Epsilon-near-zero (ENZ) media are an emerging class of nanophotonic materials that engender electromagnetic fields with small phase variation due to their approximately zero permittivity. These quasi-static fields facilitate several unique optical properties, such as subwavelength confinement, arbitrary wavefront control, and enhanced light–matter interactions, which make ENZ materials promising platforms for nanophotonic and plasmonic systems. Here, we report our analysis of single and dimer nanoantennas deposited on an aluminum-doped zinc oxide layer with an ENZ wavelength around 1.5 μm. Using near-field microscopy, far-field spectroscopy, finite-element numerical simulations, and a semi-analytic Fabry–Perot (FP) model, we show that single nanoantennas support highly dispersive plasmonic modes with less than unity effective mode index at wavelengths greater than the ENZ wavelength, which consequently fixes the resonance near the ENZ wavelength of the substrate. Furthermore, we observe a strong reduction in the near-field coupling between dimer nanoantennas via measurements of the resonance shift as a function of gap size. This reduction of near-field coupling allows one to design arrays of independently operating antennas with higher densities and thereby significantly improve the array characteristics, especially when targeting gradient metasurface implementations. Our results demonstrate the use of ENZ materials for increasing the versatility and functionality of plasmonic structures and provide foundational insight into this exotic material phenomenon.

中文翻译：

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ε接近零的基体上等离激元天线中近场耦合的抑制

Epsilon-near-zero（ENZ）介质是新兴的一类纳米光子材料，由于其介电常数约为零，因此产生的电磁场具有很小的相位变化。这些准静态场促进了几种独特的光学特性，例如亚波长限制，任意波阵面控制以及增强的光质相互作用，这使ENZ材料成为纳米光子和等离子体系统的有前途的平台。在这里，我们报告了对沉积在铝掺杂氧化锌层上且ENZ波长约为1.5μm的单个和二聚体纳米天线的分析。使用近场显微镜，远场光谱，有限元数值模拟和半解析法布里-珀罗（FP）模型，我们表明，单个纳米天线在波长大于ENZ波长的情况下支持高度分散的等离激元模态，其有效模态指数小于1，从而将谐振固定在基板的ENZ波长附近。此外，我们通过测量共振位移随间隙大小的变化，观察到二聚体纳米天线之间近场耦合的强烈降低。近场耦合的这种减少允许人们设计具有更高密度的独立工作的天线阵列，从而显着改善阵列特性，尤其是在针对梯度超表面实现时。我们的研究结果表明，使用ENZ材料可提高等离子体结构的多功能性和功能性，并为这种奇异的材料现象提供基础的见识。