04 December 2012 Nature NanoTechnology, News & Views

Prof. Niek van Hulst gives his view on recent advances in quantum plasmonics. ICREA Prof. Niek van Hulst reviews a paper on the fundamental limit to the confinement of light due to quantum tunneling in subnanometer gaps, published in Nature by Jeremy Baumberg at the Cavendish Laboratory in Cambridge, UK and co-workers from the Material Physics Center in San Sebastian, Spain and the Université Paris Sud, France.

The optical properties of plasmons are readily derived from Maxwell’s equations by plugging in bulk metal- optics parameters. Yet, it is intuitive that the classical picture must go wrong at the atomic scale, and indeed recent advances in nanofabrication have pushed Maxwell’s description to the limit. The highlighted study describes an experiment that captures the quantum regime in plasmonic nanostructures and shows that the classical plasmon resonance does indeed collapse at a distance of ~3Å. Thus quantum tunneling sets the limit for charge and field confinement with a lower limit of ~10−8 λ3 for the optical regime. Fortunately though for most current-day devices, with “only” nanometer accuracy, good old Maxwell’s theory is still perfectly valid.