Strong Coupling\nbetween Moire-Type Plasmons\nand Phonons in Suspended Monolayer Metallic Twisted Superlattices

We demonstrate both experimentally and analytically a\nstrong coupling\nphenomenon between moiré-type plasmons and phonons within moiré\nsuperlattices. We study the dependence of moiré wave vector\nand the twist angle and numerically simulate and experimentally fabricate\nmetallic moiré superlattices on a suspended thin film SiO<sub>2</sub> substrate at different twist angles. The results suggest\nthat the coupling strength initially increases and then decreases\nwith increasing twist angles. When the twist angle is at 16.26°,\nwe achieve a moiré-type plasmon-phonon strong coupling with\na Rabi splitting strength approaching 45 meV. We further analyze the\ncoupling system by utilizing the coupled-harmonic-oscillators theory\nand quantum mechanical theory. The calculations and numerical simulations\nfurther agree with the experimental results. The proposed strong coupling\nsystem has the potential to contribute substantially to electromagnetic\nfield controlling and coupling.