弱磁场下三阱光学超晶格中自旋为1的超冷原子特性研究

双阱光学超晶格中的超冷原子是近期冷原子物理领域的研究热点. 本文推广提出了实现三阱光学超晶格的方案, 并采用精确对角化的方法分别研究了弱磁场下对称三阱 光学超晶格中铁磁性和反铁磁性的自旋为1的原子系统的基态, 发现二者的相图很不相同: 反铁磁性原子对应的相图中没有沿磁场方向总自旋磁量子数为±2的基态, 而铁磁性原子对应的相图中可能有. 在负的二次塞曼能量区域, 铁磁性原子的相图中只有完全极化态. 分析了可控参数影响基态的物理本质. 由于这些量子自旋态可以通过调节外磁场和光势垒的高度非常简便而精确地控制, 适合用来研究自旋纠缠. 关键词： 三阱光学超晶格 自旋为1的原子 弱磁场     

磁耦合效应对半无限超晶格中表面电子态的影响

在有效质量近似理论下，采用有效垒高方法，研究了在沿超晶格生长方向加一有限磁场时磁耦合效应对半无限半导体超晶格中表面电子态的影响.当考虑超晶格中阱层和垒层之间电子有效质量的差别时，沿超晶格生长方向的磁场将导致磁耦合效应的出现.研究结果表明，磁耦合效应不仅引起表面电子能级的量子化，而且表面电子能级的大小及其在表面附近的局域程度也依赖于磁场的大小和朗道指数.此外，研究表明布洛赫波数的虚部可以作为一个衡量表面电子态局域程度的物理量. 关键词： 超晶格中的电子态 表面态 磁场     

三元合金缺陷层对有限超晶格中局域界面光学声子模的影响

在宏观介电连续近似下，采用转移距阵方法，研究了三元合金缺陷层对有限超晶格中局域界面光学声子模的影响.在这种有限超晶格结构中，可以清楚地看到所有界面模的演化轨迹.结果表明：存在两类局域模，它们的宏观静电势波函数分别局域在缺陷层和表面层附近，且这些模随着超晶格组分层和缺陷层的相对厚度和介电常数的改变，其局域位置和特性发生显著变化.此外，发现虽然能隙中局域模的数目不守恒，但所有界面模的总数守恒.     

Fe/Cr超晶格电子结构和磁性质的理论研究(英文)

应用密度泛函全势线性缀加平面波方法研究了Fe3/Cr3超晶格的电子结构和磁性质.结果表明,这种体系的基态相邻铁原子层间存在铁磁耦合,内禀自旋波波长大约2层厚的长度.     

Magnetic properties of 2D nano-islands II: Ising spin model with out-of-plane magnetic field

An Ising effective field theory model is presented to calculate the magnetic properties of 2D nano-islands on a nonmagnetic substrate, subject to an externally out-of-plane applied magnetic field. The system Hamiltonian contains nearest neighbor exchange interactions, single-atom magnetic anisotropies, and the Zeeman term. The calculations yield, in particular, the single site spin correlations, the magnetizations, and the isothermal susceptibilities, for the core and periphery domains of the nano-island. The choice of a spin S=1 for the atoms of the system permits the analysis of local spin fluctuations via the single site spin correlations. We investigate in this respect the effects due to the different magnetocrystalline anisotropies and reduced dimensionalities, for the core and periphery domains, and in particular the critical influence of the applied magnetic field. Detailed theoretical results are presented for the square and hexagonal lattice symmetries, with numerical applications for the 2D monolayer Co nano-islands on a Pt substrate. It is shown that the remarkable differences between the magnetic properties of the core and periphery domains in zero field are washed out when an out-of-plane field is applied. The applied field also provokes critical discontinuities for the spin correlations and magnetization reversals, for the core and periphery domains, which are especially evident for the hexagonal lattice nano-island in the range of fields of interest. The discontinuities and magnetization reversals occur over elementary temperature widths, and shift to lower temperatures with increasing field. The field-dependant isothermal susceptibilities show new features very different from those for the susceptibilities in zero field. The present Ising model does not show any blocking temperature transition to superparamagnetism.     

太赫兹场和倾斜磁场对超晶格电子动力学特性调控规律研究

微带超晶格在磁场和太赫兹场调控下表现出丰富而复杂的动力学行为, 研究微带电子在外场作用下的输运性质对于太赫兹器件设计与研制具有重要意义. 本文采用准经典的运动方程描述了超晶格微带电子在沿超晶格生长方向(z方向)的THz场和相对于z轴倾斜的磁场共同作用下的非线性动力学特性. 研究表明, 在太赫兹场和倾斜磁场共同作用下, 超晶格微带电子随时间的演化表现出周期和混沌等新奇的运动状态. 采用庞加莱分支图详细研究了微带电子在磁场和太赫兹场调控下的运动规律, 给出了电子运行于周期和混沌运动状态的参数区间. 在电场和磁场作用下, 微带电子将产生布洛赫振荡和回旋振荡, 形成复杂的协同耦合振荡. 太赫兹场与这些协同振荡模式之间的相互作用是导致电子表现出周期态、混沌态以及倍周期分叉等现象的主要原因.     

磁性硅烯超晶格中电场调制的谷极化和自旋极化

研究了基于硅烯的静电势超晶格、铁磁超晶格、反铁磁超晶格中谷极化、自旋极化以及赝自旋极化的输运性质,分析了铁磁交换场、反铁磁交换场以及化学势对输运性质的影响,讨论了电场对谷极化、自旋极化以及赝自旋极化的调控作用.结果表明:当3种超晶格的晶格数达到10以上时,在硅烯超晶格中很容易实现100%的谷极化、自旋极化和赝自旋极化,而且通过调节超晶格上的外加电场可以使极化方向发生翻转,从而在硅烯超晶格中实现外电场对谷自由度、自旋自由度以及赝自旋自由度的操控.     

Interaction of a charged extended body with Magnetic field

It is shown that the conventional energy expressions need modification for the interaction of a charged extended body with a magnetic field. It is also shown that the correction term arises as a result of the rotation of the charged extended body about its centre of mass in a magnetic field. This can provide us with an additional source of energy that can be tapped with a suitable energy conversion device.     

铁电层厚度对(BiCoO_3)_n/(La_(2/3)Sr_(1/3)MnO_3)_1超晶格磁电性质的影响

本文利用第一性原理,对由四方相BiCoO_3(BCO)和La_(2/3)Sr_(1/3)MnO_3(LSMO)所构造的超晶格的形成能、电子结构与磁电性质进行了系统研究.研究表明,超晶格中BCO层厚度变化可对超晶格的电子结构,及其极化位移与自旋极化率等磁电性质产生重要影响.特别的,在BiO/Mn_BO_2为界面构型的超晶格中,当BCO侧为一个单胞层时,超晶格表现出半金属性,可获得100%自旋极化率.上述研究结果对于新型自旋电子器件研究具有一定科学意义.     

Magnetic properties of soft layer/FePt--MgO exchange coupled composite perpendicular recording media

The magnetic properties of exchange coupled composite （ECC） media that are composed of perpendicular magnetic recording media FePt MgO and two kinds of soft layers have been studied by using an x-ray diffractometer, a polar Kerr magneto-optical system （PMOKE） and a vibrating sample magnetometer （VSM）. The results show that ECC media can reduce the coercivities of perpendicular magnetic recording media FePt-MgO. The ECC media with granular-type soft layers have weaker exchange couplings between magnetic grains and the magnetization process, for ECC media of this kind mainly follow the Stoner Wohlfarth model.     

Ground States of Ultracold Spin-1 Atoms in a Deep Double-Well Optical Superlattice in a Weak Magnetic Field

The ground states of the ultracold spin-1 atoms trapped in a deep one-dimensional double-well optical superlattice in a weak magnetic field are obtained. It is shown that the ground-state diagrams of the reduced double- well model are remarkably different for the antiferromagnetic and ferromagnetic condensates. The transition between the singlet state and nematic state is observed for the antiferromagnetic interaction atoms, which can be realized by modulating the tunneling parameter or the quadratic Zeeman energy. An experiment to distinguish the different spin states is suggested.     

Thermodynamic and magnetic properties of the electron gas in the inhomogeneous magnetic field Hr−1

The nonrelativistic and relativistic energy eigenvalues of the electron in the inhomogeneous magnetic fieldH _z =Hr ⁻¹,r=(x ² +y ²)^1/2 are derived in a form displaying the explicit spin dependence. The possibility of magnetic hydrogen atom formation and the spontaneouse ⁺ e ⁻ pair creation following from these eigenvalues is mentioned. The expressions for pressure, energy, particle number and magnetic moment of an electron gas in this IMF are calculated in the degenerate limit. The possibility of spontaneous magnetisation,i.e., ferromagnetic behaviour, is established. Further, the pressure of the electron gas in the same type of fields is an order of magnitude higher than those in a homogeneous magnetic field and crossed homogeneous electric and magnetic fields for comparable field strengths.     

Magnetic field generation by convective flows in a plane layer

Hydrodynamic and magnetohydrodynamic convective attractors in a plane horizontal layer 0≤z≤1 are investigated numerically. We consider Rayleigh-Bénard convection in Boussinesq approximation assuming stress-free boundary conditions on horizontal boundaries and periodicity with the same period L in the x and y directions. Computations have been performed for the Prandtl number P=1 for and Rayleigh numbers 0<R≤4000, and for L=4, 0<R≤2000. Fifteen different types of hydrodynamic attractors are found, including two types of steady states distinct from rolls, travelling waves, periodic and quasiperiodic flows, and chaotic attractors of heteroclinic nature. Kinematic dynamo problem has been solved for the computed convective attractors. Out of the 15 types of the observed attractors only 6 can act as kinematic dynamos. Nonlinear magnetohydrodynamic regimes have been explored assuming as initial conditions convective attractors capable of magnetic field generation, and a small seed magnetic field. After initial exponential growth, in the saturated regime magnetic energy remains much smaller than the flow kinetic energy. The final magnetohydrodynamic attractors are either quasiperiodic or chaotic.     

HIRFL-CSR实验环电子冷却装置磁场测量

在HIRFL-CSR实验环电子冷却装置上采用了独立的高精度螺线管串联产生纵向磁场的设计,获得很高的冷却段磁场平行度。使用霍尔片测量磁场的分布,使用磁针测磁方法测量冷却段磁场的磁轴偏角,并根据测量及计算结果对单个线圈磁轴进行微调。测量及调试结果表明,在施加电流为额定电流的一半时,冷却段磁感应强度为0.078 T,剩余磁场小于2×10-4 T,磁场不平行度小于1×10-4,达到了预期的设计目标。     

强磁场对不同厚度Fe-Ni纳米多晶薄膜的生长过程及磁性能的影响

有无6 T强磁场条件下, 利用分子束气相沉积方法制备了21 nm和235 nm厚的Fe-Ni纳米多晶薄膜. 研究发现, 0 T时, 21 nm厚的薄膜是晶粒堆叠而成, 晶粒尺寸为6–7 nm; 6 T时, 21 nm厚的薄膜首先在基片表面形成了晶粒相互连接的5 nm平坦层, 晶粒沿基片表面拉长, 随后以6–7 nm尺寸的晶粒堆叠而成; 0 T时, 235 nm厚度的薄膜生长初期平均晶粒尺寸为3.6 nm, 生长中期平均晶粒尺寸为5.6 nm, 生长末期薄膜近似柱状方式生长, 晶粒沿生长方向拉长; 6 T时, 235 nm厚度的薄膜在基片表面也形成了晶粒相互连接的5 nm平坦层, 晶粒沿基片表面拉长, 随后以尺寸均匀的6.1 nm晶粒堆叠而成; 而且, 6 T强磁场使得不同厚度薄膜的面外与面内矫顽力都降低.     

Dynamics of a pair of electron and hole in semiconductor superlattice under an intense electric field

This paper investigates the behavior of a pair of electron and hole in semiconductor superlattice under an external electric field with the consideration of Coulomb interaction. By numerically calculating the corresponding probability in the nearest neighbor tight binding approximation, we find that the single electron (or the hole) can not be dynamically localized due to the Coulomb interaction, while the dynamic localization of exciton (the pair of the electron and hole) still exists. Moreover we find that with the increase of the intensity of electric field, the exciton can be dynamically localized more completely.     

Performance enhancement of an InGaN light-emitting diode with an AlGaN/InGaN superlattice electron-blocking layer

The efficiency enhancement of an InGaN light-emitting diode(LED) with an AlGaN/InGaN superlattice(SL)electron-blocking layer(EBL) is studied numerically,which involves the light-current performance curve,internal quantum efficiency electrostatic field band wavefunction,energy band diagram carrier concentration,electron current density,and radiative recombination rate.The simulation results indicate that the LED with an AlGaN/InGaN SL EBL has better optical performance than the LED with a conventional rectangular AlGaN EBL or a normal AlGaN/GaN SL EBL because of the appropriately modified energy band diagram,which is favorable for the injection of holes and confinement of electrons.Additionally,the efficiency droop of the LED with an AlGaN/InGaN SL EBL is markedly improved by reducing the polarization field in the active region.     

The Influence of a Longitudinal Magnetic Fields on a Non‐Uniform Positive Column

The variations of plasma parameters of a dc discharge in a non‐uniform magnetized plasma were measured using fast floating double Langmuir probes. A solenoid is used to produce a uniform magnetic field parallel to the discharge axis. The axial changes of the plasma parameters are presented in the range of longitudinal magnetic fields 200 to 600 Gauss at the pressure range 0.3 to 2.1 Torr and discharge currents 5 and 15 mA in argon gas. The experimental results indicate that, as a consequence of the axial magnetic.eld and the variations in the discharge tube radii, the plasma parameters at small radius exhibit obvious changes in their distributions along the axis compared to the situation of unmagnetized plasma. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)