Plasmonically Induced Transparency in Graphene Oxide Quantum

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Plasmonically induced transparency in graphene oxide quantum dots with dressed phonon states Meg Mahat, Yuri Rostovtsev, Sanjay Kumar Karna, Gary N. Lim, Francis D'Souza, and Arup Neogi ACS Photonics, Just Accepted Manuscript • DOI: 10.1021/acsphotonics.7b01188 • Publication Date (Web): 27 Nov 2017 Downloaded from http://pubs.acs.org on December 1, 2017

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Plasmonically induced transparency in graphene oxide quantum dots with dressed phonon states Meg Mahat1 , Yuri Rostovtsev1,2 , Sanjay Karna1 , Gary N. Lim3 , Francis D’Souza3 , and ∗ Arup Neogi1,4 1 2

Department of Physics, University of North Texas, Denton, TX 76203

Center for Nonlinear Sciences, University of North Texas, Denton, TX 76203 3 4

Department of Chemistry, University of North Texas, Denton, TX 76203

IFFS, University of Engineering Science and Technology, Chengdu, China E-mail: Abstract

The absorption in quantum dots (QDs) embedded within a semiconductor matrix can be manipulated by resonant optical excitation of phonons. The far-field interaction of the light leading to dressed phonon states within reduced graphene oxide quantum dots has been coherently modified by a near-field optical driving field at the nanoscale limit. The near-field optical excitation was introduced by resonant excitation of localized plasmons in metal nanoparticles coupled to QDs for ultrafast light manipulation. The coherent interaction of photons due to localized plasmon induced a change in the transient absorption of graphene oxide quantum dots conjugated to silver nanoparticles. Resonant pumping of plasmons and phonons with 400 nm pump photons induces a coherent change in excitonic absorption within QDs which results in phonon-assisted plasmon induced transparency at room temperature. This novel effect can be related to the appearance of the coherent effects such as forming dark states, and coherent

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population trapping related to Fano interference. A large Rabi splitting of 120 meV has been observed within 800 fs of the preparation of the dressed phonon-photon states. A theoretical model has been developed to quantitatively demonstrate that the dark states can be still formed at ultrashort time scale corresponding to the dephasing time of the carriers in the QDs.

Quantum engineering of light-matter interaction at the nanoscale has evolved from the existing research on exotic electromagnetic properties of materials and structures with novel shape and size. 1–5 It has led not only to novel phenomenon and applications, 6,7 but has opened up the exceptional potential to tailor, control and manipulate light-matter interactions 8,9 for nanophotonics.Nano-plasmonic induced photothermal effect in membranes has been proposed to control fluid flow for distillation and desalination of salt-water. 10–12 Quantum coherence can drastically modify the optical properties of a media, 15,16 in particular, absorption practically vanishes even at the single photon level . 17,18 The changes in dispersion properties of the medium with excited quantum coherence has been initially studied theoretically 19–22 and then experimentally demonstrated in atomic or molecular systems. 23,24 Coherent interaction of plasmons to excitons in the strong coupling regime results in nonlinear effects, including plasmon- induced transparency and Fano-like interference in hybrid molecular complexes, or dimers coupled to metal nanostructures. 25–29 In case of plasmons coupled to semiconductor quantum dots, the quantum interference can lead to optical nonlinearities resulting in confined Fano effect. 30,31 The new class of two-dimensional materials such as graphene and its oxide have very strong exciton binding energies. Graphene based material coupled to metal nanostructures with optimal structural characteristics can be an ideal platform for supporting hybrid modes due to exciton-plasmon 32–34 or exciton-phonon coupling. 35,36 ecent reports has suggested the existence of coupled plasmon excitation in a metal-graphene hybrid material system at relatively low energy ( 0.2 eV). 13 These modes can be driven using external optical and electrical field 14 0.2 and 0.5 − 0.6 eV. The latter two features are assigned to the coupled plasmon2


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phonon excitation and to an interface plasmon, respectively Graphene based semiconductors have a high nonlinear optical response and exhibit Rabi oscillations under ultrafast optical excitation. 37 These Rabi oscillations are usually damped in a quantum dot under continuous wave excitation due to their interaction with phonons, while for pulsed excitation phonons can either deteriorate or assist the coherence of the system. 38 Usually a quantum dot is embedded within a micro-cavity for strong coupling necessary to increase the coherent interaction in the system . 39 In this work, we introduce a simple approach to introduce quantum coherence effects in reduced graphene oxide (rGO) quantum dots by resonance excitation of phonons and plasmons without any micro-cavity structures. Phonon mediated intermediate state exists within the bandgap of semiconductors. Electrons from the valence band to these phonon excited states cannot be excited by far-field light as these transitions are electric-dipole-forbidden. 40 However, near-field excitation due to localized plasmons in a metal-conjugated quantum dot has been used to drive these dressed-photon-phonon (DPP) states. The phonon-assisted process can activate dipole-forbidden transition 41,42 and result in plasmon induced transparency in the absorption profile of the quantum dot states. The factors influencing the first experimentally resolved Rabi spitting of the absorption peak due to phonon-assisted plasmon induced coherent process has been studied and occurs in the femtosecond time domain. The high resolution HRTEM image of Ag nanoparticles (NPs) on thin sheet of rGO is shown in Figure 1a. The coherent effects are demonstrated by using an 120 fs optical pump at 400 nm from a frequency doubled T;Sapphiere amplifier. For dressing the quantum dot states phonon states, the laser excitation wavelehngth is tuned resonantly to the phononfrequency. The same laser irradiation also resonantly excites the localized plasmons in the Ag-NP conjugated rGOQDs. To demonstrate coherent effects, we use the nondegenerate pump-probe technique in the absence and in the presence of silver nanoparticles (NPs) in their vicinity (see in Figure 1c). We engineer the Lambda-scheme in rGOQD shown in Figure 7. The π − π ∗ transition

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in rGO-QDs occurs in the ultraviolet regime (∼ 4.74 eV). The excitonic emission from rGO occurs in the visible wavelength regime (∼ 2.85 eV). 43 The state |ai in Figure 2a corresponds to this upper bound excitonic state. The level |ci is the ground state of the rGO-QD, the level |ai is the electroninc excited state of the rGO-QD. The level |bi corresponds to dressed phonon state of the rGO-QD, The broadband white light continuum probes the transition |ai-|bi (see Figure 2b) . The level |ai is close to the localized surface plasmon (LSP) modes as shown in Figure 7c. The fs optical pump at 400 nm drives the quantum dots by inducing a transition between states |ai and |ci.The frequency of the transition between |ai and |ci is close to the surface plasmonic resonance. The scheme is similar to the atomic schemes used for demonstration of coherent effects and electromagnetically induced transparency (EIT) in atomic physics. 15,16 The resonantly dressed photon-phonon graphene oxide system is designed as follows. The ultrashort strong pump laser pulse resonantly interacts with rGO-QDs. The resonant excitation of the localized plasmon results in a faster transient absorption recovery compared to the bare rGO-QD system as shown in the supplementary section (Figure S1).The frequency of the laser pulse is a resonant to the excitonic transition in QD. The ultrashort pulse has a wide broad spectrum that is broader than the vibrational frequencies of rGO-QD (for example, the absorption and Raman spectra are shown in Figure 3), thus the vibrational levels are excited by the impulsive excition. 44 The near-field excitation induced by the Ag NPs results change in the population distribution at |ai . Once, we have excited the vibrational level of rGO-QD, the delayed probe pulse resonantly interacts with the transition |ai - |bi, and it results in appearance of the absorption line in the broad spectrum of the probe pulse. An increase in the delay time results in the transient absorption recovery due to relaxation and dephasing of the carriers in the rGOQD from the excited states. In the absence of the metal nanoparticles, the probe spectra depicts the transient population relaxation between states |ai and |bi in the quantum dots that are dressed by the phonons Eventually, once the population reaches its equilibrium, the difference in absorption vanishes.

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The behavior of the spectrum of probe absorption in the case of the presence of the Ag nanoparticle is different. The rGO-QD are excited by the strong pump laser, as well as vibrational levels, but now the vibrational excitations can occur via the impulsive excitation 44 or dressed phonons together with the near field effect of the gradient force 45 because the electric field near Ag nanoparticles has much stronger electric field gradient 1/a0 (a0 is the size of NPs). Together with phonon vibrations, the plasmonic oscillations in NPs are also excited by the strong pump laser pulse. The dipole induced in Ag NPs creates the electric field that persists during relaxation time. And the relaxation time is longer than the pump laser pulse duration. So even the pump laser pulse is over, the electric field continues to drive the electronic polarization or the transitions in the rGOQDs. Once the plasmonic oscillations are excited in the nano-particle, the field drives the the |bi → |ci transition within the quantum dot. Interacting with probe laser pulse leads to appearance of the coherence effects in the probe spectrum resulting from the quantum coherence excited between levels |ai and |ci of the quantum dot under action of the plasmonic electric field and probe laser field. This is the first experimental demonstration of the coherence effects caused by the plasmonic fields. To explain qualitatively the observed results, we develop a simplified Λ-type scheme of the quantum dot near the Ag nano-particle (shown in Figure 7), and to gain physical insight into the observed change of the probe pulse in the presence of resonantly pumped phonons, we performed numerical simulations. An ultrashort strong laser pulse is exciting the quantum dot at the transition |ci → |ai; the strong laser pulse also excites the dipole polarization of the metallic nano-particle. When silver nanoparticles are present, the optical fields excite the surface plasmon that can enhance the laser fields. We can describe the induced dipole momentum by

~0 P~ = a3 Q E

where a is the radius of the nano-particle, Q =

5

(1)

−1 describes the enhancement factor due +2


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to surface plasmon, and is the metallic susceptibility at the laser pulse frequency. The polarization excited in the nanoparticle oscillates at the frequency of the surface plasmon, and these oscillations continue even after the ultra-short strong laser pulse is over. The oscillating dipole creates the electric field near nano-particle which is given by h r ~˙ i r ~˙ ~ ~ ¨ ¨ r rˆ · (P + P ) ~ r · P~ ) P + c P − 3ˆ c ~ n = P − rˆ(ˆ + E 4π0 c2 r 4π0 r3

(2)

where r is the distance between the nanoparticle and the quantum dot. The interaction Hamiltonian in the rotating wave approximation can be written as

ˆ = ~ Ω∗p ei∆p t |biha| + Ω∗d ei∆d t |cihb| + adj. H

where |biha|, and |cihb| are the atomic projection operators, Ωp = ℘ab Ep /~ and Ωd = ℘cb Ed /~ are the probe and pump Rabi frequencies, ∆p = ωab − ωp and ∆d = ωcb − ωd are detunings for probe and coupling laser beams, and ℘ab and ℘cb are the dipole momenta of the transitions, Ep (t) and Ed (t) are the probe and pump fields. The pump field consists of laser pump field EL (t) and the field created by the nano-particle En (see Eq. (2). We consider the case of the strong field of frequency ωd being the pump field and a weak field of frequency ωp being the probe field delayed with respect to the pump field. The pump field is resonant with the |ci → |ai transition (∆d = 0). The density matrix equations are given by i ˆ ∂ρ ˆ = − [H, ρ] − Γ[ρ] ∂t ~

(3)

ˆ is the matrix of relaxation rates for all components of the density matrix ρ that we where Γ[ρ] are going to take into account phenomenologically. The spectrum of the three-level Λ-type

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quantum dot (the level structure is shown in Figure 7) is given by |Ωd (t)|2 nca (t) Γca Γcb Ωωp 2 |Ωd (t)| Γab,ω + Γcb

nab (t) + ρab,ω = −i

(4)

where nab (t) = ρaa (t) − ρbb (t), nca (t) = ρcc (t) − ρaa (t), ρaa (t), ρbb (t), and ρcc (t) are the population in levels |ai, |bi, and |ci. that are obtained by solving the time-dependent density matrix equations with corresponding quantum dot relaxation rates for populations the levels as well as for the decays of coherence. The absorption spectra of the quantum dot is obtained for some delay times similar to the experimental conditions. The results of simulations and experimental results are shown in Figure 4. All calculations have been done for parameters corresponding to current experimental conditions. The typical values used for simulations are given in the following: Γab = 95 ps−1 , γ = 0.48 ps−1 γ0 = 1.42 ps−1 γF ld = 3.56 ps−1 and Ωd = 142 ps−1 (Ωd ' Γab ). All population initially is in the ground state |ci, ρaa (t = 0) = ρbb (t = 0) = 0, and ρcc (t = 0) = 1, and no coherence is excited ρab (t = 0) = ρcb (t = 0) = ρca (t = 0) = 0. Without nanoparticles, the probe spectra are showing the effect of relaxation of population in levels |ai and |bi in time. The excitation with the 400 nm pump source at the resonant plasmons results in the excitation of the coupled exciton-plasmon modes and the interface modes in the energy range 0.2 eV to 0.4 eV as reported in. 13 Eventually, once the population reaches its equilibrium, the difference absorption vanishes. The behavior of the spectrum of probe absorption in the case of the presence of the nanoparticle (Figure 5b) is different than in the case of without nanoparticle (Figure 5a). Once the surface plasmon oscillations are excited in the nano-particle, it is the field En that is created by LSPs drives the the |ci → |ai transition of the quantum dot. Because, the population in the ground state ρcc (t) ρaa (t), and ρbb (t), there exists the so-called Raman inversion, and the rGO-QD provide gain for the probe pulse (as one can see in Figure 5b)

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the absorption becomes smaller. Although, at the position of two-photon resonance, the spectral dip appears. It is the interaction of the drive laser pulse that leads to manifestation of the coherence effects in the probe spectrum resulting from the quantum coherence excited between levels |ci and |bi of the quantum dot under action of the plasmonic electric field and probe laser field. The physics of observed effects can be easily understood using the p so-called the “dark” and “bright” states given by |Di = (Ωd |bi − Ωp |ci)/ |Ωd |2 + |Ωp |2 and p |Bi = (Ωp |bi + Ωd |ci)/ |Ωd |2 + |Ωp |2 , correspondingly. The spectral distance between peaks (see, for example, Figure 5b and Figure 6a) decreases with increasing of the delay time between pump and probe pulses because of decay of the quantum dot coherence as well as the electric field of the surface plasmons in NPs. The developed theoretical approach gives us the relation between the Rabi frequency of the driving surface plasmon field and the width of quantum dot transitions with the spectral distance between peaks by v u u δω ' u t

3Ω2 − Γ2 (5) 2Ω 1+ √ Ω2 + Γ2 √ We can see that the splitting disappears at Ω ' Γ/ 3 that can be achieved either by the plasmon decay or the additional broadening of quantum dot transitions by relaxation of the energy of the surface plasmons. For case when the r Rabi frequency is larger than the Γ2 √ relaxation rate, the dependence can be simplified as δω ' Ω2 − ∼ t0 − tdelay as can be 3 seen in fitting presented in Figure 6b. In Figure 6c, one can see the comparison experimental splits with the theoretical prediction given by Eq.(5). Alternatively, it can be implied that the modification of the dressed photon-phonon coupling by the near- field effect due to the plasmon introduces additional states at 2.62 eV and 2.74 eV. These states are forbidden transitions and are not observed due to the far-field excitation of the pump laser. Only the presence of the near-field LSP at 400 nm results in the symmetry breaking and resulting in the transition between dipole forbidden states. As we can see now, the strong changes of the absorption spectra resulted from the NPs 8


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coupling to rGOQDs via localized surface plasmon interactions have been experimentally demonstrated. The observed modification of absorption spectra can be referred to as the Phonon-assisted Plasmon Induced Transparency (PaPIT) that can be related to the appearance of the coherent effects such as forming “dark states,” and coherent population trapping related to Fano interference, well-known phenomena in atomic physics. 15 The developed theoretical model quantitatively explains obtained results and clearly shows that the “dark states” can be still formed at such short times. The paper opens a new avenue to observing the coherent effects such as coherent population trapping (CPT) and electromagnetically induced transparency (EIT), 16 have been the focus of broad research activity for the last two decades, as they drastically change optical properties of media. For example, for EIT in CW and pulsed regimes, 15 absorption practically vanishes. The medium with excited quantum coherence, phaseonium, 15 can be used to make an ultra-dispersive media 19,23 that has several orders of magnitude higher angular spectral dispersion. The corresponding steep dispersion results in the ultra-slow (subluminal) or fast (superluminal) propagation of light pulses 46,47 which can produce controlable huge optical delays and can be used for drastic modification of the phase-matching conditions for Brillouin scattering, 20 four-wave mixing, 21 controllable switching between bunching and anti-bunching, 48 storage and retrieval of pulses, freezing of a light pulse, 50 and ultrahigh enhancement in absolute and relative rotation sensing using fast and slow light. 22 The demonstrated results are important for developing new modulators or switches based on high nonlinearities and their applications to optoelectronic devices. Recently, the coherent effects have been employed to theoretically demonstrate a quantum metamaterial with an all-optical and ultra-fast (on the time scale inverse of drive field Rabi frequency) control made of dense ultracold neutral atoms. 9 The so-called hyperbolic metamaterials open a new realm of physics with exciting potential applications. 2–4,8

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Method Oxidized form of graphene i.e., graphene oxide (GO) was synthesized by modified Hummers method. In this method GO was produced by oxidizing crystal graphite with a mixture of sulfuric acid (H2 SO4 ), sodium nitrate (NaNO3 ), and potassium permanganate (KMnO4 ). In general, there are three stage during the synthesis process and they are cold stage (less than 200 C), medium stage (around 350 C) and hot stage (around 980 C). In this process, 1 gm of graphite powder was mixed with 23 mL of highly concentrated (98%) of sulphuric acid at room temperature and then 0.5 gm of sodium nitrate added to the mixture. The mixture was then cooled down to 00 C.Now, it was treated with 3 gm of potassium permanganate. The solution of mixture was then maintained at 35 to 40

0

C for half an hour. Then it was

diluted with 47 mL of DI water and then 165 mL of DI water. The solution was further mixed with slow addition of hydrogen peroxide (H2 O2 ) 30%. The mixture was filtered and repeatedly washed with hydrochloric acid (HCl) 1:10. The acids and salts were removed and then dried in freeze. The horn sonicator was used to obtain aqueous dispersion of a few layer og GO. By centrifuging at 4000 rpm, the unexfoliated GO was removed. The homogeneous supernatant was obtained by completely exfoliation of GO sheets. After filtration, it was dried under vacuum at room temperature. The original solution of GO is composed of carbon 79% and oxygen 20% having flakes size of thickness of a few mono-atomic layers. Owing to the relatively high solubility of graphene oxide in de-ionized water, the GO solution is prepared in DI water. Graphene oxide complex of 0.005 mg/mL DI water is prepared and sonicated for 10 minutes. Further synthesized GO was reduced. In general, there are several ways to reduce GO such as thermal, chemical and photocatalytic. In this work GO solution was reduced by catalytic process which is non-destructive. The GO solution was reduced via photo-catalysis by exposing the solution to Xenon lamp for several hours. Ag NPs are of specific sizes are commercial available. The rGO solution was then treated with optimized concentration of silver nanoparticles (AgNPs) in solution. At lower concentrations of rGO the addition of Ag NPs in the solution makes the solution more transparent. The optimized 10


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size of of AgNPs is 40 nm of average spherical shape and the optimize concentration of AgNPs in rGO is 0.003 mg AgNPs per mL rGO. Raman measurements were carried out using a 532 nm CW laser excitation. The absorption measurements were performed using UV-VIS absorption spectrometer. The absorption spectra of the sample were measured in a 2 mm quartz cuvette. Femtosecond transient absorption spectroscopy experiments were performed using an Ultrafast Femtosecond Laser Source (Libra) by Coherent incorporating diode-pumped, mode locked Ti:Sapphire laser (Vitesse) and diode-pumped intra cavity doubled Nd:YLF laser (Evolution) to generate a compressed laser output of 1.45 W. A Helios transient absorption spectrometer coupled with a femtosecond harmonics generator both provided by Ultrafast Systems was used. The source for the pump and probe pulses were derived from the fundamental output of Libra (Compressed output 1.45 W, pulse width 100 fs) at a repetition rate of 1 kHz. About 90% of the fundamental output of the laser was introduced into harmonic generator which produces second harmonic of 400 nm, while the rest of the output was used for generation of white light continuum. 400 nm excitation pump was used in all the experiments. Spectral and kinetic traces at appropriate wavelengths were assembled from the time-resolved spectral data. Data analysis was performed using Surface Xplorer software supplied by Helios manufacturer. The detail of the experiment has been described in reference. 51

Acknowledgments We acknowledge Dr. Ryoko Shimada for TEM images of rGO and Ag-rGO,and gratefully acknowledge the support for this research from the Welch Foundation, the US Department of Energy.

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Author contribution M.M. designed the experiment and analyzed the data. Y.R. developed theory and simulation for this work, S.K. synthesized the sample G.L contributed towards the ultrafast measurement. F.D. contributed towards the analysis of results. A.N. is the group leader and directed the work presented in this paper. He also contributed towards the analysis of the results. The manuscript was written through contributions from all authors. All authors have given approval to the final version of the manuscript.

Additional information Correspondence and requests for this materials should be addressed to A.N.

Competing financial interests The authors declares no competing financial interests

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(24) Sautenkov, V.A.; Rostovtsev, Y.V.; Chen ,H.; Hsu, P.; Aggrawal, S.G.; Scully, M.O. Electromagnetically Induced Magnetochiral Anisotropy in a Resonant Medium. Phys. Rev. Lett. 2005, 94, 233601. (25) Fofang, N.T.; Grady, N.K.; Fan, G.; Govorov, A.O., Halas, J. N. Plexciton Dynamics: Exciton-Plasmon Coupling in a J-Aggregate Au Nanoshell Complex Provides a Mechanism for Nonlinearity. Nano Letters 2011, 11, 1556-1560 (26) Fofang, N.T.; Park, T.H.; Neumann, O.; Mirin, N.A.; Nordlander, P.; Halas, N.J. Plexcitonic Nanoparticles: PlasmonExciton Coupling in NanoshellJ-Aggregate Complexes. Nano Letters, 2008, 8,3481-3481. (27) Verellen, N.; Sonnefraud, Y.; Sobhani, H.; Hao,F.; Moshchalkov, V.V.; Dorpe, P.V.; Nordlander, P. ; Maier, S.A. Fano Resonances in Individual Coherent Plasmonic Nanocavities. Nano Letters, 2009, 9, 1663-1667. (28) Biswas, S.; Duan,J.; Nepal, D.; Park, P.; Pachter, R.; Vaia, R.A. Plasmon-Induced Transparency in the Visible Region via Self-Assembled Gold Nanorod Heterodimers. Nano Letters, 2013, 13, 6287-6291 . (29) Cacciola, A.; Stefano, O.D.; Stassi, R.; Saija, R.; Savasta, S., Ultrastrong Coupling of Plasmons and Excitons in a Nanoshel. ACS Nano,2014,8,11483-11492 (30) Zhang, Z.; Govorov, A.O. Quantum theory of the nonlinear Fano effect in hybrid metalsemiconductor nanostructures: The case of strong nonlinearity.Phys. Rev B. 2011, 84, 081405(R) (31) Zhang, W.; Govorov, A.O.; Bryant, G.W. Semiconductor-Metal Nanoparticle Molecules: Hybrid Excitons and the Nonlinear Fano Effect. Phy. Rev. Lett., 2006,97, 146804-146809

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(32) Hwang, E.H.; Sensarma, R.; Sarma, S.D., Plasmon-phonon coupling in graphene. Phys. Rev. B., 2010, 82, 195406 (33) Mak, K.F.; Shan, J.; Heinz, T.F. Seeing Many-Body Effects in Single- and FewLayer Graphene: Observation of Two-Dimensional Saddle-Point Excitons.Phys.Rev.Lett. 2011,106, 046401 (34) Fang,Z.; Wang, Y.; Liu, Z.; Schlather, A.; Ajayan,P.M.; Koppens, F.H.L.; Nordlander, P.; Halas, N.J. Plasmon-Induced Doping of Graphene. ACS Nano, 2012,11, 10222-10228 (35) Shang, J., Yu, T., Lin, J., Gurzadyan, G.G. Ultrafast Electron-Optical Phonon Scattering and Quasiparticle Lifetime in CVD-Grown Graphene. ACS Nano, 2011 ,5, 3278-3283 (36) Yan, H.; Low, T.; Guinea, F.; Xia, F.; Avouris, P. Tunable Phonon-Induced Transparency in Bilayer Graphene Nanoribbons. Nanoletters, 2014,14, 4581-4586 (37) Romanets, P.N. Vasko F.T. Rabi oscillations under ultrafast excitation of graphene. Phys.Rev. B. 2010, 81, 241411 R (38) Reiter, D.E.; Kuhn, T.; Glass, M.; Axt, V.M. The role of phonons for exciton and biexciton generation in an optically driven quantum dot. J. Phys.: Condens. Matter 2014, 26, 423203-423237 (39) Reiter, D.E. Time-resolved pump-probe signals of a continuously driven quantum dot aected by phonons https://arxiv.org/pdf/1702.02784.pdf (40) Ohtsu, M. Dressed photon technology. Nanophotonics. 2012, 1,83-97 . (41) Kawazoe, T.; Kobayashi, K.; Takubo, S.; Ohtsu, M. Nonadiabatic photodissociation process using an optical near field. J. Chem. Phys. 2005 ,122, 024715 . (42) Yatsui, T.; Hirata, K.; Nomura, W.; Tabata, Y.; Ohtsu. M. Realization of an ultra-flat silica surface with angstrom-scale average roughness using nonadiabatic optical near-field etching. Appl Phys B. 2008 ,93, 55-57 . 16


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(43) Karna, S.; Mahat, M.; Choi,T.Y.; Shimada, R.; Wang, Z.; Neogi, A. Competition Between Resonant Plasmonic Coupling and Electrostatic Interaction in Reduced Graphene Oxide Quantum Dots. Sci. Rep. 2016, 6, 36898 . (44) Murawski, R.K.; Rostovtsev, Y.V.; Sariyanni, Z.E.; Sautenkov, V.A.; Backus, S.; Raymondson, D.; Kapteyn, H.c.; Murnane, M.M.; Scully, M.O. Resonant uv pump-probe spectroscopy of dipicolinic acid via impulsive excitation,Phys. Rev. A . 2008, 77, 023403 (45) Ma, D.; Rostovtsev, Y.V.; Efficient excitation of Raman coherence by a gradient force. Raman Spectrosc. 2013,44, 1259-1262 . (46) Hau, L.V.; Harris, S.E.; Dutton, Z.; Behroozi, C.H. Light speed reduction to 17 metres per second in an ultracold atomic gas. Nature. 1999, 397, 594-598 . (47) Dogariu, A.; Kuzmich A.; L.J. Wang. Transparent anomalous dispersion and superluminal light-pulse propagation at a negative group velocity. Phys. Rev. A 2001, 63, 053806. (48) Sautenkov, V.A.; Rostovtsev, Y.V.;Scully, M.O. Electromagnetically Induced Magnetochiral Anisotropy in a Resonant Medium. Phys. Rev. A. 2005, 72, 065801. (49) Dey, T.N.; Agrarwal, G.S. Storage and retrieval of light pulses at moderate powers. Phys. Rev. A 2003,67, 033813 . (50) Kocharovskaya, O.; Rostovtsev, Y.V.; Scully, M.O. Stopping Light via Hot Atoms. Phys. Rev. Lett. 2001, 86, 628 . (51) Lim, G. N.; Maligaspe, E.; Zandler, M. E.; DSouza, F. A. Supramolecular tetrad featuring covalently linked ferrocene-zinc porphyrin-BODIPY coordinated to fullerene: a charge stabilizing, photosynthetic antenna-reaction center mimic, Chemistry 2014, 20, 17089-17099.

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ACS Photonics

E n e rg y (e V )

(c ) 2 .4 5

0 .0 1

2 .5 5

2 .6 5

2 .8 5

2 .7 5

A g -rG O

D iffe r e n tia l a b s o r p tio n ( a .u .)

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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0 .0 0

rG O

-0 .0 1 D e la y tim e 5 7 6 fs

-0 .0 2 5 6 7 6

2 4 5 5

4 0 6 3 W a v e n u m b e r(c m

-1

)

Figure 1: (a,b) High resolution HRTEM image of Ag NPs on thin sheet of rGO. The size of NPs is chosen so that LSP of Ag NPs are close to the emission of rGO. (c) The differential absorption spectrum of rGO and Ag-rGO for the delay time between the pump and probe laser pulses of 576 fs.

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Figure 2: (a) The quantum dot is located near a nano-particle. The level structure of GOQD: transition c a is close to the surface plasmonic resonance; transition b a is a probe transition; and the configuration of optical field: (b) without Ag-nanoparticles, (c) with Ag-nanoparticles.

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ACS Photonics

a 0 .6 A g -rG O

A b s o rb a n c e (a .u .)

0 .5 0 .4 0 .3 rG O

0 .2 0 .1 0 .0 2 .0

2 .5

3 .0

3 .5

4 .0

4 .5

5 .0

5 .5

E n e rg y (e V )

(b )

1 2 0 0 1 0 0 0 In te n s ity ( a .u .)

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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8 0 0 6 0 0 3 1 0 0

4 0 0

3 2 0 0

3 3 0 0

2 0 0 0 1 0 0 0

1 5 0 0

2 0 0 0

2 5 0 0

R a m a n S h ift ( c m

3 0 0 0 -1

3 5 0 0

)

Figure 3: (a) UV-vis absorption of rGO with and without Ag-NPs. (b) Raman spectra of rGO obtained by using a 532 nm laser excitation. The inset shows the Raman scattering that related to 3250 wavenumber phonon scattering.

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ACS Photonics

Experiment

Theory Energy (eV)

2.5

2.7

2.5

2.9

2.7

2.9

6

Wave number (cm-1)

Figure 4: Comparison of evolution of experimental spectra for probe time delays 416 fs, 470 fs, 520 fs, 550 fs, 576 fs, 603 fs, 656 fs, and 763 fs and theoretical simulations. The predicted theoretical spectra are in a qualitative agreement with the experimental ones for rGO (black) and Ag-rGO (red). 21


ACS Photonics

0.01

0.015 Intensity

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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0

0

-0.15 -0.01

-0.025 0 0.5 1

2.5

2.6

2.9 2.7 2.8

-0.02

Figure 5: Experimentally measured 3-D spectra of differential absorption of rGO (a) and Ag-rGO (b) versus the probe laser pulse delay time and the energy of probe photon. The probe pulse changes of absorption occurs for time delays in the range 400 fs to 800 fs. The evolution of absorption one the delay time and the photon energy can be clearly seen.

a

b

c

Figure 6: (a) Illustration of EIT at three different delay times. At 1000 fs showing a single spectrum with no splitting. At 630 fs the differential absorption spectrum is split into two symmetrical spectra , and at 557 fs the maximum transparency is observed showing a clear EIT phenomenon occurred in the experimentally measured data. (b) Rabi splitting as function of time. The data points are obtained from two peaks EIT modes (c)Dependence of the picks separation (eV) vs delay time (fs). Crosses show the experimental points. Broken line is the theoretical curve taking into account the broadening of quantum dot transitions and the Rabi frequency with delay time.

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ACS Photonics

Figure 7: Table of content.

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Plasmonically Induced Transparency in Graphene Oxide Quantum

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