Giant Rabi splitting between localized mixed plasmon-exciton states in a two-dimensional array of nanosize metallic disks in an organic semiconductor

We study localized surface plasmons in strong coupling with excitons of organic semiconductors. The plasmons are localized in lithographed silver nanodisks organized in square array. A giant Rabi splitting energy of 450 meV is obtained, and typical behaviors of mixed states, i.e., anticrossing of their energies and crossing of their linewidths, are observed. Three-dimensional finite-difference time-domain simulations and coupled oscillator calculations are used to analyze and corroborate the experimental results.