Two-Dimensional Ferroelastic Semiconductors in Nb2SiTe4 and Nb2GeTe4 with Promising Electronic Properties.

Two-dimensional crystals with coupling of ferroelasticity and attractive electronic properties offer unprecedented opportunities for achieving long-sought controllable devices. However, to date, the reported proposals are mainly based on hypothetical structures. Here, using first-principles calculations, we identify single-layer Nb2ATe4 (A = Si, Ge), which can be exfoliated from its layered bulk, as a promising candidate. Single-layer Nb2ATe4 is found to be dynamically, thermally, and chemically stable. It possesses excellent ferroelasticity with high reversible ferroelastic strain and a moderate ferroelastic transition energy barrier, which are beneficial for practical applications. Meanwhile, it harbors outstanding anisotropic electronic properties, including anisotropic carrier mobility and optical properties. More importantly, the anisotropic properties of single-layer Nb2ATe4 can be efficiently controlled through ferroelastic switching. These appealing properties combined with the experimental feasibility render single-layer Nb2ATe4 an extraordinary platform for realizing controllable devices.