Abstract
Materials showing electromagnetic properties that are not attainable in naturally occurring media, so-called metamaterials, have been lately, and still are, among the most active topics in optical and materials physics and engineering. Among these properties, one of the most attractive ones is the sub-diffraction resolving capability predicted for media having an index of refraction of −1. Here, we propose a fully three-dimensional, 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 a 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 a negative index in the range of 1.2–1.55 μm.
Highlights
Materials showing electromagnetic properties that are not attainable in naturally occurring media, so-called metamaterials, have been lately, and still are, among the most active topics in optical and materials physics and engineering
We study the possibility of using a spherical core–shell configuration to obtain with a single structure both electric and magnetic responses
To obtain a 3D isotropic metamaterial having negative index of refraction in the optical range of the spectrum has been one of the major challenges in the last decade for scientists and engineers devoted to electromagnetism
Summary
Materials showing electromagnetic properties that are not attainable in naturally occurring media, so-called metamaterials, have been lately, and still are, among the most active topics in optical and materials physics and engineering. 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 a negative index in the range of 1.2–1.55 μm. Calculations for core–shell structures built up with realistic materials (Ag@Si and Ag@Ge) demonstrate the possibility of obtaining NIM operating at 1.2 μm–1.55 μm Since both responses are attained directly from a single constituent, no particular arrangement of the inclusions is needed. It can immediately be realized that all information about material and geometrical properties of the core is contained in these Al and Bl coefficients
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