Strong plasmon-exciton coupling in MIM waveguide-resonator systems with WS monolayer.

The room-temperature strong plasmon-exciton coupling is first investigated in a metal-insulator-metal (MIM) waveguide-resonator system with WS monolayer. Finite-difference time-domain (FDTD) simulated results exhibit that the Fabry-Pérot (F-P) cavity is realized by the MIM plasmonic waveguide with two separated metal bars. When the F-P resonance is tuned to overlap with the A-exciton absorption peak of WS monolayer, the strong plasmon-exciton coupling is obtained at visible wavelengths. As a result, the spectral splitting response confirmed by the coupled-mode theory (CMT) appears in the transmission spectrum. Intriguingly, the switching response is handily witnessed by tuning the orientation of WS monolayer along the cavity, and the coupling strength is dynamically tuned by changing the position of the WS monolayer. Simultaneously, the anticrossing behavior with the Rabi splitting up to 109 meV is achieved by small changes in the length of the F-P cavity and the refractive index of dielectric in the cavity, respectively. The underlying physics is further revealed by the coupled oscillator model (COM). The proposed strong plasmon-exciton coupling can find utility in highly integrated plasmonic circuits for optical switching.