Moir\'e Modulation of Charge Density Waves

TL;DR

This paper explores how moiré patterns in twisted bilayer TMDs influence the behavior and phase of charge density waves, revealing complex interactions dependent on twist angle and CDW period.

Contribution

It provides a theoretical analysis of the interplay between moiré superlattices and various CDW phases in twisted bilayer TMDs, predicting specific domain structures and phase behaviors.

Findings

No geometric constraint for $\, ext{sqrt{3}}\times\text{sqrt{3}}$ CDWs.

Destruction of CDW phase in domain walls for $2\times2$ CDWs.

Formation of moiré-scale structures near 180° twist for $3\times3$ CDWs.

Abstract

Here we investigate how charge density waves (CDW), inherent to a monolayer, are effected by creating twisted van der Waals structures. Homobilayers of metallic transition metal dichalcogenides (TMDs), at small twist angles where there is significant atomic reconstruction, are utilised as an example to investigate the interplay between the moir\'e domain structure and CDWs of different periods. For $\sqrt{3}\times\sqrt{3}$ CDWs, there is no geometric constraint to prevent the CDWs from propagating throughout the moir\'e structure. Whereas for $2\times2$ CDWs, to ensure the CDWs in each layer have the most favourable interactions in the domains, the CDW phase must be destroyed in the connecting domain walls. For $3\times3$ CDWs with twist angles close to 180 degree, moir\'e-scale triangular structures can form; while close to 0 degree, moir\'e-scale dimer domains occur. The star-of-David CDW ($\sqrt{13}\times\sqrt{13}$) is found to host CDWs in the domains only, since there is one low energy stacking configuration, similar to $2\times2$ CDWs. These predictions are offered for experimental verification in twisted bilayer metallic TMDs which host CDWs, and we hope this will stimulate further research on the interplay between the moir\'e supperlattice and CDW phases intrinsic to the comprising 2D materials.