Exciton localization and transport in van der Waals heterostructuresXiaoqin Li

Transition metal dichalcogenide heterostructures provide a versatile platform to explore electronic and excitonic phases. Depending on the exciton density, several distinct phases of localized excitons, mobile exciton gases, and ionized hot plasma can be observed in heterostructures. At low excitation density, interlayer excitons can be localized by moire potential in heterostructures with a small twist angle and relatively large supercells. As the excitation density exceeds the critical Mott density, interlayer excitons are ionized into an electron-hole plasma phase. At the excitation density well exceeding the Mott density, we find a surprisingly rapid initial expansion of hot plasma to a few microns away from the excitation source within 0.2 ps. Microscopic calculations reveal that this rapid expansion is mainly driven by Fermi pressure and Coulomb repulsion, while the hot carrier effect has only a minor effect in the plasma phase. I will also discuss a completely different type of moire superlattices that can be used to localize excitons without reducing quantum efficiency in the strong confinement regime with small supercells.