On-chip degeneracy breaking of Wood’s anomaly for vibrational strong coupling

Vibrational strong coupling (VSC) provides a promising way towards not only enhanced control of infrared light but also reshaping of molecular properties, which opens up unprecedented opportunities in ultrasensitive infrared spectroscopy, modification of chemical reactions, and exploration of nonlinear quantum effects. Surface plasmon resonance, excited on simple plasmonic resonators in the infrared, has been demonstrated as a means to realize VSC, but suffers from either limited quality factor for realizing large Rabi splitting or poor reconfigurability for precise detuning control. Here we propose and experimentally demonstrate, for the first time, an on-chip plasmonic resonator based on degeneracy breaking of Wood’s anomaly for VSC. Leveraging the low damping rate of the surface state induced by this degeneracy breaking, we achieve a plasmonic resonance with a high-Q factor exceeding ~110, resulting in a Rabi splitting up to ~112 cm^-1 with a subwavelength molecular layer. Additionally, the dispersion of the surface state allows for precise control over VSC detuning by simply adjusting the incident angle of excitation light, even in the absence of photons, enabling a broad detuning range up to 300 cm^-1. These experimental results align well with our analytical model and numerical simulation. This work provides a promising integrated platform for VSC, with various potential applications in on-chip spectroscopy, polariton chemistry, and polariton devices.