Polymorphic charge density waves, magnetism, and topologies in 1T−TaTe2

Polymorphism in two-dimensional (2D) materials presents a fertile ground for introducing new functionalities and designing novel architectures. Here, using first-principles calculations, we investigate the polymorphs of monolayer 1T-TaTe₂, including the high-symmetry phase and various charge density wave (CDW) phases ($3×{}1, 4×{}1, 3×{}3, 2√3×{}2√3, √13×{}√13, 4×{}4$, and $√19×{}√19$) with diverse physical properties. The high-symmetry $1T$ phase is predicted to be a quantum anomalous Hall metal with ferromagnetism. However, after undergoing the CDW phase transitions, the ferromagnetism vanishes and the nontrivial topological properties are also altered. Particularly, the 4×4 CDW phase with the second lowest total energy exhibits a novel topological insulating state, while the 3×3 CDW phase, possessing the lowest total energy, behaves as a normal metal. We further propose that charge doping can effectively modulate the relative stability of the CDW phases. Upon introducing slight hole doping, the 4×4 CDW becomes the most energetically stable state followed by the 3×3 CDW phase. These findings show the rich landscape of structures and properties of 1T-TaTe₂, which will strongly stimulate further investigations and lay the foundation for the development of new electronic devices.