Robust valley-polarized excitonic Mott states and doublons enabled by stacking-controlled moiré geometry

Atomically-thin moiré superlattices offer a platform for interacting bosons, where strong onsite repulsion U_xx suppresses double occupancy and supports excitonic Mott states at unit filling. However, moiré confinement also enhances phonon- and disorder-assisted relaxation, challenging the robustness of these correlated states under dissipation. Here we show that stronger intersite exciton repulsion V_xx stabilizes these states. In H-stacked WSe2/WS2, moiré confinement endows interlayer excitons with an out-of-plane dipole and in-plane quadrupolar character. Helicity-resolved transient photoluminescence, supported by first-principles–informed modeling, reveals that this quadrupolar geometry increases V_xx at unit filling by at least a factor of two relative to the dipolar R-stacked excitons. Despite slightly reduced U_xx, the enhanced V_xx yields a valley-polarized excitonic Mott state at unit filling that persists for ~12 ns—more than twice as long as in R-stacks—and remains robust up to ~50 K. Beyond unit filling, this geometry supports valley-polarized doublons with fourfold longer lifetimes than in R-stacks. These results establish moiré-geometric control of intersite interactions as a route to stabilizing excitonic Mott states and doublons against dissipation. Stacking registry can reshape moiré exciton wavefunctions. Here, the authors show that H- and R-stacked WSe₂/WS₂ heterobilayers exhibit distinct intersite interaction strengths which control the robustness of a unit-filled exciton Mott state and the stability of doublons.