Active plasmonics: Merging Metals with Semiconductors

Future nano-plasmonic devices will most likely be based on active plasmonics, relying on the interplay between the strong intrinsic optical nonlinearities of excitonic nanostructures and the ability of metallic nano-objects to concentrate electromagnetic fields locally. Consequently, the optical properties of hybrid nanostructures comprising active materials, e.g., semiconductors or J-aggregated molecules, and metals are currently attracting considerable attention. In favorable geometries, their properties are governed by a new class of short-lived quasiparticles, exciton - surface plasmon polaritons with hitherto unexplored nonequilibrium dynamics. Since the polariton dynamics in hybrid nanostructures occurs on very short timescale, ultrafast spectroscopy is an essential tool for the investigation of their properties. We demonstrate ultrafast coherent manipulation of the normal mode splitting in metal/molecular-aggregate nanostructures by real-time observation of Rabi oscillations between excitons and surface-plasmon-polaritons. Oscillations in exciton density on a 10-fs timescale control the Rabi splitting.