Hot carrier drift induced EM wave instability in a magnetoactive solid state plasma

The effect of a strong longitudinal static electric field on the propagation and instability of transverse circularly polarised EM waves (left and right handed) in the presence of a static magnetic field along the direction of propagation in an InSb plasma has been studied under hot carrier conditions by a phenomenological approach. The results show the possibility of existence of wave instabilities for a wide range of system parameters. The growth rate decreases with the heating d.c. electric field and increases slightly with the static magnetic field.     

Hot carrier anisotropic conductivity of a current-carrying bismuth

The hot carrier effects and d.c. conductivity of a semi-metal (e.g. Bismuth) have been studied by using the semi-kinetic treatment and the effective temperature model. The isotropic part of carrier distribution function is taken to be Fermi-Dirac in each valley correspponding to different effective temperatures which are determined by solving the energy balance equation. The anisotropy of the electron and hole mass has been incorporated and the carriers relaxation time is assumed to be isotropic. The anisotropy of the conductivity is studied by orienting the d.c. electric field along the three crystallographic axes. It is concluded that the hot carrier (i.e. non-linear) effects can be observed in semi-metals also because of their comparatively low conductivity.     

Electro-optical transitions in a semiconductor cylindrical nanolayer

The single-electron states in a quantized cylindrical layer have been considered in the presence of a moderate homogeneous electric field, when the energy imparted to a charge carrier by the electric field becomes comparable to the energy of rotational motion of this particle. The corresponding energy spectrum and the envelopes of the wave functions of charge carriers in the layer have been obtained in an explicit form. The electro-optical absorption band of a weak electromagnetic wave has been calculated. It has been found that the absorption intensity increases with an increase in the intensity of the electric field. The external electric field leads to an explicit dependence of the absorption intensity on the effective masses of charge carriers. The absorption intensity decreases as the difference between the effective masses of charge carriers increases. There is also an effective broadening of the band gap, which is determined by the geometrical dimensions of the sample and the magnitude of the external field.     

New interior solution describing relativistic fluid sphere

Nonlinear low-frequency electrostatic waves in a magnetized, three-component plasma consisting of hot electrons, hot positrons and warm ions have been investigated. The electrons and positrons are assumed to have Boltzmann density distributions while the motion of the ions are governed by fluid equations. The system is closed with the Poisson equation. This set of equations is numerically solved for the electric field. The effects of the driving electric field, ion temperature, positron density, ion drift, Mach number and propagation angle are investigated. It is shown that depending on the driving electric field, ion temperature, positron density, ion drift, Mach number and propagation angle, the numerical solutions exhibit waveforms that are sinusoidal, sawtooth and spiky. The introduction of the Poisson equation increased the Mach number required to generate the waveforms but the driving electric field E ₀ was reduced. The results are compared with satellite observations.     

Propagation of electromagnetic waves in a conducting magnetic medium

We study helicon-spin waves (hybrid polaritons) in a ferromagnetic conducting medium in a strong static magnetic field and determine their existence domains. It is shown that the spatial dispersion of the conductivity tensor gives rise to collisionless damping of these waves when they propagate obliquely to the magnetic field. In the absence of collisionless damping (for wave propagation along the magnetic field), the conditions of amplification of hybrid polaritons in a static electric field are determined. Institute of Radiophysics and Electronics, National Academy of Sciences of Ukraine, Kharkov, Ukraine. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol.43, No. 1, pp. 38–44, January 2000.     

Chaotic dynamics of charged particles in the field of two monochromatic waves in a magnetized plasma

We study the dynamics of charged particles in the presence of two electrostatic waves propagating obliquely to an ambient magnetic field. The presence of a second wave makes the problem a two-dimensional and time-dependent one with a complicated phase space behavior. We derive a set of difference equations (maps) for the nonrelativistic particle motion limit and numerically study them to elucidate the various aspects of the phase space dynamics. For the general case of oblique propagation, we observe synergistic effects leading to the lowering of the stochasticity threshold and the concomitant reduction in electric field amplitudes for particle heating applications. These results can be understood in terms of the resonance structures associated with the two waves and we obtain approximate analytic expressions for the thresholds. For the degenerate case of omega(1)=nOmega,omega(2)=mOmega (where omega(1),omega(2) are the frequencies of the two waves, Omega is the cyclotron frequency and n,m are integers) and strictly perpendicular propagation, the problem simplifies to a one-and-one-half-dimensional one. We observe the presence of stochastic webs in this situation. (c) 1996 American Institute of Physics.     

Propagation of high power helicons in n-indium antimonide crystal

The propagation of high power helicon in n-InSb has been analysed taking into account the heating of the carriers by the electric field of the wave. The momentum and energy transfer of the electrons have been taken to be due to acoustic phonons and polar optical phonons scattering at 77°K respectively. The sample is assumed to be finite and the wave is incident on the semiconductor-free space interface. Calculations have been made for phase constant, attenuation constant, reflection coefficient and the electron temperature as function of the magnetic field and the wave amplitude. The theoretical results are found to be in qualitative agreement with the experimental observations of Laurinavichyus and Pozhela[14].     

磁光平面波导的单向传播特性

表面磁等离子体(surfacemagnetoplasmons,SMPs)是一种在电介质和偏置磁场作用下磁光材料界面处传播的近场电磁波.其独特的非互易传播特性引起了大量科研工作的关注,但在具体的波导结构设计上仍存在很多问题.本文研究了一种银-硅-磁光材料的3层平面波导结构,SMPs在磁光材料和硅的界面处传播,发现在特定的频率范围内,SMPs的基模及高阶模式均具有正向或反向的单向传播特性.分别计算了旋磁与旋电材料平面波导的色散方程,研究了硅层厚度与外加磁场对能带结构及SMPs单向传播区域的影响,发现无论是旋磁或旋电材料的结构,硅层厚度的增加使高阶模式使高阶模式出现在更低的频率位置,使单向传输带宽变小甚至消失,外加磁场的变大使磁光材料的能带结构频率增大的同时带隙中也引入了高阶模式.计算了2种磁光材料平面波导的正向和反向的单向传播带宽宽度,发现旋磁材料YIG的单向SMPs模式出现在GHz波段,最大单向带宽可达到2.45 GHz;旋电材料InSb的单向SMPs模式出现在THz波段,最大单向带宽达到3.9 THz.     

Magnetoplasma waves in anisotropic semiconductors and semimetals

The propagation of electromagnetic waves in solids with electron and hole energy surfaces of second order placed in a magnetic field is investigated. The deduced dispersion relation is compared with measurements of the Alfvén wave velocity in bismuth. The theoretical and experimental results are in good agreement. In particular, it is clearly shown that for special orientations of the magnetic field switching from one mode to the other occurs. Parameters of the energy surfaces of bismuth are given by fitting the theoretical curves to the measured phase velocity diagrams.     

Reversible electron heating vs . Wave-particle interactions in quasi-perpendicular shocks

Summary The energy necessary to explain the electron heating in quasiperpendicular collisionless shocks can be derived either from the electron acceleration in the d.c. cross shock electric potential, or by the interactions between the electrons and the waves existing in the shock. A Monte Carlo simulation has been performed to study the electron distribution function evolution through the shock structure, with and without particle diffusion on waves. This simulation has allowed us to clarify the relative importance of the two possible energy sources; in particular it has been shown that the electron parallel temperature is determined by the d.c. electromagnetic field and not by any wave-particle-induced heating. Wave particle interactions are effective in smoothing out the large gradients in phase space produced by the ?reversible? motion of the electrons, thus producing a ?cooling? of the electrons. Paper presented at the V Cosmic Physics National Conference, S. Miniato, November 27–30, 1990.     

Heating of magnons by hot charge carriers and electrical properties of HgCr2Se4

Strong variations of the conductivity and the Hall coefficient as a function of the magnetic and electric field strengths are discovered in the ferromagnetic semiconductor HgCr₂Se₄. The nature of these phenomena is discussed in connection with its electronic structure and the strong interaction between the electric and magnetic subsystems in this magnetic semiconductor. The results can be interpreted within a model of ordinary semiconductors with consideration of the strong electron-magnon interaction specific to magnetic semiconductors, the heating of magnons by hot charge carriers, and the trapping of charge carriers (the formation of ferrons) due to the s-d exchange interaction. Fiz. Tverd. Tela (St. Petersburg) 39, 664–667 (April 1997)     

Mode mixing of Alfvén waves in bismuth

We have investigated the propagation of Alfvén waves in bismuth at 4.2 K using a microwave interferometer at 34.45 GHz and applying magnetic fields up to 1 Tesla. At certain angles between the external magnetic field and the direction of propagation of the Alfvén waves in the crystal, we have observed intense oscillations of the amplitude and the phase of the interferometer curves. We explain these oscillations as due to a superposition of the two Alfvén wave modes. The phase velocities of the two modes are calculated from the measurements. Comparing them with a general dispersion relation we find good agreement between the theoretical phase velocities and the experimental values.     

Measurement of the static dielectric constant of the InSb lattice via gyrotropic sphere resonances

By application of the recent solution to the interaction of an electromagnetic plane wave with a sphere of finite conductivity in a d.c. magnetic field, the resonance field positions of various microwave resonances have been utilized to provide a direct and accurate determination of the dielectric constant and carrier concentration in InSb. A value of 16.8 ± 0.2 is reported for the static dielectric constant of the InSb lattice.     

碲化铋薄膜载能粒子相互作用的超快研究

碲化铋禁带宽度非常窄而具有高电导率和塞贝克系数,同时具有低热导率,成为已知室温下优值系数最高的热电材料。已有研究表明,纳米薄膜和超晶格是进一步提高材料热电性能的可行途径。因此超快研究碲化铋纳米薄膜中载能子间的相互作用过程对开发高性能热电材料有重要意义。本文采用飞秒激光泵浦-探测技术,实验研究了沉积在硅基底上厚度为100 nm碲化铋薄膜中各载能粒子的相互作用过程。通过改变延迟时间步长,分别观察到价带电子被光子激发跃迁至导带,激发电子在导带内与声子的能量弛豫及导带电子与空穴复合跃迁至价带,并将能量传递给声子导致声子温度升高的过程。此外,还观察到热应力产生的声波,并据此得到了碲化铋薄膜中纵波声速为2649 m s^-1。     

Interplay of parallel electric field and trapped electrons in kappa-Maxwellian auroral plasma for EMEC instability

In this paper, propagation characteristics of electromagnetic electron cyclotron(EMEC) waves based on kappa-Maxwellian distribution have been investigated to invoke the interplay of the electric field parallel to the Earth's magnetic field and auroral trapped electrons. The dispersion relation for EMEC waves in kappa-Maxwellian distributed plasma has been derived using the contribution of the parallel electric field and trapped electron speed. Numerical results show that the presence of the electric field has a stimulating effect on growth rate, which is more pronounced at low values of wave number. It is also observed that as the threshold value of trapped electron speed is surpassed, it dominates the effect of the parallel electric field and EMEC instability is enhanced significantly. The electric field acts as another source of free energy, and growth can be obtained even in the absence of trapped electron drift speed and for very small values of temperature anisotropy. Thus the present study reveals the interplay of the parallel electric field and trapped electron speed on the excitation of EMEC waves in the auroral region.     

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.     

Magnetophonon oscillations in tellurium under hot carrier conditions

The magnetoresistance of undoped tellurium crystals was measured at lattice temperatures below 4.2 K and magnetic fields up to 15 T. Under hot carrier conditions two series of magnetophonon oscillations in the longitudinal magnetoresistance with the c-axis perpendicular to the magnetic field direction were observed. On the basis of the known band parameters and an impurity binding energy of 1.4 meV, the results are explained with the capture of warm carriers at impurity sites under optical phonon emission.     

Secular free solution up to third-order of relativistic hot dissipative plasma equation for electrostatic field

The perturbation method of Lindstedt is applied to study the relativistic nonlinear effects for longitudinal electrostatic waves in a hot dissipative plasma having no static electric or magnetic field. Amplitude dependent frequency and wave-number shifts are derived including relativistic corrections.The author expresses his gratitude to Dr. B.Chakraborty of the Department of Mathematics, Jadavpur University, Calcutta for his guidance in the preparation of this paper and also wishes to thank Dr. K. P.Das of the Department of Mathematics, Kalyani University, Kalyani, for helpful discussions.     

A very simple explanation of the effects of a.c. fields on the critical currents in type II superconductors

The electric field induced in a type II superconductor foil by an a.c. magnetic field is rectified by the non-linear static voltage current characteristic of the superconductor when there is a static current, so that the static critical current seems to decrease.     

A Model for Periodic Nonlinear Electric Field Structures in Space Plasmas

In this study, we present a physical model to explain the generation mechanism of nonlinear periodic waves with a large amplitude electric field structures propagating obliquely and exactly parallel to the magnetic field. The ``Sagdeev potential' fromthe MHD equations is derived and the nonlinear electric field waveforms are obtained when the Mach number, direction of propagation, and the initial electric field satisfy certain plasma conditions. For the parallel propagation, the amplitude of theelectric field waves with ion-acoustic mode increases with the increase of initial electric field and Mach number but its frequency decreases with the increase of Mach number. The amplitude and frequency of the electric field waves with ion-cyclotron mode decrease with the increase of Mach number and become less spiky, andits amplitude increases with the increase of initial electric field. For the oblique propagation, only periodic electric field wave with an ion-cyclotron mode obtained, its amplitude and frequency increase with the increase of Mach number and become spiky. From our model the electric field structures show periodic, spiky, and saw-tooth behaviours corresponding to different plasma conditions.