Designing Structural Frustrations in Trilayer Moiré Superlattices

Moiré superlattices in small-angle twisted bilayer transition metal dichalcogenides (TMDs) undergo significant structural reconstructions that give rise to flat electronic bands. These reconstruction-driven flat bands, in turn, lead to correlated electronic phases, emergent magnetism, and novel excitonic phenomena that have been intensively explored over the past decade. Structural reconstructions in two-dimensional systems can be broadly categorized as (i) bilayers with identical lattice constants or (ii) bilayers composed of layers with different lattice constants. Here, using first-principles calculations, we demonstrate a new class of structural reconstructions realized in a frustrated trilayer system, where the middle layer simultaneously competes with two distinct superlattices formed with the bottom and top layers. We show that this frustrated configuration induces enhanced strain modulation in the middle layer and yields flatter electronic bands with unique electron localization distinct from those of individual twisted bilayers. Our results establish structurally frustrated trilayers as a promising new platform for exploring correlated phenomena in multilayer moiré materials.