Cavity Polaritons in Organic Materials

Abstract

We analyze theoretically the spectrum of excitations in a microcavity, which utilizes organic materials with broad and dispersionless electronic resonances as the optically active semiconductor. The excitations in such non-cavity materials are localized, and for these excitations the wave vector is not a “good” quantum number. We show that as a result of strong light-matter coupling two polariton branches appear which are analogous to the cavity-polariton branches observed in inorganic semiconductor structures. However, the polariton branches only exist in a certain restricted intervals of wave vectors. We show that in such materials the majority of the electronic excited states do not strongly couple to the cavity photon, and these states can be regarded as essentially incoherent.

Applying this physical picture for the microcavities containing disordered cyanine dye J-aggregates, we examine the decay of the upper cavity polaritons accompanied by the emission of an intramolecular phonon. We show that the main contribution to the upper polariton nonradiative decay rate arises from the transition to incoherent states, and the transition is very fast (of the order of 50 fs). Finally, we show that the exciton-exciton annihilation in organic microcavities is strongly suppressed due to the polaritonic effects.