Vibrational strong coupling modulated by graphene plasmons in deep metal grating structures.

We present a novel design approach for vibrational strong coupling (VSC) that enables spectrally accessible and controllable vibrational-polaritonic states using a graphene-integrated deep silver (Ag) grating. The deep Ag grating supports strong infrared resonances arising from hybrid magnetic polariton and surface plasmon modes, facilitating coherent coupling with the molecular vibrations of a test molecule, poly(methyl methacrylate) (PMMA). Integrating graphene into the deep Ag grating introduces discrete graphene plasmon (GP) modes that interact with the vibrational-polaritonic modes, providing spectral tunability and control over otherwise static polaritonic states. Consequently, the upper and lower polaritonic modes split into two distinct branches due to the sharp GP modes. The mixing ratio among the grating mode, molecular vibration, and GP mode is significantly modulated by adjusting the chemical potential applied to the graphene and varying the number of graphene layers incorporated into the grating. This ability to spectrally access and control polaritonic states makes the graphene-integrated Ag grating a promising platform for VSC applications, which potentially enables the use of polaritonic states as distinct quantum states for polaritonic chemistry.