Oral: Evidence for excitonic Mott insulator in WS₂/WSe₂ moiré superlattice

Angle-aligned transition metal dichalcogenide(TMDC) heterojunction exhibits strongly enhanced electron-electron interaction because of the moiré superlattices, which provides an interesting platform for fermionic correlated states studies. This enhancement can also be inherited at the type II heterojunction (WS₂/WSe₂ junction) when the electron and hole are separated in two different layers, which leads to long-lived valley-polarized correlated bosonic quasiparticles. With helicity-resolved PL measurement as a function of excitation power, we are able to study the spatial extent of interlayer excitons, as well as the band hierarchy of correlated states that arise from the strong interaction between interlayer excitons and electrons. The measurements also show evidence that at the filling of one exciton per moiré cell, an excitonic Mott insulator state emerges, with the valley polarization enhanced by nearly one order of magnitude. Our study demonstrates the potential of WS₂/WSe₂ interlayer for the study of correlated states of fermion, bosons, and a mixture of both.