14 May 2018

Modified Excited States Dynamics in the Localized Plasmon - Molecular Exciton Hybrids

Title: Modified Excited States Dynamics in the Localized Plasmon - Molecular Exciton Hybrids.
When: Tuesday, May 22, (2018), 12:00.
Place: Department of Condensed Matter Physics, Faculty of Sciences, Module 3, Seminar Room (5th Floor).
Speaker: Timur Shegai, Department of Physics, Chalmers University of Technology, 412 96, Göteborg, Sweden.

Strong light-matter interactions in microcavities have been long known to provide means to alter optical and nonlinear properties of the coupled system. As a result of this interaction, one typically observes the emergence of new polaritonic eigenstates of the coupled system. These states are of hybrid nature and possess both light and matter characteristics, which is reflected as so-called vacuum Rabi splitting, observed in the absorption or transmission spectra. Because of the hybrid nature of these states, the excited state temporal dynamics can be significantly altered in comparison to the uncoupled system dynamics. This, in turn, can have profound effects on the emission and photochemical processes.

Figure 1. Coupled system at various temperatures. Bottom: Dark-field (DF) scattering spectra at T=300 K (left) and 6 K (right). At room temperature the DF spectrum depicts two peaks, namely the upper and lower polaritons. At lower temperatures the DF spectrum shows three peaks that are identified as upper, middle and lower polaritons. Arrows represent the splitting caused by excitons at 300 K whereas the splitting is caused by excitons and trions at 6 K. Top: Artist view of plasmon-exciton mixture at T=300 K and plasmon-exciton-trion interaction at T=6 K.

In this talk I will discuss our recent results on individual plasmonic nanoantennas strongly coupled to molecular J-aggregates [1-4] and 2D materials [5]. In the case of J-aggregates we observe Rabi splitting up to 400 meV, i.e. ~20% of the resonance energy. Moreover, we observe mode splitting not only in elastic scattering but also in photoluminescence of individual hybrid nanosystems, which manifests a direct proof of strong coupling in plasmon-exciton nanoparticles. This situation is drastically different from the photoluminescence of uncoupled molecules, which signals the involvement of polaritonic states into the relaxation pathways of the hybrid system. I also discuss how the involvement of these pathways can modify other relevant excited state dynamics, including photo-oxidation processes [4]. In the case of 2D materials, we observe complex temperate-dependent plasmon-exciton polariton mixtures, which at low temperatures can admix trions (charged excitons) into a common polaritonic state (see Figure 1.) [5]. Such admixture can be interesting in the context of polariton-polariton interactions and potentially for the charge transport in strongly coupled systems.


1. Zengin, G.; Johansson, G.; Johansson, P.; Antosiewicz, T. J.; Käll, M.; Shegai, T. Sci. Rep. 2013, 3, 3074.
2. Zengin, G.; Wersäll, M.; Nilsson, S.; Antosiewicz, T. J.; Käll, M.; Shegai, T. Physical Review Letters 2015, 114, (15), 157401.
3. Wersäll, M.; Cuadra, J.; Antosiewicz, T. J.; Balci, S.; Shegai, T. Nano Letters 2017, 17, (1), 551-558.
4. Munkhbat, B.; Wersäll, M.; Baranov, D. G.; Antosiewicz, T. J.; Shegai, T. arXiv preprint 2018, arXiv:1802.06616.
5. Cuadra, J.; Baranov, D. G.; Wersäll, M.; Verre, R.; Antosiewicz, T. J.; Shegai, T. Nano Letters 2018.

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