Directional sorting of exciton emissions from twisted WS/WSe hetero-bilayers using self-coupled photonic crystal resonances.

Recent advances in two-dimensional semiconductor hetero-bilayers have revealed that the stacking angle between adjacent layers provides an additional degree of freedom to tune exciton states, enabling fascinating twist-angle-dependent photoluminescence. To control exciton emission properties, hetero-bilayers are usually integrated with photonic nanostructures, however, in which the contact interfaces can result in substantial luminescence suppression. To overcome this fundamental issue, we herein directly pattern photonic crystal (PhC) nanostructures in free-standing WS/WSe hetero-bilayers to avoid the involvement of contact interfaces. Such PhC nanostructured WS/WSe hetero-bilayers not only provide new exciton states but also offer guided mode resonances that can self-couple to excitons to enable light manipulation at the atomic thickness scale. Moreover, leveraging the unique momentum dispersion of guided mode resonances, exciton emissions are selectively excited and separated in the energy-momentum space. Our results may provide an important direction to unfold the prospects of emerging exciton states in the moiré heterostructures.