Simultaneous control of plasmon-exciton and plasmon-trion couplings in an Au nanosphere and monolayer WS₂hybrid system

Simultaneous control of plasmon-exciton and plasmon-trion couplings is fundamentally interesting for tailoring the strong light-matter interaction at the nanoscale and is intriguing for developing high-efficiency optoelectronic and nonlinear photonic devices. Here, we integrate the monolayer WS2 with the Au nanosphere to take full advantages of both the strong excitonic effect and local field enhancement effect to realize strong resonance couplings between the dipolar plasmon mode and the exciton, as well as the trion, at room temperature. Interestingly, from the dark-field scattering spectrum, a transition from the dominated plasmon-exciton coupling to the plasmon-exciton-trion coupling in the hybrid system by simply increasing the radius of the nanosphere is revealed. This evolution of the scattering spectrum is further analyzed using the coupled-oscillator model to extract Rabi splittings of 89 and 48 meV for plasmon-exciton and plasmon-trion couplings, implying that the hybrid system enters the moderate coupling region. The moderate coupling imparts the hybrid system with a remarkable light-emitting capacity, rendering 1265- and 680-fold photoluminescence (PL) enhancement for the exciton and trion emissions, respectively. Our findings provide a facile way for the manipulation of excitonic quasiparticles in semiconductors at room temperature.