Pliable polaritons: Wannier exciton-plasmon coupling in metal-semiconductor structures

Plasmonic structures are known to support the modes with sub-wavelength volumes in which the field/matter interactions are greatly enhanced. Coupling between the molecular excitations and plasmons leading to the formation of “plexcitons” has been investigated for a number of organic molecules. However, plasmon-exciton coupling in metal/semiconductor structures has not experienced the same degree of attention. In this work, we show that the “very strong coupling” regime in which the Rabi energy exceeds the exciton binding energy is attainable in semiconductor-cladded plasmonic nanoparticles and leads to the formation of Wannier exciton-plasmon polariton (WEPP), which is bound to the metal nanoparticle and characterized by dramatically smaller (by a factor of a few) excitonic radius and correspondingly higher ionization energy. This higher ionization energy, which exceeding approaches 100 meV for the CdS/Ag structures, may make room-temperature Bose-Einstein condensation and polariton lasing in plasmonic/semiconductor structures possible.