Oral: Incognizant 1T/1H charge-density wave in monolayer NbTe₂

In this talk we'll focus on the charge-density waves (CDWs) in monolayer NbTe₂ system. While experimental realization of multiple CDWs has been ascribed to monolayer 1T-NbTe₂, their atomic structures are still largely unclear, preventing deep understanding of their novel electronic structures. Here, comparing first-principles-calculated orbital textures with the reported STM measurements, we successfully identify the atomic structures of multiple CDWs in monolayer NbTe₂. Surprisingly, we reveal that both 1T and 1H phases could exist in the CDWs of monolayer NbTe₂, 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 external field and results in CDW-induced quantum phase transitions from Kramers-Weyl fermion to topological insulator in 1T stacking. Our study suggests NbTe₂ as an exotic platform to investigate the interplay between CDW, SDW, and topological phases, which are largely unexplored in current experiments.