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Register a new userAntiferromagnetism of hybrid metamaterials
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Added by
Andrey Miroshnichenko
Publication date
2011
fields
Physics
and research's language is
English
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We analyze a metal-dielectric structure composed of a silicon nanoparticle coupled to a stack of split-ring resonators, and reveal the possibility of optically-induced antiferromagnetic response of such a hybrid meta-molecule with a staggered pattern of the induced magnetization. We show that a hybrid metamaterial created by a periodic lattice of the meta-molecules supports antiferromagnetic modes with a checker-board pattern and the propagation of spin waves, opening new ways for manipulating artificial antiferromagnetism at high frequencies with low-loss materials.
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Condensed matter systems with topological order and metamaterials with left-handed chirality have attracted recently extensive interests in the fields of physics and optics. So far the two fields are independent, and there is no work to address their connection. Here we propose to establish the relation between the topological order in condensed matter systems and the chirality in metamaterials, by mapping explicitly Maxwells equations to the Dirac equation in one dimension. We report an experimental implement of the band inversion in the Dirac equation, which accompanies change of chirality of electromagnetic wave in metamaterials, and the first microwave measurement of topological excitations and topological phases in one dimension. Our finding provides a proof-of-principle example that electromagnetic wave in the metamaterials can be used to simulate the topological order in condensed matter systems and quantum phenomena in relativistic quantum mechanics in a controlled laboratory environment.
Hyperbolic metamaterials (HMMs) support propagating waves with arbitrarily large wavevectors over broad spectral ranges, and are uniquely valuable for engineering radiative thermal transport in the near field. Here, by employing a rational design approach based on the electromagnetic local density of states, we demonstrate the ability of HMMs to substantially rectify radiative heat flow. Our idea is to establish a forward-biased scenario where the two HMM-based terminals of a thermal diode feature overlapped hyperbolic bands which result in a large heat current, and suppress the reverse heat flow by creating spectrally mismatched density of states as the temperature bias is flipped. As an example, we present a few high-performance thermal diodes by pairing HMMs made of polar dielectrics and metal-to-insulator transition (MIT) materials in the form of periodic nanowire arrays, and considering three representative kinds of substrates. Upon optimization, we theoretically achieve a rectification ratio of 324 at a 100 nm gap, which remains greater than 148 for larger gap sizes up to 1 um over a wide temperature range. The maximum rectification represents an almost 1000-fold increase compared to a bulk diode using the same materials, and is twice that of state-of-the-art designs. Our work highlights the potential of HMMs for rectifying radiative heat flow, and may find applications in advanced thermal management and energy conversion systems.
To efficiently integrate cutting-edge terahertz technology into compact devices, the highly confined terahertz plasmons are attracting intensive attentions. Compared to plasmons at visible frequencies in metals, terahertz plasmons, typically in lightly doped semiconductors or graphene, are sensitive to carrier density (n) and thus have an easy tunability, which, however, leads to unstable or imprecise terahertz spectra. By deriving a simplified but universal form of plasmon frequencies, here we reveal a unified mechanism for generating unusual n-independent plasmons (DIPs) in all topological states with different dimensions. Remarkably, we predict that terahertz DIPs can be excited in 2D nodal-line and 1D nodal-point systems, confirmed by the first-principles calculations on almost all existing topological semimetals with diverse lattice symmetries. Besides of n independence, the feature of Fermi-velocity and degeneracy-factor dependences in DIPs can be applied to design topological superlattice and multi-walled carbon nanotube metamaterials for broadband terahertz spectroscopy and quantized terahertz plasmons, respectively. Surprisingly, high spatial confinement and quality factor, also insensitive to n, can be simultaneously achieved in these terahertz DIPs. Our findings pave the way to developing topological plasmonic devices for stable terahertz applications.
Sub-wavelength nanostructured systems with tunable electromagnetic properties, such as hyperbolic metamaterials (HMMs), provide a useful platform to tailor spontaneous emission processes. Here, we investigate a system comprising $Eu^{ 3+}(NO_{3})_{3}6H_{2}O$ nanocrystals on an HMM structure featuring a hexagonal array of Ag-nanowires in a porous $Al_{2}O_{3}$ matrix. The HMM-coupled $Eu^{ 3+}$ ions exhibit up to a 2.4-fold increase of their decay rate, accompanied by an enhancement of the emission rate of the $^{ 5}D_{0}rightarrow$ $^{ 7}F_{2}$ transition. Using finite-difference time-domain modeling, we corroborate these observations with the increase in the photonic density of states seen by the $Eu^{ 3+}$ ions in the proximity of the HMM. Our results indicate HMMs can serve as a valuable tool to control the emission from weak transitions, and hence hint at a route towards more practical applications of rare-earth ions in nanoscale optoelectronics and quantum devices.
We propose an approach to enhance and direct the spontaneous emission from isolated emitters embedded inside hyperbolic metamaterials into single photon beams. The approach rests on collective plasmonic Bloch modes of hyperbolic metamaterials which propagate in highly directional beams called quantum resonance cones. We propose a pumping scheme using the transparency window of the hyperbolic metamaterial that occurs near the topological transition. Finally, we address the challenge of outcoupling these broadband resonance cones into vacuum using a dielectric bullseye grating. We give a detailed analysis of quenching and design the metamaterial to have a huge Purcell factor in a broad bandwidth inspite of the losses in the metal. Our work should help motivate experiments in the development of single photon sources for broadband emitters such as nitrogen vacancy centers in diamond.
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