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.

Twisted van der Waals Quantum Materials: Fundamentals, Tunability, and Applications

“…The moiré excitons are produced from the periodic moiré potentials trapped interlayer excitons, , which inherit the spatially separated electrons and holes, exhibiting a permanent dipole moment, therefore providing an opportunity for studying many-body interactions and facilitating the strong correlation in the system. The dipole–dipole repulsive interactions among IXs have been widely reported in recent years, ,, which plays a crucial role in observing novel quantum phenomena such as superfluid, dipolar gases and dipolar crystals. − The effective long-range dipolar interactions can drive the system from the free-moving particles to a highly coherent aligned state, thus therefore to reach the exotic quantum phases.…”

Giant built-in electric field enabled quantum-confined Stark effects

“…Since built-in electric fields also influence the dominant relaxation pathways, manybody interactions and exciton correlations 1,23,24 ; lifetime and exciton diffusion characterizations of 1L WSe2 and HS were performed under different optical powers (Figure 3d-f and S8). As the power increases, the radiative lifetime (τ) of 1L WSe2 decreases, reaching 0.424 ns at 121.98 μW.…”