Correlated insulating states at fractional fillings of the WS2/WSe2 moiré lattice

The strong electron interactions in the minibands formed in moiré superlattices of van der Waals materials, such as twisted graphene and transition metal dichalcogenides, make such systems a fascinating platform with which to study strongly correlated states 1 – 19 . In most systems, the correlated states appear when the moiré lattice is filled by an integer number of electrons per moiré unit cell. Recently, correlated states at fractional fillings of 1/3 and 2/3 holes per moiré unit cell have been reported in the WS 2 /WSe 2 hetero-bilayer, hinting at the long-range nature of the electron interaction 16 . Here we observe a series of correlated insulating states at fractional fillings of the moiré minibands on both electron- and hole-doped sides in angle-aligned WS 2 /WSe 2 hetero-bilayers, with certain states persisting at temperatures up to 120 K. Simulations reveal that these insulating states correspond to ordering of electrons in the moiré lattice with a periodicity much larger than the moiré unit cell, indicating a surprisingly strong and long-range interaction beyond the nearest neighbours. Twisted bilayers of WS 2 and WSe 2 have correlated states that correspond to real-space ordering of the electrons on a length scale much longer than the moiré pattern.