LAUSR

A panoply of unconventional electronic states has been observed in moiré superlattices. Engineering similar bosonic phases remains, however, largely unexplored. We report the observation of a bosonic correlated insulator in tungsten diselenide/tungsten disulfide (WSe2/WS2) moiré superlattices composed of excitons, that is, tightly bound electron-hole pairs. We develop a pump probe spectroscopy method that we use to observe an exciton incompressible state at exciton filling νex = 1 and charge neutrality, indicating a correlated insulator of excitons. With varying charge density, the bosonic correlated insulator continuously transitions into an electron correlated insulator at charge filling νe = 1, suggesting a mixed correlated insulating state between the two limits. Our studies establish semiconducting moiré superlattices as an intriguing platform for engineering bosonic phases. Description Editor’s summary Moiré multilayers of graphene and transition metal dichalcogenides have been found to host a number of exotic electronic phases. In addition to charge carriers—electrons and holes—these two-dimensional structures support their pairs, called excitons, which are also expected to form correlated phases. Xiong et al. observed a correlated insulator of interlayer excitons in a bilayer consisting of tungsten diselenide, which hosted holes, and tungsten disulfide, which hosted electrons. The researchers measured the optical response of the material to excitation by light and found signatures of an incompressible state of excitons. —Jelena Stajic Pump-probe spectroscopy was used to observe an incompressible state of interlayer excitons.