Kekulé Moiré Superlattices

Abstract

Moiré superlattices from stacks of van der Waals materials offer an exciting arena in the fields of condensed matter physics and materials science. Typically, these moiré superlattices consist of materials with identical or similar structures, and the long moiré period arises from a small twist angle or lattice mismatch. In this article, we discuss that long moiré period appears in a new moiré system by stacking two dissimilar van der Waals layers with large lattice mismatch, resulting in couplings between moiré 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 Kekulé distortion in graphene, and such reconstruction becomes nearly commensurate with the second layer. This Kekulé moiré 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 Néel vector direction, stacking geometry, and external fields. With one hole per moiré supercell, we predict that the system can become a Chern insulator, of which the topology is tunable by external fields.