Active Control of Coherent Dynamics in Hybrid Plasmonic MoS₂ Monolayers with Dressed Phonons

Abstract

The near-field interaction due to a strong electromagnetic field induced by resonant localized plasmons can result in a strong coupling of excitonic states or the formation of hybrid excitonplasmon modes in quantum confined structures. The strength of this coupling can be increased by designing a system with its vibronic states resonant to the energy of the driving field induced by the localized plasmon excitation. Silver (Ag) nanoparticles (NPs) nucleated on molybdenum disulfide (MoS2) is an ideal platform for such interaction. The influence of localized plasmons (LSP) on the formation and dissociation of excitons due to resonant and off-resonant optical excitation of carriers to excitonic states is studied using ultrafast optical spectroscopy. The presence of Ag-NPs generates a local field that enhances the magnitude of the Raman modes in MoS2 under the resonant plasmon excitation. An ultrashort pulsed optical excitation at ~ 2.3 eV resonantly excites the LSP modes and the optical near-field resonantly drives the phonon modes, which leads to a coherent coupling of the A and B excitons in MoS2 with the plasmon modes. The localized near-field optical driving source induces dressed vibronic states. The resonant excitation of the LSP modes modulates the optical absorption of the probe field. The optical excitation at ~ 3.0 eV, which is resonant to the C excitonic state but off-resonant to the LSP modes, increases the electrostatic screening in the presence of excess carriers from Ag-NPs. It results in a faster dissociation of optically generated C excitons into free carriers that eventually increases the population of A and B excitonic states. The coherent interaction in the hybrid nano-plasmonic system is described using a density matrix theory.

Plasmon-Induced Enhanced Light Emission and Ultrafast Carrier Dynamics in a Tunable Molybdenum Disulfide-Gallium Nitride Heterostructure

“…Strong photobleaching of the exciton absorption is observed, which occurs within one ps as the probe is completely transparent at 2.26 eV ( Figure 4 b). After one ps, the magnitude of the photobleaching reduces as the excitons and the plasmons are decoupled, as was reported earlier [ 11 ]. However, the dynamics of the defect band are not influenced by the Pt NPs.…”

“…Recently nano-plasmonic effects have proven to be an effective means for enhancing photocurrent generation [ 7 ] or absorption for sensing [ 8 ], tunable antennae [ 9 ], and tuning the wavelength of absorption and emission [ 10 ]. Metal nanoparticles hybridized with 2D materials or graphene can modulate the absorption of the quantized states [ 11 , 12 ] in these materials, leading to coherence effects due to light-matter interaction. The plasmonic properties of the nanoparticles can be tailored by the dielectric environment both within and outside the nanoparticles [ 13 ].…”

Plasmon-exciton couplings in the MoS2/AuNP plasmonic hybrid structure

“…The observed PL spectra of MoS 2 with/without AuNP were broadened and redshifted when excitation power was higher than 100 µW. It can be explained by the thermal excitonphonon coupling and optical doping effect, as reported elsewhere 45,46 .…”

Plasmon-exciton couplings in the MoS2/AuNP plasmonic hybrid structure

“…The observed PL spectra of MoS 2 with/without AuNP were broadened and red-shifted when excitation power was higher than 100 μW. It can be explained by the thermal exciton-phonon coupling and optical doping effect, as reported elsewhere 37 , 53 .

Figure 5 Fundamental power dependence normalized PL spectra and deconvolution results.

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