Excellence in Research: Processes and Interactions in Plasmonic Systems

Nontechnical Summary This award supports theoretical and computational research and associated education on strong light-matter interactions in hybrid nanoscale systems. These systems involve metal-dielectric structures supporting surface plasmons that interact with semiconductor nanostructures or molecule ensembles. Surface plasmons are collective electron excitations resonantly excited by light in small metal nanoparticles with energies ranging across the optical spectrum to near infrared which provide means of unprecedented energy concentration and transfer on the length scale far below the diffraction limit. In hybrid plasmonic systems, strong optical interactions between surface plasmons and electronic excitations in semiconductors or molecules give rise to novel phenomena that are widely used in numerous device applications ranging from optoelectronic to biomedical applications. The focus of the current project is on complex plasmonic systems involving, for example, large numbers of molecules or quantum dots interacting with surface plasmons in metal nanostructures. The optical properties of such systems are dominated by collective and cooperative effects that strongly enhance optical interactions and energy transfer processes monitored by means of various spectroscopic techniques. The project has a significant educational and training component involving undergraduate students in research activities. Technical Summary This award supports theoretical and computational research and associated education involving modeling cooperative and quantum phenomena in complex plasmonic systems such as metal-dielectric structures conjugated with large ensembles of quantum emitters including dye molecules and semiconductor quantum dots. Optical interactions between quantum emitters situated in the regions of strong field confinement or distributed in extended regions near plasmonic structures give rise to cooperative behavior observed in plasmon-enhanced optical spectroscopy experiments. The specific research tasks of this project include studies of optical spectra of highly tunable hybrid plasmonic systems at strong exciton-plasmon coupling focusing on the role of collective bright and dark states, investigating the role of plasmon-induced coherence between quantum emitters in the emission and scattering spectra in the strong coupling regime, elucidating mechanisms for plasmon-enhanced light emission by small metal nanostructures including inter-band photoluminescence and intra-band electronic Raman scattering, probing the role of collective effects in surface-enhanced Raman scattering (SERS) for large ensembles of molecules, modeling energy transfer processes within large ensembles of molecules near metal-dielectric structures, and developing a quantum approach for emitters strongly coupled with surface plasmons accounting for temporal dispersion of the metal dielectric function. A combination of analytical and numerical methods will be used to develop quantitative models describing optical properties of complex plasmonic systems such as single nanoparticles, nanoparticle clusters, or plasmonic cavities conjugated with semiconductor quantum dots or dye molecules ensembles. The project's research tasks will address several outstanding issues in the plasmon-enhanced optical spectroscopy area while the models developed will help in interpreting the experimental data. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.