金属-电介质核壳纳米球作为光学三维各向同性负折射率超材料的构建块
Metallo-dielectric core-shell nanospheres as building blocks for optical 3D isotropic negative-index metamaterials
摘要：
显示出在自然存在的介质中无法获得的电磁特性的材料，即所谓的超材料，最近一直是并且仍然是光学和材料物理与工程中最活跃的领域之一。在这些性质中，最有吸引力的一个是亚衍射分辨能力预测的介质具有折射率为-1。在这里，我们提出了一个全3D，各向同性的超材料与强大的电和磁响应的光学制度的基础上，球形金属介电核壳纳米球。磁响应源于具有高折射率的电介质壳的最低磁偶极共振，并且可以被调谐以与负责电响应的金属芯的等离子体共振一致。由于响应不是源于结构之间的耦合，因此不需要施加特定的周期性布置。此外，由于组分的几何形状，超材料本质上是各向同性和偏振无关的。它可以用当前的制造技术用诸如银（芯）和硅或锗（壳）的材料来实现。对于这些特定的现实设计，超材料在1.2-1.55微米的范围内呈现负折射率。
英文摘要：
Materials showing electromagnetic properties that are not attainable in naturally occurring media, the so called metamaterials, have been lately, and still are, among the most active fields in optical and materials physics and engineering. Among those properties, one of the most attractive is the sub-diffraction resolving capability predicted for media having index of refraction of -1. Here we propose a fully 3D, isotropic metamaterial with strong electric and magnetic responses in the optical regime, based on spherical metallo-dielectric core-shell nanospheres. The magnetic response stems from the lowest, magnetic-dipole resonance of the dielectric shell with high refractive index, and can be tuned to coincide with the plasmon resonance of the metal core, responsible for the electric response. Since the response does not originate from coupling between structures, no particular periodic arrangement needs to be imposed. Moreover, due to the geometry of the constituents, the metamaterial is intrinsically isotropic and polarization independent. It could be realized with current fabrication techniques with materials such as Silver (core) and Silicon or Germanium (shell). For these particular realistic designs, the metamaterials present negative index in the range within 1.2-1.55 microns.
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