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 formation of hybrid exciton-plasmon modes in quantum confined structures. This coupling can be strengthed by designing a system with its vibronic states resonant to the energy of the driving field induced by the localized plasmon excitation. Silver nanoislands 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 local field due to the Ag nanoparticles (Ag-NP) enhances the magnitude of the Raman modes in MoS2 in the presence of resonant excitation. An ultrashort pulsed optical excitation at 2.3 eV resonantly excites the LSP modes and the optical near-field resonantly drive the phonon modes, which leads to a coherent coupling of the A and B excitons in MoS2 with the plasmon modes. The resonant excitation of the LSP modes modulate the optical absorption of the probe field. The resonant excitation of C exciton due to an excitation source at 3.0 eV, which is off-resonant to the LSP mode 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 increase the A and B exciton population. A 3-level density matrix theory in the presence of dressed vibronic states induced by a localized near-field optical driving source is applied to describe the coherent interaction process in the hybrid nano-plasmonic system.