Exciton-plasmon interaction in metal-semiconductor hybrid nanostructures

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The project aims at an improved microscopic understanding of the linear and nonlinear optical excitations of prototypical hybrid nanostructures comprising metal and semiconductors or molecules, specificially in systems with nanometer extension in all three spatial dimensions. We propose to investigate in particular the coherent coupling between excitons (X), the elementary optical excitations of semiconductors, and surface-plasmon (SP) polaritons (SPP), the elementary optical excitations of metallic nanostructures. Experimental methods from coherent ultrafast spectroscopy and nano-optical imaging techniques will be combined with theoretical modeling using methods from many-body theory, quantum chemistry and disorder physics as well as computer simulations of optical and electronic properties. We will use these tools to study the dynamics of SPP fields coupled to active quantum materials in the gain regime on a nanometer-femtosecond scale. Organic laser dyes such as rhodamines and inorganic colloidal quantum dots will be used as gain media. Several routes will be explored to confine the SPP field spatially as much as possible in order to increase and optimize the exciton-plasmon coupling, enabling us to strongly couple SPP fields to individual few-level quantum emitters. The ultrafast manipulation of the so-called Rabi splitting of the coupled X-SPP quantum modes demonstrated within the first funding period opens up uncharted avenues for exploring the strong- or even ultrastrong-coupling regime in such hybrid systems. We aim at demonstrating new ultrafast functionality, exploitable in future plasmonic and quantum-plasmonic devices such as plasmonic transistors or for nanoantenna-enhanced sensing of single nanoparticles. Of particular interest are (i) active materials and the physics of the gain regime, (b) single quantum emitters, quantum plasmonics, and light switching on the nanometer-femtosecond scale, as well as (c) the interplay of disorder-induced localization and the formation of hot spots with extreme local field enhancement.