Strong Coupling between Moiré-Type Plasmons and Phonons in Suspended Monolayer Metallic Twisted Superlattices

We demonstrate both experimentally and analytically a strong coupling phenomenon between moiré-type plasmons and phonons within moiré superlattices. We study the dependence of moiré wave vector and the twist angle and numerically simulate and experimentally fabricate metallic moiré superlattices on a suspended thin film SiO₂ substrate at different twist angles. The results suggest that the coupling strength initially increases and then decreases with increasing twist angles. When the twist angle is at 16.26°, we achieve a moiré-type plasmon-phonon strong coupling with a Rabi splitting strength approaching 45 meV. We further analyze the coupling system by utilizing the coupled-harmonic-oscillators theory and quantum mechanical theory. The calculations and numerical simulations further agree with the experimental results. The proposed strong coupling system has the potential to contribute substantially to electromagnetic field controlling and coupling.