Vibrational Strong Coupling in Subwavelength Nanogap Patch Antenna at the Single Resonator Level

Abstract

Vibrational strong coupling (VSC) between a vacuum field and molecules in a cavity offers promising applications in cavity-modified chemical reactions and ultrasensitive vibrational spectroscopy. At present, in order to realize VSC, bulky microcavities with large mode volume are utilized, which limits their potential applications at the nanoscale. Here, we report on the experimental realization of strong coupling between molecular vibrations and infrared photons confined within a deeply subwavelength nanogap patch antenna cavity. Our system exhibits a characteristic anticrossing dispersion, indicating a Rabi splitting of 108 cm −1 at the single resonator level with excellent angular insensitivity. The numerical simulations and theoretical analyses quantitatively reveal that the strength of coupling depends on the cavity field−molecule overlap integral and the image charge effect. VSC at the single nanogap patch antenna level paves the way for molecular-scale chemistry, ultrasensitive biosensors, and the development of ultralow-power all-optical devices in the mid-infrared spectral range.

Chemistry under Vibrational Strong Coupling

“…Strong coupling experiments are quite easy to undertake, but doing so requires some basic notions of optics and precautions in the preparation and characterization of the samples. The confined EM field necessary for light–matter strong coupling can be provided by either surface plasmons , or an optical cavity such as a Fabry–Perot (FP) cavity or distributed Bragg reflector mirrors (DBRs) . Obtaining high-quality surface plasmon modes in the infrared (IR) region is not easy due to their dissipative nature; nevertheless, there are examples of VSC of polymer films placed on mid-IR grating structures .…”

Vibrational Coupling of Water from Weak to Ultrastrong Coupling Regime via Cavity Mode Tuning

“…The vibrational coupling strength can be controlled by varying the molecular concentration. Interestingly, water is known to show a relatively high coupling strength because of its high oscillator strength. ,,, Use of water coupled to a cavity as a model system for vibrational strong coupling is thus informative for other systems with electromagnetic fields, including low-loss IR cavities, , waveguides, thin films, and plasmonic structures. − However, even when using a cavity, there is still a lack of systematic information about the vibrational coupling strength when spanning from weak to strong coupling regimes with different cavity mode orders.…”

Infrared metamaterial for surface-enhanced infrared absorption spectroscopy: pushing the frontier of ultrasensitive on-chip sensing

“…The metamaterial pattern strongly influences the plasmonic resonance of the device and its spectral response. [73][74][75][76][77] Therefore, it is an effective way to improve the EF of SEIRA by optimizing metamaterial structure design. [78,79] Specifically, reducing the distance between the metamaterial pattern units can enhance the near-field intensity, which is attributed to the near-field interaction caused by the attractive electromagnetic force.…”