Passive magnetic shielded spin polarized electron source with optical electron polarimeter

A new GaAs(100) spin polarized electron source with an optical polarimeter, which is employed in the field of polarized electron and gas atom collision, is presented in detail. The apparatus is passive-magnetic-shielded by a box and a cylinder made of nickel--iron--molybdenum soft magnetic alloy without Helmholtz coil arrangement. And a uniformly distributed residual magnetic field of less than 5×10^-7,T is obtained near the collision area. The spin polarized electron beam is transmitted and focused onto collision point from photocathode by a set of electron optics with more than 25% transmission 95cm distance through an 1mm diameter aperture. Construction and operation of the apparatus, such as vacuum and magnetic shielding system, photocathode, laser optics, electron optics and polarimeter are discussed. The polarization of the spin polarized electron beam is determined to be 30.8\pm3.5% measured with a He optical polarimeter.     

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.     

超热电子在非均匀磁场中的运动轨迹

在电子磁谱仪中实际的磁场强度分布是不均匀的,这就造成电子束在探测器上的位置和分布与均匀磁场假设下的结果的不同.根据实验测出的磁谱仪实际的磁场分布对磁谱仪中电子束的轨迹进行了研究 关键词： 电子磁谱仪     

基于金刚石色心自旋磁共振效应的微位移测量方法

基于压电陶瓷精密微位移系统的扫描探测技术是目前精密测量仪器进行微纳区域/结构性能测试的核心系统,但压电陶瓷材料存在迟滞、非线性问题,限制了对微位移分辨能力的提升.本文以金刚石氮空位色心为敏感单元,利用电子自旋效应对磁场强度的高分辨敏感机理,结合永磁体周围不同位置对应的磁场强度变化关系,提出了一种基于金刚石氮空位色心电子自旋敏感机理的微位移检测方法.通过建立电子自旋效应与微位移的关联模型,搭建了相应的微位移测量系统.经实验验证,该系统对微位移测试的灵敏度为16.67 V/mm,检测分辨率达到60 nm,实现了对微位移的高分辨率测量.并通过理论分析,该系统的微位移测量分辨率可进一步提升至亚纳米级水平,为新型微位移测量技术提供了发展方向和研究思路.     

电子自旋共振实验g因子的准确测量方法

详细分析了用可调反射式谐振腔做电子自旋共振(ESR)实验测量g因子时应注意的2个问题:一是选择正确的共振波形测量共振时的微波频率;二是选择适当的测量方法测量共振磁场以消除扫描磁场和地磁场的影响.具体讨论了微波频率对电子自旋共振信号波形的影响,从理论上解释了共振信号的变化所反映的物理过程,给出了精确测量顺磁物质g因子的具体实验方法.     

Spin concentration in a possible ESR dosimeter: An electron spin echo study on X-irradiated ammonium tartrate

Several single crystals and powder samples of ammonium tartrate, recently proposed as a possible ESR dosimeter, have been X-irradiated with different doses. The total radical concentration has been determined by quantitative cw ESR, by comparison with a standard. The samples have been studied by electron spin echo spectroscopy. The two-pulse echo decay has been obtained and simulated by a single exponential function for different values of the microwave power of the pulses and for different pulse lengths. The dependence of the phase memory time TM on the microwave power has been exploited to get information on the contribution of the instantaneous diffusion to spin dephasing. At room temperature in the range of radical concentrations of 10(18)-10(19) spins/cm3 the instantaneous diffusion is the dominant spin dephasing mechanism. The linear dependence of the instantaneous diffusion on the total concentration of the radicals is in agreement with the theory. From the latter result we conclude that the average radical-radical distance corresponds to a random distribution of the radicals in the matrix. A simple method of measuring the radical concentration by the ESE decays in powder samples of irradiated ammonium tartrate is described.     

磁聚焦法测量电子荷质比实验中励磁电流测量方法的研究

根据电荷在电场、磁场中的运动特点,分析了磁聚焦法测量电子荷质比的原理;利用磁场叠加原理,从理论角度探讨了测量磁聚焦时励磁电流的方法,并对各种方法进行了比较;从实验角度对实验数据分析处理,指出了误差产生的主要原因之一,得出了测量磁聚焦时励磁电流值的新方法.     

扫描磁场中玻色-爱因斯坦凝聚体系的奇异自旋隧穿

用平均场的方法,研究了线性扫描磁场中自旋-1玻色-爱因斯坦凝聚体系的自旋隧穿.集中考虑⁸⁷Rb这种典型的碱金属原子凝聚体,根据外磁场扫描率的不同,研究了它的隧穿动力学.在慢扫描(即绝热条件)和快扫描条件下,体系无隧穿现象.对中等大小的扫描率,发现隧穿现象,且这个隧穿动力学对磁场扫描率非常的敏感,表现为看似混沌的隧穿区的存在.然而,把这个看似混沌的区域放大,发现在扫描率精度为10^-8T/s的量级上,隧穿率对磁场扫描率的关系实际是有规律的类周期结构.此外,还发现,实 关键词： 玻色-爱因斯坦凝聚 自旋 隧穿     

扫描磁场中玻色-爱因斯坦凝聚体系的奇异自旋隧穿

用平均场的方法，研究了线性扫描磁场中自旋-1玻色-爱因斯坦凝聚体系的自旋隧穿.集中考虑⁸⁷Rb这种典型的碱金属原子凝聚体，根据外磁场扫描率的不同，研究了它的隧穿动力学.在慢扫描(即绝热条件)和快扫描条件下，体系无隧穿现象.对中等大小的扫描率，发现隧穿现象，且这个隧穿动力学对磁场扫描率非常的敏感，表现为看似混沌的隧穿区的存在.然而，把这个看似混沌的区域放大，发现在扫描率精度为10^-8T/s的量级上，隧穿率对磁场扫描率的关系实际是有规律的类周期结构.此外，还发现，实     

Nanoviscosity effect on the spin chemistry of an electron donor/Pt-complex /electron acceptor triad - classical and quantum kinetics interpretation

The magnetic-field dependent charge recombination kinetics upon ns-laser flash photolysis of a novel triarylamine/cyclometalated platinum complex/napthalenediimide triad (DPtA) have been measured in tetrahydrofuran (THF) and polytetrahydrofuran (pTHF) to study the spinchemical effect of a large increase of the macroviscosity of the solvent by a factor of about 1000. The magnetic-field dependence of the decay kinetics of the charge separated state has been accurately reproduced by a classical kinetic model, wherein the rate constants of transitions between spin substates of different Zeeman energy are represented by a single magnetic-field dependent rate constant k_±. In THF, the magnetic-field dependence of k_± is given by a double Lorentzian function which, in a double log plot, shows two characteristic steps that can be consistently assigned to the magnetic field inhibition of the coherent and incoherent i.e. relaxational spin mixing mechanism. In pTHF, the magnetic field effect on k_± is a single step function decreasing to its limiting value at about 5 times lower fields than in THF. As shown by a quantum theoretical simulation, in this solvent coherent and incoherent processes are contributing equally at all fields. The nanoviscosity of pTHF appears to be much smaller than its macroviscosity.     

Doped semiconductors in an inhomogeneous magnetic field

We show that a potential difference is generated across a semiconductor sample containing free carriers when the sample is in a magnetic field gradient in the direction of the field. A measurement of the potential difference can give direct information concerning the effective mass and effective g-factor of the free carriers.     

Nuclear spin induced collapse and revival shape of Rabi oscillations of a single electron spin in diamond

A collapse and revival shape of Rabi oscillations in an electron spin of a single nitrogen-vacancy centre has been observed in diamond at room temperature. Because of hyperfine interaction between the host ¹⁴N nuclear spin and the nitrogen-vacancy centre electron spin, different orientations of the ¹⁴N nuclear spins lead to a triplet splitting of the transition between ground state (m_s =0) and excited state (m_s =1). The manipulation of the single electron spin of nitrogen-vacancy centre is achieved by using a combination of selective microwave excitation and optical pumping at 532 nm. Microwaves can excite three transitions equally to induce three independent nutations and the shape of Rabi oscillations is a combination of the three nutations.     

电子磁矩对同步辐射频谱的修正

本文从偶极子辐射场的Heaviside-Feynman表达式出发, 用经典的电动力学方法推导了考虑内禀磁矩影响后的相对论电子辐射频谱分布的表达式, 并对做匀速圆周运动的极端相对论性电子的同步辐射, 计算了两个偏振方向上的考虑磁矩修正后的辐射谱. 计算结果表明对于特征频率为ω_c的同步辐射, 如果ħω_c≥10 keV, 内禀磁矩对辐射的修正是可观的. 通过同步辐射的内禀磁矩修正, 本文讨论了电子束极化度与辐射场偏振度的依赖关系, 并基于此关系提出一种测量电子束极化度的新方法. 关键词： 同步辐射 电子内禀磁矩 同步辐射偏振度 束流极化度     

Theoretical investigations of spin splittings in asymmetric AlSb/InAs/GaSb heterostructures and the possibility of electric field induced magnetization

We use the effective bond orbital model method to examine the spin splitting due to the Rashba effect in AlSb/InAs/GaSb asymmetric heterostructures. We find for the resulting two-dimensional electron gas (2DEG) under study that large theoretical values of the Bychkov–Rashba coefficients in the range of 30 × 10 ^{− 10}to 50 × 10 ^{− 10}eV · cm can be achieved. Finally, we present a phenomenon that might lead to a direct observation of the Rashba effect. We derive an expression, valid in the diffusive limit, for the spin polarization of the current resulting from a bias parallel to the plane of the quantum well.     

Quantum spin model of a cubic ferromagnet in a magnetic field

The zero temperature phase diagram of a one-dimensional ferromagnet with cubic single ion anisotropy in an external magnetic field is studied. The mean-field approximation and the density-matrix renormalization group method are applied. Two phases at finite magnetic fields are identified: a canted phase with spontaneously broken symmetry and a phase with magnetization along the magnetic field. Both methods predict that the canted phase exists even for the single-ion anisotropy strong enough to destroy the magnetic order at zero magnetic field. In contrast to the mean-field theory, the density-matrix renormalization group predicts a reentrant behavior for the model. The character of the phase transition at finite magnetic field has also been considered and the critical index has been found. Received 9 May 2000 and Received in final form 5 July 2000     

On the possibility of measuring magnetic fields by scattered light

In the following paper we discuss the possibility of measuring magnetic fields by scattered light. In the case of uncorrelated electrons (i.e. α ?1) the electron spectrum is modulated with the electron gyration frequency if a certain condition is fulfilled. The essential parameters are discussed and some spectra are computed numerically.     

The magnetic field effects on the frustrated antiferromagnetic spin chain

We presented a numerical study of the magnetization process of frustrated spin-1/2 chain. Using the exact diagonalization technique, we provided the evidence that a plateau at one-third of the saturation magnetization exists in the magnetization curve of frustrated antiferromagnetic spin-1/2 chain.     

On the interpretation of the electron anomalous magnetic moment

Guided by a Compton-sized model, we demonstrate that: (a) the magnetic self-energy of the electron, as estimated initially by Rasetti and Fermi, can be directly related to both the sign and the magnitude of the electron anomalous magnetic moment; and (b) the classical expression for the magnetic self-energy of the electron exhibits the same characteristic logarithmic divergence that occurs in QED. This electron model quantitatively reproduces the spin, magnetic moment, and gyromagnetic ratio of the electron, correct to first order in = e² /c. It also relates the quantum-mechanical spin projection angle to the vanishing of the electric quadrupole moment, and it is capable of reproducing point-like scattering behavior.     

Conserved spin current with a perpendicular magnetic field

Previous theoretical studies show that the spin current in spin-orbit coupled systems can be effectively conserved. In this study, we show that in the presence of an external magnetic field B perpendicular to the surface without causing Landau levels, the spin-Hall conductivity, including the conventional spin and spin-torque Hall currents exhibit an interesting symmetry, ${\sigma }_{xy}^c(B)={\sigma }_{xy}^c(-B)$ valid for k-linear and k-cubic Rashba systems. The phenomenon where the electric field generated spin z component is unaltered under $B\to -B$ is attributed to the fact that the spin precession is locked in spin-orbit coupled systems. The perpendicular magnetic field generates spin x and y components, which are linear to B, and thus, there is no time-reversal symmetry. This result provides evidence for the detection of the bulk spin-Hall current. Furthermore, the applied magnetic field breaks the degenerate point of the two-band model, and the resulting spin-Hall conductivity does not vanish even for systems with linear momentum, which implies that the Berry phase is not the principal mechanism in k-linear systems. The non-zero charge-Hall conductivity generated by the perpendicular magnetic field is discussed here.     

Teleportation and thermal entanglement in two-qubit Heisenberg X Y Z spin chain with the Dzyaloshinski-Moriya interaction and the inhomogeneous magnetic field

This paper studies the average fidelity of teleportation and thermal entanglement for a two-qubit Heisenberg X Y Z chain in the presence of both an inhomogeneous magnetic field and a Dzyaloshinski-Moriya interaction. It shows that for a fixed Dz, the increase of bz will broaden the critical temperature at the cost of decreasing the thermal entanglement. And it can modulate the inhomogeneous magnetic field and the Dzyaloshinski-Moriya interaction for the average fidelity of teleportation to be optimal.