Percolation Composites: Localization of Surface Plasmons and Enhanced Optical Nonlinearities

Abstract

In random metal-dielectric composites near the percolation threshold surface plasmons are localized in small nanometer-sized areas, hot spots, where the local field can exceed the applied field by several orders of magnitude. The high local fields result in dramatic enhancement of optical responses, especially, nonlinear ones. The local-field distributions and enhanced optical nonlinearities are described using the scale renormalization. A theory predicts that the local fields consist of spatially separated clusters of sharp peaks representing localized surface plasmons. Experimental observations are in good accord with theoretical predictions. The localization of plasmons maps the Anderson localization problem described by the random Hamiltonian with both on- and off-diagonal disorder. A feasibility of nonlinear surface-enhanced spectroscopy of single molecules and nanocrystals on percolation films is shown.