含单负特异材料一维无序扰动周期结构中的光子局域特性研究

采用传输矩阵法研究了电磁波在由单负特异材料组成的一维无序扰动周期结构中的Anderson局域(Anderson Localization)行为,分别讨论了色散和非色散两种模型.结果发现,在对应周期结构的通带位置,无序的引入对局域长度的影响较大,而在带隙位置,影响较小,几乎可以忽略.该性质与我们曾讨论的随机结构有较明显不同.导致这种局域性质的主要原因应为,光在单负材料组成的系统中的传输主要依赖于两种单负材料间的界面.在无序扰动结构中,该界面数相对于周期结构并没有减少,因此对光的传输性质影响较小,而随机结构中     

含特异材料一维超导光子晶体的带隙特性研究

利用传输矩阵法研究了含特异材料的一维超导光子晶体的带隙特性. 研究表明, 这类超导光子晶体同样具有由传统的电介质材料构成的超导光子晶体一样的低频带隙, 且在一定的参数下该低频带隙可以相当宽. 但在一定的结构参数下, 这类超导光子晶体同完全由传统的电介质构成的光子晶体一样不存在低频带隙. 还就超导光子晶体的偏振特性、光子晶体结构参数及环境温度的变化对光子带隙结构的影响进行了研究. 关键词： 超导光子晶体 传输矩阵法 特异材料 光子带隙     

利用含负折射率材料的光子晶体实现角度滤波器

利用光子晶体的共振隧穿效应，并结合由负折射材料引起的零平均折射率带隙，设计出一种新型的角度滤波器，使得对于某一频率范围内的入射电磁波仅在特定入射角度的波能够全透，而其他角度的波不能透过.这将在微波器件乃至光学器件上有广泛应用. 关键词： 光子晶体 负折射率材料 共振隧穿     

Frequency separation of surface acoustic waves in layered structures with acoustic metamaterials

We show theoretically that in elastic layered structures containing an upper layer of smoothly varied thickness and a substrate of a highly dispersive metametarial it is possible to significantly enhance spatial frequency separation of surface acoustic waves. Theory of Love surface acoustic waves propagation in waveguides with varied thickness, taking into account mutual modes coupling, is built. Appropriate structure of metamatererial with resonant frequency dependence of material parameters, making frequency separation effective, is provided. Efficiency of spatial frequency separation and modes coupling is calculated for various metamaterial parameters and wave frequencies.     

Transmission properties of Fibonacci quasi-periodic one-dimensional photonic crystals containing indefinite metamaterials

The transmission properties of Fibonacci quasi-periodic one-dimensional photonic crystals (1DPCs) containing indefinite metamaterials are theoretically studied. It is found that 1DPCs can possess an omnidirectional zero average index (zero-n?) gap which exists in all Fibonacci sequences. In contrast to Bragg gaps, such zero-n? gap is less sensitive to the incidence angle, the scale length and the polarizations of electromagnetic waves. When an impurity is introduced, a defect mode appears inside the zero-n? gap with a very weak dependence on the incidence angle and scaling.     

Characterization for defect modes of one-dimensional photonic crystals containing metamaterials

Transmission studies for one-dimensional photonic crystals(1DPCs)containing single-negative(SNG)materials inserted with multiple defects are presented.The numbers and positions of the defect modes inside zero-phase(zero-φeff)gap are found to be well characterized by effective medium theory.     

Wave propagation in double-period quasi-regular one-dimensional photonic crystals composed of single-negative metamaterials

In this paper, we theoretically study the propagation of electromagnetic waves in one-dimensional double-period quasi-regular structures consisting of negative-permittivity and negative-permeability metamaterials. A Drude-type dispersive response for both permittivity and permeability of single-negative metamaterials is considered. From the numerical results performed by transfer matrix method and effective medium theory, it is found that double-period photonic crystals can exhibit an omnidirectional gap at given microwave frequency. Such an omnidirectional gap is insensitive to incident angle and polarization, and is invariant upon the change of scale length. It is also found that this gap exists in all double-period sequences, and it is independent of structure sequence. Moreover, electromagnetic field distributions in this structures show that the fields are localized at each interface of two media. These results can lead to further applications of quasi-regular structures.     

The ballistic dimer resonance in the one-dimensional disordered photonic crystals

The propagation of electromagnetic waves in one-dimensional disordered dielectric layer stack is studied theoretically using the transfer matrix formalism. The presence of the dimer unit cells inside a host photonic crystal, as the intentionally short range disorder correlation, provides predicted dimer resonances, leading to the break down of the Anderson localization. However while suitably adjusting the intrinsic defect unit cell parameters (i.e. the defect dielectric constants), the light can be transmitted on larger localization length through a ballistic canal, opening up possibilities for performing better tailored ballistic optical filters. Moreover, by increasing the rate of disorder (i.e. the defects concentration and/or the length of the system) the quality of the transmission around the ballistic resonance can be improved with the smoother corresponding allowed mini bands.     

Photonic band gap of one-dimensional periodic structure containing dispersive left-handed metamaterials

Band structures of one-dimensional(1D)photonic crystals(PCs)containing dispersive left-handed metamaterials are studied theoretically.The results show that the structure possesses a type of photonic band gap originating from total internal reflection(TIR).In contrast to photonic band gaps corresponding to zero average refractive index and zero phase.the TIR gap exhibits sharp angular effect and has no polarization effect.It should also be noted that band structures of transverse electric(TE) and transverse magnetic(TM) mode waves are exactly the same in the PCs we studied.     

Experiment study of tunneling phenomenon occurring in the photonic heterostructure containing single-negative metamaterials

In this paper, the tunneling phenomenon occurring in the photonic heterostructure consisting of single-negative (SNG) metamaterials is experimentally studied. First, the SNG metamaterials are fabricated using coplanar waveguide with lumped-element series capacitors and shunt inductors loading. Then, the tunneling phenomenon occurring in the photonic heterostructure containing SNG media is experimentally demonstrated. Moreover, the insensitivity of the tunneling frequency to the breakdown of periodicity of phonotic crystals was also illustrated.     

Localization and interaction in two dimensions: The disordered Tomonaga model

The effect of electron-electron interactions on the localization behavior of two-dimensional disordered systems is investigated in the framework of a generalized version of Tomonaga's model. The main result is a closed expression for the dynamical conductivity which allows to predict the critical electron concentration below which localization sets in as a function of microscopic parameters only. Experimental verification is possible, although difficult.     

利用集总L-C元件构造的一维metamaterials特性的实验研究

在普通微带传输线中周期性地加载集总L C元件能够构造一维特异性材料(metamaterials)，它具有与众不同的特异性质.通过实验证实了波在这种结构中传播具有相速度与群速度方向相反的左手性通带，其折射率为负值，并发现平均折射率为零的能隙.这种结构具有结构紧凑，参数可调，制作简单的优点. 关键词： 负折射率 特异性材料 周期性结构 微带线     

含奇异材料的掺杂一维光子晶体色散关系和空间局域度理论

给出了描述掺杂的一维光子晶体结构缺陷态的变化规律及其空间局域度特性的理论表达式.该式对由具有任意色散关系材料组成的、中间掺杂、两边对称的一维光子晶体结构均成立.通过研究含奇异材料的光子晶体组态发现，当缺陷层材料为右手材料时，光子带隙中缺陷态的频移方向随缺陷层厚度的增大而红移；当缺陷层材料是左手材料时，频移方向刚好相反，表现为蓝移.该缺陷态的空间局域度只与两边对称结构有关.两边对称结构含奇异材料的光子晶体的缺陷态比传统右手材料的结构具有更强的空间局域度.     

Some open problems in the physics of disordered systems

Some problems in the physics of disordered systems are pointed out; most of these arise from experiments.     

Pressure dependence of two-level systems in disordered atomic chain

The dependence of two-level systems in disordered atomic chain on pressure, both positive and negative was studied numerically. The disorder was produced through the use of interatomic pair potentials having more than one energy minimum. It was found that there exists a correlation between the energy separation of the minima of two-level systems Δ and the variation of this separation with pressure. The correlation may have either positive or negative sign, implying that the asymmetry of two-level systems may in average increase or decrease with pressure depending on the interplay of different interactions between atoms in disordered state. The values of Δ depend on the sign of pressure.     

Elastic waves propagation in thin plate metamaterials and evidence of low frequency pseudo and local resonance bandgaps

A comprehensive numerical simulation study on elastic wave propagation for a novel engineered thin plate metamaterial structural system is presented. To enhance the accuracy of model, a mesh convergence study is validated. The wave dispersion spectra with bandgaps for three types of structures are presented. Based on local resonance phenomena, the low frequency pseudo and local resonance bandgaps are reported. Highlights are also included for the Bragg scattering induced directional bandgaps. The effects of material and geometric parameters on bandgaps are discussed. The finite element based frequency response study further validates the reported bandgaps. The conclusions provide a new perspective for designs and applications of thin plate metamaterials for subwavelength wave manipulation including seismic shielding of civil infrastructures.     

Analyticity of density of states in a gauge-invariant model for disordered electronic systems

Then-orbital gauge-invariant model of disordered electronic systems proposed by Wegner is studied in the regime of dominant diagonal disorder. Analyticity of the density of states is established in two cases: (a) when the number of orbitals is small, (b) when the number of orbitals is large and the energy is in the expected extended states region.     

Dynamically controlled asymmetric transmission of linearly polarized waves in VO2-integrated Dirac semimetal metamaterials

We numerically demonstrated a novel chiral metamaterial to achieve broadband asymmetric transmission (AT) of linearly polarized electromagnetic waves in terahertz (THz) band. The proposed metamaterial unit cell exhibits no rotational symmetry with vanadium dioxide (VO$_{2}$) inclusion embedded between Dirac semimetals (DSMs) pattern. The resonant frequency of AT can be dynamically tunable by varying the Fermi energy ($E_{\rm F}$) of the DSMs. The insulator-to-metal phase transition of VO$_{2}$ enables the amplitude of the AT to be dynamically tailored. The transmission coefficient $|T_{yx}|$ can be adjusted from 0.756 to nearly 0 by modifying the conductivity of VO$_{2}$. Meanwhile, the AT parameter intensity of linearly polarized incidence can be actively controlled from 0.55 to almost 0, leading to a switch for AT. When VO$_{2}$ is in its insulator state, the proposed device achieves broadband AT parameter greater than 0.5 from 1.21 THz to 1.80 THz with a bandwidth of 0.59 THz. When the incident wave propagates along the backward ($-z$) direction, the cross-polarized transmission $|T_{yx}|$ reaches a peak value 0.756 at 1.32 THz, whereas the value of $|T_{xy}|$ well below 0.157 in the concerned frequency. On the other hand, the co-polarized transmission $|T_{xx}|$ and $|T_{yy}|$ remained equal in the whole frequency range. This work provides a novel approach in developing broadband, tunable, as well as switchable AT electromagnetic devices.     

The superspin approach to a disordered quantum wire in the chiral-unitary symmetry class with an arbitrary number of channels

We use a superspin Hamiltonian defined on an infinite-dimensional Fock space with positive definite scalar product to study localization and delocalization of noninteracting spinless quasiparticles in quasi-one-dimensional quantum wires perturbed by weak quenched disorder. Past works using this approach have considered a single chain. Here, we extend the formalism to treat a quasi-one-dimensional system: a quantum wire with an arbitrary number of channels coupled by random hopping amplitudes. The computations are carried out explicitly for the case of a chiral quasi-one-dimensional wire with broken time-reversal symmetry (chiral-unitary symmetry class). By treating the space direction along the chains as imaginary time, the effects of the disorder are encoded in the time evolution induced by a single site superspin (non-Hermitian) Hamiltonian. We obtain the density of states near the band center of an infinitely long quantum wire. Our results agree with those based on the Dorokhov–Mello–Pereyra–Kumar equation for the chiral-unitary symmetry class.     

Transmission and reflection of waves in a one-dimensional disordered array

We study wave propagation in a one-dimensional disordered array of scattering potentials. We calculate the mean and the variance of the resistance of the array, defined as the ratio of reflected to transmitted intensity, for a rather wide class of probability distributions characterizing the disorder. Our method is based on a mapping of the wave propagation onto the motion of a two-dimensional oscillator which is perturbed parametrically.