Tunable Valley Polarized Plasmon-Exciton Polaritons in Two

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Tunable Valley Polarized Plasmon-Exciton Polaritons in Two-Dimensional Semiconductors Boyang Ding, Zhepeng Zhang, Yu-Hui Chen, Yanfeng Zhang, Richard J Blaikie, and Min Qiu ACS Nano, Just Accepted Manuscript • Publication Date (Web): 06 Feb 2019 Downloaded from http://pubs.acs.org on February 6, 2019

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Tunable Valley Polarized Plasmon-Exciton Polaritons in Two-Dimensional Semiconductors Boyang Ding1*, Zhepeng Zhang2, Yu-Hui Chen3, Yanfeng Zhang2, Richard J. Blaikie1, and Min Qiu4,5* 1

MacDiarmid Institute for Advanced Materials and Nanotechnology, Dodd-Walls Centre for Photonic and Quantum Technologies, Department of Physics, University of Otago, Dunedin 9016, New Zealand 2 Department of Materials Science and Engineering, College of Engineering, Center for Nanochemistry (CNC), College of Chemistry and Molecular Engineering, Academy for Advanced Interdisciplinary Studies, Peking University, Beijing 100871, People’s Republic of China 3 School of Physics, Beijing Institute of Technology, Beijing 10081, People’s Republic of China 4 School of Engineering, Westlake University, Hangzhou 310024, People’s Republic of China 5 Institute of Advanced Technology, Westlake Institute for Advanced Study, Hangzhou 310024, People’s Republic of China

*[email protected] *[email protected]

Abstract: Monolayers of transition metal dicalcogenides are emerged two-dimensional semiconductors with direct bandgaps at degenerate but inequivalent electronic “valleys”, supporting distinct excitons that can be selectively excited by polarized light. These valley-addressable excitons, when strongly coupled with optical resonances, lead to the formation of half-light half-matter quasiparticles, known as polaritons. Here we report self-assembled plasmonic crystals that support tungsten disulphide monolayers, in which the strong coupling of semiconductor excitons and plasmon lattice modes results in a Rabi splitting of ~160 meV in transmission spectra as well as valley-polarized photoluminescence at room temperature. More importantly we find that one can flexibly tune the degree of valley-polarization by changing either the emission angle or the excitation angle of the pump beam. Our results provide a platform that allows the detection, control and processing of optical spin and valley information at the nanoscale under ambient conditions. Keywords: strong coupling, plasmon lattice modes, two-dimensional semiconductors, valley-polarized photoluminescence, semiconductor excitons, room temperature, polaritons

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2 Two-dimensional (2D) transition metal dichalcogenides (TMDCs), such as molybdenum disulfide (MoS2), tungsten disulfide (WS2) and tungsten diselenide (WSe2) monolayers, are atomically thin semiconductors that have been viewed as promising material systems for many important applications,1,2 including optoelectronic devices, light emitting devices and photoelectrochemical systems. Their 2D-like structures enables many properties that cannot be gained in 3D bulk structures. For example, the direct band gap at both K and K’ valleys of the Brillouin zone, the absence of inversion symmetry together with the strong spin-orbit coupling allow the 2D TMDCs to support two classes of degenerate excitons with distinct responses to light of opposite circularity.3–5 As a result, exciton recombination induced photoluminescence (PL) emission from different valleys can be excited by light with opposite helicity. This property closely resembles the electron spin polarization, known as valley pseudospin or valley polarization, providing the initialization and readout of valley polarized excitons, which are critical features for future quantum electronics and computation technologies based on the valley degree of freedom.6

To date, however, it is still elusive to find an effective measure that can precisely and flexibly address distinct valleys through external control. This is mainly because the phonon-assisted inter-valley scattering and multi-particle interactions lead to multi emission channels, which significantly hampers the valley-polarization of PL emission,7 especially at room temperature, thus compromising the practical application of valley-polarization of 2D TMDCs. Various methods, for examples, excitation wavelength tuning,7,8 electrically driven9 and magnetic tuning systems,10 have been attempted to overcome this challenge. [Please refer to Section 1 and Section 5 in the supporting information (SI) for more details regarding the valley-polarized PL and phonon-assisted inter-valley scattering].


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3 Recently three groups have independently discovered that the valley-polarized PL can be observed and controlled if the TMDC monolayers are strongly coupled with an optical microcavity.11–13 These cavities confine photons between two mirrors, allowing the excitation of Fabry-Perot (FP) like electromagnetic (EM) modes or optical resonances that can rapidly exchange energy with semiconductor excitons in the embedded TMDC monolayers. This is known as the strong coupling process, resulting in half-light half-matter quasiparticles, i.e. polaritons.14,15 The light-matter hybridized states can reduce the inter-valley scattering in the exciton recombination process,12 thus facilitating the observation of valley-polarized PL even at room temperature. More importantly, by varying the detuning of the strong coupling (frequency difference between exciton and optical modes), one is able to manipulate the degree of valley polarization in TMDC monolayers.11–13 These discoveries create opportunities of addressing valley and spin in 2D TMDC semiconductors.

However there are two intrinsic drawbacks of FP-like cavities that may inhibit the further development of using cavity-assisted polaritons to control the valley-polarization: (i) the relatively large cavity mode volumes (V) of FP-like cavities lead to relatively small coupling strengths ( g v N / V , where N is the number of excitons contributing to the coupling process); and (ii) the closed structures of FP-like cavities highly suppress the PL emission from TMDC monolayers that are sandwiched between two mirrors, especially for cavities that have high quality-factors. To solve these problems, one possible solution is to achieve strong coupling of 2D TMDCs with other types of optical resonators that have much smaller mode volumes and capability to highly enhance PL emission. In this context, plasmonic cavities16–25 appear to be the best option to fulfil this task.


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4 Specifically plasmonic cavities are emerged cavity systems based on the excitation of surface plasmons, i.e. collective oscillation of electrons at the metal-dielectric interface. For example, upon light illumination, localized surface plasmons can be excited in noble metal nanoparticles, capable of highly concentrating incident light into an ultrasmall volume.26,27 When the nanoparticles are arranged in a periodically packed 2D array with lattice size comparable with light wavelength, diffractive coupling of the localized plasmon modes excites in-plane propagating plasmon waves, known as plasmon lattice modes28–30 and the periodic array of metal nanoparticles is so-called plasmonic crystals (PCs). As the results of small mode volumes, PC cavities, when coupled with TMDC nanosheets, can greatly increase the coupling strength of light-matter hybridized polaritons31–33 and considerably enhance the PL emission magnitudes34,35 of the 2D TMDC nanosheets. In addition, contemporary nano-fabrication technologies allows the development of exceptionally complex nano-architectures that can satisfy specialized coupling conditions. For example, specially designed plasmonic chiral resonators36 and metal nanowires37 have been used to achieve coupling with valley excitons, but the flexible and precise control of valley-polarized PL emission based on PC cavity platforms are yet to be developed.

In this report, we demonstrate the control of valley-polarized PL emission from WS2 monolayers that are strongly coupled with self-assembled large-area PC cavities. In particular, the PC cavities allow the excitation of two main plasmon lattice modes that are highly dispersive with respect to incident angles of light ( T inc ). These modes separately couple with the two sets of excitons, exciton A (XA) and exciton B (XB), in WS2 monolayers, at distinct T inc . It is worth noting that one set of the plasmon lattice modes strongly couple with XA,

presenting a pronounced split feature in the transmission spectrum, producing a spectral Rabi splitting up to 160 meV. 4 ACS Paragon Plus Environment

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5 In addition, in our experiments, the XA-associated PL can be excited by opposite circularly polarized pumps and we observe an identifiable difference in PL magnitude, indicating that when coupled to the PC cavities, the valley-polarized PL emission from WS2 monolayers can be sustained up to room temperature. Most importantly, by changing either the emission angle or the excitation angle of the pump beam, we are able to tune the polarization degree of the valley addressable PL. In addition, our samples are prepared using self-assembly together with chemical-vapor-deposition (CVD) techniques, which enables large-area (centimetre scale) thin-film structures, thus providing an effective on-chip platform for detecting and processing electronic valley and spin information with precise optical control at the nanoscale.


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6 Results (a)

θinc = 0o

(b)

WS2 ML

XA

XB

offset T

bare WS2 bare PC PC-WS2

Plasmonic Crystal (PC) quartz substrate

25

15

PC-01 (c)

PC-02

PC-01

transmission (%)

5 PC-02 1.6

2.0

2.4

2.8

Energy (eV)

Energy (eV)

2% 3.0 (d)

18% bare PC

3.5% 3.0 (e)

18% PC-WS2

(f)

Dispersion

3.0

2.8

2.8

2.8

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2.6

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PC-02 2.2

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XB

2.4

2.2 XA

2.0 hΩR = 160 meV

1.6 0

10 20 30 θinc (degree)

40

Energy (eV)

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0


40 0


1.8 1.6 40

Figure 1 The PC-WS2 structure and transmission spectra. (a) schematic of the plasmonic crystal coated with a monolayer of WS2. Insets: scanning electron microscope (SEM) images of this structure, where the scale bars in upper/lower insets stand for 500 nm and 2000 nm, respectively. (b) circularly polarized transmission spectra of the bare PC and PC-WS2 sample at θinc = 0o , where the green curve is the transmission spectrum of a bare WS2 monolayer wth offset magnitude. (c) simulated E-field enhancement |E/E0| in single sphere-cap unit at different frequencies, corresponding to two resonances at normal incidence (Supporting Information Fig. S1). Circularly polarized transmission spectra of (d) the bare PC and (e) the PC-WS2 sample at different angles. (f) Dispersion of transmission maxima extracted from panel (d), where the green dots indicate the maxima near exciton B (XB); the blue dots indicate maxima near exciton A (XA); and the green dots surrounded by blue circles indicate near XB maxima associated with excitonplasmon polaritons (exciton A and PC-01 mode). Notes: dotted curves in panel (d)-(e) indicate the calculated dispersion of lattice plasmons, dotted horizontal lines indicate the spectral positions of excitons in WS2 monolayers, and solid curves indicate fitted dispersions of strongly coupled plasmon-exciton polaritons. 6 ACS Paragon Plus Environment

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7 Turning to details of the experiments, as shown in Fig. 1(a), the PC comprises a hexagonally packed monolayer of silica spheres coated with a silver (Ag) thin-film and a thin silica (SiO2) protection layer. The nominal diameter of the silica spheres is 425 nm (r 5%), and the thickness of Ag and SiO2 layer are 45 ± 5 nm and 5 ± 3 nm, respectively. The metal film acquires the shape of caps on top of the spheres, forming a 2D periodic array of semishells with a hexagonal lattice, i.e. a plasmonic crystal structure.38–42 A WS2 monolayer is then transferred onto the PC top through a polystyrene-assisted transfer method. The scanning-electronic-microscope (SEM) images in Fig 1(a) show the physical structures of the PC-WS2 sample. In our experiments, it is difficult to identify the presence of WS2 monolayer using SEM, possibly due to the ultrathin thickness of the WS2 monolayer (~ 1 nm). (Please refer to Section 2 in the SI for more details about morphology on PC-WS2 surface)

The transmission spectrum of the bare PC sample at normal incidence ( T inc

0 o ) (navy

curve in Fig. 1b) displays two maxima as indicated by arrows, which are more clearly resolved in the modelled spectrum (Fig. S4, SI). These two maxima are associated with two main sets of propagating plasmon modes,38,39,42 PC-01 and PC-02 modes respectively, which are excited by diffractive coupling of localized surface plasmons28,30 in the hexagonally packed PC, with electric fields penetrating across distinct dielectric-metal interfaces. Fig. 1(c) shows the simulated field enhancement of these two modes in an individual sphere-cap, with PC-01 mode having a dipole-like distribution and PC-02 mode having a quadruple-like distribution. (Using Finite-Difference-Time-Domain method, Lumerical Solutions was used to model the transmission spectrum and field enhancement in plasmonic cavity.) As the result of being propagating modes, both PC-01 and PC-02 modes are highly dispersive with respect to angle of incidence. As shown in the multi-angle transmission spectra (Fig. 1d) of the bare PC sample, the transmission maxima associated with PC-01 and PC-02 modes rapidly 7 ACS Paragon Plus Environment

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8 redshift with increasing incident angles. The dispersion behavior is guided by white dashed curves that are calculated using a method from our previous studies.41 It is noted that the dispersive behaviours not only relate to incident angles but also depend on azimuthal angles with respect to the hexagonal lattice of plasmonic crystals. In our measurements, the detected sample area contains a number of macro crystal domains that have different azimuthal angles, therefore the presented dispersion curves are calculated by optimising the azimuthal angles to fit experimental data. (Please refer to Section 3 in the SI for more details about the dispersion)

When a monolayer of WS2 is applied onto the top of the PC the transmission spectrum at normal incidence (red curve in Fig. 1b) doesn’t change significantly as compared to the bare PC spectrum. But for a broader angle range (Fig. 1e), it is clear to see that the dispersive redshift of PC-01 and PC-02 modes are strongly interrupted at E = 2.03 eV and, to a lesser degree, at E = 2.41 eV, corresponding to the spectral positions of XA (indicated by the orange dotted horizontal line) and XB (indicated by the magenta dotted horizontal line) in WS2 monolayers, respectively. In particular, the transmission spectra present a set of minima at the XA position across the whole angle range and manifest broadened maxima at the XB position until T inc

30o . (Please see Fig. S6 in the SI for more details about the transmission spectra

of PC and PC-WS2 samples).

The spectral positions of transmission maxima in the PC-WS2 sample are extracted and plotted in Fig. 1(f). We can see that the maxima are highly shifted as compared to those in the bare PC sample (black dashed curves), with most of them surrounding the frequencies of the two WS2 excitons. In particular, the maxima near XA (blue solid dots) present an anticrossing behavior around the position of exciton A, i.e. one resonance is split into two near the crossing point of PC-01 mode and XA. This is a clear indication of strong coupling 8 ACS Paragon Plus Environment

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9 between excitons and plasmonic modes.25,43 To calculate the dispersion of the split resonances, we therefore use a coupled harmonic oscillator model, which can describe the exciton-plasmon polaritons (aka plexcitons) with the Jaynes-Cummings quantum mechanical model,32

Zr

1 1 (Z PC Z0 ) r g 2 G 2 2 4

(1)

where Z and Z represent the upper (UB) and lower (LB) plexcitonic branches, Z PC and

Z 0 are plasmon and excitonic energies respectively, and the detuning G

Z PC Z 0 . Here we

assume excitonic energy is unchanged with E = 2.03 eV for XA, and then the coupling energy :R, also called Rabi splitting, can be given by : R

(Z Z0 )(Z0 Z ) . Using these

equations, we plot the dispersion of split maxima acquired from Fig. 1(e) and 1(f) as a function of T inc , using the coupling strength g as a fitting parameter. It is evident to see the anti-crossing behavior of plasmonic and excitonic energies, where an average Rabi splitting

:R

2g of ~160meV is observed at the crossing point, which is far beyond the strong

coupling criteria g / Z 0 ! 0.01 , and is the highest coupling strength yet reported among existing studies of plasmon-exciton polaritons in 2D TMDCs.44

The transmission maxima near XB (green solid dots in Fig. 1f) are also highly altered. Specifically at low incident angles ( T inc

0 ~ 15o ) most of the transmission maxima in the

PC-WS2 sample show non-dispersive behaviors along XB. Furthermore, at this angle range, the maxima in PC-WS2 gain higher magnitudes than those in the bare PC (Fig. S6). When the incident angles are larger than 15o , these maxima (green dots) start to couple with plasmonic resonances, exhibiting red-shifts following the dispersions of PC-02 modes. In contrast to the maxima near XA, there is no evident spectral splitting of the maxima near XB, indicating that 9 ACS Paragon Plus Environment

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10 exciton B is merely weakly coupled with PC-02 mode.18,21,45–49 To further demonstrate the plasmon-exciton coupling, we have compared the linear superposition of transmission spectra of bare PC and bare WS2 ML with measured transmission spectra of PC-WS2 samples, which shows that a simple superposition is unable to explain the significant spectral features and angular responses in of the PC-WS2 samples. (See Fig. S7 in the SI for more details)


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(b)

(a) analyzer λ/4

bare WS2

300 lens

PC-WS2

PL

θPL θexc λ/4

PL Intensity (a.u.)

lens

θexc = 0o θPL = 5o

200

100

Excitation

polarizer

0 1.7 1.8 1.9 2.0 2.1 2.2 Energy (eV) σ+ PL on bare WS2 Max

σ+ PL on PC-WS2 Min

Max

σ+ PL reshaping factor Max Min

Min

17.0012.00

(c)

Energy (eV)

3.0

θexc = 0o

(d)

θexc = 0o

(e)

7.000

θexc = 0o

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1.6 40

Figure 2 PL experimental and results. (a) schematic of circularly polarized PL excitation and collection optics; (b) V+ PL spectra at TPL = 5o of WS2 and PC-WS2 under Texc = 0o excitation. The angle-resolved PL spectra of (c) bare WS2 monolayers, (d) PC-WS2 sample and (e) reshaping factors excited by V+ excitation. Notes: the dotted curve in panel (d) and (e) indicates the dispersion of lattice plasmon PC-01, dotted horizontal lines indicate the spectral positions of exciton A PL in WS2 monolayers, and solid curves indicate fitted dispersions of strongly coupled exciton-plasmon polaritons. We have also studied the photoluminescence (PL) behavior of our coupled PC-WS2 system, using the experimental arrangement shown in Fig. 2a. Similar to previous studies41 regarding dye fluorescence reshaping, the PL of a WS2 monolayer is significantly changed when coupled to a self-assembled PC. Under excitation at normal incidence ( T exc

0 o ), the

V+ PL spectrum of the bare WS2 monolayer (red solid curve in Fig. 2b) peaks at 2.01 eV. 11 ACS Paragon Plus Environment

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12 Identical to previous reports,1,2 the PL signal is slightly red-shifted as compared to the exciton absorption. When supported on a PC substrate, the intensity of PL of WS2 monolayers (red dashed curve) is enhanced and the spectrum is highly reshaped. There is an extra maximum appearing at 2.21 eV and the main maximum is blue-shifted to E = 2.06 eV.

The emission directionality of WS2 PL is also reshaped when supported on a PC. We have measured the PL as a function of frequency and PL angle T PL for both samples. It is clearly seen that the PL spectra of PC-WS2 systems (Fig. 2d) are highly dispersive with respect to T PL , in contrast to the non-dispersive PL features of bare WS2 ML (Fig. 2c). Specifically, the dispersive and broadened PL spectra of PC-WS2 coupled systems exhibit spectral and directional contours arising the strong coupling between exciton A and PC-01 mode, though lacking splitting features. To quantitatively study the spectral and directional reshaping of the PL emission, we then normalize the angularly and spectrally resolved PL from the Ag-capped PC to the PL from the bare WS2 monolayer and then we end up with a quantity that we call the spectral PL reshaping factor F

I PC WS2 ( E,T PL ) / I WS2 ( E,T PL ) ,

where the I PCWS2 and I WS2 denote the PL intensity of PC-WS2 and bare WS2 monolayers respectively.

As a result of the normalization, uncoupled emission can be largely removed from PL spectra of PC-WS2 systems. Subsequently, the angularly resolved reshaping factors (Fig. 2e) not only exhibit broadening of the PL spectra, but also display a splitting feature at the spectral position of XA-associated PL (E = 2.01 eV) across the whole angle range, which allows us to clearly resolve the anti-crossing behaviors of PL reshaping. These follow the dispersions of the polaritonic branches (orange solid curves), unambiguously indicating that


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13 PL modification in PC-WS2 systems is the result of coupling between exciton A and PC-01 mode.

It is also noted that even though the Rabi splitting in the PC-WS2 systems ( : R

160

meV obtained from transmission measurements) is much larger than those using FP-like cavities to achieve valley-polarized PL, e.g. ~40 meV in Ref.12 and ~15 meV in Ref.,13 the splitting features in PL spectra are less clearly resolved in our systems This is a common phenomenon in coupled plasmonic systems, where the splitting features and coupling strengths vary significantly with different observables,35,44,50–52 such as scattering, absorption and PL measurements. The specific mechanism of this phenomenon is yet to be explored, but is very likely relevant to the high damping loss of plasmonic resonators. More detailed discussion can be found in Section 5 of the SI.


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14 θPL = 10o

PC-WS2 PL (norm.)

1.0

(a)

θPL = 20o

θPL = 30o

(b)

(c)

θPL = 40o (d)

20 15

σ+ σ-

0.5

10

5

polarization degree (%)

0 0.0

bare WS2 PL (norm.)

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(e)

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0

0.0 1.7 1.8 1.9 2.0 2.1 2.2 Energy (eV)

1.7 1.8 1.9 2.0 2.1 2.2 Energy (eV)

1.7 1.8 1.9 2.0 2.1 2.2 Energy (eV)

1.7 1.8 1.9 2.0 2.1 2.2 Energy (eV)

Figure 3 Valley-polarized PL at different emission angles TPL. PL spectra of the PC-WS2 sample (a-d) and the bare WS2 sample (e-f) at different emission angles, excited by V+ (red) and V- (black) circularly polarized laser. The calculated polarizability (blue open circles) for each emission angle is shown in each panel. The excitation angles for all measurements are fixed at Texc = 0o Fig. 3 (a) demonstrates the PL spectrum at T PL excited by a laser beam at normal incidence ( T exc

10 o from a PC-WS2 sample that is

0 o ), comparing the results for different

circular polarization states of the excitation. We can see that V+ (red curve) and V- (black curve) PL spectra for the PC-WS2 sample acquire similar resonant structures, showing two maxima at 2.06 eV and 2.2 eV, respectively. However the V+ PL acquires slightly larger intensity than the V- PL at these two maxima. This PL difference induced by opposite circularly-polarized excitation, or PL helicity difference, can be quantified using polarization degree P, which is defined as

P

IV IV IV IV


(2)

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15 where Iσ+ and Iσ- refer to the helicity resolved PL intensity. The polarization spectrum at

T PL 10 o (blue circles in Fig. 3a) for the PC-WS2 peaks at E = 2.18 eV with a maximum value of P = 6.5%. In contrast, the PL from bare WS2 sample (Fig. 3e) shows only one maximum at 2.01 eV with narrower width as compared to the PC-supported WS2 samples. More importantly, there is almost no difference between V+ and V- PL spectra for the bare WS2 sample, showing ~0 polarization degree within the main PL spectral range. This contrast between PC-WS2 and bare WS2 samples indicates that the PL from PC-supported WS2 monolayers acquires significant valley-polarized properties at room temperature, similar to reports for bare TMDC monolayers that are excited at cryogenic temperature,3–5 electrically driven9 or strongly coupled with a FP cavity.11–13,53 In addition, the PL helicity in PC-WS2 samples highly varies with emission angles. For example, when T PL increases, the maximum in the polarization spectra gradually shifts to lower energy, peaking at T PL

20 o

with a polarization degree of P = 8% at E = 2.06 eV (Fig. 3b), and finally vanishing at

T PL

40 o (Fig. 3d). In contrast, the PL helicity difference remains at ~0% in bare WS2

samples, irrespective of the emission angle changes (Fig. 3e-h). Identical to the TMDC monolayers that are strongly coupled with FP-like cavities,11–13 the polarization degree in PC-WS2 systems highly varies with the detuning between XA and plasmonic PC-01 mode. Similar to previously reported coupled plasmonic systems,36,37 valley-polarized PL can be excited in our PC-WS2 systems that do not exhibit very clear splitting features in PL spectra. This is possibly because plasmon-exciton coupling not only provides additional channels for exciton relaxation (through cavities),11–13 but also enhances local density of states,34,54 accelerating the relaxation rates of excitons, which all contribute to the competition with inter-valley scattering, thus exciting the valley-polarized PL in coupled plasmonic systems. More detailed discussion can be found in Section 5 of the SI.


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PC-WS2 10

5

θexc = 0o θexc = 10o θexc = 22o θexc = 30o θexc = 50o

0

(c) 10

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PC-WS2 bare WS2 PC-WS2 (norm. F) bare WS2 (norm. F)

5

0

0 1.7 1.8

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1.7 1.8 1.9 2.0 2.1 2.2 Energy (eV)

10

0

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20 30 40 θexc (degree)



bare WS2

(b)

(a)


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Figure 4 valley-polarized PL at different excitation angles (Texc). Polarizabilities of PL at

TPL = 20o from the PC-WS2 sample (a) and the bare WS2 sample (b) pumped with different excitation angles. (c) the comparison of peak polarization degree between the PC-WS2 and the bare WS2 samples at different excitation angles. The red solid (dashed) curves are the normalised Fpump-PL factors for bare WS2 (PC-WS2) obtained from Fig. S6 in SI. Very noteworthy here is that the PL helicity in PC-WS2 samples are also sensitive to the excitation angle of the pump beam. Fig. 4 (a) shows the polarization spectra of PL collected from a PC-WS2 sample at T PL

20o , which is excited at angles ranging from T exc

0o to

50o . It is evident that the magnitude of polarization degree reduces as the excitation angle

increases. At T exc

50o , the PL from PC-WS2 samples shows almost 0% polarization, similar

to that of bare WS2 monolayers. On the other hand, the PL polarization degree of bare WS2 samples (Fig. 4b) shows no change to excitation angles. It is obvious that when supported on a PC structure, the PL helicity of WS2 monolayers can be flexibly tuned through modifying the excitation angles at room temperature. This tuneability (solid circles) can be clearly seen in Fig. 4c contrasting with the unchanged PL helicity in bare WS2 monolayers (open circles) as well as can be found in other T PL . Please refer to Fig. S8 in SI for more information.

Our results are contrary to a previous work12 that explicitly reports that the PL helicity shows almost zero excitation angle dependence when the TMDC monolayer is strongly coupled to a FP-like cavity.


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17 We note that the dispersive pump-to-PL conversion may relate to this excitation angle dependent valley-polarization. Specifically, as shown in Fig. S9 of the SI, the PL magnitudes decrease with higher excitation angles, whereas the absorption of the PC-WS2 sample at pump energy is enhanced at more oblique directions, suggesting that the pump-to-PL conversion declines with higher incident angles. We then compare the normalized pump-toPL conversion factors ( FpumpPL ) of PC-WS2 (red dashed curve) and bare WS2 monolayer (red solid curve) samples with their respective polarization degrees at different excitation angles (Fig. 4c), noting that they share similar excitation angle-dependence. For example, the FpumpPL for the PC-WS2 sample reduces as T exc increases, while FpumpPL remains unchanged

at the whole angle range. (Please refer to Fig. S9 in the SI for details of normalized FpumpPL ). This is possibly because at high angles, the pump energy (Fig. 1f) interacts with the PC-WS2 system through coupling with PC-02 modes that preferably facilitate the absorption of out-ofplane component other than the in-plane component of the circularly polarized pump. However, in 2D TMDCs, the exciton dipole is completely in-plane and cannot couple to outof-plane field component, thus leading to the low pump-to-PL conversion at high excitation angles in PC-WS2 systems. This picture is partially confirmed by the high similarity between p-polarized (Fig. S5b) and circularly polarized (Fig. 1e) transmission spectra, which indicate that at high incident angles the out-of-plane component of the incident light dominates the interaction with PC-WS2 system, but has lower possibility to couple to excitons in 2D TMDCs.

This dispersive pump-to-PL conversion may affect the valley-polarization in two ways. First, it may hinder sufficient populations in the semiconductor systems at high excitation angles, thus reducing the valley-polarization degree of exciton-associated PL emission. Second, it may be associated with systematic thermalisation. In particular, at higher pump 17 ACS Paragon Plus Environment

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18 angles, the PC-WS2 systems absorb more but emit less through radiative decaying channels. After being absorbed by the systems, the excess pump photons may (i) decay through nonradiative channels (in metal and semiconductor components) and (ii) increase the exciton annihilation55 in semiconductors. These two factors can both contribute to the phononassisted inter-valley scattering, leading to the suppression of valley-polarization degree of PL emission at high excitation angles.

In addition, we can also consider this problem from photon energy point of view. o Specifically, as shown in Fig. 1(f), at low excitation angles T exc 10 , the pump photon

energy (green horizontal line) overlaps with the highest polariton state (see the transmission maxima indicated by green dots surrounded by blue circles in Fig. 1f), which may provide a channel for the pump photon energy to access the polaritonic regime, facilitating the excitation of XA-associated PL at this pumping frequency, and preserving the valleyo polarization of PL. While at higher excitation angles T exc ! 15 , the pump energy runs far

away from the polariton upper branch, akin to the scenario where the pump energy is far from the bandgap,7 resulting in enhanced inter-valley scattering that hampers the valleypolarization of PL emission from WS2 monolayers.

To verify that the tunable valley-polarization relates to dispersive pump-to-PL conversion, we have also measured the valley-polarized PL with higher energy pump, which appears to be coinciding with the rule of pump-to-PL conversion too. Please refer to Section 8 in the SI for more details; the specific mechanism for this effect is yet to be explored through more experiments and modelling.


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19 Conclusions In conclusion, we have prepared self-assembled large-area plasmonic crystal cavities that are strongly coupled with WS2 monoalyers. In particular, the formed exciton-plasmon polaritons manifest through a split in the transmission spectrum with a Rabi splitting frequency of ~160 meV in transmission spectra. As a result, the XA-associated emission shows PL spectra with different magnitudes when excited by light with opposite helicity, indicating the observation of valley-polarized PL emission at room temperature. In addition, the polarization degree can be controlled by easily changing either the emission angle or the excitation angle of the pump beam. Our research reports such optical control of valleypolarized PL emission, providing a possible pathway for the practical manipulation of optical spin and valley information.

Methods Sample preparation The plasmonic crystals supporting WS2 single layer are prepared using the following procedure: A hexagonally packed monolayer of silica spheres (brand and model) was deposited on a glass substrate using self-assembly as reported elsewhere,56 which is followed by the evaporation of a silver film of 40 nm nominal thickness and a SiO2 spacer layer (10 nm). The typical sample size was about 2−4 cm2. The WS2 monolayer was prepared using CVD techniques. Specifically sulfur powder and tungsten dioxide powder will be used as S and W precursors, respectively. The coverage area of the monolayers can be flexibly tuned by adjusting the temperature and the precursors-substrates distance. The grown WS2 monolayer was transferred onto the PC surface by using the polymethyl methacrylate assisted transfer method.57 Optical characterisation


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20 The photoluminescence (PL) of the WS2 monolayer is excited and collected as shown in Fig. 2(a). Specifically a continuous-wave (CW) laser beam with a wavelength of 532 nm (2.33 eV) is used to excite the PL signal. A quarter-waveplate (QWP) together with a linear polarizer (LP) are used to convert the laser to a circularly polarized beam. Upon the illumination, polarized PL from the PC-WS2 sample is collected and analyzed. The PL helicity σ+ refers to the same circular polarization as the excitation beam while σ- refers to the different circular polarization as the excitation beam, which are resolved with the QWPLP analyzer in the PL collecting optics. Both the excitation angle ( T exc ) and the PL angle ( T PL ) can be flexibly tuned. All measurements were undertaken at room temperature (T = 300 K).

The angle-resolved transmission measurements were carried out with incident light under circular polarization, s-polarization (electric-field perpendicular to the plane of incidence) and p-polarization (electric field parallel to the plane of incidence). The transmission spectra presented in main text is the circularly polarized one with σ+ helicity (σ- helicity results show no difference from the σ+ one), while s- and p-polarized spectra are demonstrated in Fig. S5 (SI).

Supporting Information The Supporting Information is available free of charge on the ACS Publications website at xxxx. Additional experimental and simulation details as well as some supplementary results mentioned in the main text.


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21 Acknowledgements: This work was supported in part by the National Key Research and Development Program of China (No. 2017YFA0205700) and the National Natural Science Foundation of China (Nos. 61425023, 61235007, 61575177 and 51861135201). In addition, the authors acknowledge the New Idea Research Funding 2018 (Dodd-Walls Centre for photonic and quantum technologies) and Smart Ideas Fund by Ministry of Business, Innovation and Employment, New Zealand through contract UOOX1802. The authors also acknowledge the visiting Fellowship awarded by New Zealand Centre at Peking University. We thank Dr. M. Yan and Dr. F. Hong for their help in thin-film deposition, AFM and SEM measurements.

References: (1)

Splendiani, A.; Sun, L.; Zhang, Y.; Li, T.; Kim, J.; Chim, C. Y.; Galli, G.; Wang, F. Emerging Photoluminescence in Monolayer MoS2. Nano Lett. 2010, 10, 1271–1275. (2) Mak, K. F.; Lee, C.; Hone, J.; Shan, J.; Heinz, T. F. Atomically Thin MoS2: A New Direct-Gap Semiconductor. Phys. Rev. Lett. 2010, 105, 136805. (3) Mak, K. F.; He, K.; Shan, J.; Heinz, T. F. Control of Valley Polarization in Monolayer MoS2 by Optical Helicity. Nat. Nanotechnol. 2012, 7, 494–498. (4) Cao, T.; Wang, G.; Han, W.; Ye, H.; Zhu, C.; Shi, J.; Niu, Q.; Tan, P.; Wang, E.; Liu, B.; Feng, J. Valley-Selective Circular Dichroism of Monolayer Molybdenum Disulphide. Nat. Commun. 2012, 3, 885–887. (5) Zeng, H.; Dai, J.; Yao, W.; Xiao, D.; Cui, X. Valley Polarization in MoS2 Monolayers by Optical Pumping. Nat. Nanotechnol. 2012, 7, 490–493. (6) Ye, Z.; Sun, D.; Heinz, T. F. Optical Manipulation of Valley Pseudospin. Nat. Phys. 2016, 13, 26–29. (7) Kioseoglou, G.; Hanbicki, A. T.; Currie, M.; Friedman, A. L.; Gunlycke, D.; Jonker, B. T. Valley Polarization and Intervalley Scattering in Monolayer MoS2. Appl. Phys. Lett. 2012, 101, 221907. (8) Nayak, P. K.; Lin, F. C.; Yeh, C. H.; Huang, J. S.; Chiu, P. W. Robust Room Temperature Valley Polarization in Monolayer and Bilayer WS2. Nanoscale 2016, 8, 6035–6042. (9) Sie, E. J.; McIver, J. W.; Lee, Y.-H.; Fu, L.; Kong, J.; Gedik, N. Valley-Selective Optical Stark Effect in Monolayer WS2. Nat. Mater. 2014, 14, 290–294. (10) Aivazian, G.; Gong, Z.; Jones, A. M.; Chu, R.-L.; Yan, J.; Mandrus, D. G.; Zhang, C.; Cobden, D.; Yao, W.; Xu, X. Magnetic Control of Valley Pseudospin in Monolayer 21 ACS Paragon Plus Environment

ACS Nano 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

22 WSe2. Nat. Phys. 2015, 11, 148–152. (11) Sun, Z.; Gu, J.; Ghazaryan, A.; Shotan, Z.; Considine, C. R.; Dollar, M.; Chakraborty, B.; Liu, X.; Ghaemi, P.; Kéna-Cohen, S.; Menon, V. M. Optical Control of Roomerature Valley Polaritons. Nat. Photonics 2017, 11, 491–496. (12) Chen, Y.-J.; Cain, J. D.; Stanev, T. K.; Dravid, V. P.; Stern, N. P. Valley-Polarized Exciton-Polaritons in a Monolayer Semiconductor. Nat. Photonics 2017, 11, 431–436. (13) Dufferwiel, S.; Lyons, T. P.; Solnyshkov, D. D.; Trichet, A. A. P.; Withers, F.; Schwarz, S.; Malpuech, G.; Smith, J. M.; Novoselov, K. S.; Skolnick, M. S.; Krizhanovskii, D. N.; Tartakovskii, A. I. Valley Addressable Exciton-Polaritons in Atomically Thin Semiconductors. Nat. Photonics 2017, 11, 497–501. (14) Haroche, S.; Kleppner, D. Cavity Quantum Electrodynamics. Phys. Today 1989, 42, 24–30. (15) Purcell, E. M. Spontaneous Emission Probabilities at Radio Frequencies. Phys. Rev. 1946, 69, 681. (16) Zheng, D.; Zhang, S.; Deng, Q.; Kang, M.; Nordlander, P.; Xu, H. Manipulating Coherent Plasmon–Exciton Interaction in a Single Silver Nanorod on Monolayer WSe 2. Nano Lett. 2017, 17, 3809-3814 (17) Li, Y.; Li, Z.; Chi, C.; Shan, H.; Zheng, L.; Fang, Z. Plasmonics of 2D Nanomaterials: Properties and Applications. Adv. Sci. 2017, 4, 1–25. (18) Cao, E.; Lin, W.; Sun, M.; Liang, W.; Song, Y. Exciton-Plasmon Coupling Interactions: From Principle to Applications. Nanophotonics 2018, 7, 145–167. (19) Abid, I.; Chen, W.; Yuan, J.; Bohloul, A.; Najmaei, S.; Avendano, C.; Péchou, R.; Mlayah, A.; Lou, J. Temperature-Dependent Plasmon-Exciton Interactions in Hybrid Au/MoSe2Nanostructures. ACS Photonics 2017, 4, 1653–1660. (20) Hu, T.; Wang, Y.; Wu, L.; Zhang, L.; Shan, Y.; Lu, J.; Wang, J.; Luo, S.; Zhang, Z.; Liao, L.; Wu, S; Shen, X; Chen, Z. Strong Coupling between Tamm Plasmon Polariton and Two Dimensional Semiconductor Excitons. Appl. Phys. Lett. 2017, 110. (21) Liu, W.; Wang, Y.; Naylor, C. H.; Lee, B.; Zheng, B.; Liu, G.; Johnson, A. T. C.; Pan, A.; Agarwal, R. Understanding the Different Exciton-Plasmon Coupling Regimes in Two-Dimensional Semiconductors Coupled with Plasmonic Lattices: A Combined Experimental and Unified Equation of Motion Approach. ACS Photonics 2018, 5, 192–204. (22) Gonçalves, P. A. D.; Bertelsen, L. P.; Xiao, S.; Mortensen, N. A. Plasmon-Exciton Polaritons in Two-Dimensional Semiconductor/Metal Interfaces. Phys. Rev. B 2018, 97, 1–6. (23) Zhao, W.; Wang, S.; Liu, B.; Verzhbitskiy, I.; Li, S.; Giustiniano, F.; Kozawa, D.; Loh, K. P.; Matsuda, K.; Okamoto, K.; Oulton, R. F.; Eda, G. Exciton-Plasmon Coupling and Electromagnetically Induced Transparency in Monolayer Semiconductors Hybridized with Ag Nanoparticles. Adv. Mater. 2016, 28, 2709–2715. (24) Abid, I.; Chen, W.; Yuan, J.; Bohloul, A.; Najmaei, S.; Avendano, C.; Péchou, R.; Mlayah, A.; Lou, J. Temperature Dependent Plasmon-Exciton Interactions in Hybrid Au / MoSe2 Nanostructures. ACS photonics 2017, 4, 1653-1660 (25) Liu, W.; Lee, B.; Naylor, C. H.; Ee, H.; Park, J.; Charlie, A. T. Strong ExcitonPlasmon Coupling in MoS2 Coupled with Plasmonic Lattice. Nano Lett. 2016, 16, 1262–1269. (26) Gramotnev, D. K.; Bozhevolnyi, S. I. Plasmonics beyond the Diffraction Limit. Nat. Photonics 2010, 4, 83–91. (27) Schuller, J. a; Barnard, E. S.; Cai, W.; Jun, Y. C.; White, J. S.; Brongersma, M. L. Plasmonics for Extreme Light Concentration and Manipulation. Nat. Mater. 2010, 9, 193–204. 22 ACS Paragon Plus Environment

Page 22 of 25

Page 23 of 25 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

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23 (28) Kravets, V. G.; Schedin, F.; Grigorenko, A. N. Extremely Narrow Plasmon Resonances Based on Diffraction Coupling of Localized Plasmons in Arrays of Metallic Nanoparticles. Phys. Rev. Lett. 2008, 101, 087403. (29) Ebbesen, T. W.; Lezec, H. J.; Ghaemi, H. F.; Thio, T.; Wolf, P. A. Extraordinary Optical Transmission through Sub-Wavelength Hole Arrays. Nature 1998, 391, 667– 669. (30) Vecchi, G.; Giannini, V.; Gómez Rivas, J. Shaping the Fluorescent Emission by Lattice Resonances in Plasmonic Crystals of Nanoantennas. Phys. Rev. Lett. 2009, 102, 146807. (31) Chikkaraddy, R.; Nijs, B. De; Benz, F.; Barrow, S. J.; Scherman, O. A.; Fox, P.; Hess, O.; Baumberg, J. J. Single-Molecule Strong Coupling at Room Temperature in Plasmonic Nanocavities. Nature 2016, 535, 127–130. (32) Wers, M.; Nilsson, S.; Antosiewicz, T. J.; Mikael, K.; Zengin, G.; Wersäll, M.; Nilsson, S.; Antosiewicz, T. J.; Käll, M.; Shegai, T. Realizing Strong Light-Matter Interactions between Single-Nanoparticle Plasmons and Molecular Excitons at Ambient Conditions. Phys. Rev. Lett. 2015, 114, 157401. (33) Chen, X.; Chen, Y.-H.; Qin, J.; Zhao, D.; Ding, B.; Blaikie, R. J.; Qiu, M. Mode Modification of Plasmonic Gap Resonances Induced by Strong Coupling with Molecular Excitons. Nano Lett. 2017, 17, 3246–3251. (34) Wang, Z.; Dong, Z.; Gu, Y.; Chang, Y.-H.; Zhang, L.; Li, L.-J.; Zhao, W.; Eda, G.; Zhang, W.; Grinblat, G.; Maier, S. A.; Yang, J. K.W.; Qiu, C.-W.; Wee, A.T.S. Giant Photoluminescence Enhancement in Tungsten-Diselenide–gold Plasmonic Hybrid Structures. Nat. Commun. 2016, 7, 11283. (35) Wang, S.; Li, S.; Chervy, T.; Shalabney, A.; Azzini, S. Coherent Coupling of WS 2 Monolayers with Metallic Photonic Nanostructures at Room Temperature. Nano Lett. 2016, 16, 4368–4374. (36) Chervy, T.; Azzini, S.; Lorchat, E.; Wang, S.; Gorodetski, Y.; Hutchison, J. A.; Berciaud, S.; Ebbesen, T. W.; Genet, C. Chiral Coupling of Valley Excitons in a Transition Metal Dichalcogenide Monolayer. ACS Photonics 2018, 5, 1281–1287. (37) Gong, S. H.; Alpeggiani, F.; Sciacca, B.; Garnett, E. C.; Kuipers, L. Nanoscale Chiral Valley-Photon Interface through Optical Spin-Orbit Coupling. Science 2018, 359, 443–447. (38) Ding, B.; Pemble, M. E.; Korovin, A. V.; Peschel, U.; Romanov, S. G. ThreeDimensional Photonic Crystals with an Active Surface : Gold Film Terminated Opals. Phys. Rev. B 2010, 82, 035119. (39) Ding, B.; Pemble, M. E.; Korovin, a. V.; Peschel, U.; Romanov, S. G. Gold FilmTerminated 3-Dimensional Photonic Crystals. Appl. Phys. A 2011, 103, 889–894. (40) Ding, B.; Bardosova, M.; Pemble, M. E.; Korovin, A. V.; Peschel, U.; Romanov, S. G. Broadband Omnidirectional Diversion of Light in Hybrid Plasmonic-Photonic Heterocrystals. Adv. Func. Mater. 2011, 21, 4182–4192. (41) Ding, B.; Hrelescu, C.; Arnold, N.; Isic, G.; Klar, T. A. Spectral and Directional Reshaping of Fluorescence in Large Area Self-Assembled Plasmonic-Photonic Crystals. Nano Lett. 2013, 13, 378–386. (42) Landström, L.; Brodoceanu, D.; Bäuerle, D.; Garcia-Vidal, F. J.; Rodrigo, S. G.; Martin-Moreno, L. Extraordinary Transmission through Metal-Coated Monolayers of Microspheres. Opt. Express 2009, 17, 761–772. (43) Liu, X.; Galfsky, T.; Sun, Z.; Xia, F.; Lin, E. Strong Light-Matter Coupling in TwoDimensional Atomic Crystals. Nat. Photonics 2015, 9, 30–34. (44) Kleemann, M. E.; Chikkaraddy, R.; Alexeev, E. M.; Kos, D.; Carnegie, C.; Deacon, W.; De Pury, A. C.; Große, C.; De Nijs, B.; Mertens, J.; Tartakovskii, A. I.; Baumberg, 23 ACS Paragon Plus Environment

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24

(45) (46)

(47) (48) (49)

(50)

(51) (52) (53)

(54) (55) (56) (57)

J.J. Strong-Coupling of WSe2 in Ultra-Compact Plasmonic Nanocavities at Room Temperature. Nat. Commun. 2018, 8, 1296. Zheng, Y. B.; Kiraly, B.; Cheunkar, S.; Huang, T. J.; Weiss, P. S. Incident-AngleModulated Molecular Plasmonic Switches: A Case of Weak Exciton-Plasmon Coupling. Nano lett. 2011, 11, 2061–2065. Shi, L.; Hakala, T. K.; Rekola, H. T.; Martikainen, J. P.; Moerland, R. J.; Törmä, P. Spatial Coherence Properties of Organic Molecules Coupled to Plasmonic Surface Lattice Resonances in the Weak and Strong Coupling Regimes. Phys. Rev. Lett. 2014, 112, 1–5. Tran, T. T.; Wang, D.; Xu, Z. Q.; Yang, A.; Toth, M.; Odom, T. W.; Aharonovich, I. Deterministic Coupling of Quantum Emitters in 2D Materials to Plasmonic Nanocavity Arrays. Nano Lett. 2017, 17, 2634–2639. Balci, S.; Karademir, E.; Kocabas, C.; Aydinli, A. Absorption Enhancement of Molecules in the Weak Plasmon-Exciton Coupling Regime. Opt. Lett. 2014, 39, 4994– 4997. Balci, S.; Kucukoz, B.; Balci, O.; Karatay, A.; Kocabas, C.; Yaglioglu, G. Tunable Plexcitonic Nanoparticles: A Model System for Studying Plasmon–Exciton Interaction from the Weak to the Ultrastrong Coupling Regime. ACS Photonics 2016, 3, 2010– 2016. Lee, B.; Park, J.; Han, G. H.; Ee, H.-S.; Naylor, C. H.; Liu, W.; Johnson, a. T. C.; Agarwal, R. Fano Resonance and Spectrally Modified Photoluminescence Enhancement in Monolayer MoS 2 Integrated with Plasmonic Nanoantenna Array. Nano Lett. 2015, 15, 3646–3653. Wersall, M.; Cuadra, J.; Antosiewicz, T. J.; Balci, S.; Shegai, T. Observation of Mode Splitting in Photoluminescence of Individual Plasmonic Nanoparticles Strongly Coupled to Molecular Excitons. Nano Lett. 2017, 17, 551–558. Qin, J.; Zhang, Z.; Chen, Y.-H.; Zhang, Y.; Blaikie, R.; Ding, B.; Qiu, M. Revealing Strong Plasmon-Exciton Coupling Between Nano-Gap Resonators and TwoDimensional Semiconductors at Ambient Conditions. arXiv 2018, 1811.01598. Lundt, N.; Stoll, S.; Nagler, P.; Nalitov, A.; Klembt, S.; Betzold, S.; Goddard, J.; Frieling, E.; Kavokin, A. V.; Schüller, C.; Korn, T.; Höfling, S.; Schneider, C. Observation of Macroscopic Valley-Polarized Monolayer Exciton-Polaritons at Room Temperature. Phys. Rev. B 2017, 96, 241403. Akselrod, G. M.; Ming, T.; Argyropoulos, C.; Hoang, T. B.; Lin, Y.; Ling, X.; Smith, D. R.; Kong, J.; Mikkelsen, M. H. Leveraging Nanocavity Harmonics for Control of Optical Processes in 2d Semiconductors. Nano Lett. 2015, 15, 3578–3584. Ceballos, F.; Zhao, H. Ultrafast Laser Spectroscopy of Two-Dimensional Materials Beyond Graphene. Adv. Funct. Mater. 2016, 27, 1604509. Moon, G. D.; Lee, T. Il; Kim, B.; Chae, G.; Kim, J.; Kim, S.; Myoung, J.-M.; Jeong, U. Assembled Monolayers of Hydrophilic Particles on Water Surfaces. ACS Nano 2011, 5, 8600–8612. Ji, Q.; Zheng, Y.; Zhang, Y.; Liu, Z. Chemical Vapour Deposition of Group-VIB Metal Dichalcogenide Monolayers: Engineered Substrates from Amorphous to Single Crystalline. Chem. Soc. Rev. 2015, 44, 2587–2602.


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Tunable Valley Polarized Plasmon-Exciton Polaritons in Two

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