Kekul\'e Moir\'e Superlattices

Abstract

Moir\'e superlattices from stacks of van der Waals materials offer an exciting arena in the fields of condensed matter physics and materials science. Typically, these moir\'e superlattices consist of materials with identical or similar structures, and the long moir\'e period arises from a small twist angle or lattice mismatch. In this article, we discuss that long moir\'e period appears in a new moir\'e system by stacking two dissimilar van der Waals layers with large lattice mismatch, resulting in couplings between moir\'e bands from remote valleys in the momentum space. In this system, the first layer is reconstructed using a $\sqrt{3}$ by $\sqrt{3}$ supercell that resembles the Kekul\'e distortion in graphene, and such reconstruction becomes nearly commensurate with the second layer. This Kekul\'e moir\'e superlattice is realized in heterostructures of transition metal dichalcogenides and metal phosphorus trichalcogenides such as MoTe$_2$/MnPSe$_3$. By first-principles calculations, we demonstrate that the antiferromagnetic MnPSe$_3$ strongly couples the otherwise degenerate Kramers' valleys of MoTe$_2$, resulting in valley pseudospin textures that depend on N\'eel vector direction, stacking geometry, and external fields. With one hole per moir\'e supercell, we predict that the system can become a Chern insulator, of which the topology is tunable by external fields.