Reconstruction of moir\'{e} lattices in twisted transition metal dichalcogenide bilayers

TL;DR

This paper investigates the structural relaxation and lattice reconstruction in twisted transition metal dichalcogenide bilayers, revealing significant moiré lattice changes and their impact on electronic properties, including flat bands and localized states.

Contribution

It introduces novel reconstructed moiré structures in twisted TMD bilayers and analyzes their effects on electronic band structures, especially at large twist angles.

Findings

Moiré lattice undergoes dramatic reconstruction for angles greater than ~58.4°.

Curved domain walls cause the lattice reconstruction due to three-fold symmetry.

Reconstructed lattices lead to flat bands and localized electronic states.

Abstract

An important step in understanding the exotic electronic, vibrational, and optical properties of the moir\'{e} lattices is the inclusion of the effects of structural relaxation of the un-relaxed moir\'{e} lattices. Here, we propose novel structures for twisted bilayer of transition metal dichalcogenides (TMDs). For $\theta\gtrsim 58.4^{\circ}$, we show a dramatic reconstruction of the moir\'{e} lattices, leading to a trimerization of the unfavorable stackings. We show that the development of curved domain walls due to the three-fold symmetry of the stacking energy landscape is responsible for such lattice reconstruction. Furthermore, we show that the lattice reconstruction notably changes the electronic band-structure. This includes the occurrence of flat bands near the edges of the conduction as well as valence bands, with the valence band maximum, in particular, corresponding to localized states enclosed by the trimer. We also find possibilities for other complicated, entropy stabilized, lattice reconstructed structures.