Guided electromagnetic waves at the interface between a dielectric and a topological insulator

Surface electromagnetic waves that propagate within the interface between a conventional dielectric or a metamaterial and a topological insulator with an undamped surface electric current are considered. Dispersion relations are given for guided waves that are surface waves polarized differently on either side of the media interface and create a coupling state due to the magnetoelectric effect.     

左手系材料界面上的非线性TE电磁波

针对电磁波在非线性左手系材料中的传播性质, 分别研究了左、右手系材料界面以及两左手系材料界面上非线性TE表面波的传播行为讨论了导波的频率特性、色散关系以及群速度随频率的变化规律分析表明，两种界面上的非线性TE表面波均存在频率通带和禁带，且带宽是传播功率的函数揭示了在一定条件下，左、右手系材料界面上既可以支持正向传播的非线性TE表面波，也可以支持反向传播的非线性TE表面波；两左手系材料界面上表面波的传播性质因材料参量的变化差异较大，一定参量条件下，该界面上仅支持反向传播的非线性TE表面波.     

Plasmon-polariton surface waves at the interface of a dielectric and a nanocomposite with metal inclusions

The features of the propagation of the surface waves a plasmon-polariton-type at the interface of a dielectric and a nanocomposite material with spherical metal inclusions have been considered. The analysis has been performed taking into account damping of propagating waves, which results in the complexity of dispersion relations, and taking into account the nanoparticle size. The frequency dependences of the group velocity and the depth of surface wave penetration into each medium have been constructed, and the distributions of energy fluxes in the structure have been obtained.     

Surface and volume waves in ferrodielectric–magnetically active material structures

The propagation of surface waves along the interface between a ferrodielectric and a material that represents an array of amorphous ferromagnetic microwires has been studied. The dispersion characteristic of a magnetically controlled TE wave has been obtained, and frequency intervals have been found in which surface or localized, partially localized, and volume waves may exist. It has been shown that a TM wave in the given structure cannot be a surface wave.     

Phase modulation of Bloch surface waves with the use of a diffraction microrelief at the boundary of a one-dimensional photonic crystal

Phase modulation methods for surface electromagnetic waves propagating at the interface between a homogeneous medium and a one-dimensional photonic crystal have been analyzed numerically and theoretically. Modulation is performed by changing the geometrical parameters of the microrelief on the surface of the photonic crystal. The phase modulation methods under consideration can be used to create optical elements for surface waves, in particular, lenses, prisms, and diffraction gratings. A Bragg grating has been calculated as an example. According to the simulation results, the average coefficient of reflection of a surface wave in the band gap is 0.95.     

Spin Angular Momentum of a Nonlinear Surface Wave at the Interface between Ordinary and Topological Insulators

Optics and Spectroscopy - The surface waves that propagate along the interface of a dielectric with nonlinear susceptibility of the third order and topological insulator have been considered. The...     

Optical vortices in low-mode fibers: III. Dislocation reactions, phase transitions, and topological birefringence

Topological birefringence of waves in optical fibers resulting from the spin-orbit interaction in the field of optical vortices is manifested, as a rule, in the form of Rytov-Magnus unified optical effect. At the same time, the field transformations caused by this effect are not explicitly related to the evolution of phase dislocations of longitudinal and transverse components of the electric and the magnetic fields. This relation can be provided by the dislocation reactions proposed by Berry. As opposed to the Berry’s approach, where dislocation reactions at the wavefront surface are considered, it is suggested in this work that topological reactions at the specific characteristic surface of the wave field formed by the coordinate representation of the transverse components of the Poynting vector be considered. Using the action of topological birefringence in a low-mode optical fiber as an example, it is shown that the course of a topological reaction in a vector optical field is accompanied by rigorous conservation of the total topological index of the characteristic surface and does not depend on the presence of an interface (where topological charges can originate and annihilate). The total topological index of a dislocation reaction is found to be equal to the absolute value of the sum of the topological charge and the spirality of the vector wave field.     

Spin-wave spectroscopy and application of its methods to heterostructures of silicon dioxide with Co nanoparticles on a GaAs substrate

A method has been developed for determining magnetic and electrical characteristics of film nanostructures containing magnetic nanoparticles from dispersion curves of surface spin waves propagating in these nanostructures. The dispersion curves of spin waves are determined by the dynamics of the spin component described by the generalized Landau-Lifshitz equations and an alternating electromagnetic field induced by a spin wave. Since spin waves are very sensitive to inhomogeneity of magnetic parameters, spin disorder, and conductivity of an object near or inside which these waves propagate, they can be used for determining magnetic and electrical characteristics of the objects under investigation. The developed calculation method, which can be employed both in spin-wave spectroscopy and in analysis of dispersion curves obtained by other methods, has been used for determining parameters of heterostructures consisting of a SiO₂ film with Co nanoparticles on a GaAs substrate. It has been found from the shape of dispersion curves of the surface spin waves that, in the film near the interface, spins of the nanoparticles are close to a ferromagnetic ordering, whereas near the free surface, the spin orientation of nanoparticles is more chaotic. It has been revealed that a conducting layer is formed in GaAs, and the SiO₂(Co) film near the interface has an increased conductivity.     

Total transparency of a two-moving-magnetized-plasma-layer structure

In the present Letter the transparency of a two-moving-magnetized-plasma-layer structure irradiated by an electromagnetic wave is investigated theoretically and its resonant conditions are determined. Here, the direction of the external magnetic field is normal to the plasma surface and two layers move with different velocities parallel to the interface. The effects of the external magnetic field, speed of plasma layers and the magnitude of the wave number component on transparency are simulated. These investigations for S-polarized and P-polarized electromagnetic waves have been done separately.     

Exceptional surface wave as a condition of the maximum increase in the intensity of an evanescent electromagnetic wave in a transparent medium

It has been shown that the condition of the maximum increase in the intensity of TM or TE evanescent electromagnetic waves at the interface between two transparent insulators in a static electric (magnetic) field simultaneously determines the dispersion law of the corresponding exceptional surface wave for which the instantaneous energy flux through the interface is zero at any time.     

On the stability of a cylindrical jet moving in a material medium along an external electrostatic field

A dispersion relation is derived for capillary waves with arbitrary symmetry (with arbitrary azimuthal numbers) on the surface of a jet of an ideal incompressible dielectric liquid moving in an ideal incompressible dielectric medium along an external uniform electrostatic field. A tangential discontinuity in the velocity field on the jet surface is shown to cause Kelvin-Helmholtz periodical instability at the interface and destabilize axisymmetric, flexural, and flexural-deformational waves. Both the flexural and flexural-deformational instabilities have a threshold and are observed not at an arbitrarily small velocity of the jet but starting from a certain finite value. It is shown that the instability of waves generated by the tangential discontinuity of the velocity field is periodic only formally (from the pure mathematical point of view). Actually, the jet disintegrates within the time of instability development, which is shorter than the half-cycle of the wave.     

Interfacial waves with free-surface boundary conditions: an approach via a model equation

In a two-fluid system where the lower fluid is bounded below by a rigid bottom and the upper fluid is bounded above by a free surface, two kinds of solitary waves can propagate along the interface and the free surface: classical solitary waves characterized by a solitary pulse or generalized solitary waves with nondecaying oscillations in their tails in addition to the solitary pulse. The classical solitary waves move faster than the generalized solitary waves. The origin of the nonlocal solitary waves can be understood from a physical point of view. The dispersion relation for the above system shows that short waves can propagate at the same speed as a “slow” solitary wave. The interaction between the solitary wave and the short waves creates a nonlocal solitary wave. In this paper, the interfacial-wave problem is reduced to a system of ordinary differential equations by using a classical perturbation method, which takes into consideration the possible resonance between short waves and “slow” solitary waves. In the past, classical Korteweg–de Vries type models have been derived but cannot deal with the resonance. All solutions of the new system of model equations, including classical as well as generalized solitary waves, are constructed. The domain of validity of the model is discussed as well. It is also shown that fronts connecting two conjugate states cannot occur for “fast” waves. For “slow” waves, fronts exist but they have ripples in their tails.     

Energy partitioning of ultrasonic waves beyond the critical angle at flat boundaries

Energy partitioning equations for oblique longitudinal waves incident on an interface were coded for a HP 9820 calculator. Program output includes phase angles and imaginary surface wave intensities that have not been previously published. The surface wave intensities may be helpful in understanding the critical angle dip that is experimentally observed. A complete code listing and typical output are included.     

Characteristics of surface sound pressure and absorption of a finite impedance strip for a grazing incident plane wave

Distributions of sound pressure and intensity on the surface of a flat impedance strip flush-mounted on a rigid baffle are studied for a grazing incident plane wave. The distributions are obtained by superimposing the unperturbed wave (the specularly reflected wave as if the strip is rigid plus the incident wave) with the radiated wave from the surface vibration of the strip excited by the unperturbed pressure. The radiated pressure interferes with the unperturbed pressure and distorts the propagating plane wave. When the plane wave propagates in the baffle-strip-baffle direction, it encounters discontinuities in acoustical impedance at the baffle-strip and strip-baffle interfaces. The radiated pressure is highest around the baffle-strip interface, but decreases toward the strip-baffle interface where the plane wave distortion reduces accordingly. As the unperturbed and radiated waves have different magnitudes and superimpose out of phase, the surface pressure and intensity increase across the strip in the plane wave propagation direction. Therefore, the surface absorption of the strip is nonzero and nonuniform. This paper provides an understanding of the surface pressure and intensity behaviors of a finite impedance strip for a grazing incident plane wave, and of how the distributed intensity determines the sound absorption coefficient of the strip.     

Reflection and transmission of waves in pyroelectric and piezoelectric materials

The reflection and transmission theories of waves in pyroelectric and piezoelectric medium are studied in this paper. In general in an infinite homogeneous pyroelectric medium there are four bulk wave modes: quasi-longitudinal, two quasi-transversal and temperature waves. In an infinite homogeneous piezoelectric medium there are three bulk wave modes: quasi-longitudinal and two quasi-transversal waves. In the reflection and transmission problem there are five complex boundary conditions in the pyroelectric medium and four complex boundary conditions for the piezoelectric medium. In this paper, we find that the surface waves will be revealed in the reflection and transmission wave problem. The surface waves have the same wave vector component with the incident waves on the interface plane. The two dimensional reflection problem of waves at the interface between the semi-infinite pyroelectric medium and vacuum is researched in greater detail and a numerical example is given.     

Reflection of spin and spin-elastic waves at the interface of a ferromagnetic half-space

This paper considers the reflection of pure spin and spin-elastic (or magneto-elastic) waves at the interface of a ferromagnetic half-space and a vacuum. For pure spin waves two cases are considered, with exchange effects, and without. It is shown that when exchange effects are taken into account, volume spin waves in the ferromagnetic half space incident at the boundary with the vacuum generate a reflected volume spin wave, and an accompanying compound surface wave propagating along the boundary and consisting of two partial inhomogeneous spin waves in the ferromagnetic half-space and a partial magneto-static inhomogeneous surface wave in the vacuum. When exchange effects are neglected the incident wave generates only a reflected volume wave in the ferromagnetic half-space.

Reflection and transmission of spin-elastic (or magneto-elastic) waves has been considered only in the case of the absence of exchange effects. An incident volume wave generates a volume spin-elastic reflected wave and one inhomogeneous magneto-static accompanying surface wave.

Excitations of the magnetic field are not transmitted into the vacuum in both cases when the exchange effect is neglected. In all cases the reflection of a spin wave has the character of a full internal reflection.     

Backscattered indicatrix from surfaces with random impedance

Intensity enhancement in the retroreflection direction is studied for waves scattered by a random interface which has a bound state (surface wave). We have found that an enhanced backscattered peak appears as the result of competition of two mechanisms: multiple scattering of a surface wave along the interface, and its leakage to upper half-space. The last one is the important distinction of surface scattering, which shifts the diffuse pole and eliminates in a natural way the divergence of second moments, which is the crucial difficulty in existing theories. New results, valid when there is no real absorption in the medium, are obtained for the diffuse scattered intensity as a function of the angles near the antispecular direction.     

液面位置对流-固交界面上伪瑞利波幅度影响的数值模拟

研究了流体半空间中存在气-液交界面并且其位置发生改变时,流-固交界面上伪瑞利波的传播特性和幅度响应特征。借助有限差分的方法,实现了对不同气-液交界面位置时振动方向垂直于流-固交界面的脉冲面源所激发表面波声场的数值模拟,分别讨论了气-液交界面自身的散射作用与伪瑞利波传播过程中的能量泄漏对伪瑞利波幅度的影响。数值模拟结果表明:气-液交界面自身对伪瑞利波的散射作用对伪瑞利波幅度仅有极微小的影响,而能量泄漏才是引起伪瑞利波衰减的决定性因素;随着气-液交界面位置的升高,脉冲伪瑞利波幅度呈指数规律下降,与此同时主频向低频偏移。所得研究结果可以发展为一种利用伪瑞利波幅度进行液位检测的可靠方法。      

Reflection of surface acoustic waves in the bulk of a hexagonal single crystal

It has been shown that surface acoustic waves in some hexagonal crystals can include not only the waves outgoing from the surface into the bulk of the crystal but also the reflected waves, i.e., those coming from the bulk of an infinite single crystal. The outgoing and reflected waves decay exponentially with the distance from the surface. It has been found that the reflected wave can exist if the velocity of its propagation is below the critical value, which does not exist for some crystals. The numerical calculations have shown in what real hexagonal crystals the reflected wave can exist. The values of the critical velocity have been found for a number of hexagonal crystals.     

Tailoring edge and interface states in topological metastructures exhibiting the acoustic valley Hall effect

In this study, we investigate the acoustic topological insulator or topological metastructure, where an acoustic wave can exist only in an edge or interface state instead of propagating in bulk. Breaking the structural symmetry enables the opening of the Dirac cone in the band structure and the generation of a new band gap, wherein a topological edge or interface state emerges.Further, we systematically analyze two types of topological states that stem from the acoustic valley Hall effect mechanism;one type is confined to the boundary, whereas the other type can be observed at the interface between two topologically different structures. Results denote that the selection of different boundaries along with appropriately designed interfaces provides the acoustic waves in the band gap range with abilities of one-way propagation, dual-channel propagation, immunity from backscattering at sharp corners, and/or transition between propagation at interfaces and boundaries. Furthermore, we show that the acoustic wave propagation paths can be tailored in diverse and arbitrary ways by combing the two aforementioned types of topological states.