Hybridization influence on the plasmon-mediated lasing effect in active metamaterials

The plasmon-mediated lasing with orders of magnitude amplification is available for a double-fishnet structure, however, it gradually disappears for multilayered fishnet stacks because of the layer-to-layer plasmon hybridization, while instead a broadened incoherent transmission with full loss compensation can always be obtained regardless of the stacking layers.     

Resonant-induced transparency and coupled modes in layered metamaterials

We present an overview of some of our work on transmission properties and mode characteristics of layered metamaterials and their potential applications. In particular, we will show how layered metamaterials exhibit unusual transmission properties and unconventional features of guided modes, such as resonance-induced transparency in multilayer structures and slope reversal of dispersion curves in coupled waveguides. PACS 78.67.-n; 73.21.Ac; 61.46.+w; 42.25.Bs; 42.82.Et     

超构材料中的光学量子自旋霍尔效应

电子的量子自旋霍尔效应的发现推进了当今凝聚态物理学的发展,它是一种电子自旋依赖的具有量子行为的输运效应.近年来,大量的理论和实验研究表明,描述电磁波场运动规律的麦克斯韦方程组内禀了光的量子自旋霍尔效应,存在于界面的倏逝波表现出强烈的自旋与动量关联性.得益于新兴的光学材料:超构材料(metamaterials)的发展,不仅能够任意设定光学参数,同时也能引入很多复杂的自旋-轨道耦合机理,让我们能够更加清晰地了解和验证其中的物理机理.本文对超构材料中量子自旋霍尔效应做了简要的介绍,内容主要包括真空中光的量子自旋霍尔效应的物理本质、电单负和磁单负超构材料能带反转导致的不同拓扑相的界面态、拓扑电路系统中光量子自旋霍尔效应等.     

Photonic spin Hall effect in PT symmetric metamaterials

We proposed and demonstrated that PT symmetric metamaterials could be used to achieve enhanced spin Hall effect (SHE) of light. We find that when laser mode is excited in PT symmetric system, the enhanced SHE could be obtained in both transmitted and reflected beams. In addition, as exceptional points (EPs) of PT symmetric system can happen for both p- and s-polarizations, the enhanced SHE of reflected light can function for both horizontally and vertically polarized incident beams. Particularly, these EPs can lead to unidirectional reflectionlessness, asymmetric SHE with maximum contrast ratio of 48 is obtained by launching light beams near EPs. Our work opens up a new path to obtain enhanced transverse displacement for both reflected and transmitted light and enables more opportunities in manipulating photonic SHE.     

可见光波段超材料的平面聚焦效应

基于超材料双鱼网结构物理模型,设计了树枝状结构+树枝状结构、树枝状结构+银膜和树枝状结构+氧化铟锡玻璃三种可见光波段超材料复合结构.采用双模板辅助化学电沉积方法,制备出金属银树枝状结构阵列和银膜,分别实现了这三种复合结构.透射和反射实验表明,三种复合结构具有类似的行为.比较发现,树枝状结构+氧化铟锡玻璃复合结构具有损耗低和平面聚焦效应明显的优点.通过调节实验条件,分别制备出能够实现平面聚焦的红绿蓝三种可见光波段超材料. 关键词： 超材料 银树枝状结构 可见光 平面聚焦     

Optical Magnus effect in metamaterials fabricated from ferromagnetic microwires

In homogeneous negative phase velocity media, the Doppler and Cherenkov-Vavilov effects and the refraction and pressure of light are anomalous: they are inverse with respect to the corresponding effects in conventional media. Using the geometrical optics approximation, it is shown that the optical Magnus effect in inhomogeneous negative phase velocity media is also anomalous. The effect is demonstrated by considering a metamaterial consisting of parallel amorphous ferromagnetic microwires in a magnetic field. The metamaterial proves to be a left-handed one in the realistic region of the electromagnetic spectrum. The optical properties of such a left-handed medium can be controlled by the external magnetic field.     

Theory of pump-probe experiments of metallic metamaterials coupled to a gain medium

We establish a new approach for pump-probe simulations of metallic metamaterials coupled to the gain materials. It is of vital importance to understand the mechanism of the coupling of metamaterials with the gain medium. Using a four-level gain system, we have studied light amplification of arrays of metallic split-ring resonators with a gain layer underneath. We find that the differential transmittance ΔT/T can be negative for split-ring resonators on the top of the gain substrate, which is not expected, and ΔT/T is positive for the gain substrate alone. These simulations agree with pump-probe experiments and can help to design new experiments to compensate for the losses of metamaterials.     

Different configurations of metamaterials coupled with an RF coil for MRI Applications

In this paper, the effect of coupling two kinds of metamaterial cells with a coil to achieve Magnetic Resonance Imaging (MRI) is investigated. Both an array of four spirals then a single spiral-shaped metamaterial are put on the top of the coil antenna. These metamaterial based resonant structures are designed to work at 63?MHz. They are intended to increase the sensitivity of the whole system and to improve the homogeneity of the RF magnetic field pattern. The spiral-shaped metamaterials added on the top of the antenna gave very promising numerical results. The calculated magnetic fields are homogeneous and their magnitudes are multiplied by factor of 4 up to?6. We are fabricating both structures using microfabrication techniques because of the small size of the structures.     

Spin Hall effect of a light beam in anisotropic metamaterials

<正>We theoretically investigate a switchable spin Hall effect of light(SHEL) in reflection for three specific dispersion relations at an air-anisotropic metamaterial interface.The displacements of horizontal and vertical polarization components vary with the incident angle at different dispersion relations.The transverse displacements can be obtained with the relevant metamaterial whose refractive index can be arbitrarily tailed.The results of the SHEL in the metarnaterial provide a new way for manipulating the transverse displacements of a specific polarization component.     

Hybridization effect on the Falicov-Kimball model

The extended Falicov-Kimball model which includes the hybridization effect between the localized electron state and the conduction band is treated within the Hartree-Fock approximation at T=0 K. The occupation number n_e of the conduction band is calculated as a function of the localized level. The both discontinuous and continuous changes of n_e appear in a certain region of parameters. This result may correspond to the experimental facts of samarium-monochalcogenides under pressure.     

Hybridization effect on phase transitions in the Falicov-Kimball model

The Falicov-Kimball model extended by the hybridization between the localized electron states and the conduction band states is studied in Hartree-Fock approximation. Taking into account the periodicity of the system, the occupation number of the localized levels always varies continuously with the level energy for non-vanishing hybridization. This result is in contradiction with earlier mean-field calculations which are not self- consistent for the periodic model. Since first order phase transitions in intermediate valence compounds such as SmS have been observed experimentally, it follows that their explanation needs a more general theoretical frame than the model considered here.     

声学超构材料

2000年报道的具有局域共振带隙的声学材料是声学超构材料的前身,也是最早实现的声学超构材料.同光学、电磁超构材料一样,近年来声学超构材料也引起了许多学者的研究兴趣.文章介绍了到目前为止声学超构材料的主要研究进展,内容包括含共振单元的声学超构材料的负有效声学参数（包括质量密度、体模量等）的实现,以及不含共振单元的声学超构材料的一些有效声学参数的确定等,最后对声学超构材料的可能应用进行了简单展望.     

Plasmon-induced transparency in metamaterials

A plasmonic "molecule" consisting of a radiative element coupled with a subradiant (dark) element is theoretically investigated. The plasmonic molecule shows electromagnetic response that closely resembles the electromagnetically induced transparency in an atomic system. Because of its subwavelength dimension, this electromagnetically induced transparency-like molecule can be used as a building block to construct a "slow light" plasmonic metamaterial.     

Gap solitons in metamaterials

Electromagnetic localization and the existence of gap solitons in nonlinear metamaterials, which exhibit a stop band in their linear spectral response, is theoretically investigated. For a self-focusing Kerr nonlinearity, the equation for the electric field envelope with carrier frequency in the stop band—where the magnetic permeability µ(?) is positive and the dielectric permittivity ε(?) is negative—is described by a nonlinear Klein-Gordon equation with a dispersive nonlinear term. A family of standing and moving localized waves for both electric and magnetic fields is found, and the role played by the nonlinear dispersive term on solitary wave stability is discussed.     

Plasmon-induced transparency effect in hybrid terahertz metamaterials with active control and multi-dark modes

We numerically demonstrate a photo-excited plasmon-induced transparency (PIT) effect in hybrid terahertz (THz) metamaterials. The proposed metamaterials are regular arrays of hybrid unit cells composed of a metallic cut wire and four metallic split-ring resonators (SRRs) whose gaps are filled with photosensitive semiconductor gallium arsenide (GaAs) patches. We simulate the PIT effect controlled by external infrared light intensity to change the conductivity of GaAs. In the absence of photo excitation, the conductivity of GaAs is 0, thus the SRR gaps are disconnected, and the PIT effect is not observed since the dark resonator (supported by the hybrid SRRs) cannot be stimulated. When the conductivity of GaAs is increased via photo excitation, the conductivity of GaAs can increase rapidly from 0 S/m to 1×10⁶ S/m and GaAs can connect the metal aluminum SRR gaps, and the dark resonator is excited through coupling with the bright resonator (supported by the cut wire), which leads to the PIT effect. Therefore, the PIT effect can be dynamically tuned between the on and off states by controlling the intensity of the external infrared light. We also discuss couplings between one bright mode (CW) and several dark modes (SRRs) with different sizes. The interference analytically described by the coupled Lorentz oscillator model elucidates the coupling mechanism between one bright mode and two dark modes. The phenomenon can be considered the result of linear superposition of the coupling between the bright mode and each dark mode. The proposed metamaterials are promising for application in the fields of THz communications, optical storage, optical display, and imaging.     

暗声学超材料研究

由于普通材料的固有耗散在低频区域的微弱性,长久以来,低频声波的衰减一直都是一个颇具挑战性的任务.为了能够在100—1000Hz范围内完全吸收某些频率的低频声波,文章作者设计了一种薄膜型的暗声学超材料样品:它是由在弹性薄膜上镶嵌有一些非对称性的硬质金属片而制成.实验表明,该样品在低频区域几乎能够百分之百地吸收声波,而在共振吸收频率处,空气中的声波波长要比薄膜的厚度大3个数量级以上.当共振发生时,硬质金属片的"拍动"导致很大的弹性曲率能量聚集在金属片的边界附近.由于薄膜的拍动模式与声波的辐射模式仅存在微弱的耦合作用,而弹性薄膜的整体能量密度又比入射声波的能量密度大2—3个数量级,该样品本质上是一个开放的共振腔,这也是它能够高效地吸收低频声波的原因所在.     

Transient chaos in optical metamaterials

We investigate the dynamics of light rays in two classes of optical metamaterial systems: (1) time-dependent system with a volcano-shaped, inhomogeneous and isotropic refractive-index distribution, subject to external electromagnetic perturbations and (2) time-independent system consisting of three overlapping or non-overlapping refractive-index distributions. Utilizing a mechanical-optical analogy and coordinate transformation, the wave-propagation problem governed by the Maxwell's equations can be modeled by a set of ordinary differential equations for light rays. We find that transient chaotic dynamics, hyperbolic or nonhyperbolic, are common in optical metamaterial systems. Due to the analogy between light-ray dynamics in metamaterials and the motion of light in matter as described by general relativity, our results reinforce the recent idea that chaos in gravitational systems can be observed and studied in laboratory experiments.     

Periodic waves in nonlinear metamaterials

Periodic waves are presented in this Letter. With symbolic computation, equations for monochromatic waves are studied, and analytic periodic waves are obtained. Factors affecting properties of periodic waves are analyzed. Nonlinear metamaterials, with the continuous distribution of the dielectric permittivity obtained, are different from the ones with the discrete distribution.     

热超构材料的研究进展

由于光波、声波、地震波和水波都遵循波动方程,所以,2006年光学隐身衣(optical cloak)原理在Science杂志上发表后,光学隐身衣的设想很快就从最初的光波推广到了声波、地震波和水波,至今方兴未艾.由于热传导满足的是扩散方程,并且波动方程与扩散方程在物理机制上迥异,这就使得把光学隐身衣推广到热学隐身衣的尝试不得不面临来自原理上的挑战,可能也正因为如此,国际上对热超构材料的研究非常缓慢:早在2008年,就有学者在光学隐身衣的启发下,通过有限元模拟,揭示了热学隐身衣和热流反转等反常热功能或热现象,从而提出热超构材料(thermal metamaterial)的概念,但是,直到2012年,这个概念才被实验验证.由于其中蕴含着巨大的潜在应用价值,该实验工作发表后,热超构材料开始得到国际同行的广泛关注.文章的主要目的就是向读者介绍这一类新型功能材料——热超构材料的物理原理、发展历程及其理论和实验研究进展.