Correlated insulator of excitons in WSe2/WS2 moiré superlattices
We observed a bosonic correlated insulator in WSe2/WS2 moiré superlattices composed of excitons, tightly bound electron-hole pairs. In our experiment, we built a novel optical pump–probe technique, which is an optical counterpart of electrical capacitance measurement and distinctively different from conventional pump–probe concepts. We directly obtained exciton chemical potential depending on exciton density and identified an incompressible state of exciton at filling $\nu_{\text{ex}} = 1$, the hallmark of a bosonic correlated insulator. By further varying charge density with gate, we also observed a mixed correlated insulator involving both fermionic electrons and bosonic excitons. These observations are well captured by a Bose-Fermi-Hubbard model.
