PNNL

Abstract

Excitons, Coulomb bound electron-hole pairs, play a fundamental role in both optical excitation and correlated phenomena in solids1. When an exciton interacts with other quasi-particles, few- and many-body excited states, such as trions2-4, exciton Fermi-polarons5, Mahan excitons6, and other exotic excitonic phases7-9 will appear. Here, we report a new interaction between exciton and charges enabled by unusual quantum confinement in 2D moiré superlattices, which results in novel exciton many-body ground states composed of moiré excitons and correlated electron lattices. Unique to H-stacked (or 60o-twisted) WS2/WSe2 heterobilayer, we found that the interlayer atomic registry and moiré structural reconstruction lead to distinct spatial distribution for the frontier conduction and valence bands in WS2 and WSe2, respectively. This gives rise to interlayer moiré excitons (IMEs) with a novel 3D structure, i.e., the hole in one layer is surrounded by its partner electron’s wavefunction spread among three adjacent moiré traps in another layer. Thus, this new type of IME can possess large in-plane electrical quadrupole moments in addition to the vertical dipole. Upon doping, the electric quadrupole enables the binding of IME to the charges in neighboring moiré cells, forming an intercell charged exciton complex distinct from trions2-4. The exciton complex is unveiled by the IME photoluminescence energy jumps when the electron lattices form at both fractional and integer fillings of moiré minibands, with replica like spectral features between successive integer moiré fillings. Our work provides the framework in understanding and engineering novel exciton many-body states in moiré superlattices with correlated charge orders.