Imaging local discharge cascades for correlated electrons in WS2/WSe2 moiré superlattices

Transition metal dichalcogenide moiré heterostructures provide an ideal platform to explore the extended Hubbard model1, where long-range Coulomb interactions play a critical role in determining strongly correlated electron states. This has led to experimental observations of Mott insulator states at half filling2–4 as well as a variety of extended Wigner crystal states at different fractional fillings5–9. However, a microscopic understanding of these emerging quantum phases is still lacking. Here we describe a scanning tunnelling microscopy (STM) technique for the local sensing and manipulation of correlated electrons in a gated WS2/WSe2 moiré superlattice, which enables the experimental extraction of fundamental extended Hubbard model parameters. We demonstrate that the charge state of the local moiré sites can be imaged by their influence on the STM tunnelling current. In addition to imaging, we are also able to manipulate the charge state of correlated electrons. When we ramp the bias on the STM tip, there is a local discharge cascade of correlated electrons in the moiré superlattice, which allows us to estimate the nearest-neighbour Coulomb interaction. Two-dimensional mapping of the moiré electron charge states also enables us to determine the on-site energy fluctuations at different moiré sites. Our technique should be broadly applicable to many semiconductor moiré systems, offering a powerful tool for the microscopic characterization and control of strongly correlated states in moiré superlattices. The Hubbard model describes many fascinating phenomena, but relating it to complicated quantum materials is difficult. Now, atomic-resolution measurements can estimate the interaction parameters that appear in the model for real materials.