Lateral heterophase electric polar topological superstructures of monolayer SnS: a first-principles computational study

Ferroelectric topological structures in two-dimensional (2D) materials have emerged as a promising platform for exploring novel topological electronic properties and applications. To date, the reported topological structures have been limited to single-phase 2D materials with spatially varying polarization distributions. Many 2D materials exhibit multiple ferroelectric phases; however, topological structures that combine these phases remain largely unexplored. This is significant because the coexistence of multiple phases plays a fundamental role in the ferroelectric properties of three-dimensional ferroelectrics. In this study, lateral heterophase superstructures (LHPSs) consisting of the α and δ phases of SnS are investigated using first-principles computational methods. A similar threefold bonding of the α and δ phases facilitates the formation of atomically sharp and stable morphotropic phase boundaries (MPBs) in one-dimensional (1D) LHPSs. The 2D-LHPS with a topological ferroelectric flux-closure can be designed, where the two rectangular and polarized structures (the α and δ phases) are assembled into square superstructures, exhibiting distinctive nested flux-closure polarization patterns. This work extends the family of ferroelectric topological structures to encompass 2D ferroelectric materials, contributing to the advancement of miniaturized and highly integrated ferroelectric topological electronics.