Optical spectroscopy of novel correlated states in semiconducting moiré superlattices

Monolayer transition metal dichalcogenides (TMDs, e.g. MoSe₂, WS₂, and WSe₂) exhibit remarkable optical, optoelectronic, excitonic, and valleytronic properties for novel applications. When two TMD monolayers are stacked together, the mismatch of their lattice constants and/or orientation angles can produce moiré superlattices with substantial confinement and correlation effect. In this talk, I will present our investigations of the novel correlated states in TMD moiré superlattices by optical spectroscopy. We observe optical signatures of trions confined by the moiré potential in the WSe₂/MoSe₂ moiré superlattices. Such moiré trions exhibit sharp emission lines and complex charge-density dependence, in stark contrast to the behavior of conventional trions. Moreover, we investigate the optical signatures of correlated electronic phases at fractional fillings of the WSe₂/WS₂ moiré superlattices. These correlated electronic phases can couple to the trion states to modulate the spectra and valley polarization of the trions. Our results demonstrate moiré superlattices as an excellent platform to explore novel correlated phenomena.