自旋和声子之间相互作用对TlBr晶体中表经极化子性质的影响

在考虑电子自旋和声子之间相互作用的同时,采用线性组合算符和微扰法研究半无限Ｔ１Ｂｒ晶体内表面磁极化子处于基态时的振动频率和诱生势与磁场Ｂ和距晶体表面距离（坐标）ｚ之间的依赖关系。     

强耦合半无限极性晶体中磁极化子的激发能量

采用线性组合算符和幺正变换,利用变分法计算了多原子半无限极性晶体中由电子和光学声子强耦合相互作用所产生的磁极化子的第一激发能量及平均声子数,并通过适当的数值计算图示了它们与磁场的关系。结果表明:在不同的磁场条件下,电子无限接近晶体表面和电子处于晶体深处时,磁极化子的第一激发能量和平均声子数都有所不同。     

极性半导体的表面电子

有不少的极性半导休,电子与表面声学声子和体纵光学声子的耦合弱,但与表面光学声手的耦台强.本文同时考虑体纵光学声子、表面光学声子以及表面声学声予的影响,研究这类半导体的表面电予的性质,采用线性组合算符和拉格朗日乘子法,导出其有效哈密顿量和重正化质量。     

表面磁极化子的回旋共振性质

在磁场中有不少的极性晶体,电子和体纵光学声子的耦合弱,而与表面光学声子的耦合强。本文讨论电子和体纵光学声子耦合弱,与表面光学声子耦合强时对表面磁极化子的性质的影响。采用改进了的线性组合算符法导出了磁场中表面极化子的回旋共振频率和回旋共振质量,对AgCl晶体进行了数值计算。结果表明,磁场中表面极化子的回旋共振频率和回旋共振质量随磁场的增加而增加。     

六极子磁场中自旋轨道耦合玻色-爱因斯坦凝聚体的基态结构

研究囚禁在环形势中的Rashba自旋轨道耦合玻色-爱因斯坦凝聚体在六极子磁场中的基态特性。在这种情况下,磁场破坏了自旋轨道耦合哈密顿量的旋转对称性,但系统仍具有2π/3的离散对称性。数值结果发现:在弱相互作用情况下,六极子磁场和Rashba自旋轨道耦合使环形囚禁的凝聚体呈类六边形的基态密度分布,当磁场强度超过某一临界值时,凝聚体将崩塌;在强相互作用情况下,半量子涡旋出现在凝聚体中,且被六极子磁场钉在方位角Ф=nπ/3的径向位置,涡旋的旋转方向取决于径向磁场的方向。     

轴向磁场下感应耦合放电模式转换的实验研究

为探究轴向磁场对纯Ar感应耦合等离子体放电模式转换的影响,设计并搭建一整套等离子体产生装置展开实验研究,引入阻抗分析法对放电模式转换进行判断,并得到了朗缪尔探针法的验证。实验发现,当气压为10 Pa时,轴向磁场强度的增加使得E-H和H-E模式转换的阈值功率增大;同时,随着轴向磁场的增强,放电中心区域的电子密度不断降低。初步分析认为,这是由于带电粒子在洛伦兹力作用下做回旋运动,导致高能电子在垂直磁场方向上的碰撞减少,降低了电子密度以及感应耦合效率。进一步分析电子能量概率函数(EEPF)发现,在E模式下,轴向磁场对电子运动的约束作用更加明显,高能电子(>27 eV)所占比例增多,电子能量分布更加均匀。     

Hall conductivity for two-dimensional magnetic systems

A Kubo inspired formalism is proposed to compute the longitudinal and transverse dynamical conductivities of an electron in a plane (or a gas of electrons at zero temperature) coupled to the potential vector of an external local magnetic field, with the additional coupling of the spin degree of freedom of the electron to the local magnetic field (Pauli Hamiltonian). As an example, the homogeneous magnetic field Ha]] conductivity is rederived. The case of the vortex at the origin is worked out in detail. This system happens to display a transverse Ha]] conductivity (P breaking effect) which is subleading in volume compared to the homogeneous field case, but diverging at small frequencies like 1/ω². A perturbative analysis is proposed for the conductivity in the random magnetic impurity problem (Poissonian vortices in the plane). At first order in perturbation theory, the Ha]] conductivity displays oscillations close to the classical straight line conductivity of the mean magnetic field.     

Toroidal plasma rotation induced by the dynamic ergodic divertor in the TEXTOR tokamak

The first results of the Dynamic Ergodic Divertor in TEXTOR, when operating in the m/n=3/1 mode configuration, are presented. The deeply penetrating external magnetic field perturbation of this configuration increases the toroidal plasma rotation. Staying below the excitation threshold for the m/n=2/1 tearing mode, this toroidal rotation is always in the direction of the plasma current, even if the toroidal projection of the rotating magnetic field perturbation is in the opposite direction. The observed toroidal rotation direction is consistent with a radial electric field, generated by an enhanced electron transport in the ergodic layers near the resonances of the perturbation. This is an effect different from theoretical predictions, which assume a direct coupling between rotating perturbation and plasma to be the dominant effect of momentum transfer.     

Hydrodynamic fluctuations in heavy fermion systems

A theory of hydrodynamic fluctuations in heavy fermion systems is presented. It is used to compute the attenuation and velocity of longitudinal ultrasound. The attenuation is dominated by the coupling of phonons to electronic density fluctuations. A discrepancy is resolved between theory and experiments on UPt₃, which has been existing with respect to the absolute magnitude of the temperature dependent attenuation. The latter provides direct proof for a large Fermi liquid parameterF ₀ ^s . The phonon Green's function is found to have a four-pole structure, resulting in two diffusive modes. One is the conventional one due to heat diffusion while the other is due to electron density diffusion and is a characteristic feature of heavy fermion systems. The two modes are coupled at finite temperatures. With the help of a model Hamiltonian (slave boson mean-field formulation of the Anderson lattice Hamiltonian) the ultrasound attenuation is calculated for low temperatures.     

极性晶体中强耦合表面磁极化子特性

研究极性晶体中表面磁极化子的特性。采用Huybrechts线性组合算符和幺正变换方法,导出了晶体中强耦合表面磁极化子处于基态的振动频率和有效哈密顿量,讨论了坐标z的两种极限情况,对RbCl晶体进行了数值计算。结果表明:振动频率和平行有效哈密顿量随磁场的增加而增大。     

Energy of a bound polaron in a magnetic field in asymmetric polar semiconductor heterostructures

In this paper, a new modified Hamiltonian of a polaron bound to a donor impurity in asymmetric step quantum wells (QWs) in the presence of an arbitrary magnetic field is given, in which the coupling of an electron with confined bulk-like LO phonons, half-space LO phonons and interface phonon modes is included. Especially, the interaction of the impurity with all possible optical-phonon modes is also considered. The ionization energy of a bound polaron in a magnetic field for asymmetric step QWs are studied by using a modified Lee-Low-Pines (LLP) variational method. The effects of the finite electronic confinement potential and the subband nonparabolicity are also considered. The relative importance of the donor impurity located at the well and the step is analyzed. Our results show the interaction between the impurity and the phonon field in screening the Coulomb interaction has a significant influence on the binding energy of bound polaron. The influence of subband non-parabolicity is appreciable on the bound polaron effects for the narrow well. The binding energy of bound polaron given in this paper are excellent agreement with the experimental measurement.     

Two-dimensional model of a large area, inductively coupled,rectangular plasma source for chemical vapor deposition

A novel design for an inductively coupled, rectangular plasma source is described. The design encompasses several key issues of large area thin film growth by chemical vapor deposition: structural integrity, electrostatic screening, substrate temperature control and maximal growth surface. A test reactor has been utilized to grow diamond films over ~1800 cm² at 13 MHz and ~1 torr pressure with 45 kW coupled power. The design is readily scalable to larger areas. To analyze the axial plasma uniformity, a two-dimensional (2-D) simulation model is presented. The electromagnetic coupling, nonequilibrium plasma chemistry and multispecies diffusion are self-consistently treated. In this 2-D approach, the slotted Faraday screen behaves as a diamagnetic medium in transmitting the magnetic field. Results are compared with experimental data for the hydrogen plasma extent, electron and gas temperatures. Neutral gas thermal conduction and hydrogen recombination dominate the energy deposition to the wall and in turn govern the plasma length. A tradeoff between quality and growth area is predicted for the reactor as the pressure is decreased     

Attenuation properties of EM wave by magnetized nonuniform plasma slab coated on perfect conductor plane

The total amplitude reflection coefficient of EM wave in a nonuniform plasma slab coated on perfect conductor plane is newly derived by using the scattering matrix method (SMM), and the attenuation is calculated. Three types of plasma electron density profile, that is the hyperbolic, sinusoidal, and linear profiles, are used. The external magnetic field and plasma parameters such as the maximum electron density and collision frequencies are discussed to calculate the attenuation of EM wave. The calculation results show that the plasma electron density profile and maximum electron density exert a large effect to the attenuation of EM wave and the attenuation under the uniform external magnetic field is taken place by the electron cyclotron resonance absorption, the up hybrid resonance absorption and geometric resonances absorption.     

Coupled scalar field equations for nonlinear wave modulations in dispersive media

A review of the generic features as well as the exact analytical solutions of a class of coupled scalar field equations governing nonlinear wave modulations in dispersive media like plasmas is presented. The equations are derivable from a Hamiltonian function which, in most cases, has the unusual property that the associated kinetic energy is not positive definite. To start with, a simplified derivation of the nonlinear Schrödinger equation for the coupling of an amplitude modulated high-frequency wave to a suitable low-frequency wave is discussed. Coupled sets of time-evolution equations like the Zakharov system, the Schrödinger-Boussinesq system and the Schrödinger-Korteweg-de Vries system are then introduced. For stationary propagation of the coupled waves, the latter two systems yield a generic system of a pair of coupled, ordinary differential equations with many free parameters. Different classes of exact analytical solutions of the generic system of equations are then reviewed. A comparison between the various sets of governing equations as well as between their exact analytical solutions is presented. Parameter regimes for the existence of different types of localized solutions are also discussed. The generic system of equations has a Hamiltonian structure, and is closely related to the well-known Hénon-Heiles system which has been extensively studied in the field of nonlinear dynamics. In fact, the associated generic Hamiltonian is identically the same as the generalized Hénon-Heiles Hamiltonian for the case of coupled waves in a magnetized plasma with negative group dispersion. When the group dispersion is positive, there exists a novel Hamiltonian which is structurally same as the generalized Hénon-Heiles Hamiltonian but with indefinite kinetic energy. The above correspondence between the two systems has been exploited to obtain the parameter regimes for the complete integrability of the coupled waves. There exists a direct one-to-one correspondence between the known integrable cases of the generic Hamiltonian and the stationary Hamiltonian flows associated with the only integrable nonlinear evolution equations (of polynomial and autonomous type) with a scale-weight of seven. The relevance of the generic system to other equations like the self-dual Yang-Mills equations, the complex Korteweg-de Vries equation and the complexified classical dynamical equations has also been discussed.     

Magnetic field studies of the frictional drag between coupled two-dimensional electronic systems – Coulomb versus phonon coupling

The coupling between systems of two spatially separated two-dimensional (2D) electron gases and between systems of a separated 2D electron gas and a 2D hole gas is studied as a function of magnetic field . The small barrier (30 nm) separated coupled electron gases showed a transition from a phonon dominated interaction at to a Coulomb dominated one at quantising fields. For large barriers (190 nm) phonons have been found to be the dominant coupling mechanism both at zero and finite fields. However, for all barriers investigated we could observe novel screening effects manifested in a suppression of the coupling at half-filled Landau levels. For the coupled electron–hole gases we have investigated samples with large barriers ( ) so that the coupling is both in zero and finite fields dominated by phonon mediated processes. The enhanced screening effects could not be observed in those samples possibly due to the less pronounced quantisation of the hole gas.     

磁场中准二维强耦合磁极化子的有效质量

采用改进的线性组合算符和LLP变分法,研究了外磁场对量子阱中电子与界面光学声子强耦合、与体纵光学声子弱耦合磁极化子的有效质量的影响。对AgCl/KI量子阱进行了数值计算,结果表明,磁极化子的有效质量随阱宽的增加而减小,随磁场的增强而增大,但不同支声子与电子和磁场相互作用对磁极化子有效质量的贡献大不相同。     

Ultracold RbSr molecules can be formed by magnetoassociation

We investigate the interactions between ultracold alkali-metal atoms and closed-shell atoms using electronic structure calculations on the prototype system Rb+Sr. There are molecular bound states that can be tuned across atomic thresholds with a magnetic field and previously neglected terms in the collision Hamiltonian that can produce zero-energy Feshbach resonances with significant widths. The largest effect comes from the interaction-induced variation of the Rb hyperfine coupling. The resonances may be used to form paramagnetic polar molecules if the magnetic field can be controlled precisely enough.     

Quantum mechanical Hamiltonians with large ground-state degeneracy

Nonrelativistic Hamiltonians with large, even infinite, ground-state degeneracy are studied by connecting the degeneracy to the property of a Dirac operator. We then identify a special class of Hamiltonians, for which the full space of degenerate ground states in any spatial dimension can be exhibited explicitly. The two-dimensional version of the latter coincides with the Pauli Hamiltonian, and recently-discussed models leading to higher-dimensional Landau levels are obtained as special cases of the higher-dimensional version of this Hamiltonian. But, in our framework, it is only the asymptotic behavior of the background ‘potential’ that matters for the ground-state degeneracy. We work out in detail the ground states of the three-dimensional model in the presence of a uniform magnetic field and such potential. In the latter case one can see degenerate stacking of all 2d Landau levels along the magnetic field axis.     

New polaron effect in magnetooptic phenomena in a quantum well

It is predicted that resonance coupling between two discrete electron energy levels corresponding to different size-quantization quantum numbers and different Landau quantum numbers can occur in a quantum well in a quantizing magnetic field. The resonance coupling is due to the interaction of an electron with LO phonons and results in the formation of polaron states of a new type. It is shown that for a certain value of the magnetic field, which depends on the splitting of the electron size-quantization levels, the absorption peak and the two-phonon resonance Raman scattering peak split into two components, the separation between which is determined by the electron-phonon coupling constant. The resonance coupling between size-quantization levels with the same Landau quantum numbers is also studied. The splitting of the peaks in this case is virtually independent of the magnetic field and can be observed in much weaker fields. The experimental observation of the effect will make it possible to determine the relative position of the electronic levels and the electron-phonon coupling constant. Pis’ma Zh. éksp. Teor. Fiz. 65, No. 7, 511–515 (10 April 1997)     

极性晶体中与形变势相互作用的表面极化子

有不少的极性晶体,电子与表面光学(SO)声子耦合强,但与表面声学(SA)声子耦合弱.研究电子与SO声子耦合强,与SA声子耦合弱的极性晶体中与形变势相互作用的表面极化子的性质.采用改进了的线性组合算符和微扰法导出了极性晶体中与形变势相互作用的表面极化子的有效哈密顿量.在计及电子在反冲效应中发射和吸收不同波矢的声子之间的相互作用时,讨论对表面极化子的有效哈密顿量、有效质量和有效相互作用势的影响.