Intercell Moir\'e Exciton Complexes in Electron Lattices

TL;DR

This paper uncovers a new type of exciton many-body state in 2D moiré superlattices, driven by unique quantum confinement and charge interactions, revealing complex exciton-charge phenomena in correlated electron lattices.

Contribution

It introduces a novel interlayer moiré exciton and its many-body interactions with charges in twisted 2D heterobilayers, expanding understanding of exciton physics in moiré materials.

Findings

Discovery of interlayer moiré excitons with 3D structure

Observation of exciton energy jumps at moiré miniband fillings

Identification of exciton-charge bound complexes facilitated by quadrupole moments

Abstract

Excitons, Coulomb-bound electron-hole pairs, play a fundamental role in both optical excitation and correlated phenomena in solids. When an exciton interacts with other quasi-particles, few- and many-body excited states, such as trions, exciton Fermi-polarons, Mahan excitons can appear. Here, we report a new interaction between exciton and charges enabled by unusual quantum confinement in 2D moir\'e superlattices, which results in novel exciton many-body ground states composed of moir\'e excitons and correlated electron lattices. Unique to H-stacked (or 60o-twisted) WS2/WSe2 heterobilayer, we found that the interlayer atomic registry and moir\'e structural reconstruction leads to an interlayer moir\'e exciton (IME) whose hole in one layer is surrounded by its partner electron's wavefunction spread among three adjacent moir\'e traps in the other layer. This 3D excitonic structure can enable large in-plane electrical quadrupole moments in addition to the vertical dipole. Upon doping, the electric quadrupole facilitates the binding of IME to the charges in neighboring moir\'e cells, forming an intercell charged exciton complex. The exciton complex is unveiled by the IME photoluminescence energy jumps when the electron lattices form at both fractional and integer-filled moir\'e minibands, with replica-like spectral features between successive integer moir\'e fillings. Our work provides the framework in understanding and engineering emergent exciton many-body states in correlated moir\'e charge orders.