Sen Shao, Wei-Chi Chiu, et al.

Physical Review Letters 136, 156101 (2026)

Chiral charge-density-wave order can emerge from relative phases of CDW vectors between adjacent layers. Using first-principles calculations, we showed that this overlooked interlayer phase degree of freedom drives chiral structural distortions, reproduces measured electronic and optical responses, and offers a route to tune chirality through electron filling.

ACS Nano 19 (19), 18108-18116 (2025)

Emergence of topological states in strongly correlated systems, particularly two- dimensional (2D) transition-metal dichalcogenides, presents unique opportunities for manipulating electronic properties in quantum materials. However, a comprehensive understanding of the intricate interplay between correlations and topology remains elusive. Here we employ first-principles modeling to reveal two distinct 2×2 charge density wave (CDW) phases in monolayer 1H-NbSe2, which become energetically favorable over the conventional 3×3 CDWs under modest biaxial tensile strain of about 1%. These strain-induced CDW phases coexist with numerous topological states characterized by Z2 topology, high mirror Chern numbers, topological nodal lines, and higher-order topo- logical states, which we have verified rigorously by computing the topological indices and the presence of robust edge states and localized corner states. Remarkably, these topological properties emerge because of the CDW rather than a pre-existing topology in the pristine phase. Our findings advance the fundamental understanding of the interplay between correlations, topology, and geometry in 2D materials, opening new opportunities to engineer topological states through strain-induced correlation effects in materials with initially trivial topology. These results hold promise for applications in electronics, spintronics, and other advanced quantum devices, where robust and tunable topological states are crucial.