Light funneling into localized acoustic graphene plasmons for extreme infrared and terahertz field enhancement and confinement

Enhancing light-matter interaction through deep subwavelength-scale confinement is crucial for numerous applications like molecular sensing, optoelectronic devices, and non-linear optics. Here, we report the excitation of localized acoustic graphene plasmons (LAGPs) confined in a sub-micro- wide, nanometer-thick layer using a metal slit antenna. This approach enables light funneling in the infrared and terahertz regimes, leading to strong field enhancement and confinement. LAGPs exhibit broad-band excitation characteristics, with the number of excited modes adjustable via the symmetry of the relative positioning between graphene and the metal slit. Detailed analysis indicates that the local field intensities of LAGPs are critically influenced by both the periodicity of the device structure and the electron relaxation time of graphene. These findings are effectively elucidated using temporal coupled mode theory. In comparison to conventional non-localized acoustic graphene plasmons, LAGPs demonstrate significantly improved field confinement and enhancement attributed to the funneling effect. Our study presents a promising avenue for achieving robust light-matter interaction and holds potential for various applications in the infrared and terahertz domains.