Electronic correlation and excitons in 2D moiré superlattices

Moiré superlattices formed by van der Waals materials with small lattice mismatch or twist angle open an unprecedented opportunity to tailor interactions between quantum particles and their coupling to electromagnetic field. In this talk, I will describe optical spectroscopy studies on 2D moiré superlattices formed by semiconductor transition metal dichalcogenides (TMDs). I will discuss a recent experimental realization of the two-dimensional triangular lattice Hubbard model. In the presence of strong correlation, we observe an antiferromagnetic Mott insulating state at the doping level of one electron or hole per moiré superlattice cell (i.e. half filling of the first moiré miniband). We also observe layer-hybridized moiré excitons (electron-hole pairs) whose energy and oscillator strength are highly tunable by the quantum-confined Stark effect and are strongly influenced by the formation of the Mott state.