Abstract
The small size of plasmonic nanostructures compared to the wavelength of light is one of their most distinct and defining characteristics. It results in the strong compression of an incident wave to intense hot spots which have been used most remarkably for molecular sensing and nanoscale lasers. But another important direction for research is to use this ability to design miniaturized interconnects and modulators between fast, loss-less photonic components. Here we show that despite their high absorption, conductors are still the best materials to reach the sub-wavelength regime for efficient antennae when compared to polar crystals and high-index dielectrics, two classes of material which have shown a lot of potential recently in nanophotonic applications. By identifying the relevant dimensionless properties for the three materials considered, we present an unified understanding of the behaviour of sub-wavelength components which are at the heart of current photonic research and cast the upper achievable limits for radiative antennae crucial to the development of real-life implementation.
Highlights
Plasmonics is a relatively new and striving field of research of which one important goal is that of merging photonic technology to electronic components [1]
There is a strong deviation from microwave antenna theory as the driving frequency is increased caused by the so-called skin effect, which is an increased complex character of the conductivity of a metal [6]. This allows for an additional miniaturization which cannot take place in a near-perfect conductor and is the source of some of the most striking plasmonic applications, such as emitters engineering [7], surface-enhanced spectroscopy and molecular sensing [8, 9] or photothermal therapy [10], where optical antennae serve as an interface between the wavelength of light and the size of molecules
For lower tolerances on loss, such as η ≥ 99%, there is close to no acceptable tan δ for the parameter space probed and one is limited by the quality of materials. This condition brings the miniaturization closer to the microwave limit of λres/D ∼ 2 so that there is little gain compared to using the sophisticated designs which have been developed for perfect electric conductor (PEC) at low frequencies
Summary
Plasmonics is a relatively new and striving field of research of which one important goal is that of merging photonic technology to electronic components [1]. This is traditionally achieved by using the field confinement capability of nanostructured metal where the coupling between the charge density fluctuations of the conduction electrons and electromagnetic waves results in bound modes called surface plasmon polaritons [2] These extremely appealing excitations combine the properties of both photons and electric currents and are foreseen as the most promising entities to achieve the aforementioned merging [3]. To noble metals, semiconductors exhibit plasmonic properties which can be tuned across a wide spectral range, from the near-infrared down to the terahertz regime, by varying their carrier concentration [11, 12] This is the case for the promising 2D material graphene, where the atomic thickness can produce an unprecedented compression of the field [13,14,15]. We will study the influence of the background refractive index and the redshift caused by the assembling of particles
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