Observation of hybrid plasmon-photon modes in microwave transmission of coplanar microresonators

Microwave transmission of a coplanar microresonator deposited on a sample surface over a two-dimensional electron system has been studied. The transmission signal reveals a series of resonances corresponding to the excitation of hybrid cavity plasmon-photon modes, and ultrastrong plasmon-photon coupling has been realized. The hybridization frequency (Rabi frequency) is shown to be anomalously larger than the frequencies of unperturbed modes and it reaches values of up to 25 GHz. The effect of electron density and magnetic field on the excitation spectrum of cavity polariton has been investigated.