Optical read-out of Coulomb staircases in a moire superlattice via trapped interlayer trions

Moire patterns with a superlattice potential can be formed by vertically stacking two layered materials with a relative twist or lattice constant mismatch. In transition metal dichalcogenide-based systems, the moire potential landscape can trap interlayer excitons (IXs) at specific atomic registries. Here, we report that spatially isolated trapped IXs in a molybdenum diselenide/tungsten diselenide heterobilayer device provide a sensitive optical probe of carrier filling in their immediate environment. By mapping the spatial positions of individual trapped IXs, we are able to spectrally track the emitters as the moire lattice is filled with excess carriers. Upon initial doping of the heterobilayer, neutral trapped IXs form charged IXs (IX trions) uniformly with a binding energy of similar to 7 meV. Upon further doping, the empty superlattice sites sequentially fill, creating a Coulomb staircase: stepwise changes in the IX trion emission energy due to Coulomb interactions with carriers at nearest-neighbour moire sites. This non-invasive, highly local technique can complement transport and non-local optical sensing techniques to characterize Coulomb interaction energies, visualize charge correlated states, or probe local disorder in a moire superlattice.

Automated summary

Trapped excitons in a molybdenum diselenide/tungsten diselenide heterobilayer device can serve as a sensitive optical probe for carrier filling. By mapping the spatial positions of individual trapped excitons, it is possible to spectrally track the emitters as the moire lattice is filled with excess carriers, providing insights into Coulomb interaction energies and visualizing charge correlated states.