Hybrid dark excitons in large-angle incommensurate moiré bilayers of transition metal dichalcogenides

Recently, large-angle incommensurate bilayers of TMDCs have been reported to host mixed dark excitonic states that are hybridized with their bright counterparts. This hybridization arises out of a broken out-of-plane reflection symmetry and altered optical selection rules, making these dark states optically detectable in the photoluminescence spectra. Temperature dependent measurements have unveiled the thermodynamic interplay between the bright and dark excitons. Hybrid dark excitons seem to acquire a valley addressability that is absent in monolayers. In MoSe₂, these excitons have been shown to exhibit large valley polarizations that exceed their bright counterparts.

In order to study the valleytronic potential of these hybrid dark excitons, we fabricate dual-gated large-angle bilayer devices of MoSe₂ and WSe₂. Molybdenum and tungsten-based monolayers are known to have opposite energetic ordering of bright and dark excitons. We will present the evolution of the valley polarization as a function of vertical electric field and doping density. We will present results on whether the dark exciton valley addressability survives at non-cryogenic temperatures under large electric fields.