基于镜像电荷法探测液氦表面电子的自旋态

文献[Phys.Rev.A,2006,74:052338]的理论研究表明液氦上电子自旋具有长达100秒的相干时间,因此在实施量子信息处理方面具有很大的应用前景.然而,这一理论还未得到实验的证实.液氦上电子的自旋-轨道耦合可以为电子自旋探测提供一种可选的方法.理论上,电子自旋-轨道耦合可以由液氦膜下方的微电极电流产生.在微波驱动下,电子发生电偶极跃迁,导致电子距离液氦表面的平均高度发生改变.利用镜像电荷法[Phys.Rev.Lett.,2019,123:086801],电子的这种轨道运动可以被实验测量.建立基于液氦上电子-自旋轨道耦合的密度矩阵方程,并数值求解镜像电荷的振动行为.结果表明不同的自旋态将会引起不同的感应电流,这种差异提供了一种可选的电子自旋探测方法.     

电子（镜像质子）电荷模型的作用

寻求与“电子电荷”相反的电荷、相反的运动方向的“镜像质子电荷”,并建立起对应的模型,如图1所示．     

过渡金属氧化物中新奇量子态与电荷-自旋互转换研究进展

为了满足信息技术时代下海量数据的高效存储及处理,具有低功耗、非易失性的自旋电子器件受到极大关注.能够高效产生自旋流的自旋源材料是新型自旋-轨道力矩器件的重要组成部分.近二十年来,在探索具有高效产生自旋流的材料体系,以及理解材料相关物理机制两方面都取得了较大的进展.最近,在过渡金属氧化物中涌现出许多与产生自旋流密切相关的新奇量子态,成为自旋源的新兴材料体系被广泛研究.研究结果表明,过渡金属氧化物具有对电子结构高度敏感、显著且灵活可调的电荷-自旋转换效率,具有巨大的应用潜力.本文主要综述了过渡金属氧化物中新奇的电子能带结构及其与电荷-自旋互转换的关联机制,并对未来的发展趋势进行了展望.     

二维自旋轨道耦合电子气中持续自旋螺旋态的稳定性的研究

本文利用半经典的自旋密度矩阵方法对二维自旋轨道耦合电子气中持续自旋螺旋态的稳定性进行了一些研究, 重点研究了自旋螺旋态的寿命与其波矢、载流子迁移率、温度、自旋轨道耦合强度、外电场强度等因素之间的关系, 并将部分理论计算结果与最近的一些相关实验结果进行了比较,发现两者之间大致是符合的.     

关于自旋电子的一些为什么——浅谈与超导电性对抗的磁性元素Fe,Co,Ni为什么形成化合物就超导了？

在近20年来的凝聚态物理研究中,人们在铜基氧化物中发现了高温超导电性,在锰基钙钛矿中发现了巨磁电阻效应,以及近年来发现由铁、钴、镍等传统认为与超导对抗的元素组成化合物后可以形成超导.这些不同的体系有着迥然不同的物理行为,却具有一个共同的特征：这些铜、锰、铁、钴、镍基化合物都是3d电子材料.那么,同为3d电子,为什么在不同的环境中表现出完全不同甚至对抗的行为？文章对这些现象提出了一系列为什么,并对其进行了探讨.     

关于自旋电子的一些为什么——浅谈与超导电性对抗的磁性元素Fe,Co,Ni为什么形成化合物就超导了?

在近20年来的凝聚态物理研究中,人们在铜基氧化物中发现了高温超导电性,在锰基钙钛矿中发现了巨磁电阻效应,以及近年来发现由铁、钴、镍等传统认为与超导对抗的元素组成化合物后可以形成超导.这些不同的体系有着迥然不同的物理行为,却具有一个共同的特征:这些铜、锰、铁、钴、镍基化合物都是3d电子材料.那么,同为3d电子,为什么在不同的环境中表现出完全不同甚至对抗的行为?文章对这些现象提出了一系列为什么,并对其进行了探讨.     

液氦薄膜表面电子-涟波子系统的有效质量

研究了液氦薄膜表面电子与涟波弱耦合的性质，采用线性组合算符和微扰法导出电子－涟波子系统的有效质量。当计及电子在反冲效应中发射和吸收不同波矢的涟波子之间相互作用时，讨论对电子－涟波子系统有效质量的影响。     

一维电声系统中的自旋-电荷分离

文章作者结合团簇微扰理论和优化声子基近似的方法,通过单电子谱函数的计算,研究了一维关联系统中声子效应对自旋-电荷分离的影响,发现由于有限声子频率带来的推迟效应抑制自旋-电荷分离,使之在谱函数中不可见,同时还得到电子对和极化子劈裂的信息.     

自旋-轨道耦合系统的电子涡旋

在轨道角动量守恒的无自旋-轨道耦合系统中存在带轨道角动量量子数的电子涡旋波解,研究了存在自旋-轨道耦合,轨道角动量不守恒的系统,发现携带总角动量量子数的电子旋量波函数也有涡旋波解,表现为自旋波函数和涡旋波波函数的纠缠波函数.以中心力场中的电子为例,构建了自旋-轨道耦合导致的轨道角动量不守恒但总角动量守恒的情况下,携带固定总角动量量子数的电子沿z轴传播的涡旋波旋量波函数结构.对自旋-涡旋纠缠中相应的电子涡旋波进行了微扰求解,并结合Foldy-Wouthuysen变换,说明了在相对论情况下,中心力场中携带固定总角动量量子数的电子沿z轴传播时也确实存在四分量旋量的涡旋解,从而为有自旋-轨道耦合导致的轨道角动量不守恒但总角动量守恒的系统提供了存在涡旋结构的理论支持.     

Rashba自旋轨道耦合作用下电荷流散粒噪声与自旋极化的关系研究

根据存在自旋轨道耦合时基于散射理论的电流表达式和散粒噪声表达式,并利用自旋密度矩阵推导出沿自旋量子化坐标的自旋极化率表达式.解析计算了单通道的情况,发现自旋极化率和电荷流散粒噪声无关.由于多通道解析推导的困难,使用非平衡格林函数技巧,数值计算了包含自旋轨道耦合效应的纯净二维电子气的多通道情况.分别改变偏压、自旋轨道耦合系数、导体长度,研究了这三种不同条件下的自旋极化率与电荷流散粒噪声Fano因子的相关性.两者的相关性表明,相关性定量关系的建立可能为自旋极化的全电学检测提供新思路. 关键词： 散粒噪声 自旋极化 Rashba自旋轨道耦合 散射矩阵     

Anomalous behavior of conductivity of the confined Q1D electron system over liquid helium

Conductivity of electrons in a quasi-one-dimensional (Q1D) system over liquid helium in narrow channels with the parabolic profile of the potential well has been investigated at temperature T, from 0.4 to 1.8 K, for different driving electric fields and radius of channel curvature. The interval of linear electron densities varied from 2.18×10³ up to 1.7×10⁶ cm⁻¹.

The inverse mobility (1/μ_eff) in the electron-ripplon scattering region at the high linear densities of charges in the channel increases with temperature decreasing. This anomalous behavior of the electron transport in the low-temperature region has been explained by either the electron ordering or the polaronic effects in confined conducting channels. The nonlinear behavior of the electron velocity as a function of a driving electric field is supposed to be due to Breg–Cherenkov radiation of the ripplons. The radiation occurred if the velocity of electrons in the channel approaches to the critical value.     

Preparation of cluster states with trapped electrons on a liquid helium surface

We present a scheme for the preparation of one-dimensional (1D) and two-dimensional (2D) cluster states with electrons trapped on a liquid helium surface and driven by a classical laser beam. The two lowest levels of the vertical motion of the electron act as a two-level system, and the quantized vibration of the electron along one of the parallel directions (the x direction) serves as the bosonic mode. The degrees of freedom of the vertical and parallel motions of the trapped electron can be coupled together by a classical laser field. With the proper frequency of the laser field, the cluster states can be realized.     

Plasma modes in low-dimensional electron system over surface of liquid helium

The collective plasma modes in a quasi-two-dimensional (Q2D) electron system located over the free surface of liquid helium are studied theoretically within many-body dielectric formalism. The dispersion of modes is considered both over bulk liquid and over helium film where the essential modification of interelectron interaction occurs due to screening effects in the substrate with a large value of dielectric constant. It is shown that the plasma spectrum consists of longitudinal and transverse branches which dispersion laws depend on the values of the dielectric constant of helium and the film thickness. For the helium film covering metal, the longitudinal mode is acoustic differing of that for the surface electron (SE) system over bulk helium.     

Influence of electron energy distribution on helium recombining plasma diagnostics using line emissions

The influence of electron energy distribution on helium recombining plasma diagnostics is investigated using a helium collisional‐radiative model. The population densities of excited helium atoms are calculated for Maxwellian and non‐Maxwellian distribution plasma cases. In the case of the Maxwellian distribution plasma, the electron temperature and electron density determined by the Boltzmann plot method agree well with the input plasma parameters. On the other hand, it is indicated that the electron temperature and electron density are significantly underestimated in the bi‐Maxwellian distribution plasma case, even though the density of the hot electron components is three orders smaller than that of the bulk electrons. This result indicates that in a non‐Maxwellian helium recombining plasma, evaluation of the particle balance based on line emissions from excited helium atoms would be difficult because the reaction rate of atomic and molecular processes is strongly dependent on the electron temperature and density.     

Coupling Distant Spins of Surface-State Electrons by Manipulating Their Collective Vibrations

The system of electrons on liquid helium is an interesting candidate to implement quantum computation, due to the long coherence times of the qubits encoded by the electronic spins. In order to implement the quantum logic operations between the spins, we propose here a configuration, similarly to the cooled ions in a trap, to couple the distant electrons via manipulating their center of mass （CM） vibrations. First, we show that the electrons could be confined in a common harmonic oscillator potential by using an electrostatic field. Then, with a single current pulse （applied on the micro-electrode below the liquid helium） the distant electronic spins can be coupled simultaneously to the CM mode. Finally, by adiabatically eliminating the CM mode, effective interaction between the distant spins is induced for implementing the desired quantum computing.     

Theory of electron escape from the surface of liquid helium

We have studied the properties of an electron bubble close to the surface of liquid³ He, by using a Density Functional approach. We find that up to an electron-surface distanced ₀ 23 Åthe bubble is stable, while at smaller distances it becomes unstable and bursts. A potential energy barrier /K _B 38°K for the thermal emission of electrons is obtained from our results, in agreement with experiments. Even when the electron-surface distance is larger thand ₀, however, tunneling through the surface layer dominates the electron escape probability. Large deviations of the electron potential energy from its ideal value are found close to the surface. These deviations have a profound effect on the calculated decay rates of the tunneling curent, which are much smaller than those obtained previously and in semi-quantitative agreement with experiments.     

Effect of conduction band nonprabolicity on the Rashba spin splitting of AlGaN/GaN QWs

By using the perturbation expansion method and self-consistent iterative method, we evaluate the effect of the conduction band nonprabolicity on the wave vector (k_t) dependent Rashba coefficient (α) and nonlinear Rashba spin splitting (ΔE) in the Al_0.5Ga_0.5N/GaN quantum well (QW). The effective mass (energy) under the first order approximation m_t1 (E_k1) is in proximity to the iterative result m_tp (E_kp) and m_t1>m_tp, E_k1<E_kp, showing the higher order contributions to m_t (E_k) are small. The sign of the nonparabolic correction to E_k is just opposite to that of the correction to m_t. The increase of α and ΔE due to the conduction band nonparabolicity reaches about 3% at k_t=1 nm⁻¹. Around the left heterointerface, the probability density is high and E_k0>E_kp>E_k1, so α₀<α_p<α₁, ΔE₀<ΔE_p<ΔE₁. With increasing k_t, α decreases, and ΔE increases slowly. For small k_t, α₀ (ΔE₀), α₁ (ΔE₁) and α_p (ΔE_p) are nearly the same. While for large k_t, the difference between α₀ and α₁ (α_p) increases rapidly, but the difference between ΔE₀ and ΔE₁ (ΔE_p) increases slowly.     

利用介质阻挡探针法测量大气压氦等离子体射流电子密度

分别利用电子的漂移速度和等离子体的传播速度计算了大气压下氦等离子体射流的电子密度。     

氦原子及类氦离子基态的二参数变分法研究

提出了一种计算氦原子及类氦离子基态能量和波函数的二参数变分法,包括试探波函数的设计和基态能量表达式的推导,并用Mathematica 5.0软件的优化计算功能方便快捷地计算出基态能量,将计算结果与实验结果和部分所列文献的结果进行对比.结果表明,本文所得精度较高,变分参数个数较少.同时强调交换对称性和量子态的交缠在双电子原子体系问题中的重要性.