Tunable strong exciton&#x2013;plasmon&#x2013;exciton coupling in WS<sub>2</sub>&#x2013;J-aggregates&#x2013;plasmonic nanocavity

Ping Jiang; Gang Song; Yilin Wang; Chao Li; Lulu Wang; Li Yu

doi:10.1364/OE.27.016613

1. Introduction

Strong light-matter interactions have attracted intense interest due to their great potentials in single-atom lasers [1], quantum information processing [2–4], and ultrafast single-photon switches [5,6]. When the rate of energy exchange between two individual systems exceeds the damping of either, an extraordinary regime of strong light-matter interactions called strong coupling is achieved [7–15]. Strong coupling between different emitters: excitons in transition metal dichalcogenides (TMDs) or J-aggregated dye molecules and surface plasmon polaritons (SPPs) supported by plasmonic nanocavities has been widely studied [7,16–28]. SPPs are electromagnetic excitations propagating at the interface between dielectric and metal, which can enhance the local field with high field confinement [29]. Thus the strong coupling between excitons and plasmons can be achieved in various plasmonic nanocavities [16–28].

Recently, TMDs and J-aggregated dye molecules have attracted tremendous attention for studying strong coupling between excitons and plasmons. Monolayers of TMDs are semiconductor materials with high optical absorption reaching values of 15% for WS₂ at the A exciton resonance around 2 eV [30] and a direct band gap at the Κ (Κ’) points of the Brillouin zone. Because of the reduced dielectric screening, giant excitonic effect dominates the band gap transition in monolayers TMDs, possessing a large transition dipole moment μ that achieves strong coupling [31,32]. Additionally, TMDs are chemically stable at ambient conditions, and the strong coupling between TMDs and plasmonic nanocavities can be active controlled via electrostatic gating [33], temperature control [8,34,35] and femtosecond pumping [36,37]. J-aggregated dye molecules are self-organised molecular crystals which possess narrow, red-shifted absorption bands with high oscillator strength [10,38]. The strong coupling between J-aggregated dye molecules and plasmonic nanocavities can be controlled by varying the concentration of J-aggregates [39,40].

Multimode couplings in hybrid excitonic systems have been studied widely because they have more energy dissipation channels and greater modulation [41–44]. For example, the exciton–plasmon–exciton coupling system which consists of a microcavity containing two different J-aggregated dyes is used to study energy transfer processes [41]. Strong plasmon–exciton–trion interaction between localized surface plasmon resonances (LSPRs) in silver nanoprisms and excitons and trions in monolayer WS₂ has been achieved at low temperature, which open up a possibility to exploit electrically charged polaritons at the single nanoparticle level [8]. Plasmon–exciton–plasmon couplings in Ag–J-aggregates–Ag nanostructures have been also studied. Strong couplings among LSPRs, exciton resonances, and SPPs were modulated by varying the original localized surface plasmon resonance mode [44]. However, the strong interaction between LSPRs in silver nanoprisms and excitons in J-aggregated dyes molecules and monolayer WS₂ has not been studied. This hybrid system is endowed with a hybrid plexciton state with distinct excitons which provides a potential technological route towards active control of strong exciton–plasmon–exciton coupling by modulating different excitons.

In this paper we investigate WS₂ excitons and J-aggregate excitons coupling with LSPRs in the Ag–J-aggregates–WS₂ hybrid nanostructure. The strong couplings among the WS₂ excitons, J-aggregate excitons, and LSPRs are achieved, resulting in three plexciton branches. Coupled oscillator model is used to calculate scattering spectra of the hybrid nanostructure and analyze the exciton–plasmon–exciton coupling behavior. Weighting efficiencies of original modes in the upper (UPB), middle (MPB) and lower plexciton branches (LPB) states are calculated. The weighting efficiencies are used to analyzing the hybrid modes in the coupling system. In addition, the strong exciton–plasmon–exciton coupling can be modulated by tuning the temperature or the concentration of J-aggregates.

2. Methods

To investigate the strong exciton–plasmon–exciton coupling in the hybrid system, finite-difference time-domain (FDTD) simulations are performed to obtain its optical response. The hybrid nanostructure investigated here composed of a silver nanoprism separated from a monolayer WS₂ by J-aggregates, as depicted in Fig. 1. The inset shows the cross section view of the hybrid system. The silver nanoprisms are triangular with side length in the range of 45–65 nm, thickness 10 nm, and corner rounding of 3 nm. The mesh size for the Ag nanoprism is 0.5 nm in the x-, y- and z-directions. The mesh size for the WS₂ and J-aggregates layer are 0.5 nm in the x- and y- directions, and 0.1 nm in the z- directions. The permittivities of silver are taken from Johnson and Christy data [45]. The dielectric function of J-aggregates and the monolayer WS₂ can be described by the superposition of several Lorentz models [31,46–48]:

ε (E) = ε_{B} - \sum_{j = 1}^{N} \frac{f_{j} E_{0 j}^{2}}{E^{2} - E_{0 j}^{2} + i γ_{0 j} E}

Here

ε_{B}

represents the background permittivity,

E

is the photon energy (in unit of eV),

E_{0 j},

γ_{0 j},

and

f_{j}

are resonance energy, damping rate of the oscillator, and oscillator strength with index

j,

respectively. In terms of J-aggregates: we set

N = 1,

ε_{B} = 2.1,

γ_{0} = 50

meV following that used in [22]. The oscillator strength

f

varies from 0.02 to 0.1, which is consistent with previous experiments [49,50]. In the case of WS₂:

N = 5,

ε_{B} = 1,

these parameters applied in the simulation are taken from the data in [46], and the measured transmittance optical spectra of a monolayer WS₂ flake on the silica substrate have been well reproduced by using Eq. (1). In our simulation, we use the measured damping rate of the A exciton resonance

γ_{X} = 28

meV [46]. Both J-aggregates and monolayer WS₂ exhibit pure exciton absorption in the hybrid system [51]. Furthermore, temperature dependence of the semiconductor bandgap is conveniently described by the O’Donell model for the temperature dependency of the A excitonic transition energy [8,34,52]:

E_{g} (T) = E_{g} (0) - S 〈 ℏ ω 〉 {c o t h [\frac{〈 ℏ ω 〉}{2 k_{B} T}] - 1},

where

E_{g} (0)

is excitonic transition energy at 0 K,

S

is a dimensionless coupling constant that represents electron-phonon coupling strength, and

〈 ℏ ω 〉

is the average phonon energy. In our simulation the O’Donnel model gives the following values of

E_{g} (0) = 2.07

eV,

S = 1.78,

and

〈 ℏ ω 〉 = 25

meV, which is taken from the data in [8]. Thus, we can get the A exciton resonances of WS₂ varies with temperature.

Fig. 1 Schematic diagram of the Ag–J-aggregates–WS₂ nanostructure. The inset shows the cross section of the hybrid nanostructure with the thickness of Ag nanoprism 10 nm. The thickness of J-aggregates and monolayer WS₂ both are 1 nm.

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In order to provide physical insight into the exciton–plasmon–exciton coupling, we further focus on the line shape analysis of the scattering spectra. Hence, we fit the calculation results by using coupled oscillator model [53]. In our hybrid system, the coupled oscillator is composed of an oscillator representing plasmon, an oscillator representing J-aggregates exciton, and an oscillator representing the A exciton resonance of WS₂. The equations of motion for the three oscillators are:

{\ddot{x}}_{P L} (t) + γ_{P L} {\dot{x}}_{P L} (t) + ω_{P L}^{2} x_{P L} (t) + g_{J} {\dot{x}}_{J} (t) + g_{X} {\dot{x}}_{X} (t) = F_{P L} (t),

{\ddot{x}}_{J} (t) + γ_{J} {\dot{x}}_{J} (t) + ω_{J}^{2} x_{J} (t) - g_{J} {\dot{x}}_{P L} (t) = F_{J} (t),

{\ddot{x}}_{X} (t) + γ_{X} {\dot{x}}_{X} (t) + ω_{X}^{2} x_{X} (t) - g_{X} {\dot{x}}_{P L} (t) = F_{X} (t),

where

x_{P L},

x_{J},

and

x_{X}

are the coordinates of plasmon, J-aggregates exciton oscillator, and A exciton oscillator, respectively.

γ_{P L},

γ_{J},

and

γ_{X}

are the damping rate of plasmon, J-aggregates exciton, and A exciton, respectively.

ω_{P L},

ω_{J},

and

ω_{X}

are the resonance frequencies of plasmon, J-aggregates exciton, and A exciton, respectively.

g_{J}

is the coupling rate between plasmon and J-aggregates exciton.

g_{X}

is the coupling rate between plasmon and A exciton.

F_{P L},

F_{J},

and

F_{X}

represent the driving forces because of the external source. We assume that the A exciton and J-aggregates exciton are both entirely driven by the plasmon oscillator, hence, we set

F_{P L} (t) = F_{P L} e^{- i ω t},

where

ω

is the frequency of the electric field,

F_{J} (t) = 0,

F_{X} (t) = 0.

Finally,

x_{P L} (t),

x_{J} (t),

and

x_{X} (t)

can be derived from Eq. (3), (4), and (5). In our hybrid nanostructure, the dimensions of the structure are small compared to the optical wavelength, thus the scattering cross-section can be calculated in quasi-limit [54]. In this limit, scattering cross-section is

(8 π / 3) \cdot k^{4} {| F_{P L} x_{P L} |}^{2},

where

k = ω n / c

is the wavevector of light. By substituting

x_{P L} (t)

into

(8 π / 3) \cdot k^{4} {| F_{P L} x_{P L} |}^{2}

and using incident light energy

E

replaces the incident light frequency

ω,

one can obtain the scattering cross-section:

σ_{s c a t} (E) = \frac{8 π}{3} k^{4} {| F_{P L} x_{P L} |}^{2} \propto E^{4} {| \frac{a b}{a b (E^{2} - E_{P L}^{2} + i E γ_{P L}) - E^{2} g_{J}^{2} b - E^{2} g_{X}^{2} a} |}^{2},

where

a = E^{2} - E_{J}^{2} + i E γ_{J},

b = E^{2} - E_{X}^{2} + i E γ_{X} .

To reveal the underlying exciton–plasmon–exciton coupling behaviors in the hybrid nanostructure, we use the classic coupled oscillator model to study the multimode coupling. In order to simplify the oscillator model, the damping losses are not taken into account [41,42,44]. The exciton–plasmon–exciton system can be modeled as three coupled harmonic oscillators:

[\begin{matrix} E_{P L} & g_{X} & g_{J} \\ g_{X} & E_{X} & 0 \\ g_{J} & 0 & E_{J} \end{matrix}] [\begin{matrix} α_{1} \\ α_{2} \\ α_{3} \end{matrix}] = E [\begin{matrix} α_{1} \\ α_{2} \\ α_{3} \end{matrix}],

where

E_{P L},

E_{X},

and

E_{J}

are the energies of plasmon, A exciton, and J-aggregates exciton, respectively.

g_{X}

is the interaction constant between

E_{P L}

and

E_{X}

modes.

g_{J}

is the interaction constant between

E_{P L}

and

E_{J}

modes. The interaction constant between

E_{X}

and

E_{J}

modes is zero.

α_{1},

α_{2},

and

α_{3}

are the eigenvector components (Hopfield coefficients), the corresponding

{| α_{1} |}^{2},

{| α_{2} |}^{2},

and

{| α_{3} |}^{2}

represent the weighting efficiencies and satisfy

{| α_{1} |}^{2} + {| α_{2} |}^{2} + {| α_{3} |}^{2} = 1.

3. Results and discussion

We investigate the optical properties of the Ag nanoprism at first. Figure 2(a) presents the simulated scattering spectra of the Ag nanoprisms, showing the LSPRs at 1.93 eV, 1.99 eV, and 2.03 eV, respectively. The resonance spectral width ( $γ_{P L} = 80$ meV) hardly varies with the plasmon resonance. Figure 2(b) gives the simulated transmission spectrum $T$ of the monolayer WS₂. We can get the A exciton resonance at $E_{X} = 2.02$ eV with the resonance spectral width $γ_{X} = 28$ meV, which is consistent with the experimental result [46]. Figure 2(c) shows the electric field distribution of the Ag nanoprism at 624 nm and polarization along the x-direction axis, the maximum field enhancement occurs at the tips of the Ag nanoprism. The corresponding charge distributions revealed dipole mode and surface charge distribution of the Ag nanoprism at 624 nm as shown in Fig. 2(d).

Fig. 2 (a) Scattering spectra of the Ag nanoprisms. The corresponding LSPRs energies are 1.93 eV, 1.99 eV, and 2.03 eV, respectively. (b) Simulated transmission spectrum of the monolayer WS₂ flake. (c) The electric field distribution of the Ag nanoprism at wavelength of 624 nm (1.99 eV). (d) The corresponding charge distributions of the Ag nanoprism at 624 nm wavelength.

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Then, we study the strong coupling between J-aggregates and Ag nanoprisms, and strong coupling between WS₂ and Ag nanoprisms, respectively. Figure 3(a) shows the resulting successive scattering spectra of J-aggregates coupled with Ag nanoprisms. The color scale represents the scattering efficiency. The “energy” axis of the horizontal represents plasmon resonance energy of Ag nanoprisms (plasmon resonance energy varies with the size of Ag nanoprisms). The “energy” axis of the vertical represents the incident light wavelength (“wavelength” is converted into “energy”).The solid white lines are fit to the coupled oscillator model [10]:

[\begin{matrix} E_{P L} - i \frac{γ_{P L}}{2} & g \\ g & E_{t} - i \frac{γ_{t}}{2} \end{matrix}] [\begin{matrix} α \\ β \end{matrix}] = E [\begin{matrix} α \\ β \end{matrix}],

here,

E_{P L}

is various with the size of Ag nanoprism,

γ_{P L} = 80

meV,

t \in {J, X}

,

E_{J} = 1.94

eV,

E_{X} = 2.02

eV,

γ_{J} = 50

meV,

γ_{X} = 28

meV. The energy of the UPB and LPB exhibits a clear anticrossing behavior which indicates the strong coupling between J-aggregates exciton and LSPR mode. The Rabi splitting is extracted as the minimal splitting between the two polariton branches. A vacuum Rabi splitting of

Ω = 140

meV is obtained at zero detuning (

Δ = E_{P L} - E_{J} = 0

eV). It rigorously satisfies the criteria for strong coupling

Ω > γ_{P L} > (γ_{P L} + γ_{J}) / 2.

Fig. 3(b) shows weighting efficiencies for LSPR mode and J-aggregates exciton contributions to UPB and LPB states as a function of plasmon resonance. This displays a standard plasmon-exciton intermixing behavior, whose weighting efficiencies vary monotonically with the plasmon–exciton detuning. A zero detuning (

E_{P L} = E_{J} = 1.94

eV) corresponds to two polaritons with identical excitonic and plasmonic fractions. A negative detuning (

Δ < 0

) corresponds to the larger excitonic fraction in UPB and smaller excitonic fraction in LPB. A positive detuning (

Δ > 0

) corresponds to the larger plasmonic fraction in UPB and smaller plasmonic fraction in LPB. In our system, the detuning is modulated by LSPRs. The strong coupling between WS₂ and Ag nanoprism is similar to strong coupling between J-aggregates and Ag nanoprism. Figure 3(c) shows the resulting successive scattering spectra of WS₂ coupled with Ag nanoprisms. A vacuum Rabi splitting of

Ω = 148

meV is obtained at zero detuning and

Ω > γ_{P L} > (γ_{P L} + γ_{X}) / 2

satisfies the strong coupling criteria. The weighting efficiencies for LSPR mode and the A exciton contributions to UPB and LPB states are shown in Fig. 3(d).

Fig. 3 (a) Successive scattering spectra of J-aggregates coupled with Ag nanoprisms. The black scattered-diamonds and scattered-triangles represent simulated upper and lower plexciton branches as a function of plasmon resonance position extracted from scattering the spectrum of individual Ag–J-aggregates hybrids of various sizes. The solid white lines are fit to the coupled oscillator model, giving a splitting of 140 meV. The dashed diagonal line and horizontal line correspond to uncoupled LSPR mode and exciton resonance, respectively. The color scale represents the scattering efficiency. The “energy” axis of the horizontal represents plasmon resonance energy of Ag nanoprisms (plasmon resonance energy varies with the size of Ag nanoprisms). The “energy” axis of the vertical represents the incident light wavelength (“wavelength” is converted into “energy”). (b) Weighting efficiencies for LSPR mode and J-aggregates exciton contributions to UPB and LPB states as a function of plasmon resonance. (c) Successive scattering spectra of WS₂ coupled with Ag nanoprisms. (d) Weighting efficiencies for LSPR mode and the A exciton contributions to UPB and LPB states as a function of plasmon resonance.

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Let us now turn our attention to the exciton–plasmon–exciton coupling in Ag–J-aggregates–WS₂ hybrid nanostructures. Figure 4(a) shows scattering cross sections spectra of the hybrids nanostructure. We suppose that there is no directly interaction between the A exciton and J-aggregates exciton. Therefore, the interaction constant between the A exciton and J-aggregates exciton is zero and the exciton–plasmon–exciton coupling can be investigated through three-oscillator model with Eq. (7). The solid white lines in Fig. 4(a) indicate three anticrossed bands corresponding to UPB, MPB and LPB based on Eq. (7). The solid white lines match well with the numerical simulation results (black scattered-diamonds, scattered-circles and scattered-triangles in Fig. 4(a)). The couplings of the plasmon mode with the A exciton and J-aggregates exciton mode result in two anticrossings at around $E_{X} = 2.02$ eV and $E_{J} = 1.94$ eV, respectively. The corresponding coupling strength are $g_{X} = 65$ meV and $g_{J} = 85$ meV, respectively. Therefore, the splitting extracted at the zero detuning between the UPB and MPB is $Ω_{U P B - M P B} = 130$ meV, and the splitting extracted at the zero detuning between MPB and LPB is $Ω_{M P B - L P B} = 170$ meV. Note that the damping losses were not taken into account, since the calculated Rabi splittings are slightly larger than the actual results. Both of them satisfy a simplified strong coupling criterion as $Ω_{U P B - M P B} > γ_{P L} > (γ_{P L} + γ_{X}) / 2 = 54$ meV and $Ω_{M P B - L P B} > γ_{P L} > (γ_{P L} + γ_{J}) / 2 = 65$ meV. Moreover, the minimal splitting between the upper and lower polariton branches is around $Ω_{U P B - L P B} = 227$ meV, and this satisfies a simplified strong coupling condition as $Ω_{U P B - L P B} > (γ_{P L} + γ_{X} + γ_{J}) / 2 = 79$ meV. Figure 4(b) depicts normalized scattering spectrum of J-aggregates and WS₂ coupled with Ag nanoprism simulated by FDTD method (red solid line) and calculated by the three-oscillator model based on Eq. (6) (blue circle). The calculated scattering spectrum by the coupled oscillator model matches well with the simulated one, despite there is a little different between amplitude of the scattering spectrum. The coupled oscillator model further reveals the complicated spectral changes as strong coupling. Figure 4(c) shows the weighting efficiencies for LSPR mode, the A exciton of WS₂ and J-aggregates exciton contributions to three polariton branches (UPB, MPB and LPB) as a function of plasmon resonance. For simplicity, we discuss the J-aggregates exciton fractions in three polariton branches states. The J-aggregates excitonic fraction is nearly zero in UPB. However, it decreases monotonically with plasmon resonance energies in MPB and increases monotonically with plasmon resonance energies in LPB.

Fig. 4 (a) Scattering cross sections spectra of J-aggregates and WS₂ coupled with Ag nanoprisms. The black scattered-diamonds, scattered-circles and scattered-triangles represent simulated upper, middle and lower plexciton branches as a function of plasmon resonance position extracted from the scattering spectrum of individual Ag–J-aggregates–WS₂ hybrid nanostructure of various sizes. The solid white lines are fit to the coupled oscillator model. The dashed diagonal line and horizontal line correspond to uncoupled LSPR mode and two different exciton resonances, respectively. (b) Normalized scattering spectrum of J-aggregates and WS₂ coupled with Ag nanoprism simulated by FDTD solution (red solid line) and calculated by the coupled oscillator model (blue circle). (c) Weighting efficiencies for LSPR mode, the A exciton of WS₂ and J-aggregates exciton contributions to UPB, MPB and LPB states as a function of plasmon resonance.

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Normalized scattering spectra of J-aggregates and WS₂ coupled with Ag nanoprism for the thickness of Ag nanoprism in the range of 8-13 nm are shown in Fig. 5(a). With increasing the thickness of Ag nanoprism, the plasmon resonance energy will show a blue-shift and moves through two exciton modes one after another. As a result, the scattering spectra of strong coupling system have a blue-shift with increasing the thickness of Ag nanoprism as shown in Fig. 5(a). Normalized scattering spectra of J-aggregates and WS₂ coupled with Ag nanoprism for the thickness of J-aggregates layer in the range of 1-8 nm are shown in Fig. 5(b). When the thickness of the J-aggregates layer increases from 1 nm to 7 nm, the coupling strength between J-aggregates exciton and plasmon resonance is increased, resulting in increased Rabi splitting. This phenomenon can be explained by the fact that the coupled J-aggregates excitons are increase with thickness of the J-aggregates layer. When the thickness of J-aggregates layer is increased to 8 nm, the normalized scattering spectrum of the hybrid system hardly changes, which can be attributed to the saturation of coupled J-aggregates excitons. In addition, as the thickness of the J-aggregates layer increases, the coupling strength of WS₂ and plasmon decrease. As a result, three plexciton branches of scattering spectra become two plexciton branches. Therefore, when the middle plexciton branches disappear, there is a maximum thickness of J-aggregates layer to observe strong coupling among J-aggregates excitons, WS₂ excitons and plasmon resonances.

Fig. 5 (a) Normalized scattering spectra of J-aggregates and WS₂ coupled with Ag nanoprism for the thickness of Ag nanoprism in the range of 8-13 nm. The dashed vertical line correspond to uncoupled J-aggregates exciton and WS₂ exciton modes, respectively. (b) Normalized scattering spectra of J-aggregates and WS₂ coupled with Ag nanoprism for the thickness of J-aggregates layer in the range of 1-8 nm.

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Finally, we discuss the modulation of strong couplings in the Ag–J-aggregates–WS₂ hybrid nanostructures. Figure 6(a) shows normalized scattering spectra of J-aggregates and WS₂ coupled with Ag nanoprism for the temperature range from 220K to 380K. The red dash line in Fig. 6(a) indicates that low energy peak positions ( $E_{L P B}^{220 K} = 1.884$ eV, $E_{L P B}^{380 K} = 1.880$ eV) of scattering spectra hardly change with increase of the temperature. This phenomenon is due to the little contribution of WS₂ excitons to the LPB for temperature range from 220K to 380K as shown in Fig. 4(c). The blue dash line shows middle energy peak positions ( $E_{M P B}^{220 K} = 2.004$ eV, $E_{M P B}^{380 K} = 1.972$ eV) of scattering spectra have a red-shift with increase of temperature, and the green dash line shows high energy peak positions ( $E_{U P B}^{220 K} = 2.127$ eV, $E_{U P B}^{380 K} = 2.110$ eV) of scattering spectra have a red-shift with increase of temperature. However, the splitting ( $Δ^{220 K} = E_{U P B}^{220 K} - E_{M P B}^{220 K} = 123$ meV, $Δ^{380 K} = E_{U P B}^{380 K} - E_{M P B}^{380 K} = 138$ meV) between high energy and middle energy increases with increase of temperature. This can be explained by the fact that the A exciton resonances of WS₂ have a red-shift with increase of temperature, effectively tuning WS₂ excitons close to LSPR, the coupling strength increase result in the increase of the Rabi splitting. Figure 6(b) depicts normalized scattering spectra of J-aggregates and WS₂ coupled with Ag nanoprism for oscillator strength of J-aggregates range from 0.02 to 0.1. It is obvious that the splitting ( $Δ^{0.02} = E_{M P B}^{0.02} - E_{L P B}^{0.02} = 64$ meV, $Δ^{0.1} = E_{M P B}^{0.1} - E_{L P B}^{0.1} = 124$ meV) between middle energy and low energy increases with increase of oscillator strength. However, the splitting ( $Δ^{0.02} = E_{U P B}^{0.02} - E_{M P B}^{0.02} = 138$ meV, $Δ^{0.1} = E_{U P B}^{0.1} - E_{M P B}^{0.1} = 118$ meV) between high energy and middle energy decreases with increase of oscillator strength, because that the coupling between plasmon and the A excitons is suppressed by the coupling between plasmon and J-aggregate excitons. Therefore, the strong couplings in the Ag–J-aggregates–WS₂ hybrid nanostructures could be modulated by adjusting WS₂ excitons or J-aggregate excitons individually.

Fig. 6 (a) Normalized scattering spectra of J-aggregates and WS₂ coupled with Ag nanoprism for different temperature. (b) Normalized scattering spectra of J-aggregates and WS₂ coupled with Ag nanoprism for different oscillator strength of J-aggregates.

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4. Conclusions

In summary, we investigated the exciton–plasmon–exciton couplings in the Ag–J-aggregates–WS₂ hybrid nanostructures based on the FDTD method and the coupled oscillator model. The scattering spectrum computed by the FDTD is consistent with scattering spectrum calculated by the coupled oscillator model. The strong couplings among the LSPR, J-aggregates exciton, and the A exciton modes leads to three plexciton branches (UPB, MPB, LPB). We further analyzed the exciton–plasmon–exciton coupling behaviors using classic oscillator models and obtained the weighting efficiencies of the original modes in three plexciton branches. It is found that WS₂ excitons have little contribution to the LPB, thus we could modulate the strong couplings in the Ag–J-aggregates–WS₂ hybrid nanostructures by adjusting WS₂ excitons through temperature control without change LPB. Furthermore, the coupling between plasmon and the A excitons is suppressed by the coupling between plasmon and J-aggregates with the increase of J-aggregate excitons oscillator strength, thus we could modulate the strong couplings in the Ag–J-aggregates–WS₂ hybrid nanostructures by adjusting J-aggregate excitons through control concentration of J-aggregates.

Funding

Ministry of Science and Technology of the People's Republic of China (2016YFA0301300); National Natural Science Foundation of China (NSFC) (11574035, 11374041, 11604020); State Key Laboratory of Information Photonics and Optical Communications.

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Tunable strong exciton–plasmon–exciton coupling in WS₂–J-aggregates–plasmonic nanocavity

Abstract

1. Introduction

2. Methods

3. Results and discussion

4. Conclusions

Funding

References

Cited By

Figures (6)

Equations (8)

Optics Express