Elucidating and Controlling the Coupling Between Plasmonic Nanostructures and 2D Semiconductors

Two-dimensional transition metal dichalcogenides (2D TMDCs) are a promising materials platform to integrate with nanophotonic structures due to their strong and unique optical responses in the visible spectral range. In particular, their strong exciton resonances are stable even at room temperature and allow facile coupling with resonant semiconductor and plasmonic nanostructures. Furthermore, the optical properties of 2D TMDCs are very susceptible to external stimuli because they are atomically thin. Their exciton resonance location (and hence the optical permittivity) can be controlled by methods such as electrical gating, dielectric screening, and strain. This paves the way towards the realization of practical and tunable nanophotonic devices.<br/>In this work, we investigate the coupling between plasmonic nanostructures and monolayer tungsten disulfide (WS₂) using strain and electrical gating approaches. By straining the monolayer WS₂, we are able to shift the exciton resonance location by more than half of its linewidth (FWHM). Hence, we can detune the spectral location of the exciton resonance from that of the plasmon resonance. Through electrical gating, we control the strength of the exciton resonance. In particular, we have achieved &gt;90% suppression of the exciton resonance. This allows us to actively control the coupling between the two resonances. By comparing experimental results with full field simulations and coupled mode theory, we study the spectral evolution and nature of the coupling in the plasmonic-WS₂ structure. Since we can control the scattering amplitude and/or phase of this coupled system, they can serve as building blocks for tunable nanophotonic devices and metasurfaces. Further understanding of the different coupling regimes will also guide the design of optical devices with different functionalities such as photodetectors and modulators.