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PhD Defense: Haixu Leng

Tuesday, December 18, 2018
1:30 PM - 4:30 PM
Physics : 401
ADVISOR: Dr. Matthew Pelton

TITLE: Discrete Metal-Semiconductor Nanoparticle Assemblies for Controlled Plasmon-Exciton Coupling

We studied the interaction between individual gold nanoparticles (plasmon) and quantum dots (exciton) experimentally and theoretically at a nanoscale. Coupling optical emitters (quantum dots) to plasmon resonances in metal nanostructures has long been investigated as a means to increase their spontaneous emission rates. This increased rate occurs for weak coupling between the emitter and plasmon; for intermediate coupling, the Fano resonance will be seen; under strong coupling the system undergoes Rabi splitting into new, hybrid modes. To date, efforts at achieving strong coupling between plasmons and single emitters have mostly been studied in scattering measurements; however, Rabi splitting in the scattering spectrum is difficult to distinguish from the Fano interference, or induced transparency, that occurs at intermediate coupling strengths. Here, we report measurements of scattering and photoluminescence (PL) from individual coupled plasmon-emitter systems that consist of a single quantum dot (QD) in the gap between a gold nanoparticle and a silver film. Splitting of the modes in PL is a signature of the strong coupling effect. The measurements unambiguously demonstrated weak, intermediate, and strong coupling at room temperature. In a separate study, we found that the PL of the quantum dot splits into two modes as the gold nanotip approaches the quantum dots on a gold substrate. The splitting in both cases was over 150 meV, which exceeded the plasmon cavity loss. These studies opened up the possibility of single-photon nonlinearities and other extreme light-matter interactions at the nanoscale at room temperature.