Plasmons in two-dimensional (2D) materials beyond graphene have recently gained much attention. However, the experimental investigation is limited due to the lack of suitable materials. Here, we experimentally demonstrate localized plasmons in a correlated 2D charge-density-wave (CDW) material: 2H-TaSe₂. The plasmon resonance can cover a broad spectral range from the terahertz (40 μm) to the telecom (1.55 μm) region, which is further tunable by changing thickness and dielectric environments. The plasmon dispersion flattens at large wave vectors, resulted from the universal screening effect of interband transitions. More interestingly, anomalous temperature dependence of plasmon resonances associated with CDW excitations is observed. In the CDW phase, the plasmon peak close to the CDW excitation frequency becomes wider and asymmetric, mimicking two coupled oscillators. Our study not only reveals the universal role of the intrinsic screening on 2D plasmons, but also opens an avenue for tunable plasmons in 2D correlated materials.

石墨烯以外的二维（2D）材料中的等离激子最近受到了广泛关注。但是，由于缺乏合适的材料，实验研究受到了限制。在这里，我们通过实验证明了相关2D电荷密度波（CDW）材料中的局部等离激元：2H-TaSe ₂。等离子体激元共振可以覆盖从太赫兹（40μm）到电信（1.55μm）区域的较宽频谱范围，可通过更改厚度和介电环境进一步对其进行调谐。由于带间跃迁的普遍屏蔽效应，等离激元色散在大波矢处变平。更有趣的是，观察到与CDW激发相关的等离子体激元共振的温度依赖性。在CDW阶段，接近CDW激发频率的等离子体激元峰变得更宽且不对称，模仿了两个耦合的振荡器。我们的研究不仅揭示了2D等离子体激元固有筛选的普遍作用，而且还为2D相关材料中的可调等离子体激元开辟了道路。