Quadrupolar excitons and hybridized interlayer Mott insulator in a trilayer moiré superlattice

Abstract

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.

Dipolar interactions enhanced by two-dimensional dielectric screening in few-layer van der Waals structures

“…The formed IX can have an electric dipole pointing upward or downward, or can be in their coherent superposition which has zero electric dipole but a finite electric quadrupole, see illustrations in figure 3(a). Such quadrupolar excitons have been realized and detected in a series of recent experiments [25,[45][46][47]. In this section, we investigate the effects of 2D dielectric screening on the related dipolar and quadrupolar interactions in trilayer TMDs.…”

Excitonic Complexes in Two-Dimensional Transition Metal Dichalcogenides

“…Recently, a quadrupolar exciton state (Fig. 2e ), which is composed of an electron in the middle layer and a hole delocalized between the top layer and the bottom layer 28 was reported in angle-aligned TMDC heterotrilayers 29 – 33 . PL spectra suggest that the quadrupolar exciton exhibits an energy shift as a quadratic function of the out-of-plane electric field, in stark contrast to the linear energy shift expected from dipolar interlayer excitons in heterobilayers.…”

“…Bottom: PL spectra as a function of the out-of-plane electric field from a WSe 2 /WS 2 /WSe 2 hetero-trilayer at 10 K. Reproduced from ref. 29 under a Creative Common license ( http://creativecommons.org/licenses/by/4.0/ ). f Top: schematic of the three-level hybridized excitons in trilayer WSe 2 /monolayer WS 2 moiré superlattices.…”

DNA as a perfect quantum computer based on the quantum physics principles

“…In addition to Cooper pairs, condensation phenomena of different types of bosonic systems have been described, such as ultracold atoms 79 , magnons 79 , excitons 80 , 81 , and surface plasmons 82 , 83 . Some conditions must be met for the A-T or C-G system proposed here to be a candidate for BEC.…”