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Structural reconstructions drive moiré exciton localization

We performed GW-BSE calculations using the pristine unit-cell matrix projection approach to understand the role of structural reconstructions in the formation and modulation of moiré excitons in rotationally aligned WS2/WSe2 superlattice. We found that the structural rearrangement within the moiré superlattice drives the splitting of the exciton peaks in the absorption spectrum and the localization of the excitons. In particular, we found the lowest energy intralayer exciton to have a Wannier character and localized at the AA stacking. Scanning transmission electron microscopy and electron energy loss spectroscopy (STEM-EELS) enabled the simultaneous observation of structural changes and the concomitant localization of the lowest-energy intralayer moiré exciton. The experimental measurement of the  structural reconstruction, location and radius of exciton center-of-mass localization demonstrated a remarkable agreement with the theoretical predictions. 

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