Tunable Strong Plasmon-Exciton Coupling in a Low-Loss Nanocuboid Dimer with Monolayer WS₂

Strong coupling between plasmons and excitons in two-dimensional materials offers a powerful route for manipulating light-matter interactions at the nanoscale, with potential applications in quantum optics, nanophotonics, and polaritonic devices. Here, we design and numerically investigate a low-loss coupling platform composed of a silver nanocuboid dimer and monolayer of WS₂ using finite-difference time-domain (FDTD) simulations. The dimer supports a subradiant bonding plasmonic mode with a linewidth as narrow as 60 meV. This ultralow-loss feature enables strong coupling with monolayer WS₂ at relatively low coupling strengths. FDTD simulations combined with the coupled oscillator model reveal a Rabi splitting of ~60 meV and characteristic anticrossing behavior in the dispersion relations. Importantly, we propose and demonstrate two independent tuning mechanisms-loss engineering through nanocuboid tilt and coupling-strength modulation through the number of WS₂ layers-that enable transitions between weak and strong coupling regimes. This work provides a low-loss and tunable plasmonic platform for studying and controlling strong light-matter interactions in plasmon-two-dimensional material systems, with potential for room-temperature quantum and optoelectronic devices.