Ultrafast Moiré-Resolved Spectroscopy of Interlayer-Exciton Thermalization in Twisted WSe_{2}/WS_{2} Heterobilayers.

Interlayer excitons (IXs) in transition metal dichalcogenide moiré heterobilayers offer a versatile platform for exploring strongly correlated quantum phases. Despite recent progress in probing excitonic properties, the thermalization dynamics of IXs, particularly within moiré superlattices, remain poorly understood due to their intrinsic weak oscillator strength. Here, we investigate how IXs are thermalized in both R- and H-stacked WSe_{2}/WS_{2} heterobilayers using a moiré-resolved ultrafast spectroscopy that probes intralayer exciton states with distinct atomic registry and spatial localization. We resolve the formation and cooling kinetics of IXs, revealing that thermalization proceeds via phonon-mediated scattering on a timescale of ∼15  ps. Our results highlight the role of exciton localization and site-specific interactions in governing IX dynamics and establish a spatially sensitive approach to exciton spectroscopy beyond the conventional momentum-space framework.