Nanospectroscopy of a single patch antenna strongly coupled to a mid-infrared intersubband transition in a quantum well

R. Gillibert, M. Malerba, D. Spirito, V. Giliberti, L. Li, A. G. Davies, E. H. Linfield, L. Baldassarre, R. Colombelli and M. Ortolani

Appl. Phys. Lett. 117, 101104 (2020)
Scanning-probe-assisted mid-infrared nano-spectroscopy is employed to reveal the polaritonic dispersion of individual MIM (metal-insulator-metal) square patch antennas whose modes can be strongly coupled to a mid-infrared intersubband transition. The patch antenna side length L sets the resonances between λ = 5.5 μm and 12.5 μm. The active region consists of a highly doped AlInAs/InGaAs/AlInAs single quantum well that presents an intersubband transition at 1190 cm−1 (λ = 8.4 μm). When the patch antenna optical resonance approaches and matches the intersubband transition frequency (L ∼ 1.8 μm), a clear anticrossing behavior—evidence of strong coupling—is observed in the near-field scattering phase spectra of individual antennas. The measured Rabi splitting is 4.5 THz. The near-field scattering spectra agree with the far-field extinction spectra acquired on arrays of identical antennas.