Nanometric Cavities for Mid-infrared Light Using Graphene Plasmons

Detecting small molecular signatures in the Mid-infrared and THz spectra requires a sufficient field intensity, especially in the case of few molecules. Graphene plasmons (GPs) are capable of confining MIR\THz light to very small dimensions [1], which become even smaller if a metallic surface is near the graphene, screening the GPs and enabling their compression up to 300 times their free-space wavelength [2].This large confinement, however, is also the reason why GP excitation is challenging and has been limited to micron-scale structures, hindering their actual confinement potential.

We introduce a new approach to create nanoscale cavities for GPs by depositing nanometric silver cubes over the graphene [3]. This graphene/nanocube system supports a graphene-plasmon-magnetic-resonance (GPMR) mode, which allows for each nanocube to act as a single cavity, compressing GPs to the nanometric volume between the graphene and cube, to a volume over a billion times smaller than the free-space mode volume.

Our approach may enable efficient detection of molecular materials and GP-based sensors.

References:
[1] Jablan et al, PRB 80, 245435(2009).
[2] Alonso-González et al, Nat. Nanotech.12, 31(2017).
[3] Epstein et al, Science 368, 1219-1223(2020)