Observation of double indirect interlayer exciton in WSe2/WS2 heterostructure.

Interlayer excitons (IX) are produced by the spatially separated electron-hole pairs due to the robust Coulomb interactions in van der Waals transition metal dichalcogenide (TMDC) heterostructures (HSS). IX is characterized by a larger binding energy, and its lifetime is orders of magnitude longer than that of the direct excitons, providing a significant platform for the manufacture of long-lived exciton devices and the exploration of exciton quantum gas. However, the studies are restricted to the single interlayer exciton, and the simultaneous capture and study of double IX remain challenging in the WSe2/WS2 HS. Here, we demonstrate the existence of double indirect IX in the WSe2/WS2 HS with the emission centers at 1.4585eV (∼25.9meV wide) and 1.4885 eV (∼14.4 meV wide) at cryogenic temperature. Interestingly, the intensities of the double IX emission peaks are almost equal, and the energy difference between them is in a good agreement with the cleavage value of the WS2 conduction band (CB). Additionally, diverse types of excitons in the individual materials were successfully observed in the PL spectra at 8 K. Such unique double IX features, in combination with excellent exciton identification, open up new opportunities for further investigations for new physical properties of TMDCs and explorations for the technological innovation of exciton devices.