Thermally tunable mid-infrared nanocavity resonance of coupled surface plasmon-phonon polaritons

Phase-change materials (PCMs) are essential for achieving tunability of metasurfaces. However, they frequently face limitations in the long-wave infrared range because of their lossy behavior. Here, we experimentally demonstrate a thermally tunable mid-infrared nanocavity resonance from coupled surface plasmon-phonon polaritons that are supported within a trilayer structure of metal-PCM layer-polar dielectric (Au-VO₂-SiC). The top metal structures configure the Fabry-Perot cavity resonance near 840 cm^-1 (11.9 μm), which is sensitively tunable and reversible with small changes in the VO₂ refractive index Δn near below its insulator-to-metal phase transition temperature where the loss is small. The maximum resonance shift of 7.7 cm^-1 is induced by a small Δn = 0.3 over a temperature change of 3°C. The tuning figure of merit is comparable to the current standard in photonic modulator applications.