Origin and Evolution of Ultraflatbands in Twisted Bilayer Transition Metal Dichalcogenides: Realization of Triangular Quantum Dot Array

TL;DR

This study investigates the origin and evolution of ultraflatbands in twisted bilayer MoS2, revealing distinct mechanisms at different twist angles and proposing their potential for creating ordered quantum dot arrays.

Contribution

It provides a detailed multiscale computational analysis of ultraflatbands in twisted bilayer MoS2, highlighting the absence of magic angles and the formation of quantum dot-like states at specific twist angles.

Findings

Ultraflatbands form near 0° and 60° twist angles with different origins.

At 0°, flatbands result from hybridization in the moiré superlattice.

At 60°, local strains create potential wells leading to quantum dot states.

Abstract

Using a multiscale computational approach, we probe the origin and evolution of ultraflatbands in moir\'e superlattices of twisted bilayer MoS$_2$, a prototypical transition metal dichalcogenide. Unlike twisted bilayer graphene, we find no unique magic angles in twisted bilayer MoS$_2$ for flatband formation. Ultraflatbands form at the valence band edge for twist angles ($\theta$) close to 0$^\circ$ and at both the valence and conduction band edges for $\theta$ close to 60$^\circ$, and have distinct origins. For$ \theta$ close to 0$^\circ$, inhomogeneous hybridization in the reconstructed moir\'e superlattice is sufficient to explain the formation of flatbands. For $\theta$ close to 60$^\circ$, additionally, local strains cause the formation of modulating triangular potential wells such that electrons and holes are spatially separated. This leads to multiple energy-separated ultraflatbands at the band edges closely resembling eigenfunctions of a quantum particle in an equilateral triangle well. Twisted bilayer transition metal dichalcogenides are thus suitable candidates for the realisation of ordered quantum dot array.