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.