Coexisting charge density waves in twisted bilayer NbSe2

Monolayers of NbSe2, a metallic transition metal dichalcogenide (TMD), host charge density waves, which are symmetry broken states that lead to 3x3 unit cell atomic reconstructions. In this work, we performed large-scale first-principles density-functional theory calculations on twisted bilayers of NbSe2 to study the influence of a moiré superlattice on charge density waves.

On the one hand, we observe the usual long-range atomic relaxations observed in twisted bilayers of semiconducting TMDs. On the other hand, we found that different types of charge density waves coexist in the moiré unit cell. We found that the strain arising from the long-range atomic relaxations stabilize charge density waves which are metastable in the monolayer. Our analysis sheds light on the interactions between short-range symmetry broken states and long-range moiré relaxations, and can be tested experimentally with scanning tunneling microscopy.

[1] Christopher T. S. Cheung, Zachary A. H. Goodwin, Yixuan Han, Jiong Lu, Arash A. Mostofi, and Johannes Lischner Nano Letters 2024 24 (39), 12088-12094