Negetive mass trion polariton*

Atomically thin monolayers of transition metal dichalcogenides supports strongly bound excitons in two dimensions. In this work we use monolayer of MoSe₂ as an active material inside a planer microcavity structure to show strong coupling between exciton and cavity photon. Unintentional doping in the exfoliated monolayer results into formation of trions, the bound state of an electron and exciton. We observed an inverted trion dispersion with negative curvature near zero in-plane momentum. Our theoretical analysis show that such negative curvature in the dispersion or the negative mass can only arise due to electron mediated interaction between the lower exciton-polariton branch and the trion-polariton. Our work suggest a pathway for studying interesting regimes in quantum many-body physics yielding possible new phases of quantum matter.