Strong Exciton–Plasmon Coupling in a WS₂ Monolayer on Au Film Hybrid Structures Mediated by Liquid Ga Nanoparticles

Abstract

Realizing and manipulating strong light–matter coupling in 2D monolayer semiconductors is of paramount importance in the development of novel photonic devices. Here, it is revealed by numerical simulation that strong coupling between the excitons in a WS2 monolayer and the surface plasmon polaritons propagating on the surface of a thin Au film can be realized when the surface plasmon polaritons are generated via the Kretschmann–Raether configuration. The use of liquid Ga nanoparticles, which exhibit broad scattering spectra in visible light, is proposed to identify the strong exciton–plasmon coupling. It is demonstrated numerically and experimentally that the exciton–plasmon coupling strength, which is manifested in Rabi splitting, can be further enhanced by the in‐plane localization of the electric field provided by liquid Ga nanoparticles. Anti‐crossing of the scattering spectra can be observed by tuning the angle of the incident light and Rabi splitting exceeding 120 meV can be obtained. The results open new horizons for realizing strong exciton‐plasmon coupling in hybrid structures composed of monolayer semiconductors and thin metal films and pave the way for the practical applications of strong light–matter interaction in nanoscale photonic devices.

Optical Scattering of Liquid Gallium Nanoparticles Coupled to Thin Metal Films

“…This unique feature makes it possible to use large Ga NPs in combination with a thin metal film for constructing plasmonic nanocavities with significantly enhanced electric field. Such nanocavities with embedded two-dimensional materials are suitable for studying strong plasmon-exciton coupling because the broad scattering spectra ensure the clear identification of energy splitting while the large sizes enhance the signal-to-noise ratio [ 48 ]. In this work, the scattering properties of a Ga NP excited by the propagating SPPs generated on the Au film surface were experimentally studied.…”

“…A enhancement as large as ∼150 was observed at the gap region between the Ga NP and the Au film, implying the feasibility of using such a nanocavity with an embedded two-dimensional material for investigating strong plasmon-exciton coupling [ 45 , 46 , 47 ]. In this case, the two-dimensional materials could be grown on a sapphire substrate and then transferred to the Au film [ 48 ]. Ga NPs with different diameters could be fabricated in water and dispersed on the two-dimensional materials by drop-casting [ 44 ].…”

“…The scattering spectrum became not sensitive to the diameter of the Ga NP. Strong enhancement of the electric field is expected in the gap of the Ga NP placed on Au film based on numerical simulation, which may be useful for studying strong light-matter interaction [ 45 , 46 , 47 , 48 ]. To gain a deep insight into the plasmonic modes of the Ga NPs coupled to the thin metal film, the scattering spectra and the radiation patterns ware analyzed by using a polarizer with different polarization angles [ 49 , 50 , 51 ].…”

Hybrid Plasmonics and Two-Dimensional Materials: Theory and Applications

“…Such an interaction has recently been revealed experimentally by introducing Ga nanoparticles as Mie scatterers placed on the Au/WS 2 hybrid structure, which resulted in a clear Rabi splitting in the scattering spectra. 100 The surface plasmon-exciton interaction has been utilized to create a nonlinear plasmonic modulator. A monolayer WSe 2 encapsulated in hBN is placed onto a plasmonic waveguide, which then shows a pronounced dip in the transmission spectra.…”

A Semiclassical Model for Plasmon-Exciton Interaction From Weak to Strong Coupling Regime

“…Thus, the plasmon-exciton coupling has attracted great interest in recent years [5][6][7][8][9][10][11]. When a surface plasmon mode strongly interacts with excitonic material, new plasmon-exciton hybrid states called plexcitons emerge [12][13][14]. which have significant applications such as Bose-Einstein condensation, [15] low threshold laser [16], and quantum information processing [17].…”