Incognizant 1T/1H Charge-Density-Wave Phases in Monolayer NbTe₂

Abstract

While experimental realization of multiple charge-density waves (CDWs) has been ascribed to monolayer 1T-NbTe 2 , their atomic structures are still largely unclear, preventing a deep understanding of their novel electronic structures. Here, comparing first-principles-calculated orbital textures with reported STM measurements, we successfully identify multiple CDWs in monolayer NbTe 2 . Surprisingly, we reveal that both 1T/ 1H phases could exist in monolayer NbTe 2 , which was incognizant before. Particularly, we find that the experimentally observed 4 × 1 and 4 × 4 CDWs could be attributed to 1H stacking, while the observed × 19 19 phase could possess 1T stacking. The existence of 1T/1H phases results in competition between CDW, spin-density wave (SDW), and ferromagnetism in 1H stacking under an external field and results in CDW-induced quantum phase transitions from a Kramers−Weyl fermion to a topological insulator in 1T stacking. Our study suggests NbTe 2 as an exotic platform to investigate the interplay between CDW, SDW, and topological phases, which are largely unexplored in current experiments.