Near-Field Mediated Plexcitonic Coupling and Giant Rabi Splitting in Individual Metallic Dimers

Abstract

Strong coupling between resonantly matched localized surface plasmons and molecular excitons results in the formation of new hybridized energy states called plexcitons. Understanding the nature and tunability of these hybrid nanostructures is important for both fundamental studies and the development of new applications. We investigate the interactions between J-aggregate excitons and single plasmonic dimers and report for the first time a unique strong coupling regime in individual plexcitonic nanostructures. Dark-field scattering measurements and finite-difference time-domain simulations of the hybrid nanostructures show strong plexcitonic coupling mediated by the near-field inside each dimer gap, which can be actively controlled by rotating the polarization of the optical excitation. The plexciton dispersion curves, obtained from coupled harmonic oscillator models, show anticrossing behavior at the exciton transition energy and giant Rabi splitting ranging between 230 and 400 meV. These energies are, to the best of our knowledge, the largest obtained on individual hybrid nanostructures.

Plexciton Quenching by Resonant Electron Transfer from Quantum Emitter to Metallic Nanoantenna

“…13,14 Similar results have been reported in recent experiments. 23 Despite the work of Schalter et al 23 has been performed for an individual metallic dimer surrounded by a layer of J-aggregates, the authors demonstrate the decisive role of the molecules located in the junction and thus subjected to the strong plasmonic field enhancement. In our calculations shown in the right panels of Figure 4, that is, neglecting the RET into the metal, two plexciton modes are always distinguishable for the variation of the system geometry as considered in the present work.…”

“…On the theoretical side, classical and quantum calculations for a QE placed in the middle of the junction of a plasmonic dimer show that the hybrid structure undergoes dramatic changes in the absorption cross section as compared to individual components. [12][13][14][15]23 Thus, the electromagnetic coupling between the QE and the plasmonic nanoparticles has been tackled both theoretically and experimentally leading to the advanced understanding of the underlying phenomena. However, much less is known on the role of the direct electronic coupling between the QE and the plasmonic nanoparticle.…”

Modified optical absorption of molecules on metallic nanoparticles at sub-monolayer coverage

“…1 a general description of the problem, using Mie theory to model the optical response of silver colloids, and a standard isotropic effective medium [22,25,27,30,31,33,35,36] for the thin coating layer arXiv:1509.07216v1 [physics.optics]…”

“…Many of these existing and emerging applications are underpinned by the fact that the optical (electronic) absorption of molecules on the surface of metallic NPs is enhanced. But spectral changes induced by molecular adsorption are often ignored because of the experimental challenge of measuring surface absorbance spectra on nanoparticles, despite early attempts more than 30 years ago [21].This question is not directly addressed in the great number of recent studies devoted to the topic of strongcoupling between plasmons and molecules [22][23][24][25][26][27][28][29][30][31][32][33][34][35][36]; in this regime, the plasmon-molecule interaction is evidenced by a typical anti-crossing of the two resonances as a function of detuning [25,33], but in such a strongly interacting system the molecular response cannot be isolated. Moreover, in such studies the dye concentration is often large (typically monolayer coverage and above) to maximize dye/plasmon interactions.…”

Theoretical Criteria for Scattering Dark States in Nanostructured Particles

“…1 Subwavelength structures on resonance can have scattering cross sections much larger than their geometrical sizes, 2,3 and the presence of multiple resonances leads to even more possibilities through mode hybridization 4 and interference effects. [5][6][7][8][9] A particularly interesting phenomenon is the suppressed scattering in nanostructures with multiple plasmonic resonances, [10][11][12][13][14][15][16][17][18][19][20][21][22][23] plasmonic and excitonic resonances, [24][25][26][27][28][29][30] or dielectric resonances, 31,32 referred to collectively as a "scattering dark state." A wealth of models has been employed to describe this suppressed scattering, ranging from perturbative models, 12 generalization of the Fano formula, [13][14][15] and electrostatic approximation, 22,23 to coupled-mechanical-oscillator models.…”