Correlations of two-dimensional super-paramagnetic colloids in tilted external magnetic fields

We outline the formalism of liquid integral equation theory for anisotropic interactions in two dimensions and subsequently apply this theory to one-component super-paramagnetic particles exposed to a tilted magnetic field. Inhomogeneous local ordering of the particles is observed for different in-plane directions. The anisotropy of the interaction as well as of the liquid structure is increased by increasing the tilt angle. Furthermore, the particles favour an alignment in the direction of the in-plane component of the magnetic field. For increasing tilt angle, the anisotropy of the structural correlations is qualitatively similar to that of the corresponding solid lattice which is stable at lower temperatures. However, the mean-square displacements behave qualitatively different in the solid and fluid phases as a function of the tilt angle.     

Anisotropy of spin splitting and spin relaxation in lateral quantum dots

Inelastic spin relaxation and spin splitting epsilon(s) in lateral quantum dots are studied in the regime of strong in-plane magnetic field. Because of both the g-factor energy dependence and spin-orbit coupling, epsilon(s) demonstrates a substantial nonlinear magnetic field dependence similar to that observed by Hanson et al. [Phys. Rev. Lett. 91, 196802 (2003)]. It also varies with the in-plane orientation of the magnetic field due to crystalline anisotropy of the spin-orbit coupling. The spin relaxation rate is also anisotropic, the anisotropy increasing with the field. When the magnetic length is less than the "thickness" of the GaAs dot, the relaxation can be an order of magnitude faster for B ||[100] than for B || [110].     

Excited states of two-dimensional hydrogen atom in tilted magnetic field: Quantum chaos

The aim of the current work is the research of the influence of a tilted magnetic field direction on the spectrum and the energy level spacing distribution of a two-dimensional (2D) hydrogen atom and of an exciton in GaAs/Al_0.33Ga_0.67As quantum well. It was discovered that the quantum chaos (QC) is initiated with an increasing angle α between the magnetic field direction and the normal to the atomic plane. It is characterized by the repulsion of levels leading to the eliminating of the shell structure and by changing the spectrum statistical properties. The statement about the initiation of chaos and its dominance over regular motion with increasing angle α is confirmed by the results of our calculations of the classical dynamics presented in this paper. The evolution of the spatial distribution of the square of the absolute value of the wave function at an increasing angle α was observed. The differences of calculated dependencies of energies for various excited states on the tilt angle at a wide range of the magnetic field strength were described.     

抛物量子点中弱耦合磁极化子的振动频率和相互作用能

采用改进的线性组合算符和幺正变换方法研究磁场中抛物量子点弱耦合磁极化子的性质,导出抛物量子点中磁极化子的振动频率和相互作用能与磁场、受限强度和电子声子耦合强度的关系.对GaAs晶体进行数值计算,结果表明,量子点受限强度越大,量子点弱耦合磁极化子的振动频率和相互作用能越大.     

Anisotropic Transport on Monolayer and Multilayer Phosphorene in the Presence of an Electric Field

We demonstrate theoretically the anisotropic quantum transport of electrons through an electric field on monolayer and multilayer phosphorene. Using the long-wavelength Hamiltonian with continuum approximation, we find that the transmission probability for transport through an electric field is an oscillating function of incident angle, electric field intensity, as well as the incident energy of electrons. By tuning the electric field intensity and incident angle, the channels can be transited from opaque to transparent. The conductance through the quantum waveguides depends sensitively on the transport direction because of the anisotropic effective mass, and the anisotropy of the conductance can be tuned by the electric field intensity and the number of layers. These behaviors provide us an efficient way to control the transport of phosphorene-based microstructures.     

Effects of anisotropy and magnetic fields on the specific heat of a quasi-two-dimensional Boltzmann gas in an elliptical parabolic quantum dot

We investigate the effects due to anisotropy and magnetic field interaction for a quasi-two-dimensional Boltzmann gas in an elliptical parabolic quantum dot. The specific heat is studied with varying temperature, anisotropy, and magnetic field strength. The cases without and with the inclusion of the spin Zeeman interaction are considered.     

Magnetic anisotropy of strained epitaxial manganite films

The in-plane magnetic anisotropy of epitaxial La_0.7Sr_0.3MnO₃ (LSMO) films is studied at room temperature by the following three independent techniques: magnetooptical Kerr effect, ferromagnetic resonance at a frequency of 9.61 GHz, and recording of absorption spectra of electromagnetic radiation at a frequency of 290.6 MHz. The films are deposited onto NdGaO₃ (NGO) substrates in which the (110)NGO plane is tilted at an angle of 0–25.7° to the substrate plane. The uniaxial magnetic anisotropy induced by the strain of the film is found to increase with the tilt angle of the (110)NGO plane. A model is proposed to describe the change in the magnetic anisotropy energy with the tilt angle. A sharp increase in the radio-frequency absorption in a narrow angular range of a dc magnetic field near a hard magnetization axis is detected The anisotropy parameters of the LSMO films grown on (110)NGO, (001)SrTiO₃, and (001)[(LaAlO₃)_0.3 + (Sr₂AlTaO₆)_0.7] substrates are compared.     

The Spectra of Low-Lying States of Three-Dimensional Quantum Dots in a Magnetic Field

We have studied three-electron systems in three-dimensional anisotropic parabolic quantum dots with the cylindrical symmetry in magnetic fields by means of the method of few-body physics. The results show that the energy levels of a number of states are the lowest, as the magic angular momentum states of two-dimensional quantum dots.     

Intersubband excitations in single-and double-layer electron systems in a parallel magnetic field

The spectrum of neutral intersubband excitations in single and double quantum wells has been studied by the inelastic light scattering method. It is shown that excitation energies in an external magnetic field have an anisotropic component proportional to the dipole moment of excitations along the growth axis of the quantum wells. Consequently, the measurement of excitation energy in a magnetic field makes it possible to experimentally estimate the quantitative measure of asymmetry of the quantum wells (dipole moment of the intersubband transition). In addition, a parallel magnetic field makes it possible to considerably extend the range of momenta studied since it shifts the dispersion curves in the momentum space by the value of the anisotropic component. A new method is proposed for determining the symmetry of double quantum wells. In asymmetric wells, intersubband excitations appear between the layers and have a large dipole moment along the growth axis. In symmetric wells, the magnetic field itself induces the dipole moment of intersubband excitations so that the excitation spectrum does not change upon magnetic field inversion. Analysis of energy anisotropy in intersubband excitations in double quantum wells makes it possible to determine the symmetry of double wells to a high degree of accuracy.     

Analytical Ground-State of an Exciton Trapped in a Circular Parabolic Quantum Dot in the Presence of a Magnetic Field

The quasi-exact properties of an exciton are investigated theoretically in the presence of an external magnetic field using the effective-mass approach in GaAs parabolic quantum dot. The energy spectrum is obtained analytically as a function of the dot radius, interaction strength and magnetic field. It is established that, a steady bound state of an exciton in the ground state exists under the effect of a strong magnetic field; also I noticed that the exciton binding energy decreases by increasing both the radius of the dot and the magnetic field strength and the reduction becomes pronounced for larger dots. As expected, it has been found that the exciton total energy decreases with increasing the size of the dot and it enhances by increasing the magnetic field. It appears that the exciton total energy strongly depends on the magnetic field for dots with big size. The magnetic field effect on the exciton size also has been studied. It is shown that the increase in the magnetic field leads to a reduction in the exciton size; due to magnetic field confinement, while the size of an exciton reach its bulk limit as the dot size increases. Moreover, it is shown that, if the dot radius is sufficiently large the oscillator strength saturates and it becomes insensitive to the magnetic field while the increase in the magnetic field gradually weakened the oscillator strength. I have calculated the ground-state distribution for both the electron and the hole. It is found that the localization of the electron/hole increases in the presence of a magnetic field. Moreover, the ground-state optical-absorption intensity is investigated. Finally, the dependence of the lowest five states of an exciton on both the dot radius and the magnetic field are discussed.

     

Structure of Flux Line Lattices in Tilt Magnetic Fields of Anisotropic Superconductos

We study here, by the minimization of the total energy of flux line systems, the zero temperature structure of flux lines of uniaxial anisotropic superconductors in a tilt magnetic field. The anisotropic London model is used and an efficient method is developed to make the total energy calculation manageable. Two degenerate structures are found, one is a deformed triangular structure and the other is a superlattice with three lines per unit cell.     

在磁场作用下含有杂质的半导体量子环中电子的能级

由于量子环特殊的结构,我们尝试过不少方法,发现一般传统方法很难求解薛定谔方程,故很难求出它的波函数和能级。国内外很多学者从事这方面的研究,但发表的文献非常少。有必要寻找一些新的方法从事这方面的研究工作,本文中采用了B样条函数近似拟合波函数的方法,计算了一个在谐振子束缚势和磁场作用下含有杂质的二维量子环中的电子能级。研究了电子能级随磁场强度、束缚势的变化关系以及电子能级与量子环半径的关系。我们发现电子能级随磁场强度、束缚势强度的增强而增强;每一个能级都有一个最小值在特定的量子环半径上,并且随着能级的增加,最小值的位置向半径大的方向偏移。     

Shape of the magnetic resonance line in a thin film on the surface of an anisotropic superconductor

The shape of the EPR line in a thin (=λ/2, where λ is the London penetration depth of the magnetic field in the superconductor) paramagnetic film deposited on the surface of an anisotropic superconductor is calculated in an oblique magnetic field with allowance for the inhomogeneity of the local magnetic field of the Abrikosov vortex lattice. It is shown that, as the tilt angle of the external magnetic field is varied, the shape of the EPR line changes noticeably. This fact can give additional information about the superconductor parameters (the symmetry type of the vortex lattice and the anisotropy parameter of the superconductor). Fiz. Tverd. Tela (St. Petersburg) 41, 386–388 (March 1999)     

Hydrostatic pressure and electric and magnetic field effects on the binding energy of a hydrogenic donor impurity in InAs Pöschl-Teller quantum ring

We consider the effects of electric and magnetic fields as well as of hydrostatic pressure on the donor binding energy in InAs Pöschl-Teller quantum rings. The ground state energy and the electron wave function are calculated within the effective mass and parabolic band approximations, using the variational method. The binding energy dependencies on the electric field strength and the hydrostatic pressure are reported for different values of quantum ring size and shape, the parameters of the Pöschl-Teller confining potential, and the magnetic field induction. The results show that the binding energy is an increasing or decreasing function of the electric field, depending on the chosen parameters of the confining potential. Also, we have observed that the binding energy is an increasing/decreasing function of hydrostatic pressure/magnetic field induction. Likewise, the impurity binding energy behaves as an increasing/decreasing function of the inner/outer radii of the quantum ring nanostructure.     

光学极化子性质对耦合强度和磁场的依赖性

应用线性组合算符和幺正变换方法,研究磁场和耦合强度对光学极化子性质的影响。数值计算表明:当电子接近晶体表面时,光学极化子的振动频率、基态能量和第一激发能仅与磁场有关,且随磁场强度的增强而增大;当电子远离晶体表面时,基态能量和第一激发能与磁场强度和耦合参数均有关,且随磁场强度和耦合参数的增加而增加。     

抛物量子点中强耦合束缚磁极化子的性质

采用Pekar类型的变分方法研究了抛物量子点中强耦合束缚磁极化子的基态和激发态的性质.计算了束缚磁极化子的基态和激发态的能量、光学声子平均数以及束缚磁极化子的共振频率.讨论了这些量对回旋频率和有效束缚强度以及库仑束缚势的依赖关系.数值计算结果表明:量子点中强耦合束缚磁极化子的基态能量和共振频率以及光学声子平均数均随量子点的有效束缚强度的增加而减小,基态能量随库仑束缚势的增加而减小,随回旋频率的增加而增大.     

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.     

Ordering of Ground State Energy Levels of Two-Electron Quantum Dot in a Magnetic Field

The energy levels structure of two interacting electrons in a parabolic quantum dot under an external magnetic field of arbitrary strength is studied via the asymptotic iteration method. The method gives accurate results over the full range of quantum dot parameters. A crossings between spin-singlet and spin-triplet ground states energies as a function of the magnetic field is predicted.     

施加电场的半抛物量子阱中束缚态的能级结构

采用位移谐振子与数值求解相结合的方法,研究和讨论了施加电场的半抛物量子阱中束缚态的能级结构,得到了体系的本征能量与本征函数的表达式．数值结果显示,随着电场强度的增大,束缚态的能量几乎线性地下降,电场对半抛物束缚势频率较低的系统以及系统的高能级的影响较大,相邻能级间隔也随着电场强度的增大而减小,这与施加电场的抛物量子阱中的情况明显不同．     

外磁场与带轴夹角对非晶FeSiB/Cu/FeSiB三明治薄带巨磁阻抗特性的影响

采用层间胶合方法制备了淬态非晶FeSiB/Cu/FeSiB三明治薄带,研究了同尺寸单层薄带和三明治薄带的巨磁阻抗(giant magneto-impedance, GMI)随外磁场与带轴夹角β的变化特性.结果表明,FeSiB单层薄带在7.0 MHz最佳响应频率下,GMI仅约30%,外磁场与带轴夹角对单层薄带GMI几乎没有影响;三明治薄带的GMI效应则十分显著,在0.6 MHz最佳响应频率下,纵、横向GMI比分别达到272%和464%, GMI随β的增大而增强;所有β角的三明治薄带GMI曲线都出现各向异性峰,各向异性峰随β的增大而展宽.根据磁畴转动模型推导了薄带横向磁导率与各向异性场及β之间的函数关系式.结果显示,三明治薄带GMI随夹角β变化的特性与理论推算的横向磁导率变化有较好的一致性,而单层薄带则不然.该磁畴转动模型能定性解释三明治薄带GMI随外磁场方向变化特性.