A negative index of refraction in a three-dimensional collection of coated nano-spheres is observed in the terahertz (THz) spectral region. This negative-index metamaterial is a binary composite of two different types of coated nano-spheres (SiO2@SiC/SiO2@AZO); in one type SiO2 spheres coated with a semiconductor (SiC) nano-shell and in another one, nano-shells made of a plasmonic material (AZO). The effective medium parameters derived by extended Maxwell-Garnett (EMG) effective medium theory by specifying the Mie resonances of the coated nano-spheres in the binary composite. The results are supplemented with frequency band structure and transmission curves, calculated by an accurate electromagnetic multiple-scattering technique. The predictions of the EMG theory are in agreement with those of the multiple-scattering technique, providing the effective medium approximation a helpful guide for the experimental works in this field.
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机译:在太赫兹(THz)光谱区域中观察到了涂层纳米球的三维集合中的负折射率。这种负折射率超材料是两种不同类型的涂层纳米球(SiO2 @ SiC / SiO2 @ AZO)的二元复合材料。一种是用半导体(SiC)纳米壳包覆的SiO2球,另一种是用等离激元材料(AZO)制成的纳米壳。有效介质参数由扩展的Maxwell-Garnett(EMG)有效介质理论得出,方法是指定二元复合材料中包覆纳米球的Mie共振。通过精确的电磁多重散射技术计算出的频带结构和传输曲线,对结果进行了补充。 EMG理论的预测与多重散射技术的预测一致,为有效的介质近似提供了对该领域实验工作的有益指导。
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