Fraction of a Millimeter Propagation of Exciton Polaritons in Photoexcited Nanofibers of Organic Dye

We report propagation of exciton polaritons ( EPs) in photoexcited nanofibers of thiacyanine dye over a few hundred micrometers at room temperature. We determine the complex refractive index along the nanofibers by fluorescence microscopy measurements on single nanofibers and observe its anomalous behavior due to the EP effect. The longitudinal- transverse splitting energy (Delta E(L-T)) is evaluated to be similar to 1 eV. The large Delta E(L-T) and waveguide function of the nanofibers allow a millimeter propagation of EPs at room temperature, which is hardly realized in other systems.