Charge density waves and moiré reconstruction in twisted NbSe2/NbSe2 bilayers​

Twisted moiré bilayers are two-dimensional materials formed by stacking and rotating two monolayer materials. The lattice mismatch generated by such rotation generates a large moiré cell that can contain thousands of atoms and which can give rise to novel electronic properties. For instance, twisted moiré bilayers of semiconducting transition metal dichalcogenides have been found to host flat electronic bands and correlated electronic phases.

Here we focus on twisted bilayers of metallic NbSe2. On the one hand, the different local stacking arrangements in the moiré cell cause atomic relaxations (both in-plane and out-of-plane). On the other hand, monolayer NbSe2 exhibits spontaneous symmetry breaking into a charge density wave state with a 3x3 unit cell lattice reconstruction. In this project we use first-principles density functional theory calculations to study and understand the coexistence of these two types of atomic relaxation in twisted NbSe2 bilayers.