Correlated interlayer exciton insulator in heterostructures of monolayer WSe2 and moiré WS2/WSe2

Moiré superlattices in van der Waals heterostructures have emerged as a powerful tool for engineering quantum phenomena. Here we report the observation of a correlated interlayer exciton insulator in a double-layer heterostructure composed of a WSe2 monolayer and a WS2/WSe2 moiré bilayer that are separated by ultrathin hexagonal boron nitride. The moiré WS2/WSe2 bilayer features a Mott insulator state when the density of holes is one per moiré lattice site. When electrons are added to the Mott insulator in the WS2/WSe2 moiré bilayer and an equal number of holes are injected into the WSe2 monolayer, a new interlayer exciton insulator emerges with the holes in the WSe2 monolayer and the electrons in the doped Mott insulator bound together through interlayer Coulomb interactions. The interlayer exciton insulator is stable up to a critical hole density in the WSe2 monolayer, beyond which the interlayer exciton dissociates. Our study highlights the opportunities for realizing quantum phases in double-layer moiré systems due to the interplay between the moiré flat band and strong interlayer electron interactions. When independent layers of electrons and holes are in close proximity to each other, their Coulomb interaction allows them to pair into neutral bosons and form an insulating state. This phenomenon is reported in a heterostructure of 2D materials.