NEGATIVE DONOR CENTER QUANTUM DOTS IN MAGNETIC FIELDS

The method of few-body physics is applied to treat a D^{-<\sup> center quantum dot system in a magnetic field. The magnetic field is applied in the z direction. Using this method, we investigate the energy spectra of low-lying states of D-<\sup> center quantum dots as a function of magnetic field. The dependence of the binding energies of the ground-state of the D-<\sup> center are calculated as a function of the dot radius with a few values of the magnetic field strength and compared with other results.}     

Role of Interactions in Electronic Structure of a Two-Electron Quantum Dot Molecule

We have studied a two-electron quantum dot molecule in a magnetic field. The electron interaction is treated accurately by the direct diagonalization of the Hamiltonian matrix. We calculate two lowest energy levels of the two-electron quantum dot molecule in a magnetic field. Our results show that the electron interactions are significant, as they can change the total spin of the two-electron ground state of the system by adjusting the magnetic field between S = 0 and S = 1. The energy difference AE between the lowest S = 0 and S = 1 states is shown as a function of the axial magnetic field. We found that the energy difference between the lowest S = 0 and S = 1 states in the strong-B S = 0 state varies linearly. Our results provide a possible realization for a qubit to be fabricated by current growth techniques.     

Electronegative Plasma Sheath Structure in a Magnetic Field

The structure of an electronegative plasma sheath in an oblique magnetic field is investigated with a fluid model. We assume the system consists of hot electrons and negative ions as well as cold positive ions. Densities of particles and distributions of the spacious potential in various states of magnetic field are studied. The result shows that the existence of magnetic field and negative ions has great effects on the plasma sheath structures. In addition, the effects of negative ion density and temperature on the structure of the electronegative plasma sheath are discussed.     

Energy Spectrum of Helium Confined to a Two-Dimensional Space

Making use of the adiabatic hyperspherical approach, we report a calculation for the energy spectrum of the ground and low-excited states of a two-dimensional helium in a magnetic field. The results show that the ground and low-excited states of helium in low-dimensional space are more stable than those in three-dimensional space and there may exist more bound states.     

A Helium Atom Confined by a Spherical Gaussian Potential Well

The helium atom confined by a non-impenetrable spherical box, i.e., a spherical Gaussian potential well which possesses finite height and range, is studied employing the exact diagonalization method. Total energies of the ground and three low-excited states are obtained as a function of the confined potential radii. We find that the confinement may cause accidental degeneracies between levels with different low-excited states and the inversion of the energy values. The results for the three-dimensional spherical potential well and the two-dimensional disc-like potential well are compared with each other： in general, the energies of the states decrease and the energy intervals between states increase with the reduction of the space dimensions.     

The Electron－Hole Pair in a Single Quantum Dot and That in a Vertically Coupled Quantum Dot

The energy spectra of low-lying states of an exciton in a single and a vertically coupled quantum dots are studied under the influence of a perpendicularly applied magnetic field. Calculations are made by using the method of numerical diagonalization of the Hamiltonian within the effective-mass approximation. We also calculated the binding energy of the ground and the excited states of an exciton in a single quantum dot and that in a vertically coupled quantum dot as a function of the dot radius for different vaJues of the distance and the magnetic field strength.     

Entropy squeezing and atomic inversion in the h-photon Jaynes-Cummings model in the presence of the Stark shift and a Kerr medium： A full nonlinear approach

The interaction between a two-level atom and a single-mode field in the k-photon Jaynes-Cummings model （JCM） in the presence of the Stark shift and a Kerr medium is studied. All terms in the Hamiltonian, such as the single-mode field, its interaction with the atom, the contribution of the Stark shift and the Kerr medium effects are considered to be f-deformed. In particular, the effect of the initial state of the radiation field on the dynamical evolution of some physical properties such as atomic inversion and entropy squeezing are investigated by considering different initial field states （coherent, squeezed and thermal states）.     

High Accuracy Calculation for Excited-State Energies of H Atoms in a Magnetic Field

Using the recently developed finite-basis-set method with B splines, excited states of H atoms in a magnetic field have been calculated. Energy levels are presented for the ten excited states, 2so, 3d＇0, 3po, 3p-1, 3d_1, 4d-1, 3d-2, 4d-2, 4f-2 , and 5f-2 as a function of magnetic field strengths with a range from zero up to 2.35 × 10^6 T. The obtained results are compared with available high accuracy theoretical data reported in the literature and found to be in excellent agreement. The comparison also shows that the current method can produce energy levels with an accuracy higher than the existing high accuracy method [Phys. Rev. A 54 （1996） 287]. Here high accuracy energy levels are for the first time reported for the 3d＇0, 4d-1, 4d-2, 4f-2, and 5f-2 states.     

Energy and fine structure of 1s2np(n≤9) states for lithium-like systems from Z=11 to 20

A new variation method is extended to study the atomic systems with higher nuclear charges and in more highly excited states. The non-relativistic energies of 1s^2np (n≤9) states for the lithium-like systems from Z=11 to 20 are calculated using a full-core-plus-correlation method with multi-configuration interaction wavefunctions. Relativistic and mass-polarization effects on the energy are calculated as the first-order perturbation corrections. The fine structures are determined from the expectation values of spin-orbit and spin-other-orbit interaction operators in the Pauli－Breit approximation. The quantum-electrodynamics correction is also included. Our results are compared with experimental data in the literature.     

Atomic NOON state generation in distant cavities by virtual excitations

A general scheme of generating NOON states of virtually-excited 2N atoms is proposed. The two cavities are fibre-connected with N atoms in each cavity. Although we focus on the case of N = 2, the system can be extended to a few atoms with N 〉2. It is found that all 2N atoms can be entangled in the form of NOON states if the atoms in the first cavity are initially in the excited states and atoms in the second cavity are all in the ground states. The feasibility of the scheme is carefully discussed, it shows that the NOON state with a few atoms can be generated with good fidelity and the scheme is feasible in experiment.     

Arithmetic of the Integer Quantum Hall Effect

The integer quantum Hall effect (IQHE) is analysed, considering the degeneracies of localized and extended states separately. Occupied localized and extended states are counted, and their variation is studied as a function of magnetic field. The number of current-carrying electrons is found to have a saw-tooth variation with magnetic field. The analysis addresses certain basic questions in the IQHE, particularly the one about floatation of extended states as the magnetic field tends to zero.     

Spin polarization transitions in the FQHE

The spin polarization of the FQHE ground states at fixed filling factors is analyzed within a composite fermion model. As a function of the perpendicular magnetic field several cross‐overs between differently polarized ground states are predicted, in agreement with recent experimental investigations. The magnetic field and temperature scalings of the polarization, as well as the magnetic field dependence of the spin‐flip gap are studied.     

Phase transitions and multidomain states in magnetic nanostructures with competing anisotropies

The evolution of the magnetic states in nanostructures with competing surface and bulk anisotropies was studied under a variation in the applied magnetic field. For spatially uniform magnetic states, the energy functional reduces to the energy of a bulk magnet in which the effective anisotropy depends on the thickness of the ferromagnetic layer. This dependence results in spin reorientation as the nanolayer thickness varies. The lines of first-order phase transitions and the equilibrium parameters of multidomain structures and domains of competing phases were determined. The calculated magnetic phase diagrams are used to analyze magnetic states and to construct magnetization curves.     

The symmetry of three-electron states in a quantized magnetic field

The states of itinerant electrons on the finite square lattice in a quantized magnetic field are discussed. The single-electron states are classified by irreducible representations (IRs) of the magnetic translation group.The representation correspond to the Landau level, whereas its basis functions are analogs of the cyclotronic orbits. The filling factor of the Landau level is considered in the frame of multi-electron functions. Corresponding states are classified by the IR of MTG as well as by the irreducible representation of a symmetric group (permuting the electrons) and a unitary group (permuting electron states). The discussion is restricted to the case when the magnetic flux per unit cell of the two-dimensional square lattice is a rational number in terms of magnetic flux quanta. The additional parameter of the model is the Hubbard interaction between electrons.     

Phase diagram of a two-dimensional square lattice of magnetic particles with perpendicular anisotropy

The ground state of an array of small single-domain magnetic particles having perpendicular anisotropy and forming a square two-dimensional lattice is studied in the presence of a magnetic field. The stability of some basic states with respect to nonuniform perturbations is analyzed in a linear approximation, and analytical model calculations and numerical simulation are used for an analysis. The entire set of states at various anisotropy constants and magnetic fields is considered when a field is normal to the array plane. Two main classes of states are possible for an infinite system, namely, collinear and noncollinear states. For collinear states, the magnetic moments of all particles are normal to the array plane. At a sufficiently high anisotropy, a wide class of collinear states exists. At low fields, a staggered antiferromagnetic order of magnetic moments takes place. An increase in the magnetic field causes an unsaturated state, and this state transforms into a saturated (ferromagnetic) state with a parallel orientation of the magnetic moments of all particles at a sufficiently high field. At a lower anisotropy, the ground state of the system is represented by noncollinear states, which include a complex four-sublattice structure for the components of the magnetic moments in the array plane and a nonzero projection of the magnetic moments of the particles onto the field direction. A phase diagram is plotted for the states of an array of anisotropic magnetic particles in the anisotropy constant-magnetic field coordinates. For a finite array of particles, sample boundaries are shown to play a significant role, which is particularly important for noncollinear states. As a result of the effect of the boundaries at a moderate field or anisotropy, substantially heterogeneous noncollinear states with a heterogeneity size comparable with the sample size can appear in the system.     

Unexpected features in the magnetoresistance of a quantum well at room temperature

Well-resolved oscillations are reported in the resistivity of an InGaAs quantum well as a function of applied magnetic field below 1 Tesla. The oscillations are observed at room temperature and their magnetic field position depends on the component of the magnetic field in the plane of the well. Because of these unusual properties, the results cannot be due to bound states within the well but it is suggested that they can be explained by quantised states lying above the well in energy. The condition for the formation of the states is satisfied at lower magnetic fields than for normal Landau levels and the states are separated by larger energy intervals.     

Composite Anderson-Newns model and chemisorption characteristics of nickel-hydrogen system

The composite Anderson-Newns model and triangular weighted density of states are used to study the electron density of states, magnetic moment and charge transfer of adatoms for a chemisorbed system. The model has been applied to hydrogen chemisorbed on nickel. It has been observed that with the increase in coverage, number of B-AB states as well as bond strength increases, whereas the magnetic moment and adatom charge decrease with coverage. These results match with the experimental data.     

垂直自由层倾斜极化层自旋阀结构中的磁矩翻转和进动

在理论上研究了垂直自由层和倾斜极化层自旋阀结构中自旋转移矩驱动的磁矩翻转和进动.通过线性展开包括自旋转移矩项的Landau-Lifshitz-Gilbert方程并使用稳定性分析方法,得到了包括准平行稳定态、准反平行稳定态、伸出膜面进动态以及双稳态的磁性状态相图.发现通过调节电流密度和外磁场的大小可以实现磁矩从稳定态到进动态之间的转化以及在两个稳定态之间的翻转.翻转电流随外磁场的增加而增加,并且受自旋极化方向的影响.当自旋极化方向和自由层易磁化轴方向平行时,翻转电流最小;当自旋极化方向和自由层易磁化轴方向垂直时,翻转电流最大.通过数值求解微分方程,给出了不同磁性状态磁矩随时间的演化轨迹并验证了相图的正确性.     

W(110)基底上的铁纳米岛初始自发磁化态的微磁学模拟

用微磁学模拟研究W(110)基底上铁纳米岛的初始自发磁化态的磁畴结构,确定了不规则形状、椭圆形和矩形岛中不同磁畴态之间的各向异性常数的临界点,得到了纳米岛的磁化态作为各向异性常数和厚度函数的完整相图,相图中存在一较宽的过渡区,把双畴态与涡旋态和菱形态分开,过渡区两侧的边界是不确定的.计算结果表明,初始自发磁化态的磁畴结构主要由各向异性及岛的厚度决定,而且岛的边沿形状对涡旋态和菱形态的磁畴结构有重要影响.准确的铁纳米岛的各向异性常数仍有待于进一步确定. 关键词： 初始自发磁化磁畴结构 铁纳米岛 微磁学模拟 各向异性     

Magnetic quantum ring in two-dimensional topological insulators

The quantum properties of topological insulator magnetic quantum rings formed by inhomogeneous magnetic fields are investigated using a series expansion method for the modified Dirac equation. Cycloid-like and snake-like magnetic edge states are respectively found in the bulk gap for the normal and inverted magnetic field profiles. The energy spectra, current densities and classical trajectories of the magnetic edge states are discussed in detail. The bulk band inversion is found to manifest itself through the angular momentum transition in the ground state for the cycloid-like states and the resonance tunneling effect for the snake-like states.