switchable through interlayer movement [1,2,3]. This method of building ferroelectrics out of non-ferroelectrics can be generalized to other bipartite materials, such as transition metal dichalcogenides (TMDs) [4]. The natural 2H phase of TMDs is centrosymmetric. Here, we demonstrate that robust ferroelectricity exists in parallel-stacked bilayer TMDs. The polarization of the bilayer is probed via an adjacent graphene layer. Our demonstration of ferroelectricity in stacking-engineered TMD bilayers consolidates the feasibility of engineering 2D ferroelectric semiconductors and opens up a broad way of engineering various functional heterostructures out of non-ferroelectrics.
[1] K. Yasuda et al., arXiv: 2010.06600
[2] C. R. Woods et al., arXiv: 2010.06914
[3] M. V. Stern et al., arXiv: 2010.05182
[4] L. Li et al., ACS Nano. 11, 6382 (2017)