Identification of spin, valley and moiré quasi-angular momentum of interlayer excitons

Moire superlattices provide a powerful way to engineer the properties of electrons and excitons in two-dimensional van der Waals heterostructures1–8. The moire effect can be especially strong for interlayer excitons, where electrons and holes reside in different layers and can be addressed separately. In particular, it was recently proposed that the moire superlattice potential not only localizes interlayer exciton states at different superlattice positions, but also hosts an emerging moire quasi-angular momentum (QAM) that periodically switches the optical selection rules for interlayer excitons at different moire sites9,10. Here, we report the observation of multiple interlayer exciton states coexisting in a WSe2/WS2 moire superlattice and unambiguously determine their spin, valley and moire QAM through novel resonant optical pump–probe spectroscopy and photoluminescence excitation spectroscopy. We demonstrate that interlayer excitons localized at different moire sites can exhibit opposite optical selection rules due to the spatially varying moire QAM. Our observation reveals new opportunities to engineer interlayer exciton states and valley physics with moire superlattices for optoelectronic and valleytronic applications. Stacked 2D materials can host excitons with distinct valley selection rules due to the spatial variation of the moire pattern. The authors demonstrate this via optical spectroscopy, opening a route for control of optoelectronic devices.