Quadrupolar Excitons and Hybridized Interlayer Mott Insulator in a Trilayer Moir\'e Superlattice

TL;DR

This paper reports the discovery of quadrupolar excitons and an interlayer Mott insulator in a symmetric trilayer moiré superlattice, revealing new correlated states and electric field tunability in TMDC heterostructures.

Contribution

It introduces quadrupolar excitons in a symmetric trilayer moiré system and demonstrates their hybridization with flatbands, along with the realization of an interlayer Mott insulator state.

Findings

Quadrupolar excitons show quadratic Stark shift, unlike dipolar excitons.

Interlayer Mott insulator state with tunable hole occupation.

Electric field induces transition from quadrupolar to dipolar excitons.

Abstract

Transition metal dichalcogenide (TMDC) moir\'e superlattices, owing to the moir\'e flatbands and strong correlation, can host periodic electron crystals and fascinating correlated physics. The TMDC heterojunctions in the type-II alignment also enable long-lived interlayer excitons that are promising for correlated bosonic states, while the interaction is dictated by the asymmetry of the heterojunction. Here we demonstrate a new excitonic state, quadrupolar exciton, in a symmetric WSe2-WS2-WSe2 trilayer moir\'e superlattice. The quadrupolar excitons exhibit a quadratic dependence on the electric field, distinctively different from the linear Stark shift of the dipolar excitons in heterobilayers. This quadrupolar exciton stems from the hybridization of WSe2 valence moir\'e flatbands. The same mechanism also gives rise to an interlayer Mott insulator state, in which the two WSe2 layers share one hole laterally confined in one moir\'e unit cell. In contrast, the hole occupation probability in each layer can be continuously tuned via an out-of-plane electric field, reaching 100% in the top or bottom WSe2 under a large electric field, accompanying the transition from quadrupolar excitons to dipolar excitons. Our work demonstrates a trilayer moir\'e system as a new exciting playground for realizing novel correlated states and engineering quantum phase transitions.