Intralayer charge-transfer moire excitons in van der Waals superlattices

Moire patterns of transition metal dichalcogenide heterobilayers have proved to be an ideal platform on which to host unusual correlated electronic phases, emerging magnetism and correlated exciton physics. Whereas the existence of new moire excitonic states is established(1-4) through optical measurements, the microscopic nature of these states is still poorly understood, often relying on empirically fit models. Here, combining large-scale first-principles GW (where G and W denote the one-particle Green's function and the screened Coulomb interaction, respectively) plus Bethe-Salpeter calculations and micro-reflection spectroscopy, we identify the nature of the exciton resonances in WSe2/WS2 moire superlattices, discovering a rich set of moire excitons that cannot be captured by prevailing continuum models. Our calculations show moire excitons with distinct characters, including modulated Wannier excitons and previously unidentified intralayer charge-transfer excitons. Signatures of these distinct excitonic characters are confirmed experimentally by the unique carrier-density and magnetic-field dependences of different moire exciton resonances. Our study highlights the highly non-trivial exciton states that can emerge in transition metal dichalcogenide moire superlattices, and suggests new ways of tuning many-body physics in moire systems by engineering excited-states with specific spatial characters.

Automated summary

The nature of exciton resonances in WSe2/WS2 moire superlattices is identified using large-scale first-principles GW and Bethe-Salpeter calculations, along with micro-reflection spectroscopy. A rich set of moire excitons, including modulated Wannier excitons and previously unidentified intralayer charge-transfer excitons, is discovered, indicating highly non-trivial exciton states that can emerge in transition metal dichalcogenide moire superlattices.