Transition metal dichalcogenide (TMDC) moiré superlattices, owing to the moiré 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 moiré 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 moiré 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 moiré 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 moiré system as a new exciting playground for realizing novel correlated states and engineering quantum phase transitions.

过渡金属二硫属化物（TMDC）莫尔超晶格，由于莫尔平带和强相关性，可以容纳周期性电子晶体和令人着迷的相关物理。 II 型排列中的 TMDC 异质结还能够实现长寿命的层间激子，这有望实现相关玻色子态，而相互作用则由异质结的不对称性决定。在这里，我们在对称的WSe ₂ -WS ₂ -WSe ₂三层莫尔超晶格中展示了一种新的激子态，四极激子。四极激子表现出对电场的二次依赖性，与异双层中偶极激子的线性斯塔克位移明显不同。该四极激子源自WSe ₂价莫尔平带的杂化。相同的机制还产生层间莫特绝缘体状态，其中两个WSe ₂层共享一个横向限制在一个莫尔晶胞中的孔。相比之下，每层中的空穴占据概率可以通过面外电场连续调节，在大电场下在顶部或底部WSe ₂中达到100%，伴随着从四极激子到偶极激子的转变。我们的工作展示了三层莫尔系统作为实现新颖相关态和工程量子相变的新的令人兴奋的游乐场。