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arXiv 2212.02434physics.opticscond-mat.mtrl-scicond-mat.soft
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具有空间色散的等离激元纳米粒子致密团簇的等效介质描述

Effective medium description of dense clusters of plasmonic nanoparticles with spatial dispersion

Ranjeet Dwivedi, Ashod Aradian, Virginie Ponsinet, Kevin Vynck, Alexandre Baron

AI总结:

本研究针对致密等离激元纳米粒子团簇,通过T矩阵计算验证了考虑空间色散的三参数等效介质模型可精确复现其电磁场,揭示了人工磁性和纵模的关键作用,为超材料设计提供了高效计算方法。

摘要:

我们研究了由数百个等离激元纳米粒子构成的致密球形团簇在平面波照射下的电磁行为。借助高精度T矩阵数值计算,我们计算了半径最大为80 nm、粒子体积分数最高达44%的团簇的多极响应。随后我们探究了能否以完全自洽的方式考虑弱空间色散,得到这类团簇的等效介质描述。我们发现,通过将扩展Mie理论应用于一个以三个等效参数表征的等效均匀球体,即可精确复现球形团簇的平均散射场以及平均内部场:这三个参数分别是与横模相关的介电常数$\varepsilon_{\mathrm{eff}}$和磁导率$μ_{\mathrm{eff}}$,以及与球体内纵模相关的波矢$k_\mathrm{L}$。我们的结果表明,尽管团簇中的单个内含物不存在任何磁偶极矩,但致密团簇中的粒子间耦合会产生人工磁性。我们还发现,纵模的存在对于精确复现团簇的场至关重要,其作用与人工磁性相当,而这一点在超材料相关文献中很大程度上被忽视了。因此,本研究证明,即使内含物浓度很高,也可以凭经验将等离激元粒子团簇视为由具有空间色散的均匀介质构成的球体。这为计算此类致密随机介质在多种感兴趣构型下的电磁响应提供了实用方案,可用于超材料和超表面的设计。

英文摘要:

We study the electromagnetic behaviour of dense, spherical clusters made of hundreds of plasmonic nanoparticules under illumination by a plane wave. Using high-precision T-matrix numerical calculations, we compute the multipolar response of clusters up to 80 nm in radius and up to 44\% in particle volume fraction. We then investigate whether it is possible to obtain an effective medium description for the clusters, taking into account weak spatial dispersion in a fully consistent way. We find that the average scattered field as well as the average inner field of the spherical cluster can be accurately reproduced by applying an extended Mie theory to an equivalent homogeneous sphere characterized by three effective parameters: an electric permittivity $\varepsilon_{\mathrm{eff}}$ and a magnetic permeability $μ_{\mathrm{eff}}$, associated to transverse modes, and a wavevector $k_\mathrm{L}$, associated to a longitudinal mode in the sphere. Our results show that artificial magnetism arises from interparticle couplings in the dense cluster, despite inclusions not displaying any individual magnetic dipole. We also find that, although largely overlooked in the literature on metamaterials, the presence of the longitudinal mode is essential to accurately reproduce the fields of the cluster, on par with the role of artificial magnetism. Our study therefore proves that, even for high concentration in inclusions, it is possible empirically to treat a cluster of plasmonic particles as a sphere made of a spatially-dispersive homogeneous medium. This offers a practical solution facilitating the computation of electromagnetic responses of such dense random media in diverse configurations of interest for the design of metamaterials and metasurfaces.

机构、总结、中文摘要均由AI分析而来,可能存在错误,请以论文正文为准。

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