Optical Chirality In A Strong Coupling System Consisting Of Gold Chiral Helicoid Nanoparticles And Emitters

The advantages of the plasmon micro-nano structures are its ultrasmall mode volume and its ability to achieve strong light-matter interactions at room temperature.One of the research hotspots in this field is the construction of strong coupling systems between metal microcavities and excitons,and the addition of chirality can add a new dimension to the regulation of the strong coupling process.The far and near field chirality properties are usually characterized by circular dichroism(CD)and optical chirality(OC),respectively.The current research on strong coupling systems containing chiral structures is mainly focused on far-field properties,and little work has been done to concentrate on the changes of near-field chiral electromagnetic modes during the coupling process.However,the study of the near-field properties of chiral plexcitonic states will promote the development of chiral optics and provide new perspectives on chiral modulation.The preparation of chiral plasmonic gold helicoid nanoparticle(GHNP)has pioneering significance in precisely inducing chiral growth at the nanoscale.And the representative threedimensional complex chiral structure of this particle gives it abundant electromagnetic modes.In this paper,we investigated the preparation process of GHNP and its near and far field properties before and after coupling with excitons in order to explore the mechanism of chirality further.We found that the electromagnetic field distribution of GHNP consists of one dark mode and two bright modes.The dark mode is observed more clearly in CD than in extinction spectra.Two bright modes can strongly couple with excitons respectively,which is confirmed by the anticrossing behavior and mode splitting exhibited in extinction and CD spectra.We also analyzed the nearfield OC distribution of the GHNP hybrid system,and obtained the chiral responses as well as the spectral correspondence between OC and CD.Furthermore,although the strong coupling interaction changes the energy levels resulting in mode splitting,the chiral hotspots distributions of both the upper polariton branch and lower polariton branch are consistent with the original bright mode in OC maps.Our findings provide guidance for the design of structures with strong chiral responses and enhance the comprehension of chiral strong coupling systems.