Plasmon Engineering in Intercalated 2H-TaS₂

Plasmons in low-dimensional materials provide a powerful platform for nanoscale control of light-matter interactions, yet strategies to tailor their coherence and dissipation remain limited. Here, we demonstrate that transition-metal intercalation offers a fundamentally distinct route to engineer plasmonic response in layered materials. By combining high-resolution core-level photoemission spectroscopy with first-principles calculations, we show that Fe and Co intercalation in 2H-TaS₂ does not act as conventional electron doping but reshapes the low-energy electronic structure through orbital hybridization and structural reconstruction. This process introduces a dense continuum of low-energy states that ultimately suppresses the plasmon mode. First-principle calculations of the energy-loss function reveal a transition from a well-defined collective excitation to an overdamped response. Our results establish intercalation as a chemically controlled pathway to tune plasmon losses and dielectric response in quantum van der Waals materials, providing a new design principle for plasmonic and optoelectronic functionalities at the nanoscale.