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Gebhardt, Christian; Förg, Michael; Yamaguchi, Hisato; Bilgin, Ismail; Mohite, Aditya D.; Gies, Christopher; Florian, Matthias; Hartmann, Malte; Hänsch, Theodor W.; Högele, Alexander; Hunger, David (2019): Polariton hyperspectral imaging of two-dimensional semiconductor crystals. In: Scientific Reports, Vol. 9, 13756
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Atomically thin crystals of transition metal dichalcogenides (TMDs) host excitons with strong binding energies and sizable light-matter interactions. Coupled to optical cavities, monolayer TMDs routinely reach the regime of strong light-matter coupling, where excitons and photons admix coherently to form polaritons up to room temperature. Here, we explore the two-dimensional nature of TMD polaritons with scanning-cavity hyperspectral imaging. We record a spatial map of polariton properties of extended WS2 monolayers coupled to a tunable micro cavity in the strong coupling regime, and correlate it with maps of exciton extinction and fluorescence taken from the same flake with the cavity. We find a high level of homogeneity, and show that polariton splitting variations are correlated with intrinsic exciton properties such as oscillator strength and linewidth. Moreover, we observe a deviation from thermal equilibrium in the resonant polariton population, which we ascribe to non-Markovian polariton-phonon coupling. Our measurements reveal a promisingly consistent polariton landscape, and highlight the importance of phonons for future polaritonic devices.