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 $U_{\mathrm{xx}}$ 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 $V_{\mathrm{xx}}$ 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 $V_{\mathrm{xx}}$ at unit filling by at least a factor of two relative to the dipolar R-stacked excitons. Despite slightly reduced $U_{\mathrm{xx}}$ , the enhanced $V_{\mathrm{xx}}$ 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.