Opposite Sign of Polarization Splitting in Ultrastrongly Coupled Organic Tamm Plasmon Structures

The properties of the ultrastrongly coupled Tamm plasmon cavity filled with a high-oscillator-strength organic material DPAVBi (4,4′-bis­[4-(di-p-tolylamino)­styryl]­biphenyl) are studied using theoretical and experimental methods. An analytical model predicts the opposite sign of polarization splitting for the lower and upper polariton cases and a giant absolute value of the splitting. A set of organic Tamm plasmon cavities with different detuning parameters are fabricated. We demonstrate that all structures are operating in the ultrastrong coupling regime: the values of the Rabi splitting are close to a 20% fraction of the exciton energy. The measured angle-dependent reflectivity spectra structure for both transverse electric (TE) and transverse magnetic (TM) polarizations confirm the predicted theoretical model. We obtained a giant value of the polarization splitting of up to 180 meV for both polariton branches. We believe that it is the first demonstration of such peculiar polarization splitting behavior of polaritons in the ultrastrong coupling regime.