Topological mosaic in Moir\'e superlattices of van der Waals heterobilayers

TL;DR

This paper demonstrates that Moiré superlattices in van der Waals heterobilayers of massive Dirac materials can host periodic topological phase modulations, enabling electrically tunable topological insulator and normal insulator regions with protected edge modes.

Contribution

It reveals a new topological mosaic pattern in Moiré superlattices and shows how to control topological phases via interlayer bias in vdW heterostructures.

Findings

Moiré superlattices can induce local topological order variations.

Interlayer bias can switch heterobilayers between topological and normal insulator phases.

Topologically protected helical modes exist at phase boundaries.

Abstract

Van der Waals (vdW) heterostructures formed by 2D atomic crystals provide a powerful approach towards designer condensed matter systems. Incommensurate heterobilayers with small twisting and/or lattice mismatch lead to the interesting concept of Moir\'e superlattice, where the atomic registry is locally indistinguishable from commensurate bilayers but has local-to-local variation over long range. Here we show that such Moir\'e superlattice can lead to periodic modulation of local topological order in vdW heterobilayers formed by two massive Dirac materials. By tuning the vdW heterojunction from normal to the inverted type-II regime via an interlayer bias, the commensurate heterobilayer can become a topological insulator (TI), depending on the interlayer hybridization controlled by the atomic registry between the vdW layers. This results in mosaic pattern of TI regions and normal insulator (NI) regions in Moir\'e superlattices, where topologically protected helical modes exist at the TI/NI phase boundaries. By using symmetry based k.p and tight-binding models, we predict that this topological phenomenon can be present in inverted transition metal dichalcogenides heterobilayers. Our work points to a new means of realizing programmable and electrically switchable topological superstructures from 2D arrays of TI nano-dots to 1D arrays of TI nano-stripes.