Organic DAST Single Crystal Meta-Cavity Resonances at Terahertz Frequencies

Light–matter coupling in the terahertz (THz) regime is an important asset for future THz lasing, sensing, and quantum technologies, but it was previously realized in complex inorganic microcavities at cryogenic temperatures. Here we report on a simple organic meta-cavity formed with a patch-antenna array on an organic 4-N,N-dimethylamino-4′-N′-methyl-stilbazolium tosylate (DAST) single crystal, and particularly, the resultant observation of resonances and Rabi splitting in the THz regime. This is resulted from the coupling between two oscillators: a DAST optical phonon mode and the patch-antenna array meta-cavity. The birefringence of the DAST single crystal manifests itself in a polarization dependent response of the geometrically symmetric structure, with which the resonance of the cavity can be tuned close to that of DAST. A large Rabi splitting of 0.28 THz, corresponding to 25% of the DAST resonant absorption frequency, was experimentally measured at room temperature. Besides the incident polarization angle, the coupling can also be tuned by the operating temperature. This work presents the first experimental realization of room temperature coupling Rabi splitting in an organic single crystal at THz frequencies, opening up a promising organic avenue toward otherwise unattainable performance and inspiring the development of new organic THz devices.