Probing interlayer excitons in transition-metal dichalcogenide heterostructures using time- and angle-resolved photoemission spectroscopy

Van der Waals heterostructures of monolayer transition metal dichalcogenides (TMDCs) host interlayer excitons (ILX), electron-hole pairs bound across the interlayer gap. Their charge separation leads to long lifetimes and the possibility of reaching high densities[1], with pronounced exciton-exciton many-body effects like Mott transitions[1] and exciton condensates[2]. However, so far ILXs in TMDC heterostructures have been probed mostly by their luminescence[3,4], accessing only a narrow range of momentum space, and leaving many open questions about the ILXs' density and size, which are key for studying their many-body interactions. In this talk, we present our direct observation of the full momentum-space image of ILXs in a WSe₂/MoS₂ heterostructure using time-resolved, angle-resolved photoemission spectroscopy. These data enable us to determine for the first time the location, distribution size, and density of ILXs in momentum space, without prior assumptions about their lifetime or formation dynamics.
References :
[1] Wang et al. Sci. Adv. eaax0145 (2019). [2] Wang et al. Nature 574,76-80 (2019). [3] Rivera et al. Nature Commun. 6,6242 (2015). [4] Karni et al. PRL 123, 247402 (2019).