Prediction of Strong Transversal s(TE) Exciton-Polaritons in C₆₀ Thin Crystalline Films

If an exciton and a photon can change each other's properties, indicating that the regime of their strong bond is achieved, it usually happens in standard microcavity devices, where the large overlap between the 'confined' cavity photons and the 2D excitons enable the hybridization and the band gap opening in the parabolic photonic branch (as clear evidence of the strong exciton-photon coupling). Here, we show that the strong light-matter coupling can occur beyond the microcavity device setup, i.e., between the 'free' s(TE) photons and excitons. The s(TE) exciton-polariton is a polarization mode, which (contrary to the p(TM) mode) appears only as a coexistence of a photon and an exciton, i.e., it vanishes in the non-retarded limit (c→∞). We show that a thin fullerene C60 crystalline film (consisting of N C60 single layers) deposited on an Al2O3 dielectric surface supports strong evanescent s(TE)-polarized exciton-polariton. The calculated Rabi splitting is more than Ω=500 meV for N=10, with a tendency to increase with N, indicating a very strong photonic character of the exciton-polariton.