Shan, H.H.ShanLackner, L.L.LacknerHan, B.B.HanSedov, E.E.SedovRupprecht, C.C.RupprechtKnopf, H.H.KnopfEilenberger, F.F.EilenbergerBeierlein, J.J.BeierleinKunte, N.N.KunteEsmann, M.M.EsmannYumigeta, K.K.YumigetaWatanabe, K.K.WatanabeTaniguchi, T.T.TaniguchiKlembt, S.S.KlembtHöfling, S.S.HöflingKavokin, A.V.A.V.KavokinTongay, S.S.TongaySchneider, C.C.SchneiderAnton-Solanas, C.C.Anton-Solanas2022-03-062022-03-062021https://publica.fraunhofer.de/handle/publica/27129710.1038/s41467-021-26715-9The emergence of spatial and temporal coherence of light emitted from solid-state systems is a fundamental phenomenon intrinsically aligned with the control of light-matter coupling. It is canonical for laser oscillation, emerges in the superradiance of collective emitters, and has been investigated in bosonic condensates of thermalized light, as well as exciton-polaritons. Our room temperature experiments show the strong light-matter coupling between microcavity photons and excitons in atomically thin WSe2. We evidence the density-dependent expansion of spatial and temporal coherence of the emitted light from the spatially confined system ground-state, which is accompanied by a threshold-like response of the emitted light intensity. Additionally, valley-physics is manifested in the presence of an external magnetic field, which allows us to manipulate K and K' polaritons via the valley-Zeeman-effect. Our findings validate the potential of atomically thin crystals as versatile components of coherent light-sources, and in valleytronic applications at room temperature.endetection methodemergencelaser methodtemperature effect620journal article