A subwavelength plasmonic metamolecule exhibiting magnetic-based optical Fano resonance
A subwavelength plasmonic metamolecule exhibiting magnetic-based optical Fano resonance
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DOI：
10.1038/nnano.2012.249
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发表时间：
2013-02-01
影响因子：
38.3
通讯作者：
Li, Xiaoqin
中科院分区：
文献类型：
--
作者：
Shafiei, Farbod;Monticone, Francesco;Li, Xiaoqin
电荷和磁荷之间缺乏对称性，这是精细结构常数(1)值很小的基本结果，与光学材料(2，3)中磁效应的弱化直接相关。最近，适当定制的等离子体纳米团簇被提出来诱导人工光磁(4-7)，其原理是磁效应与光学频率下的介电常数的特定形式的空间色散是无法区分的(1)。在不同的背景下，等离子体法诺共振引起了人们的极大兴趣，特别是在受益于尖锐的光谱特征和极场局部化的传感应用中(8-12)。在没有自然磁性的情况下，光学Fano共振到目前为止都是基于纯粹的电效应。在这封信中，我们证明了由四个紧密间隔的金纳米颗粒组成的亚波长等离子体偏分子支持与广泛的电共振耦合的强大的磁响应。组装纳米环中的微小结构不对称使得电和磁模式之间能够相互作用，导致在光学频率处首次观察到基于磁性的法诺散射共振。我们的发现得到了与模拟和分析计算的良好一致性的支持，并代表着朝着寻求光学频率(13-15)的人工磁性和负折射率超材料迈出的重要一步。
The lack of symmetry between electric and magnetic charges, a fundamental consequence of the small value of the fine-structure constant(1), is directly related to the weakness of magnetic effects in optical materials(2,3). Properly tailored plasmonic nanoclusters have been proposed recently to induce artificial optical magnetism(4-7) based on the principle that magnetic effects are indistinguishable from specific forms of spatial dispersion of permittivity at optical frequencies(1). In a different context, plasmonic Fano resonances have generated a great deal of interest, particularly for use in sensing applications that benefit from sharp spectral features and extreme field localization(8-12). In the absence of natural magnetism, optical Fano resonances have so far been based on purely electric effects. In this Letter, we demonstrate that a subwavelength plasmonic metamolecule consisting of four closely spaced gold nanoparticles supports a strong magnetic response coupled to a broad electric resonance. Small structural asymmetries in the assembled nanoring enable the interaction between electric and magnetic modes, leading to the first observation of a magnetic-based Fano scattering resonance at optical frequencies. Our findings are supported by excellent agreement with simulations and analytical calculations, and represent an important step towards the quest for artificial magnetism and negative refractive index metamaterials at optical frequencies(13-15).