Correlated Insulating States at Fractional Fillings of the WS2/WSe2 Moiré Lattice

Moiré superlattices of van der Waals materials, such as twisted graphene and transitional metal dichalcogenides, have recently emerged as a fascinating platform to study strongly correlated states in two dimensions, thanks to the strong electron interaction in the moiré minibands. In most systems, the correlated states appear when the moiré lattice is filled by integer number of electrons per moiré unit cell. Recent research in the WS₂/WSe₂ heterobilayer reported the correlated states at fractional fillings of 1/3 and 2/3 holes per moiré unit cell, hinting a long-range electron interaction in this system. In this work, employing a scanning microwave impedance microscopy technique that is sensitive to local electrical properties, 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 WS₂/WSe₂ hetero-bilayers, with certain states persisting at temperatures up to 120 K. Our Monte Carlo 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 neighbors.