In-Plane and Out-of-Plane Investigation of Resonant Tunneling Polaritons in Metal-Dielectric-Metal Cavities.

Patra, Aniket; Caligiuri, Vincenzo; Zappone, Bruno; Krahne, Roman; De Luca, Antonio · Nano Lett · 2023

basic_science · Level V

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Abstract

Polaritons can be generated by tuning the optical transitions of a light emitter to the resonances of a photonic cavity. We show that a dye-doped cavity generates resonant tunneling polaritons with Epsilon-Near-Zero (ENZ) effective permittivity. We studied the polariton spectral dispersion in dye-doped metal-dielectric-metal (MDM) cavities as a function of the in-plane (<i>k</i><sub>||</sub>) and out-of-plane (<i>k</i><sub>⊥</sub>) components of the incident wavevector. The dependence on <i>k</i><sub>||</sub> was investigated through ellipsometry, revealing the ENZ modes. The <i>k</i><sub>⊥</sub> dependence was measured by varying the cavity thickness under normal incidence using a Surface Force Apparatus (SFA). Both methods revealed a large Rabi splitting well exceeding 100 meV. The SFA-based investigation highlighted the collective nature of strong coupling by producing a splitting proportional to the square root of the involved photons. This study demonstrates the possibility of generating ENZ polaritons and introduces the SFA as a powerful tool for the characterization of strong light-matter interactions.