Observation of Robust Interlayer Biexcitons in Twisted Homobilayer Superlattices

Abstract Moiré superlattices are formed by stacking 2D materials with a twist angle and have recently gained attention as a platform for investigating the interactions and correlations of moiré-trapped interlayer excitons (IXs). However, understanding these excitons remains challenging, as theoretical predictions suggest the existence of both parallel and antiparallel dipole-dipole interactions, while only repulsive interactions with a parallel configuration have been experimentally observed. Here, we investigate the localization of strain-induced moiré interlayer excitons in twisted transition metal dichalcogenide (TMDC) superlattices. Our results reveal that modulating the moiré trap in strain-engineered homobilayers leads to a higher density and emission efficiency of IXs, while also enhancing dipole-dipole interactions. In particular, we observe a transition in the nature of the moiré interlayer exciton-dipole interaction from repulsion to attraction in a twist-angle homostructure, resulting in a stable interlayer biexciton (IXX) phase with an antiparallel configuration, which had only been theoretically predicted before. Moreover, the moiré trap in homobilayers can be modulated by adjusting the spacing of the Au nanoarrays, which enabled us to achieve IXX emission up to 150 K, the highest temperature reported to date. This breakthrough is expected to pave the way for the observation of a Bose-Einstein condensate at room temperature. Our findings provide new opportunities for studying correlated many-body systems and have implications for developing novel optoelectronic devices and controllable nonlinear optics.