Diverse and Tunable Charge Density Waves, Superconductivity, and Band Topology in Two-dimensional 1T-M₂S (M = Zr, Hf)

Nowadays, understanding the competition and coexistence of multiple phases in 2D materials is crucial. In this work, the competition and coexistence of charge density waves (CDW), superconductivity, and nontrivial topology in a new kind of 2D material 1T-M₂S with M = Zr, Hf are investigated, which are CDW materials. On one hand, 2 × 2 CDW ground state and superconductivity coexist, and the CDW phase can be eliminated by anharmonic effect at room temperature. On the other hand, under biaxial compressive strain, weak and strong competitive interactions in Zr₂S and Hf₂S are discovered, respectively, which also display the coexistence of superconductivity and non-trivial topological properties. By solving the anisotropic Eliashberg equations, the strained Zr₂S and Hf₂S are demonstrated to be anisotropic single-gap superconductors. These findings provide valuable perspectives to understand the complex interaction between CDW and superconductivity and the interplay of exotic quantum states in 2D materials.