窄禁带稀磁半导体二维电子气的拍频振荡

通过对调制掺杂的n型Hg_0.82Cd_0.16Mn_0.02Te/Hg_0.3Cd_0.7Te第一类量子阱中磁性二维电子气磁阻拍频振荡的研究，发现温度、栅压的变化都会引起磁阻拍频节点位置的变化.从对拍频的分析中，可以将依赖于栅压的Rashba自旋-轨道分裂和依赖于温度的巨大塞曼分裂区分开来. 关键词： 磁性二维电子气 自旋分裂 sp-d交换相互作用 拍频     

HgTe/HgCdTe量子阱中巨大电子Rashba自旋分裂

主要研究具有倒置能带结构的n-HgTe/HgCdTe第三类量子阱Shubnikov-de Haas（SdH）振荡中的拍频现象.发现在量子阱中电子存在强烈的Rashba自旋分裂，通过对SdH振荡进行三种不同方法的分析：SdH振荡对1/B关系的快速傅里叶变换、SdH振荡中拍频节点分析和对SdH振荡拍频数值拟合，得到了完全一致的电子Rashba自旋分裂能量（28—36 meV）. 关键词： n-HgTe/HgCdTe Shubnikov-de Haas振荡 Rashba自旋分裂     

含δ势垒的铁磁/半导体/铁磁异质结中的自旋输运和渡越时间

研究了含δ势垒的铁磁/半导体/铁磁异质结中自旋相关的透射概率和渡越时间，讨论了量子尺寸效应和Rashba自旋轨道耦合效应对隧穿特性的影响.研究结果表明：δ势垒的存在降低了自旋电子的透射概率，改变了透射概率的位相.Rashba自旋轨道耦合强度的增加加大了透射概率的振荡频率.不同自旋取向的电子隧穿异质结时，渡越时间随着半导体长度、Rashba自旋轨道耦合强度以及两铁磁电极中的磁化方向的夹角的变化而变化. 关键词： δ势垒')" href="#">δ势垒 铁磁/半导体/铁磁异质结 Rashba自旋轨道耦合效应 渡越时间     

双量子阱中光子辅助电子自旋隧穿

采用单电子有效质量近似理论, Floquet理论和传递矩阵方法, 对包含时间周期场的双量子阱中单电子的自旋隧穿特性进行了研究, 对InP/InAs半导体材料进行了数值计算. 重点研究了Rashba型和Dresselhaus型自旋轨道耦合、量子阱结构以及偏压对电子隧穿的影响. 这些结果可以为设计和调控半导体自旋电子器件提供一定的理论依据. 关键词： 光子辅助隧穿 隧穿概率 量子阱     

Al0.6Ga0.4N/GaN/Al0.3Ga0.7N/Al0.6Ga0.4N量子阱中的Rashba自旋劈裂

正如人们所知, 可以通过电场或者设计非对称的半导体异质结构来调控体系的结构反演不对称性(SIA)和Rashba自旋劈裂. 本文研究了Al_0.6Ga_0.4N/GaN/Al_0.3Ga_0.7N/Al_0.6Ga_0.4N量子阱中第一子带的Rashba 系数和Rashba自旋劈裂随Al_0.3Ga_0.7N插入层(右阱)的厚度w_s以及外加电场的变化关系, 其中GaN层(左阱)的厚度为40-w_s Å. 发现随着w_s的增加, 第一子带的Rashba系数和Rashba自旋劈裂首先增加, 然后在w_s>20 Å 时它们迅速减小, 但是w_s>30 Å时Rashba自旋劈裂减小得更快, 因为此时k_f也迅速减小. 阱层对Rashba系数的贡献最大, 界面的贡献次之且随w_s变化不是太明显, 垒层的贡献相对比较小. 然后, 我们假w_s=20 Å, 发现外加电场可以很大程度上调制该体系的Rashba系数和Rashba自旋劈裂, 当外加电场的方向同极化电场方向相同(相反)时, 它们随着外加电场的增加而增加(减小). 当外加电场从-1.5×10⁸ V·m^-1到1.5×10⁸ V· m^-1变化时, Rashba系数随着外加电场的改变而近似线性变化, Rashba自旋劈裂先增加得很快, 然后近似线性增加, 最后缓慢增加. 研究结果表明可以通过改变GaN层和Al_0.3Ga_0.7N层的相对厚度以及外加电场来调节Al_0.6Ga_0.4N/GaN/Al_0.3Ga_0.7N/Al_0.6Ga_0.4N量子阱中的Rashba 系数和Rashba自旋劈裂, 这对于设计自旋电子学器件有些启示.     

InAIAs／InGaAs／IIAlAs量子阱高迁移率二维电子气系统中的反弱局域效应研究

研究了si重δ掺杂In0．52Al0.48/In0.53Ga0.47As／In0.52Al0.48As单量子阱内高迁移率二维电子气系统中的反弱局域效应．研究表明，强的Rashba自旋轨道相互作用来源于量子阱高的结构反演不对称．高迁移率系统中，粒子的运动基于弹道输运而非扩散输运．因此，旧的理论模型不能用于拟合实验结果．由于最新的模型在实际拟合中过于复杂，一种简单可行的近似用于处理实验结果，并获得了自旋分裂能△。和自旋轨道耦合常数a两个重要的物理参数．该结果与对纵向电阻的Shubnikov-de Haas--SdH振荡分析获得的结果一致．高迁移率系统中的反弱局域效应研究表明，发展有效的反弱局域理论模型，对于利用Rashba自旋轨道相互作用来设计自旋器件尤为重要.     

Ⅳ-Ⅵ族化合物半导体异质结二维电子气研究进展

半导体异质结在探索新奇物理和发展器件应用等方面一直发挥着不可替代的作用.得益于其特有的能带性质,相对较窄的带隙和足够大的自旋轨道耦合相互作用,Ⅳ-Ⅵ族化合物半导体异质结不仅在红外器件应用方面具有重要的研究价值,而且在拓扑绝缘体和自旋电子学等前沿领域引起了广泛的关注.尤为重要的是,在以CdTe/PbTe为代表的Ⅳ-Ⅵ族化合物半导体异质结界面上发现了高浓度、高迁移率的二维电子气.该电子气的形成归因于Ⅳ-Ⅵ族化合物半导体异质结独特的扭转界面.进一步的研究表明,该二维电子气体系不仅对红外辐射有明显响应,而且它还表现出狄拉克费米子的性质.本文系统综述了近年来Ⅳ-Ⅵ族化合物半导体异质结二维电子气研究取得的主要进展.首先对Ⅳ-Ⅵ族化合物半导体异质结扭转界面二维电子气的形成机理进行了介绍;然后讨论该二维电子气在低温强磁场下的输运性质,并分析了它的拓扑性质以及在自旋器件方面的应用前景;最后,展示了基于该二维电子气研制的中红外光电探测器.     

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     

Rashba效应影响下量子点中弱耦合束缚极化子的性质

采用改进的线性组合算符和幺正变换的方法研究了Rashba效应影响下量子点中弱耦合束缚极化子的性质,导出了Rashba效应影响下量子点中弱耦合束缚极化子的振动频率、有效质量、基态分裂能和相互作用能。数值计算结果表明随Rashba自旋-轨道耦合常数的增加,由于声子作用产生的附加能量能对零磁场时自旋分裂能的影响占有绝对优势。库仑势对束缚极化子的基态能量的影响同时也占有绝对优势。所以,研究Rashba自旋轨道相互作时声子的影响不可忽略。     

Rashba效应影响下量子点中弱耦合束缚极化子的性质

采用改进的线性组合算符和幺正变换的方法研究了Rashba效应影响下量子点中弱耦合束缚极化子的性质,导出了Rashba效应影响下量子点中弱耦合束缚极化子的振动频率、有效质量、基态分裂能和相互作用能。数值计算结果表明随Rashba自旋-轨道耦合常数的增加,由于声子作用产生的附加能量能对零磁场时自旋分裂能的影响占有绝对优势。库仑势对束缚极化子的基态能量的影响同时也占有绝对优势。所以,研究Rashba自旋轨道相互作时声子的影响不可忽略。     

Electron–hole symmetry and spin–orbit splitting in IV–VI asymmetric quantum wells

It is shown that, due to the electron–hole symmetry of the fundamental gap of the lead–salts (PbTe, PbSe and PbS), the Rashba spin splitting in their flat band asymmetric quantum wells is much reduced with the usual equal conduction and valence band-offsets. Different from the III–V case, we find that the important structure inversion asymmetry for the Rashba splitting in IV–VI quantum wells with different left and right barriers is not a material property (i.e., barrier height, effective mass or band gap) but results from the band alignment. This is shown by specific envelope function calculations of the spin-dependent subband structure of Pb_1−xEu_xTe/PbTe/Pb_1−yEu_yTe asymmetric quantum wells (x≠y), based on a simple but accurate four-band kp model for the bulk band structure near the gap, which takes into account band anisotropy, nonparabolicity and multi-valley effects.     

Anisotropic Spin Splitting in Step Quantum Wells

By the method of finite difference, the anisotropic spin splitting of the AlxGa1-xAs/GaAs/Aly Ga1-yAs/AlxGal-xAs step quantum wells （QWs） are theoretically investigated considering the interplay of the bulk inversion asymmetry and structure inversion asymmetry induced by step quantum well structure and external electric field. We demonstrate that the anisotropy of the total spin splitting can be controlled by the shape of the QWs and the external electric field. The interface related Rashba effect plays an important effect on the anisotropic spin splitting by influencing the magnitude of the spin splitting and the direction of electron spin. The Rashba spin splitting presents in the step quantum wells due to the interface related Rashba effect even without external electric field or magnetic field.     

不同晶体取向下纳米压痕的多尺度模拟

采用准连续介质多尺度方法模拟面心立方金属铝单晶薄膜的纳米压痕变形过程.对薄膜分别采用三种不同的晶体取向(分别为x［1 1 1］,y［1 1 0］,z［1 1 2］; x［1 1 2］,y［1 1 1］,z［1 1 0］;x［1 1 0］,y［0 0 1］,x［1 1 0］),得到载荷-位移响应曲线.加载过程中,对晶体内部变形比较剧烈的部分画出原子图,并从微观角度分析产生剧烈变形的原 关键词： 纳米压痕 准连续介质方法 晶体取向 位错成核     

Growth and studies of Hg1−xCdxTe based low dimensional structures

The band structure of HgTe quantum wells (QWs) has been determined from absorption experiments on superlattices in conjunction with calculations based on an 8×8 k·p model. The band structure combined with self-consistent Hartree calculations has enabled transport results to be quantitatively explained.Rashba spin–orbit, (SO) splitting has been investigated in n-type modulation doped HgTe QWs by means of Shubnikov–de Haas oscillations (SdH) in gated Hall bars. The heavy hole nature of the H1 conduction subband in QWs with an inverted band structure greatly enhances the Rashba SO splitting, with values up to 17 meV.By analyzing the SdH oscillations of a magnetic two-dimensional electron gas (2DEG) in modulation-doped n-type Hg_1−xMn_xTe QWs, we have been able to separate the gate voltage-dependent Rashba SO splitting from the temperature-dependent giant Zeeman splitting, which are of comparable magnitudes. In addition, hot electrons and Mn ions in a magnetic 2DEG have been investigated as a function of current.Nano-scale structures of lower dimensions are planned and experiments on sub-micrometer magneto-transport structures have resulted in the first evidence for ballistic transport in quasi-1D HgTe QW structures.     

Dynamical nonlinear refraction in PbTe/Pb1−xSnxTe MQWs

An analysis of nonlinear refraction due to the dynamical free carrier filling of minibands in PbTe/Pb_1−xSn_xTe (X = 0.2) MQEs on (111) BaF₂ substrates is presented. The results are compared with those for bulk Pb_1−xSn_xTe layers. The abrupt substantial increase of n(I) in MQWs is connected with crossing of the minibands in oblique valleys of Pb_1−xSn_xTe wells by the Fermi quasi-level.     

On the type of superlattices in leadtintelluride system

It is predicted in the PbTePb_1?xSn_xTe superlattice (SL) that the bottom of the quantum well is situated at the PbTe layer in n-type specimens and the top at the Pb_1?xSn_xTe layer in p-type ones for x<0.23, and for x>0.23, SLs are of type II. These predictions are based upon an experimental tin concentration dependence of the band edge energies relative to the Fermi level pinned by amphoteric indium impurities in bulk Pb_1?xSn_xTe. In n-type PbTePb_0.8Sn_0.2Te SL, cyclotron resonances together with Hall coefficient and Shubnikov de Haas (SdH) oscillation experiments support the existence of the PbTe wells. The results of submillimeter cyclotron resonances for n-type PbSe_0.08Te_0.92Pb_0.8Sn_0.2Te and PbSePb_0.88Sn_0.12Se SLs are also presented.     

Magnetooptical investigation of PbTe/Pb1−xSnxTe superlattices

Intra- and interband magnetooptical experiments were carried out on PbTe/Pb_1?xSn_xTe superlattices (x=0.135) with layer thicknesses ranging from 13 – 225 nm. For the magnetic field parallel to the [111] growth direction, the Landau levels for the superlattice band structure are calculated within the framework of the envelope function approach for the [111] and the three obliquely oriented valleys. The experimental intra- and interband data agree qualitatively with the results of the model calculation and are consistent with the predictions of a LCAO calculation according to which the electrons or holes are confined in the Pb_1?xSn_xTe layers.     

Lattice and electronic properties and g-value of Pb1−xSnxTe

The lattice dielectric property and the band edge structure in Pb_1-xSn_xTe are investigated by magnetoplasma reflection using a strip-line technique with several submillimeter laser lines, which are in the Reststrahlen region in the vicinity of the TO-phonon energy. The TO-phonon frequency, the dielectric constant and the effective mass in PbTe and Pb_0.7Sn_0.3Te at 4.2K are obtained. The additional new fine structure in PbTe is identified as a spin flip combined resonance from which we determine the effective g-value and its angular dependence.     

NiFe/Mo多层膜界面的电子显微学研究

用高分辨电子显微学方法研究了Ni₈₀Fe₂₀/Mo磁性多层膜，结果表明：(1)多层膜的结晶状态，随Mo非磁性层厚度而变化.当Mo层厚度为0.7nm时，多层膜基本为非晶；当Mo层厚度大于1.6nm时，Mo层和NiFe层内分别结晶为体心立方和面心立方多晶，层内晶粒尺寸为2—6nm.(2)在Mo层厚度为1.6和2.1nm的多层膜中，NiFe层和Mo层之间存在两种取向关系：(110)_Mo∥(111)_NiFe,［111］_关键词：     

Tb0.3Dy0.7(Fe0.9T0.1)1.95合金的结构、自旋重取向和穆斯堡尔谱

系统研究了室温下Tb_0.3Dy_0.7(Fe_0.9T_0.1)_1.95(过渡金属元素T=Mn，Fe，Co，B，Al，Ga)合金中ⅢA族金属和过渡金属元素T替代Fe对结构、自旋重取向和穆斯堡尔谱的影响.结果发现，不同金属T替代Fe，Tb_0.3Dy_0.7(Fe_0.9T_0.1)_1.95，合金具有相同的MgCu₂型立方Laves相结构；Al，Ga替代使Tb_0.3Dy_0.7(Fe_0.9T_0.1)_1.95合金的易磁化方向在{110}面逐渐偏离了立方晶体的主对称轴，即自旋重取向，B，Mn，Co替代未使易磁化轴发生明显转动；Al，Ga元素替代使超精细场H_hf略有下降，B，Mn替代对超精细场H_hf的影响不大，而Co元素替代使超精细场H_hf有较大增加；所有元素替代使同质异能移IS有所增加；B，Al，Ga和Mn替代使四极劈裂Q_s增加，而Co替代使四极劈裂Q_s下降. 关键词： 立方Laves相 自旋重取向 穆斯堡尔谱