Phase behaviour of lyotropic liquid crystals in external fields and confinement

This mini-review discusses the influence of external fields on the phase behaviour of lyotropic colloidal liquid crystals. The liquid crystal phases reviewed, formed in suspensions of highly anisotropic particles ranging from rod- to board- to plate-like particles, include nematic, smectic and columnar phases. The external fields considered are the earth gravitational field and electric and magnetic fields. For electric and magnetic fields single particle alignment, collective reorientation behaviour of ordered phases and field-induced liquid crystal phase transitions are discussed. Additionally, liquid crystal phase behaviour in various confining geometries, e.g. slit-pore, circular and spherical confinement will be reviewed.     

Confinement physics for thermal, neutral, high-charge-state plasmas in nested-well solenoidal traps

A theoretical study is presented which indicates that it is possible to confine a neutral plasma using static electric and solenoidal magnetic fields. The plasma consists of equal temperature electrons and highly stripped ions. The solenoidal magnetic field provides radial confinement, while the electric field, which produces an axial nested-well potential profile, provides axial confinement. A self-consistent, multidimensional numerical solution for the electric potential is obtained, and a fully kinetic theoretical treatment on axial transport is used to determine an axial confinement time scale. The effect on confinement of the presence of a radial electric field is explored with the use of ion trajectory calculations. A thermal, neutral, high-charge-state plasma confined in a nested-well trap opens new possibilities for fundamental studies on plasma recombination and cross-field transport processes under highly controlled conditions.     

声子之间的相互作用对量子线中磁极化子性质的影响

研究了量子线中弱耦合磁极化子的性质.采用线性组合算符和微扰法导出量子线中弱耦合磁极化子的基态能量.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,讨论了量子线的受限强度、电子-LO声子耦合强度和声子之间相互作用对量子线中弱耦合磁极化子的基态能量的影响.数值计算结果表明:量子线中弱耦合磁极化子的基态能量随量子线的受限强度ω₀的增大而迅速增大.当受限强度ω₀取相同值时,电子-声子耦合强度α越大基态能量E₀越小,磁场的回旋频率ω_e越大基态能量E₀越大.在弱磁场情况下,当ω₀<0.5时,随着量子线的受限强度ω₀的减少p值迅速增大,即对于弱磁场声子之间相互作用的影响不能忽略.     

Electrical manipulation of spins in a nanowire with Rashba interaction

We investigate the influence of external electric fields on the spins of a ballistic nanowire in terms of variations of the Rashba parameter and modification of the confinement potential. For a weak Rashba effect, the spins along the confinement direction in a given subband nearly assume full quantization. In the presence of a perpendicular magnetic field, the state of quantization can be manipulated using a transverse electric. This process requires modifications in the spin textures. If an in-plane magnetic field is applied, spins suffer rigid displacement to one edge of the wire and their expectation value becomes independent of the transverse electric field.     

Combined effects of magnetic and electric fields on the interband optical transitions in InAs/InP quantum wire

Combined effects of magnetic and electric fields on the confined exciton in an InAs_1−xP_x/InP (x=0.2) quantum well wire are investigated taking into account the geometrical confinement effect. Variational formulism, within the frame work of effective mass approximation, is applied to obtain the exciton binding energy. The second order harmonic generation and the optical gain are carried out using compact density method. The strain effects are included with the confinement potential in the Hamiltonian. The energy difference of the ground and the first excited state is found in the presence of magnetic and electric fields taking into the consideration of spatial confinement effect. The result shows that the optical properties are more influenced taking into account the effects of geometrical confinement, magnetic field and electric field. It is shown that the telecommunication wavelength can be achieved with the suitable doping barrier material with the wire material and the external perturbations.     

先进磁镜装置中径向电场对高能粒子的约束性能研究

本文运用Boris算法对紧凑型聚变反应装置(compact fusion reactor, CFR)中高能a粒子的运动轨道进行了数值模拟,分析了高能a粒子在不同径向电场作用下运动轨道的差异性;探究了不同径向电场对CFR装置中不同位置处a粒子约束性能的影响.研究结果表明,当正、负径向电场强度达到一定临界值时,都能够使高能a粒子很好地约束在CFR装置内部,但不同位置处径向电场强度临界值与a粒子初始条件有关.     

The magnetic properties of GaAs parabolic quantum dot in the presence of donor impurity,magnetic and electric fields

The magnetization and the magnetic susceptibility quantities of a single electron moving in a two-dimensional (2D) parabolic quantum dot are studied under the influence of external uniform electric and magnetic fields, in the presence of a donor impurity. The Hamiltonian was solved using shifted 1/N expansion method within the effective mass approximation. The results have been displayed as a function of physical parameters: confinement strength ω₀, magnetic field strength ω_c, temperature T and electric field strength F.     

Improved confinement due to open ergodic field lines imposed by the dynamic ergodic divertor in TEXTOR

The ergodization of the magnetic field lines imposed by the dynamic ergodic diverter (DED) in TEXTOR can lead both to confinement improvement and to confinement deterioration. The cases of substantial improvement are in resonant ways related to particular conditions in which magnetic flux tubes starting at the X points of induced islands are connected with the wall. This opening process is connected with a characteristic modification of the heat deposition pattern at the divertor target plate and leads to a substantial increase and steepening of the core plasma density and pressure. The improvement is tentatively attributed to a modification of the electric potential in the plasma carried by the open field lines. The confinement improvement bases on a spontaneous density built up due to the application of the DED and is primarily a particle confinement improvement.     

GaAs抛物量子线中弱耦合极化子的磁场效应

应用变分法和改进的线性组合算符法,研究了磁场对抛物量子线中弱耦合极化子振动频率和相互作用能的影响.给出了GaAs抛物量子线中弱耦合极化子的振动频率和相互作用能与磁场和约束强度的依赖关系.对GaAs晶体作了数值计算,结果显示:极化子振动频率和相互作用能都随约束强度和外磁场的增加而增大.     

Universal magnetic domain wall dynamics in the presence of weak disorder

The motion of elastic interfaces in disordered media is a broad topic relevant to many branches of physics. Field-driven magnetic domain wall motion in ultrathin ferromagnetic Pt/Co/Pt films can be well interpreted within the framework of theories developed to describe elastic interface dynamics in the presence of weak disorder. Indeed, the three theoretically predicted dynamic regimes of creep, depinning, and flow have all been directly evidenced in this model experimental system. We discuss these dynamic regimes and demonstrate how field-driven creep can be controlled not only by temperature and pinning, but also via interactions with magnetic entities located inside or outside the magnetic layer. Consequences of confinement effects in nano-devices are briefly reviewed, as some recent results on domain wall motion driven by an electric current or assisted by an electric field. Finally new theoretical developments and perspectives are discussed.     

Electronic states and interband light absorption in semi-spherical quantum dot under the influence of strong magnetic field

In the framework of effective mass approximation the electronic states in semi-spherical quantum lens under the influence of strong magnetic field are investigated. We have used the adiabatic approximation for the case of strong magnetic field. The eigenfunctions and eigenvalues of this problem are determined. In strong confinement regime interband optical absorption of light is investigated in quantum lens from InAs. The threshold frequencies of absorption are determined. The comparison with the case of film under the influence of strong magnetic field with infinitely high confinement potential is performed.     

Magnetic-field-induced insulator-conductor transition in SU(2) quenched lattice gauge theory

We study the correlator of two vector currents in quenched SU(2) lattice gauge theory with a chirally invariant lattice Dirac operator with a constant external magnetic field. It is found that in the confinement phase the correlator of the components of the current parallel to the magnetic field decays much slower than in the absence of a magnetic field, while for other components the correlation length slightly decreases. We apply the maximal entropy method to extract the corresponding spectral function. In the limit of zero frequency this spectral function yields the electric conductivity of quenched theory. We find that in the confinement phase the external magnetic field induces nonzero electric conductivity along the direction of the field, transforming the system from an insulator into an anisotropic conductor. In the deconfinement phase the conductivity does not exhibit any sizable dependence on the magnetic field.     

Hydrostatic pressure,impurity position and electric and magnetic field effects on the binding energy and photo-ionization cross section of a hydrogenic donor impurity in an InAs Pöschl-Teller quantum ring

Using the variational method and the effective mass and parabolic band approximations, the behaviour of the binding energy and photo-ionization cross section of a hydrogenic-like donor impurity in an InAs quantum ring, with Pöschl-Teller confinement potential along the axial direction, has been studied. In the investigation, the combined effects of hydrostatic pressure and electric and magnetic fields applied in the direction of growth have been taken into account. Parallel polarization of the incident radiation and several values of the applied electric and magnetic fields, hydrostatic pressure, and parameters of the Pöschl-Teller confinement potential were considered. The results obtained can be summarised as follows: (1) the influence of the applied electric and magnetic fields and the asymmetry degree of the Pöschl-Teller confinement potential on the donor binding energy is strongly dependent on the impurity position along the growth and radial directions of the quantum ring, (2) the binding energy is an increasing function of hydrostatic pressure and (3) the decrease (increase) in the binding energy with the electric and magnetic fields and parameters of the confinement potential (hydrostatic pressure) leads to a red shift (blue shift) of the maximum of the photo-ionization cross section spectrum of the on-centre impurity.     

Impurity-related electronic properties in quantum dots under electric and magnetic fields

This paper presents a systematic study of the ground-state binding energies of a hydrogenic impurity in quantum dots subjected to external electric and magnetic fields.The quantum dot is modeled by superposing a lateral parabolic potential,a Gaussian potential and the energies are calculated via the finite-difference method within the effectivemass approximation.The variation of the binding energy with the lateral confinement,external field,position of the impurity,and quantum-size is studied in detail.All these factors lead to complicated binding energies of the donor,and the following results are found:(1) the binding energies of the donor increase with the increasing magnetic strength and lateral confinement,and reduce with the increasing electric strength and the dot size;(2) there is a maximum value of the binding energies as the impurity placed in different positions along the z direction;(3) the electric field destroys the symmetric behaviour of the donor binding energies as the position of the impurity.     

磁边界效应对径向磁场中等离子体束流运动轨迹的影响

根据离子与径向磁场的约束关系,用面向对象的单元粒子法模拟了极向偏转器中等离子体束流在均匀和非均匀径向磁场中的运动情况,得到了在磁边界效应下极向偏转器内部畸变电场的分布,分析了对质量分离的影响。模拟成果对质量分离器、质谱分析仪及材料提纯等装置的研制、特殊位形电磁场控制多质量束流等相关领域的研究有参考价值。     

Nonlinear optical rectification of a hydrogenic impurity in a disc-like quantum dot

An investigation of the nonlinear optical rectification of a hydrogenic impurity, which is in a two-dimensional disc-like quantum dot (QD) with parabolic confinement potential, has been performed by using the perturbation method in the effective mass approximation. Both the electric field and the confinement effects on the energy are investigated in detail. The results are presented as a function of the incident photon energy for the different values of the confinement strength and the electric field. It is found that the nonlinear optical properties of hydrogenic impurity states in a disc-like QD are strongly affected by the confinement strength and the electric field.     

Gyrocenter shift of low-temperature plasmas and the retrograde motion of cathode spots in arc discharges

The gyrocenter shift phenomenon explained the mechanism of radial electric field formation at the high confinement mode transition in fusion devices. This Letter reports that the theory of gyrocenter shift is also applicable to low temperature high collisional plasmas such as arc discharges by the generalization of the theory resulting from a short mean free path compared with the gyroradius. The retrograde motion of cathode spots in the arc discharge is investigated through a model with the expanded formula of gyrocenter shift. It is found that a reversed electric field is formed in front of the cathode spots when they are under a magnetic field, and this reversed electric field generates a rotation of cathode spots opposite to the Amperian direction. The ion drift velocity profiles calculated from the model are in agreement with the experimental results as functions of magnetic flux density and gas pressure.     

Experimental measurement of neoclassical mobility in an annular malmberg-penning trap

An annular Malmberg-Penning trap confining a non-neutral plasma of electrons has been operated with an azimuthal magnetic field to create drifts orthogonal to the magnetic flux surfaces. An applied electric field and collisions with added helium drive transport by electric mobility. The measured confinement times have the expected neoclassical magnetic-field dependence, are approximately 0.8 of the value based upon the neoclassical mobility, and differ from the classical value by more than a factor of 3 at the highest value of azimuthal field.     

Electronic states in a narrow band gap semiconductor microcrystal with parabolic confinement in magnetic field

The energy levels of electrons in a narrow band gap semiconductor microcrystal under the influence of magnetic field are investigated. The confinement potential of microcrystal is approximated as parabolic, and the electron dispersion law is considered within the framework of two-band Kane model. It has been shown that nonparabolicity of dispersion law results in the appearance of the “anharmonic” term in Hamiltonian. The values of magnetic field at which the “anharmonic” term can be considered as perturbation are found. Results of electron energy of nonperturbed Hamiltonian dependencies on values of magnetic field and frequency of microcrystal confinement potential are presented. A comparison of the obtained results with the other cases has been done.