Attractive and Repulsive Dipolar Interactions in Semiconductor van der Waals Heterotrilayers

Single-atom thick layers of transition metal dichalcogenides (TMD monolayers) have emerged as a promising platform for investigating quantum many-body physics through the study of interactions between their optical excitations. A key feature of TMD monolayers is their direct band-gap, which allows for efficient optical generation of excitons. Heterobilayers made by stacking two monolayers of different TMDs can host optically active interlayer excitons (IXs), where the electron and hole occupy different layers. Previous work has shown that heterobilayer IXs share a mutually parallel permanent electric dipole and therefore interact via dipole-dipole repulsion. In this work we show that, unlike in heterobilayers, heterotrilayer TMD structures show both attractive and repulsive dipole-dipole interactions because they allow for IXs with both parallel and antiparallel dipole arrangements. These findings are a step towards understanding more complicated quantum many-body states that have been predicted for these systems, including exciton lattices and droplets.