Strong Light-Matter Interactions in Single Open Plasmonic Nanocavities at the Quantum Optics Limit

Renming Liu, Zhang-Kai Zhou, Yi-Cong Yu, Tengwei Zhang, Hao Wang, Guanghui Liu, Yuming Wei, Huanjun Chen, and Xue-Hua Wang

Phys. Rev. Lett. 118, 237401 – Published 8 June 2017

Abstract

Reaching the quantum optics limit of strong light-matter interactions between a single exciton and a plasmon mode is highly desirable, because it opens up possibilities to explore room-temperature quantum devices operating at the single-photon level. However, two challenges severely hinder the realization of this limit: the integration of single-exciton emitters with plasmonic nanostructures and making the coupling strength at the single-exciton level overcome the large damping of the plasmon mode. Here, we demonstrate that these two hindrances can be overcome by attaching individual $J$ aggregates to single cuboid Au@Ag nanorods. In such hybrid nanosystems, both the ultrasmall mode volume of $\sim 71 {nm}^{3}$ and the ultrashort interaction distance of less than 0.9 nm make the coupling coefficient between a single $J$ -aggregate exciton and the cuboid nanorod as high as $\sim 41.6 meV$ , enabling strong light-matter interactions to be achieved at the quantum optics limit in single open plasmonic nanocavities.

Received 28 July 2016

DOI:https://doi.org/10.1103/PhysRevLett.118.237401

Physics Subject Headings (PhySH)

Hybrid quantum systems Nanocrystals Plasmonics Quantum optics

Quantum Information, Science & TechnologyAtomic, Molecular & Optical

Authors & Affiliations

Renming Liu¹, Zhang-Kai Zhou¹, Yi-Cong Yu², Tengwei Zhang¹, Hao Wang³, Guanghui Liu¹, Yuming Wei¹, Huanjun Chen¹, and Xue-Hua Wang^1,*

¹State Key Laboratory of Optoelectronic Materials and Technologies, School of Physics, Sun Yat-sen University, Guangzhou 510275, China
²School of Physics and Optoelectronic Engineering, Foshan University, Foshan 528000, China
³Guangdong Province Key Laboratory of Display Material and Technology, Sun Yat-sen University, Guangzhou 510275, China

^*Corresponding author. wangxueh@mail.sysu.edu.cn

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Vol. 118, Iss. 23 — 9 June 2017

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Images

Figure 1
(a) Transmission electron microscopy (TEM) images of (I) a Au NR and (II)–(IV) Au@Ag NRs with capsule and cuboid shapes. (b) Left: (I)–(IV) Schematic views of the NRs shown in (a). Right: Finite-difference time-domain (FDTD) simulated EF distributions of the LLSPR mode supported by (V) the Au NR (length, 58 nm; diameter, 16 nm) and Au@Ag NRs modeled as (VI) a capsule with a 1.5 nm Ag nanoshell and (VII),(VIII) cuboids with Ag nanoshells of 2 and 4 nm in length and 3 and 11.5 nm in width, respectively. The cuboid NRs have eight slightly rounded corners (the curvature radius at each corner is 1 nm). (c) Normalized EF $f_{d}$ ( $r$ ) and $g_{d c}$ as functions of the emitter distance from the vertex of the corner along the direction of the maximum EF [dashed white arrows in (b)]. The dashed pink lines and blue stars are the $g_{d c}$ obtained from Eq. (2) and using ab initio calculations, respectively. $μ_{c}$ was set to 0.7 e nm.
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Figure 2
(a) Extinction spectra of (I) bare Au@Ag NRs, (II) pristine (PIC) $J$ aggregates, and (III) Au@Ag $NR / J$ -aggregate ensembles. (b) Dispersions of the hybrid states extracted from the experimental data (blue and red dots) and calculated using Eq. (3) (blue and red lines). In the calculations, $N_{x} = 4.8$ , ${\bar{Γ}}_{d} \sim 164 meV$ (a mean value for the Au@Ag NR ensembles with different MARs), $Γ_{c} \sim 25 meV$ , and $g_{d c} \sim 41.6 meV$ were used. The dashed black and green lines represent the uncoupled exciton and LLSPR energies, respectively. The ensembles were treated with $5.0 μ M$ dye solution. (c) Typical extinction spectra of the Au@Ag NRs with $λ_{LLSPR} = 575 \pm 5 nm$ strongly coupled to $J$ aggregates and treated with $0.8 - 12.0 μ M$ dye solutions. The individual curves are offset vertically for clarity. (d) ${(ℏ Ω_{R})}^{2}$ as a function of the dye concentration. The red line is the linear fit of ${(ℏ Ω_{R})}^{2}$ for the samples treated with $0.8 - 5.0 μ M$ dye solutions. The error bars in (b) and (d) represent the standard deviations calculated from the three extinction spectra measured in each case.
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Figure 3
(a) Left: Schematics of the optical measurements for (I) a bare Au@Ag NR, (II) $J$ aggregates, and (III) a strongly coupled Au@Ag $NR / J$ -aggregate hybrid. The insets are dark-field images of the individual NRs and a photograph of the $J$ -aggregate solution in the reaction vessel used for the measurements. Right: (IV)–(VI) Spectra obtained by performing the measurements as shown in the left panel. The dashed lines represent the Lorenz-fitted results. (b) Scattering spectra of three individual Au@Ag $NR / J$ -aggregate hybrids with different detunings ( $Δ < 0$ , $Δ = 0$ , and $Δ > 0$ ). The insets are dark-field and SEM images of the corresponding hybrid NRs. The scale bar is 50 nm. (c),(d) (I) Scattering spectra of the individual Au@Ag $NR / J$ aggregates ordered according to detuning for the ensembles treated with (c) 2.0 and (d) $5.0 μ M$ PIC dye solutions. (II) Extinction spectra calculated for (c) ${\bar{N}}_{x} = 1.7$ and (d) ${\bar{N}}_{x} = 4.6$ using Eq. (1). In the calculations, ${\bar{Γ}}_{d} \sim 135 meV$ (a mean value for the bare Au@Ag NRs, Fig. S14 [30]), $Γ_{c}$ $\sim 25 meV$ , and ${\bar{g}}_{d c} \sim 41.3 meV$ were used. The dashed black and pink lines represent the uncoupled exciton transition and LLSPR wavelengths, respectively.
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Figure 4
(a) Black lines: Representative scattering spectra of the individual hybrid Au@Ag $NR / J$ aggregates with different $ℏ Ω_{R}$ . The individual hybrids (I)–(VI) were isolated from the ensembles treated with 0.8, 2.0, 3.0, 4.0, 5.0, and $0.8 μ M$ dye solutions. Dashed red lines are extinction spectra of the strongly coupled hybrids calculated using Eq. (1). The insets are SEM images of the corresponding hybrid NRs. The scale bar is 50 nm. (b) Statistics of the $h Ω_{R}$ measured for individual hybrid NRs and the corresponding ${\bar{N}}_{x}$ calculated using Eq. (1) for each dye concentration. About 20–30 hybrid NRs were counted in each case (Fig. S18 [30]). In the calculations, ${\bar{g}}_{d c} \sim 41.3 meV$ , ${\bar{Γ}}_{d} \sim 135 meV$ (the mean value for the bare Au@Ag NRs, Fig. S14 [30]), and $Γ_{c} \sim 25 meV$ were used. The dashed red line is a linear fit of ${\bar{N}}_{x}$ corresponding to the various dye concentrations. (c) (I)–(III) TEM images of Au@Ag $NR / J$ aggregates with different dye layer thicknesses and (IV),(V) high-resolution TEM (HRTEM) images of the edges of a single Au@Ag $NR / J$ -aggregate hybrid and a bare Au@Ag NR, respectively.
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