Two-dimensional ferroelastic topological insulators in single-layer Janus transition metal dichalcogenides MSSe(M=Mo,W)

Two-dimensional topological insulators and two-dimensional materials with\nferroelastic characteristics are intriguing materials and many examples have\nbeen reported both experimentally and theoretically. Here, we present the\ncombination of both features - a two-dimensional ferroelastic topological\ninsulator that simultaneously possesses ferroelastic and quantum spin Hall\ncharacteristics. Using first-principles calculations, we demonstrate Janus\nsingle-layer MSSe (M=Mo, W) stable two-dimensional crystals that show the\nlong-sought ferroelastic topological insulator properties. The material\nfeatures low switching barriers and strong ferroelastic signals, beneficial for\napplications in nonvolatile memory devices. Moreover, their topological phases\nharbor sizeable nontrivial band gaps, which supports the quantum spin Hall\neffect. The unique coexistence of excellent ferroelastic and quantum spin Hall\nphases in single-layer MSSe provides extraordinary platforms for realizing\nmulti-purpose and controllable devices.\n