Negative circular polarization emissions from epitaxially grown WSe₂/MoSe₂ commensurate heterobilayers

Interlayer excitons in van der Waals heterobilayers of transition metal dichalcogenides (TMDs) possess enriched spin-valley coupling of carriers in different layers and emerge as a new platform for exploring advanced spin/valleytronic applications. It has been theoretically predicted that the optical properties (polarization selection rule, transition dipole strength, etc.) of interlayer excitons are sensitive to interlayer atomic registry. Manually stacked TMD heterobilayers, however, are incommensurate with inevitable interlayer twist and/or lattice mismatch, which could smear the effects. Here we report on the distinct polarization properties of valley-specific interlayer excitons using epitaxially grown, commensurate WSe₂/MoSe₂ heterobilayers with well-defined atomic registry (AA and AB). We observed circularly polarized photoluminescence from interlayer excitons, but with a helicity opposite to the optical excitation. The negative circular polarization arises from the quantum interference imposed by interlayer atomic registry, giving rise to distinct polarization selection rules. Using selective excitation of excitons in different monolayers, we demonstrate the optical addressability for interlayer excitons with different valley configurations and polarization helicities.