Correlated Insulating States at Fractional Fillings of the WS2/WSe2 Moir\'e Lattice

TL;DR

This study reports the observation of correlated insulating states at fractional fillings in WS2/WSe2 moiré heterobilayers, revealing strong, long-range electron interactions and their persistence at relatively high temperatures, advancing understanding of 2D strongly correlated systems.

Contribution

First direct imaging of fractional filling correlated states in WS2/WSe2 heterobilayers using microwave impedance microscopy, demonstrating long-range electron interactions beyond nearest neighbors.

Findings

Correlated insulating states observed at fractional fillings up to 120 K.

Electron ordering with large periodicity indicates long-range interactions.

States persist on both electron- and hole-doped sides.

Abstract

Moir\'e 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 moir\'e minibands. In most systems, the correlated states appear when the moir\'e lattice is filled by integer number of electrons per moir\'e unit cell. Recently, correlated states at fractional fillings of 1/3 and 2/3 holes per moir\'e unit cell has been reported in the WS2/WSe2 heterobilayer, hinting the long range nature of the electron interaction. 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 moir\'e 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. Monte Carlo simulations reveal that these insulating states correspond to ordering of electrons in the moir\'e lattice with a periodicity much larger than the moir\'e unit cell, indicating a surprisingly strong and long-range interaction beyond the nearest neighbors. Our findings usher in unprecedented opportunities in the study of strongly correlated states in two dimensions.