磁台阶势垒结构中二维电子气的自旋极化输运

运用散射矩阵方法,研究了台阶磁势垒量子结构中二维电子气的隧穿输运性质.结果表明：在零偏压下,电子传输概率的自旋极化曲线随入射能量的增加而振荡衰减;随着磁台阶数的增加,电子传输概率的自旋极化度最大值减小,同时电子传输概率的自旋极化度振荡衰减也越来越慢;随着磁台阶的总宽度增加,电子传输概率的自旋极化曲线出现更明显的振荡,电子隧穿磁台阶势垒表现出明显的量子尺寸效应;在偏置电压的作用下,电子传输概率的自旋极化度在宽广的入射能量区出现明显的振荡增大,电子隧穿磁台阶势垒表现出更明显的自旋过滤效应. 关键词： 磁台阶势垒 自旋极化 自旋过滤     

恒定电场下双磁垒结构中的电子输运行为

对磁量子结构中电子在外加恒定电场下的输运性质进行了研究.分别计算了电子隧穿相同磁垒磁阱和不同磁垒磁阱构成的两种磁量子结构的传输概率和电流密度.计算结果表明,在相当宽广的非共振电子入射能区,外加电场下电子的传输概率比无电场时增加.对于电子隧穿相同磁垒磁阱构成的双磁垒结构,共振减弱;对于电子隧穿不同磁垒磁阱构成的双磁垒结构,无电场作用时的非完全共振在适当的偏置电压下转化为完全共振,这时的电子可实现理想的共振隧穿.研究同时表明,磁量子结构中存在着显著的量子尺寸效应和负微分电导.     

磁电垒结构中自旋极化输运性质的研究

研究了电子隧穿几类磁电垒结构的自旋极化输运性质，导出统一的传输概率公式，揭示了非 均匀磁场的分布与自旋过滤的关系，同时表明采用有效朗德因子较大的半导体材料可以显著 增强磁电垒结构的自旋过滤效果. 关键词： 磁电垒 自旋过滤 自旋电子学 自旋极化     

对称双势垒量子阱中自旋极化输运的时间特性

电子的隧穿时间是描述量子器件动态工作范围的重要指标. 本文考虑k³ Dresselhaus 自旋轨道耦合效应对系统哈密顿量的修正, 结合转移矩阵方法和龙格-库塔法来解含时薛定谔方程, 进而讨论了电子在非磁半导体对称双势垒结构中的透射系数及隧穿寿命等问题. 研究结果发现:由于k³ Dresselhaus 自旋轨道耦合效应使自旋简并消除, 并在时间域内得到了表达, 导致自旋向上和自旋向下电子的透射峰发生了自旋劈裂; 不同自旋取向的电子构建时间和隧穿寿命不同, 这是导致自旋极化的原因之一; 电子的自旋极化在时间上趋于稳定. 关键词： 自旋极化输运 透射系数 隧穿寿命 自旋极化率     

磁电势垒结构中光场辅助电子自旋输运特性

基于Floquet理论和传输矩阵方法,理论研究了光场对电子隧穿两类磁电垒结构的自旋极化输运特性的影响,计算结果表明光场对两类磁电垒结构中电子的输运有显著影响:首先,原来不存在自旋过滤特性的结构应用光场后会产生低能区域明显的自旋过滤效应;其次,原来存在自旋过滤特性的结构应用光场后自旋过滤明显增强,增幅超过一个数量级.这些为新的自旋极化源的产生和自旋过滤现象的深入研究有一定的指导性意义.     

铁磁金属量子阱态的共振隧穿

非铁磁金属层中的量子阱态在磁输运过程中的重要性已被广泛认识．铁磁金属层中自旋极化的量子阱态以前并没有详尽的理论研究；实验上也没有清晰地观测到自旋极化量子阱态的隧穿．文章介绍了最近由卢仲毅、张晓光和Pantelides预言的Fe／MgO／FeO／Fe／Cr和其他铁磁量子阱隧道结中的共振隧穿，并解释铁、钴、铬的△1能带的对称性在这种共振隧穿中的作用．     

光场辐照下稀磁半导体/半导体超晶格中自旋电子输运特性研究

基于单电子有效质量近似理论和传递矩阵方法,理论研究了稀磁半导体/半导体超晶格结构中电子的自旋极化输运特性.主要讨论了光场和磁场联合调制对自旋极化输运的影响,以及不同自旋电子在该超晶格结构中的隧穿时间.理论和数值计算结果表明,由于导带电子与掺杂Mn离子之间的sp-d电子相互作用引起巨塞曼劈裂,因此在磁场调制下,不同自旋电子在该结构中感受到的势函数不同而呈现出自旋过滤效应,不同自旋电子的共振透射能带的位置和宽度可以通过磁场进行调制.同时在该结构中考虑光场时,自旋依赖的透射谱会因为吸收和发射光子而呈现出对光场的强度和频率响应;最后,通过不同自旋电子的高斯波包在该结构中随时间的演化给出了不同自旋电子的隧穿时间.本文研究结果对研究和设计基于稀磁半导体/半导体超晶格结构的高速量子器件具有一定的指导意义.     

磁性纳米电机单电子晶体管的自旋输运特性

文章作者在研究磁性隧道结的自旋输运中引入量子点的机械振动自由度,将单电子隧穿和振动自由度耦合所导致的shuttle输运理论应用到自旋电子学中,研究结果表明,shuttle输运对自旋极化输运有很大的影响,其独特的输运性质可以用来设计自旋电子器件,文章在理论上提出具有巨磁效应的自旋阀、高性能的半导体自旋注入器以及电流的整流器.     

多层结构双自旋过滤隧道结中的电子输运特性

在转移矩阵方法及Mireles和Kirczenow的量子相干输运理论的基础上,研究了正常金属层/磁性半导体层/非磁绝缘层/磁性半导体层/正常金属层型双自旋过滤隧道结中Rashba自旋轨道耦合效应和自旋过滤效应对自旋相关输运的影响.讨论了隧穿磁电阻（TMR）、隧穿电导与各材料层厚度、Rashba自旋轨道耦合强度以及两磁性半导体中磁矩的相对夹角θ之间的关系.研究表明：含磁性半导体层的双自旋过滤隧道结由于磁性半导体层的自旋过滤效应和Rashba自旋轨道耦合作用可获得极大的TMR值.另外TMR和隧穿电导随着Rashba自旋轨道耦合强度的变化而振荡,振荡周期随Rashba自旋轨道耦合强度的增大逐渐减小. 关键词： 双自旋过滤隧道结 Rashba自旋轨道耦合 隧穿磁电阻 隧穿电导     

半导体超晶格系统中的磁电调控电子自旋输运研究

通过采用转移矩阵方法求解自旋电子隧穿过程,理论研究了半导体超晶格系统中电子自旋输运的磁电调控行为.结果表明：仅对超晶格系统施以磁调制,隧穿系数将出现自旋分裂,随磁场增强,电导自旋极化率变大且展宽于费米能区;若选取不变磁场情况,同时施以间隔周期电场调制,超晶格的电子极化率将有更为显著地提高.进一步发现,随电场强度的改变,电子自旋输运行为显然存在两个明显不同区域,下自旋电子将在不同调制区域表现为不同的变化趋势.然而,若对周期磁超晶格施加间隔两周期的电调制,自旋电导输运的临界行为消失,电导极化率在高能区的共振峰 关键词： 半导体超晶格 自旋输运 磁电调控     

The electron transport characters in a nanostructure with the periodic magnetic-electric barriers

This paper detailedly studies the transmission probability, the spin polarization and the conductance of the ballistic electron in a nanostrueture with the periodic magnetic-electric barriers These observable quantities are found to be strongly dependent not only on the magnetic configuration, the incident electron energy and the incident wave vector, but also on the number of the periodic magnetic-electric barriers The transmission coefficient and the spin polarization show a periodic pattern with the increase of the separation between two adjacent magnetic fields, and the resonance splitting increases as the number of periods increases. Surprisingly, it is found that a polarization can be achieved by spin-dependent resonant tunnelling in this structure, although the average magnetic field of the structure is zero.     

The electron transport characters in a nanostructure with the periodic magnetic-electric barriers

This paper detailedly studies the transmission probability, the spin polarization and the conductance of the ballistic electron in a nanostructure with the periodic magnetic-electric barriers. These observable quantities are found to be strongly dependent not only on the magnetic configuration, the incident electron energy and the incident wave vector, but also on the number of the periodic magnetic-electric barriers. The transmission coefficient and the spin polarization show a periodic pattern with the increase of the separation between two adjacent magnetic fields, and the resonance splitting increases as the number of periods increases. Surprisingly, it is found that a polarization can be achieved by spin-dependent resonant tunnelling in this structure, although the average magnetic field of the structure is zero.     

Energy dependent spin filtering by using Fano effect in open quantum rings

An open quantum ring containing magnetic quantum structures which is subjected to the Rashba spin–orbit coupling and Zeeman effect is considered. One dimensional quantum wave guide theory is developed and Transfer matrix method in conjunction with spin-dependent Griffith’s boundary condition is used to calculate the transmission coefficients of the corresponding one-electron scattering problem. Investigations into spin-dependent transport show the characteristic oscillations which are affected by impurities. The existence of Rashba spin–orbit coupling leads to the appearance of Fano resonances in transport. The results indicate that the orientation of Fano line shapes is under the influence of impurities. Also, it is shown that by using Fano resonances the system under study can be used as a cent percent spin-filtering device. The spin-filtering property of this system as a function of energy is affected by impurities and can be used in order to design optimized nanodevices.     

0.7 Structure and zero bias anomaly in ballistic hole quantum wires

We study the anomalous conductance plateau around G=0.7(2e2/h) and the zero bias anomaly in ballistic hole quantum wires with respect to in-plane magnetic fields applied parallel B parallel and perpendicular B perpendicular to the quantum wire. As seen in electron quantum wires, the magnetic fields shift the 0.7 structure down to G=0.5(2e2/h) and simultaneously quench the zero bias anomaly. However, these effects are strongly dependent on the orientation of the magnetic field, owing to the highly anisotropic effective Landé g-factor g* in hole quantum wires. Our results highlight the fundamental role that spin plays in both the 0.7 structure and zero bias anomaly.     

铁磁/半导体/铁磁结构的双量子环自旋输运的特性

研究了与铁磁/半导体/铁磁结构相关的双量子环自旋输运的规律,研究结果表明：总磁通为零条件下,铁磁电极磁化方向反平行时,双量子环与单量子环相比提高了自旋电子透射概率的平均值.铁磁电极磁化方向平行时,双量子环对提高自旋向下电子平均透射概率的效果更明显;双量子环受到Rashba自旋轨道耦合作用影响时,自旋电子的平均透射概率明显高于单量子环,即使再加上外加磁场的影响,透射概率较高这一特征依然存在;双量子环所含的δ势垒具有阻碍自旋电子输运的作用,随δ势垒强度Z的增大透射概率 关键词： 双量子环 Rashba自旋轨道耦合 透射概率 δ势垒')" href="#">δ势垒     

可控磁性量子点杂质引起的单电子自旋过滤器

本文提出一种基于电子-电子自旋交换相互作用获得自旋极化电流的模型. 该方案中, 需要两个距离相近的量子点. 其中一个是开放系统, 另一个是封闭系统. 开放系统能完成单电子输运, 封闭系统产生比较强的局域磁场, 两个系统之间有电子-电子自旋交换相互作用. 该相互作用会影响电子输运, 从而可以对电子输运产生自旋过滤效应. 我们用量子主方程描述开放系统的演化, 在有效哈密顿量的基础上, 可以得到解析结果. 结果显示, 在低温条件下, 交换相互作用足够强的时候, 系统给出的自旋过滤效率接近1 .     

Pure spin-current diode based on interacting quantum dot tunneling junction

A magnetic field-controlled spin-current diode is theoretically proposed, which consists of a junction with an interacting quantum dot sandwiched between a pair of nonmagnetic electrodes. By applying a spin bias V_S across the junction, a pure spin current can be obtained in a certain gate voltage regime,regardless of whether the Coulomb repulsion energy exists. More interestingly, if we applied an external magnetic field on the quantum dot, we observed a clear asymmetry in the spectrum of spin current I_S as a function of spin bias, while the charge current always decays to zero in the Coulomb blockade regime. Such asymmetry in the current profile suggests a spin diode-like behavior with respect to the spin bias, while the net charge through the device is almost zero. Different from the traditional charge current diode, this design can change the polarity direction and rectifying ability by adjusting the external magnetic field, which is very convenient. This device scheme can be compatible with current technologies and has potential applications in spintronics or quantum processing.     

Quantized magnetic flux through the ground-state orbit of the hydrogen atom

We have investigated the spin-dependent quantized magnetic fluxes through the ground-state electronic orbit of the hydrogen atom. We show that the corresponding fluxes are (1/2)Φ₀ for the spin-up case and (3/2)Φ ₀ for the spin-down case, respectively, where Φ₀ = hc/e is the flux quantum. Using the energy-flux proportionality, we also show that the spin-up case (where the electron spin is antiparallel to the proton spin, resulting in zero total spin) is the spin-dependent ground state of the hydrogen atom. The present result helps to understand the spin flip-flop in excitonic transitions in nanostructures.     

First-principles study of transport of V doped boron nitride nanotube

We perform first-principles calculations of spin-dependent quantum transport in V doped boron nitride nanotube: the junction of pristine (6,0) boron nitride nanotube in contact with V doped (6,0) boron nitride nanotube electrodes. Large tunnel magnetoresistance and perfect spin filtration effect are obtained. The zero bias tunnel magnetoresistance is found to be several thousand percent, it reduces monotonically to zero with a voltage scale of about 0.65 V, and eventually goes to negative values after the bias of 0.65 V. The ratio of spin injection is above 95% till the bias of 0.85 V and is even as large as 99% for the bias from 0.25 eV to 0.55 eV when the magnetic configurations of two electrodes are parallel. The understanding of the spin-dependent nonequilibrium transport is presented by investigating microscopic details of the transmission coefficients.