Abstract

Atomically-thin moiré superlattices offer an optically accessible platform for interacting bosons, where strong onsite repulsion Uxx 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 strengthening the intersite exciton repulsion Vxx between neighboring moiré cells offers a distinct route to stabilizing unit-filling excitonic Mott states. In H-stacked WSe₂/WS2, moiré confinement endows interlayer excitons with an out-of-plane dipole and a pronounced in-plane quadrupolar charge distribution. Helicity-resolved transient photoluminescence, supported by first-principles-informed modelling, reveals that this quadrupolar geometry increases Vxx at unit filling by at least a factor of two relative to the dipolar R-stacked excitons. Despite a slight reduction in Uxx, the enhanced Vxx yields a long-lived, 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, the same 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 in solids.

Abstract

Atomically-thin moiré superlattices offer an optically accessible platform for interacting bosons, where strong onsite repulsion Uxx 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 strengthening the intersite exciton repulsion Vxx between neighboring moiré cells offers a distinct route to stabilizing unit-filling excitonic Mott states. In H-stacked WSe₂/WS2, moiré confinement endows interlayer excitons with an out-of-plane dipole and a pronounced in-plane quadrupolar charge distribution. Helicity-resolved transient photoluminescence, supported by first-principles-informed modelling, reveals that this quadrupolar geometry increases Vxx at unit filling by at least a factor of two relative to the dipolar R-stacked excitons. Despite a slight reduction in Uxx, the enhanced Vxx yields a long-lived, 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, the same 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 in solids.

Abstract

Atomically-thin moiré superlattices offer an optically accessible platform for interacting bosons, where strong onsite repulsion Uxx 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 strengthening the intersite exciton repulsion Vxx between neighboring moiré cells offers a distinct route to stabilizing unit-filling excitonic Mott states. In H-stacked WSe₂/WS2, moiré confinement endows interlayer excitons with an out-of-plane dipole and a pronounced in-plane quadrupolar charge distribution. Helicity-resolved transient photoluminescence, supported by first-principles-informed modelling, reveals that this quadrupolar geometry increases Vxx at unit filling by at least a factor of two relative to the dipolar R-stacked excitons. Despite a slight reduction in Uxx, the enhanced Vxx yields a long-lived, 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, the same 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 in solids.

Abstract

Atomically-thin moiré superlattices offer an optically accessible platform for interacting bosons, where strong onsite repulsion Uxx 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 strengthening the intersite exciton repulsion Vxx between neighboring moiré cells offers a distinct route to stabilizing unit-filling excitonic Mott states. In H-stacked WSe₂/WS2, moiré confinement endows interlayer excitons with an out-of-plane dipole and a pronounced in-plane quadrupolar charge distribution. Helicity-resolved transient photoluminescence, supported by first-principles-informed modelling, reveals that this quadrupolar geometry increases Vxx at unit filling by at least a factor of two relative to the dipolar R-stacked excitons. Despite a slight reduction in Uxx, the enhanced Vxx yields a long-lived, 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, the same 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 in solids.