Correlated interlayer exciton insulator in double layers of monolayer WSe2 and moir\'e WS2/WSe2

TL;DR

This paper reports the discovery of a correlated interlayer exciton insulator in a double-layer heterostructure combining WSe2 monolayer and moiré WS2/WSe2 bilayer, revealing new quantum phases driven by moiré flat bands and interlayer interactions.

Contribution

It demonstrates the formation of a stable interlayer exciton insulator in a moiré heterostructure with strong interlayer Coulomb interactions, a novel quantum phase not previously observed.

Findings

Observation of a Mott insulator state at hole density p/p0=1 in WS2/WSe2 bilayer.

Emergence of a stable interlayer exciton insulator at specific doping levels.

System transitions to metallic state beyond a critical hole density of ~0.5p0.

Abstract

Moir\'e superlattices in van der Waals heterostructures have emerged as a powerful tool for engineering novel 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 moir\'e bilayer that are separated by an ultrathin hexagonal boron nitride (hBN). The moir\'e WS2/WSe2 bilayer features a Mott insulator state at hole density p/p0 = 1, where p0 corresponds to one hole per moir\'e lattice site. When electrons are added to the Mott insulator in the WS2/WSe2 moir\'e 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 excitonic insulator is stable up to a critical hole density of ~ 0.5p0 in the WSe2 monolayer, beyond which the system becomes metallic. Our study highlights the opportunities for realizing novel quantum phases in double-layer moir\'e systems due to the interplay between the moir\'e flat band and strong interlayer electron interactions.