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 $1T\text{\ensuremath{-}}{\mathrm{TaTe}}_{2}$, including the high-symmetry phase and various charge density wave (CDW) phases ($3\ifmmode\times\else\texttimes\fi{}1, 4\ifmmode\times\else\texttimes\fi{}1, 3\ifmmode\times\else\texttimes\fi{}3, 2\sqrt{3}\ifmmode\times\else\texttimes\fi{}2\sqrt{3}, \sqrt{13}\ifmmode\times\else\texttimes\fi{}\sqrt{13}, 4\ifmmode\times\else\texttimes\fi{}4$, and $\sqrt{19}\ifmmode\times\else\texttimes\fi{}\sqrt{19}$) 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 $4\ifmmode\times\else\texttimes\fi{}4$ CDW phase with the second lowest total energy exhibits a novel topological insulating state, while the $3\ifmmode\times\else\texttimes\fi{}3$ 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 $4\ifmmode\times\else\texttimes\fi{}4$ CDW becomes the most energetically stable state followed by the $3\ifmmode\times\else\texttimes\fi{}3$ CDW phase. These findings show the rich landscape of structures and properties of $1T\text{\ensuremath{-}}{\mathrm{TaTe}}_{2}$, which will strongly stimulate further investigations and lay the foundation for the development of new electronic devices.