Interlayer Exciton in atomically reconstructed MoSe2/WSe2 van der Waals Heterostructure

Interlayer exciton (ILE) can be created by artificially stacking MoSe₂ onto WSe₂ to form a heterostructure with type II band alignment. With hBN encapsulation and a relative rotational angle close to 60 degrees, well pronounced ILE emission is observed at room temperature and further splits into two distinct peaks (ILE1 and ILE2) at low temp. Furthermore, we demonstrate that the ILE emission peaks have opposite circular polarizations when excited by circularly polarized light. Ab initio calculations provide an explanation of this unique and potentially useful property and indicate that it is a result of the indirect character of both transitions. We further investigate the atomic structure arrangement of MoSe₂/WSe₂ by TEM and reveal that the heterostructure indeed reconstructs under a small twist angle ( ≤ 1°) between the TMDs. With a small twist angle, periodic domains form with commensurate stacking within the domain. On the other hand, a rigid moiré structure is also observed by TEM when a larger twist angle (≥ 3°) is applied. These results may provide fundamental insights into the mechanical and optical behavior of this exciting class of semiconductor heterostructure.