Gate-tunable interlayer excitons in WSe₂/WS₂/WSe₂ heterotrilayers

Atomically-thin semiconductors can be stacked with heterogeneous material combinations, enabling the formation of so-called interlayer excitons, where electrons and holes reside in separate layers in systems with staggered band alignment. Such interlayer excitons feature large Stark shifts in photoluminescence energy. However, interlayer excitons have so far been mostly studied in heterobilayers. Here, we investigate interlayer exictons in heterotrilayers, with the material combination of WSe₂/WS₂/WSe₂ and with dual-gated structures. Precise angle alignment between the outer WSe₂ layers was achieved via combining two half layers cut from the same original flake, whereas that between WSe₂ and WS₂ layers achieved via second harmonic generation measurement. From the spatial regions of upper and lower heterobilayers, we observed Stark shifts of opposite slopes, confirming contrasting polarity and thus orientation of interlayer excitons. In the heterotrilayer region, we study photoluminescence, its dependence on gating fields, and the relation of the observed behavior to that seen in the heterobilayer system.  We further probe the nature of interactions of the interlayer excitons through study of dependence of the photoluminescence on the laser excitation power and, hence, exciton density.