Strong coupling in molecular exciton-plasmon Au nanorod array systems

Abstract

We demonstrate here strong coupling between localized surface plasmon modes in self-standing nanorods with excitons in a molecular J-aggregate layer though angular tuning. The enhanced exciton−plasmon coupling creates a Fano like line shape in the differential reflection spectra associated with the formation of hybrid states, leading to anti-crossing of the upper and lower polaritons with a Rabi frequency of 125 meV. The recreation of a Fano like line shape was found in photoluminescence demonstrating changes in the emission spectral profile under strong coupling. PaperDevelopments in top-down and bottom-up nanofabrication techniques have enabled the development of active plasmonic nanomaterials such as arrays of gold nanorods with size-and shape-tunable plasmonic resonances [1][2][3][4]. Active plasmonics nanomaterials can be coupled with excitonic systems to give rise to hybrid plasmon-exciton modes (Plexcitons) when in the strong coupling regime [5][6][7][8]. Such systems when within the strong coupling limit effect changes in the optical processes of an emitter or absorber excitonic system. This offers potential to enhance or control exciton processes in excitonic systems such as organic semiconductors which offers opportunities for enhanced photonic device designs such as in light harvesting, optical sensing or artificial light sources [1,9,10]. An understanding of light mater interactions of plasmon-exciton complexes is central in fully realizing the potential of such complexes.A number of studies have demonstrated plasmon-exciton in the strong coupling limit between an organic exciton semiconductor and a surface plasmons [11,12] and localized surface plasmons geometries [13][14][15][16][17]. Studies have demonstrated that colloidal Au nanoshell-J-aggregate particles exhibit strong coupling between the localized plasmons of a nanoshell and the excitons of molecular J-aggregates adsorbed on its surface [13]. The interaction of an organic exciton in a J-aggregate and surface plasmon polariton modes of nanostructured hole arrays or of nanosize metallic disks with different array periods was reported to exhibit strong coupling [14][15][16]. Tuning of plasmon-exciton coupling strength has been reported for strongly coupled exciton-plasmon states in Au nanodisk arrays coated with J-aggregate molecules achieved by changing the incident angle of incoming light, rather than changing the geometry 2 of the plasmonic nanomaterial. Using such an angle resolved approach plasmon-exciton coupling of variable strengths was achieved [17].Strong coupling between plasmons on oriented gold nanorods arrays and J-aggregate molecular exciton has been demonstrated using a series of arrays with different architectures to control the spatial and spectral overlap between the plasmonic structure and exciton molecular aggregates [18]. Here we demonstrate tuning/detuning of strong coupling in self-standing nanorod arrays achieved though angular tuning. We report a Fano line shape in the differential reflection spectra associated...

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