High-order Magnetic Resonance Research Articles

High-order magnetic resonance in the presence of strong longitudinal radio-frequency magnetic field based on atomic alignment states

High-order magnetic resonance in the presence of strong longitudinal radio-frequency magnetic field based on atomic alignment states

Prominently enhanced luminescence from a continuous monolayer of transition metal dichalcogenide on all-dielectric metasurfaces

Abstract 2D materials such as transition metal dichalcogenides (TMDCs) are a new class of atomic-layer materials possessing optical and electric properties that significantly depend on the number of layers. Electronic transitions can be manipulated in artificial resonant electromagnetic (EM) fields using metasurfaces and other designed nanostructures. Here, we demonstrate prominently resonant enhancement in the photoluminescence (PL) of atomic monolayer, WS2, doped with a small quantity of Mo. The excitonic PL showed a strong enhancement effect on a higher-order magnetic resonance of all-dielectric metasurfaces consisting of periodic arrays of Si nanopellets. The PL intensity witnessed a 300-fold enhancement compared to the reference PL intensity on a flat silicon dioxide (SiO2) layer, which suggests a drastic change in the dynamics of photoexcited states. Confocal PL microscopy and the analysis revealed that the single photons were coherently emitted from the TMDC monolayer on the metasurface. Furthermore, examining the PL lifetime in the ps and ns timescales clarified two exponential components at the prominent exciton PL: a short-time component decaying in 22 ps and a long-time component lasting over 10 ns. Therefore, we can infer that the radiative components were significantly activated in the TMDC monolayer on the metasurfaces in comparison to the reference monolayer on a flat SiO2 layer.

Near-perfect ultrabroadband metal-free ultrathin THz absorber

An ultrathin metal-free terahertz (THz) absorber is implemented and numerically analyzed. The absorber structure with a rectangular graphite resonator is designed to operate with the fundamental magnetic resonance in the lower- and higher-order magnetic resonance in the upper band. Carving the slots in the graphite resonator converts the magnetic resonance into the electric resonance at the upper frequency and merges the resonance spectra. The proposed absorber provides near-perfect flat broadband absorption of more than 99% in the 7.28–11.21 THz frequency range. Further, the absorber provides absorption of more than 90% and 80% in the 6.26–13.05 and 5.69–14.25 THz frequency range, respectively. The absorber structure utilizes a graphite-based resonator and backreflecting plane and provides the polarization insensitive response with the allowed incidence angle of more than 20° with the absorption more than 99%. The absorber response is validated through a transmission line method-based equivalent electrical circuit. Moreover, the reliability of the implemented absorber for its use in electromagnetic shields and stealth applications is calculated in terms of shielding effectiveness, which remains high in range of 50 to 250 dB.

Observation of Collective Resonance Modes in a Chiral Spin Soliton Lattice with Tunable Magnon Dispersion.

A chiral spin soliton lattice (CSL), one of the representative systems of a magnetic superstructure, exhibits reconfigurability in periodicity over a macroscopic length scale. Such coherent and tunable characteristics of the CSL lead to an emergence of elementary excitation of the CSL as phononlike modes due to translational symmetry breaking and bring a controllability of the dispersion relation of the CSL phonon. Using a broadband microwave spectroscopy technique, we directly found that higher-order magnetic resonance modes appear in the CSL phase of a chiral helimagnet CrNb_{3}S_{6}, which is ascribed to the CSL phonon response. The resonance frequency of the CSL phonon can be tuned between 16 and 40GHz in the vicinity of the critical field, where the CSL period alters rapidly. The frequency range of the CSL phonon is expected to extend over 100GHz as extrapolated on the basis of the theoretical model. The present results indicate that chiral helimagnets could work as materials useful for broadband signal processing in the millimeter-wave band.

Dual-Band, Polarization-Insensitive, Ultrathin and Flexible Metamaterial Absorber Based on High-Order Magnetic Resonance

We demonstrate a dual-band, polarization-insensitive, ultrathin and flexible metamaterial absorber (MA), based on high-order magnetic resonance. By exploiting a flexible polyimide substrate, the thickness of MA came to be 1/148 of the working wavelength. The absorption performance of the proposed structure was investigated for both planar and bending models. In the case of the planar model, a single peak was achieved at a frequency of 4.3 GHz, with an absorption of 98%. Furthermore, additional high-order absorption peaks were obtained by the bending structure on a cylindrical surface, while the fundamental peak with a high absorption was maintained well. Our work might be useful for the realization and the development of future devices, such as emitters, detectors, sensors, and energy converters.

Multiband Metamaterial Absorber in a Ring Structure Base on High-order Magnetic Resonance

We proposed a multi-band metamaterial absorber (MA) based on high-order magnetic resonance using ring-shaped structures. We obtained three absorption peaks at 4.71 GHz (the fundamental resonance), 13.39 GHz (the third-order behavior), and 19.91 GHz (the fifth-order behavior) with correspondent absorptions of 90%, 100%, and 99.33%, respectively. Therefore, these high-order perfect absorptions are the potential to make the easier fabrication for the next generation of MAs, especially in high-frequency regions. Particular, the obtained results are further controlled using the LC circuit model. Besides, by scaling down the unit-cell size, the third- and fifth-order absorptions are created in the THz frequency band.

Tunable Thermal Camouflage Based on GST Plasmonic Metamaterial.

Thermal radiation control has attracted increasing attention in a wide range of field, including infrared detection, radiative cooling, thermal management, and thermal camouflage. Previously reported thermal emitters for thermal camouflage presented disadvantages of lacking either tunability or thermal stability. In this paper, we propose a tunable thermal emitter consisting of metal-insulator-metal (MIM) plasmonic metamaterial based on phase-change material Ge2Sb2Te5 (GST) to realize tunable control of thermal radiation in wavelength ranges from 3 μm to 14 μm. Meanwhile, the proposed thermal emitter possesses near unity emissivity at the wavelength of 6.3 μm to increase radiation heat dissipation, maintaining the thermal stability of the system. The underlying mechanism relies on fundamental magnetic resonance and the interaction between the high-order magnetic resonance and anti-reflection resonance. When the environmental background is blackbody, the tunable emitter maintains signal reduction rates greater than 80% in middle-IR and longer-IR regions from 450 K to 800 K and from room temperature to 800 K, respectively. The dependences of thermal camouflage on crystallization fraction of GST, incident angles and polarization angles have been investigated in detail. In addition, the thermal emitter can continuously realize thermal camouflage for various background temperatures and environmental background in atmospheric window in the range of 3–5 μm.

Numerical Analysis of Magnetic Plasmonic Resonance Modes in Three-Dimension Split Ring Resonator Metamaterials

Magnetic resonators based on metamaterials are valuable for numerous applications including perfect absorber, sensing and medical imaging. However, due to the existence of the difficulty in magnetic excitation in planar metasurface, the study of magnetic metamaterial resonators is less reported, particularly in contrast to the electrical resonators. In this paper, the three-dimensional split ring resonator (SRR) metamaterials featuring dual-band magnetic plasmonic resonance modes are proposed and numerically analyzed. We calculate the electromagnetic field distributions of the three-dimensional metamaterials at the resonant frequencies to elucidate the resonant characteristics of the dual modes (fundamental LC mode and high-order magnetic plasmonic resonance mode). The influences of geometric parameters of the constituent meta-atoms on the resonance frequencies of the two resonance modes are analyzed by numerical calculations. The results show that the resonance frequency of the high-order magnetic resonance mode is nearly independent of the standing columns of the metamaterials owing to the special resonant characteristic of the high-order mode. Benefiting from the independence, the frequency interval between the dual modes can be customized by adjusting the dimensions of the column. In addition, by tuning the dimension of the columns, the quality factors of the resonances can reach the highest value of 176 for LC mode and 270 for the high-order mode, respectively. In light of practical application, we evaluate refractive index sensing performance of the proposed metamaterials, the maximum sensitivity can reach 474 GHz/RIU for LC mode and 446 GHz/RIU for high-order resonance, respectively. We also explore the universality of the special resonant characteristic of the high-order mode in other similar three-dimension SRR metamaterials, which shows all of these three-dimension magnetic plasmonic metamaterials provide potential platforms for multiband magnetic metamaterial applications.

Design of a six-band terahertz metamaterial absorber for temperature sensing application

We present a simple design of a six-band terahertz metamaterial absorber (MMA). The unit-cell of the MMA consists of a metallic cross-cave-patch (CCP) structure and an InSb dielectric spacing layer stands on a ground-plane. The permittivity of the InSb dielectric layer can be adjusted efficiently by the variation of external temperature. The numerical simulation results show that the MMA has six distinct absorption peaks from 0.4 THz to 2.2 THz, and the absorption peak frequencies can be tuned easily by changing the external temperature. The surface current distributions of the top layer and back layer of the unit-cell structure are studied to better understand the physical mechanism of the proposed MMA. The six-band strong absorption of the MMA is originated from the excitations of high-order magnetic resonance. In addition, the sensitivity S is investigated to explore temperature sensing performance of the device, and the value of S is 10.3 GHz/K, 8.1 GHz/K, 6.7 GHz/K, 6.4 GHz/K, 5.5 GHz/K and 5.4 GHz/K, respectively. The design of the MMA could find potential applications in temperature sensing or other optoelectronic related areas in terahertz region.

Negative-index metamaterial at visible frequencies based on high order plasmon resonance

A type of negative-index metamaterial composed of periodic arrays of SRRs is proposed and numerically investigated in the visible frequencies. Employing the high order magnetic resonance to induce negative permeability, negative refractive index is obtained between 395 THz and 430 THz with the maximum FOM=4.59. The effective permeability exhibits a rapid convergence with increasing number of metamaterial layers. Different responses from the electric and magnetic resonances to the changing geometric parameters are compared and analyzed in terms of the field distribution. Simulation results show that the high order magnetic resonance can be greatly enhanced at visible frequencies as well as effectively tuned over a wide spectral range without notably altering the coupling between unit cells.

Transition between corrugated metal films and split-ring-resonator arrays

We fabricate split-ring-resonator arrays via direct laser writing of polymers, followed by atomic-layer deposition of titania, chemical vapor deposition of silver, and focused-ion-beam milling. While structures like that have been fabricated previously by other means, our approach here allows for a direct comparison with the optical properties of corrugated metal surfaces, which are fabricated along the same lines. This comparison reveals substantial differences regarding the magnetic metamaterial properties. In particular, we find that the optical response of the corrugated metal surfaces is due to a higher-order magnetic resonance, whereas that of the split-ring resonators stems from their fundamental magnetic resonance.

Magnetic Metamaterials at Telecommunication and Visible Frequencies

Arrays of gold split rings with a 50-nm minimum feature size and with an LC resonance at 200 THz frequency (1.5 microm wavelength) are fabricated. For normal-incidence conditions, they exhibit a pronounced fundamental magnetic mode, arising from a coupling via the electric component of the incident light. For oblique incidence, a coupling via the magnetic component is demonstrated as well. Moreover, we identify a novel higher-order magnetic resonance at around 370 THz (800 nm wavelength) that evolves out of the Mie resonance for oblique incidence. Comparison with theory delivers good agreement and also shows that the structures allow for a negative magnetic permeability.