Substrate effects on the in-plane ferroelectric polarization of two-dimensional SnTe

Recent experiments confirm that two-dimensional (2D) SnTe films possess strong in-plane ferroelectricity. For controlling or improving this 2D ferroelectricity, the substrate effects should be a prevailing concern. In this work first-principle calculations are performed to investigate the substrate effects on the ferroelectric polarization in this 2D system. Our results indicate that suitable substrates can significantly enhance the ferroelectricity of 2D SnTe. We investigated a series of metals, semiconductors, and insulator materials used as the substrates (Ni, Pd, Pt, Si, Ge, CaO, MgO, etc.), which have different interaction types and bonding strength with the 2D SnTe. For these SnTe/substrate heterostructures, both geometric and electronic structures are explored. It is found that in Pt- and MgO-supported SnTe films, the in-plane polar displacement is significantly enhanced, which can be understood under the theory of lone-pair electrons. Importantly, the substrates show very interesting controlling behaviors for the ferroelectricity of SnTe originating from electronic level, such as enhancing ferroelectric polarization and inducing magnetism. In SnTe/MgO(001) heterostructure, substrate-enhanced ferroelectricity is discussed in detail. In addition, substrate-induced magnetism of SnTe films is observed in Ni-supported SnTe, which indicates a possible scheme to obtain the multiferroics in 2D SnTe. This study suggests that it is a potential method to tune the ferroelectricity of 2D SnTe films by different substrates.