Abstract

Nanoplasmonic structures may exhibit nonlocal response when shrinking their characteristic dimensions to a regime where quantum phenomena are commonly expected to become important. This talk will address a semi-classical hydrodynamic description as a first natural attempt that goes beyond the common description based on the local-response approximation [1,2. Including the hydrodynamic response of the Fermi gas adds an intrinsic length scale to the electrodynamics, thus smearing the induced surface charge over a sub-nanometric scale in the near vicinity of the metal surface. In turn, this smearing also prohibits the possible development of a singular re-sponse inherent to the local-response approximation. The theory is used to explain size-dependent frequency shift and line broadening in individual metallic nanoparticles and the gap-dependent broadening in dimers [3. Some-what surprising, the semi-classical gives a good account of the plasmon dynamics even deep into the anticipated quantum regime where dimers are only separated by sub-nanometer gaps. We also discuss nonlocal effects and consequences for light-matter interactions, such as dipole emitters in very close proximity to metallic particles [4. Turning to graphene flakes, we compare semiclassical and quantum descriptions of the plasmon response, focusing again on the size-dependence of plasmonic resonances. In particular, we find that nonlocal effects in absorption cross sections scale similarly with size as do effects of quantum mechanical edge states [5. Interestingly, atomic-scale details and edge-state contributions are important for the optical properties even for graphene flakes as large as 20 nanometers [6.

© 2015 IEEE