Extreme nanophotonics from ultrathin metallic gaps

Abstract

Ultrathin dielectric gaps between metals can trap plasmonic optical modes with surprisingly low loss and with volumes below 1 nm3. We review the origin and subtle properties of these modes, and show how they can be well accounted for by simple models. Particularly important is the mixing between radiating antennas and confined nanogap modes, which is extremely sensitive to precise nanogeometry, right down to the single-atom level. Coupling nanogap plasmons to electronic and vibronic transitions yields a host of phenomena including single-molecule strong coupling and molecular optomechanics, opening access to atomic-scale chemistry and materials science, as well as quantum metamaterials. Ultimate low-energy devices such as robust bottom-up assembled single-atom switches are thus in prospect.

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Fig. 1: Impedance matched coupling of light from free space to atomic scale.
Fig. 2: Nanogap modes.
Fig. 3: Emitters in nanocavities.
Fig. 4: Nanogap vibrational spectroscopy for chemistry and molecular optomechanics.
Fig. 5: Tuning nanocavities with conductivity.
Fig. 6: Exploitation of nanocavities for new devices: molecular spintronics, thermo-optics, electro-optics.

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Acknowledgements

We acknowledge support from UK EPSRC grants EP/G060649/1, EP/L027151/1, EP/G037221/1, EPSRC NanoDTC, ERC grant LINASS 320503, and FIS2016-80174-P from Spanish Ministry MINECO. M.H.M. acknowledges support from the Air Force Office of Scientific Research (AFOSR, grant no. FA9550‐15‐1‐0301) and the National Science Foundation (DMR-1454523). We appreciate extensive data and discussions on the mode scaling with A. Demetriadou, and enormous contributions from many members of our research groups over the past decade.

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Correspondence to Jeremy J. Baumberg.

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Baumberg, J.J., Aizpurua, J., Mikkelsen, M.H. et al. Extreme nanophotonics from ultrathin metallic gaps. Nat. Mater. 18, 668–678 (2019). https://doi.org/10.1038/s41563-019-0290-y

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