绿宝石晶体自旋二重态对基态能级的影响及Jahn-Teller效应

应用不可约张量方法和群的理论构造了三角对称晶场中考虑自旋 轨道相互作用,自旋 自旋相互作用和自旋 其它轨道相互作用的3d3/3d7态离子的可完全对角化的120阶微扰哈密顿矩阵.利用该矩阵计算了绿宝石晶体的基态能级、零场分裂参量,研究了自旋二重态对基态能级的贡献.理论计算值与实验值相符合,证明二重态对基态的贡献是不可忽略的.在此基础上,进一步研究了自旋 自旋相互作用、自旋 其它轨道相互作用和自旋 轨道相互作用对绿宝石晶体的光谱精细结构和零场分裂参量的影响,发现自旋 自旋和自旋 其它轨道相互作用对绿宝石晶体基态能级和零场分裂参量的影响都是不可忽略的.从而通过理论计算值和实验值的比较,证实了在绿宝石晶体中Jahn Teller效应的存在,它能够对光谱精细结构的分裂提出一些更加合理的解释.     

YAG∶Cr^3＋晶体的基态能级分裂及扬-特勒效应

应用不可约张量法和群的理论构造了三角对称晶场中3d3/3d7态离子的可完全对角化的120阶微扰哈密顿矩阵。矩阵中考虑了自旋-轨道相互作用,自旋-自旋相互作用和自旋-其他轨道相互作用,利用该矩阵计算了YAG∶Cr3 晶体的基态能级、零场分裂参量,研究了自旋二重态对基态能级的贡献,理论计算值与实验值相符合,证明二重态对基态的贡献是不可忽略的。在此基础上,进一步研究了自旋-轨道相互作用、自旋-自旋相互作用和自旋-其他轨道相互作用对YAG∶Cr3 晶体的光谱精细结构和零场分裂参量的影响,发现自旋-自旋和自旋-其他轨道相互作用对YAG晶体基态光谱精细结构和零场分裂参量的影响都是不可忽略的。通过理论计算值和实验值的比较,证实了在YAG∶Cr3 晶体光谱中扬-特勒效应的存在。     

Fe_2P_2S_6晶体基态能级的精细结构及其Jahn-Teller效应的研究

在弱场图像下,利用Racah不可约张量算符方法得到了三角对称3d4/3d6电子组态的完整的哈密顿矩阵。研究了Fe2P2S6晶体中Fe2+的基态能级和晶体结构,考虑了自旋-轨道耦合与自旋-自旋耦合对基态能级的影响,对Fe2P2S6晶体基态能级和电子顺磁共振的零场分裂进行了计算。计算结果与实验值符合得较好。基于此计算结果,对基态能级和零场分裂中的自旋-轨道耦合、自旋-自旋耦合以及3 L低自旋态进行了更深入的研究,并对Fe2P2S6晶体的Jahn-Teller效应进行了研究。     

YAG:Cr3+晶体的基态能级分裂及扬-特勒效应

应用不可约张量法和群的理论构造了三角对称晶场中3d3/3d7态离子的可完全对角化的120阶微扰哈密顿矩阵.矩阵中考虑了自旋-轨道相互作用,自旋-自旋相互作用和自旋-其他轨道相互作用,利用该矩阵计算了YAG.Cr3 晶体的基态能级、零场分裂参量,研究了自旋二重态对基态能级的贡献,理论计算值与实验值相符合,证明二重态对基态的贡献是不可忽略的.在此基础上,进一步研究了自旋-轨道相互作用、自旋-自旋相互作用和自旋-其他轨道相互作用对YAG:Cr3 晶体的光谱精细结构和零场分裂参量的影响,发现自旋-自旋和自旋-其他轨道相互作用对YAG晶体基态光谱精细结构和零场分裂参量的影响都是不可忽略的.通过理论计算值和实验值的比较,证实了在YAG:Cr3 晶体光谱中扬-特勒效应的存在.     

Cr~(3 )∶MgAl_2O_4晶体的基态能级分裂及Jahn-Teller效应

构造了3d3/3d7离子在三角对称晶场中考虑自旋-轨道相互作用,自旋-自旋相互作用和自旋-其它轨道相互作用的120阶微扰哈密顿矩阵.利用完全对角化该矩阵的方法计算了Cr3 ∶MgAl2O4晶体的基态能级、零场分裂参量,理论计算值与实验值相符合.定量研究了自旋二重态对基态能级的贡献,证明该贡献是不可忽略的.定量研究了自旋-轨道相互作用、自旋-自旋相互作用和自旋-其它轨道相互作用对Cr3 ∶MgAl2O4晶体的光谱精细结构和零场分裂参量的影响,发现自旋-轨道和自旋-自旋相互作用对基态能级和零场分裂参量的影响的程度和方式是不同的,自旋-其它轨道相互作用的影响也是不可忽略的.通过理论计算值和实验值的比较,证实了在Cr3 ∶MgAl2O4晶体中Jahn-Teller效应的存在,解释了该晶体的光谱精细结构的成因.     

Cr3+∶MgAl2O4晶体的基态能级分裂及Jahn-Teller效应*

构造了3d3/3d7离子在三角对称晶场中考虑自旋-轨道相互作用,自旋-自旋相互作用和自旋-其它轨道相互作用的120阶微扰哈密顿矩阵.利用完全对角化该矩阵的方法计算了Cr3+∶MgAl2O4晶体的基态能级、零场分裂参量,理论计算值与实验值相符合.定量研究了自旋二重态对基态能级的贡献,证明该贡献是不可忽略的.定量研究了自旋-轨道相互作用、自旋-自旋相互作用和自旋-其它轨道相互作用对Cr3+∶MgAl2O4晶体的光谱精细结构和零场分裂参量的影响,发现自旋-轨道和自旋-自旋相互作用对基态能级和零场分裂参量的影响的程度和方式是不同的,自旋-其它轨道相互作用的影响也是不可忽略的.通过理论计算值和实验值的比较,证实了在Cr3+∶MgAl2O4晶体中Jahn-Teller效应的存在,解释了该晶体的光谱精细结构的成因.     

类氩体系基态能量的相对论修正

以相对论修正哈密顿(包括质量修正、单体和双体达尔文修正、自旋-自旋接触相互作用)的张量形式为基础,借助不可约张量理论导出了类氩体系基态能量的相对论修正的解析表达式.在斯莱特表象中完成了所有的角向积分和自旋求和计算,能量的相对论修正式用径向矩阵元的线性组合来表示.对类氩体系基态能量的相对论修正值进行了具体计算,修正后基态能量与实验值的相对误差小于0.0459%.     

Rashba效应下量子线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相结合的方法研究了Rashba效应对量子线中弱耦合束缚极化子性质的影响.数值计算结果表明Rashba效应影响下,极化子基态能量和有效质量曲线分别分裂成上下两条,有效质量比随着电子-声子耦合强度的增加而增大;当自旋向上时,有效质量比随电子面密度的增加而线性增加,自旋向下则得相反结论;随着振动频率的增加极化子基态能量和基态分裂能均增加.     

掺入V3+离子α-Al2O3晶体的基态精细光谱和晶体局域结构及J-T效应的研究

应用晶体场理论和不可约张量算符方法构造了3d2/3d8态离子在C3v对称晶场中包含自旋-轨道相互作用、自旋-自旋相互作用、自旋-其它轨道相互作用和其它轨道-其它轨道相互作用四种微观磁效应的完全能量哈密顿矩阵。利用该矩阵,计算了V3+:α-Al2O3晶体的光谱精细结构和晶体局域结构,进一步研究了V3+:α-Al2O3晶体的自旋-轨道相互作用、自旋-自旋相互作用、自旋-其它轨道相互作用和其它轨道-其它轨道相互作用和它们对光谱精细结构影响及Jahn-Teller效应。理论计算值和实验值相符合。结果发现,掺杂没有改变晶体的对称性、同时发现并合理解释了V3+对α-Al2O3晶体基态精细光谱中J-T效应的存在机理。     

掺有Ni~(2+)的α-Al_2O_3晶体的基态精细光谱、晶体局域结构和Jahn-Teller效应

应用晶体场理论和不可约张量算符方法构造了3d2/3d8态离子在C3v对称晶场中包含自旋-轨道相互作用、自旋-自旋相互作用、自旋-其它轨道相互作用和其它轨道-其它轨道相互作用四种微观磁效应的45阶可完全对角化的能量哈密顿矩阵.利用该矩阵,计算了Ni2+∶α-Al2O3晶体的光谱精细结构和晶体局域结构,深入研究了Ni2+∶α-Al2O3晶体的自旋-轨道相互作用、自旋-自旋相互作用、自旋-其它轨道相互作用和其它轨道-其它轨道相互作用和它们对光谱精细结构的影响及Jahn-Teller效应.理论计算值和实验值相符合.研究发现,掺杂没有改变晶体的对称性、同时发现并合理解释了Ni2+对α-Al2O3晶体基态精细光谱中Jahn-Teller效应的存在机理.     

Energy gap of spin nanotube

Recently some quantum spin systems on tube lattices, so-called spin nanotubes, have been synthesized. They are expected to be interesting low-dimensional systems like the carbon nanotubes. As a first step of theoretical study on the spin nanotube, we investigate the three-leg spin tube, which is the simplest one, using numerical analyses of finite clusters and a finite-size scaling technique. The spin gap, which is one of the most interesting quantities reflecting the macroscopic quantum effect, was revealed to be open for any finite rung exchange couplings, in contrast to the three-leg spin ladder system which is gapless. We also found a quantum phase transition caused by an asymmetric rung interaction. When one of the three rung coupling constants is changed, the spin gap vanishes very rapidly.     

Electrical generation of pure spin current with oscillating spin-orbit interaction

We propose an electrical scheme for the generation of a pure spin current without a charge current in a two-terminal device, which consists of a scattering region of a two-dimensional electron gas (2DEG) with Rashba (R) and/or Dresselhaus (S) spin-orbit interaction (SOI) and two normal leads. The SOI is modulated by a time-dependent gate voltage to pump a spin current. Based on a tight-binding model and the Keldysh Green’s function technique, we obtain the analytical expression of the spin current. It is shown that a pure spin current can be pumped out, and its magnitude could be modulated by device parameters such as the oscillating frequency of the SOI, as well as the SOI strength. Moreover, the spin polarisation direction of the spin current could also be tuned by the strength ratio between RSOI and DSOI. Our proposal provides not only a fully electrical means to generate a pure spin current but also a way to control the spin polarisation direction of the generated spin current.     

Electrically driven spin dynamics of paramagnetic impurities

The spin dynamics of dilute paramagnetic impurities embedded in a semiconductor GaAs channel of a conventional lateral spin valve has been investigated. It is observed that the electron spin of paramagnetic Mn atoms can be polarized electrically when driven by a spin valve in the antiparallel configuration. The transient current through the MnAs/GaAs/MnAs spin valve bears the signature of the underlying spin dynamics driven by the exchange interaction between the conduction band electrons in GaAs and the localized Mn electron spins. The time constant for this interaction is observed to be dependent on temperature and is estimated to be 80 ns at 15 K.     

自旋注入有机物的扩散理论

根据自旋注入半导体的相关理论， 考虑到有机体内可能同时含有带自旋的单极化子和不带自旋的双极化子两种载流子，从扩散 理论和欧姆定律出发，建立了自旋注入有机体的唯象模型.通过计算发现，适当选择铁磁层极化率或两层的电导率可以使得有机层内电流具有高的自旋极化.进一步研究了单极化子浓度等因素对注入电流极化的影响. 关键词： 自旋电子学 自旋注入 有机聚合物 极化子     

Spin Polarization and Spin‐Flip Through Phosphorene Superlattice

The spin‐dependent transport properties, including spin polarization and spin‐flip for phosphorene superlattice in the presence of an extrinsic Rashba spin‐orbit interaction (RSOI) based on the transfer matrix method, are studied. The results show that the number of barriers in the superlattice structure plays a dominant role in output spin polarization, which can be used in designing optimized spintronic devices. In addition, by controlling on the Rashba strength, an incident spin‐up electron can be transmitted as a spin‐down electron. Also, it enables to convert the unpolarized incident electronic beam (with zero spin polarization) into an arbitrary output spin polarization, which plays a significant role in qubit circuits.     

Long time evolution of a spin interacting with a spin bath in arbitrary magnetic field

We introduce a completely different method to calculate the evolution of a spin interacting with a sufficient large spin bath,especially suitable for treating the central spin model in a quantum dot(QD).With only an approximation on the envelope of central spin,the symmetry can be exploited to reduce a huge Hilbert space which cannot be calculated with computers to many small ones which can be solved exactly.This method can be used to calculate spin-bath evolution for a spin bath containing many(say,1000)spins,without a perturbative limit such as strong magnetic field condition,and works for long-time regime with sufficient accuracy.As the spin-bath evolution can be calculated for a wide range of time and magnetic field,an optimal dynamic of spin flip-flop can be found,and more sophisticated approaches to achieve extremely high polarization of nuclear spins in a QD could be developed.     

Theory of the electron and nuclear spin coherence times of shallow donor spin qubits in isotopically and chemically purified zinc oxide

In this article, I present a theoretical study of the electron and nuclear spin coherence times of shallow donor spin qubits in zinc oxide (ZnO) at low temperature. The influence of different spin-phonon processes as well as different spin-spin processes on the spin coherence time of shallow donors in ZnO is considered, both in the case of an electron spin qubit and in the case of a nuclear spin qubit encoded on a shallow donor. It is estimated that the electron spin coherence time of an isolated indium shallow donor in natural quasi-intrinsic ZnO is on the order of hundreds of microseconds, limited by the nuclear spectral diffusion process. The electron spin coherence time of an isolated indium shallow donor can be extended to few milliseconds in isotopically and chemically purified quasi-intrinsic ZnO. In this optimal case, the electron spin coherence time of an isolated indium shallow donor is only limited by a spin-lattice decoherence process. It is also estimated that the nuclear spin coherence time of an isolated indium shallow donor in natural quasi-intrinsic ZnO is on the order of hundreds of milliseconds, limited by the nuclear spectral diffusion process. The nuclear spin coherence time of an isolated indium shallow donor can be extended to few seconds in isotopically and chemically purified quasi-intrinsic ZnO. In this optimal case, the nuclear spin coherence time of an isolated indium shallow donor is only limited by the cross relaxation decoherence process. This study thus shows the great potential of electron and nuclear spin qubits encoded on shallow donors in isotopically and chemically purified quasi-intrinsic ZnO for the implementation of quantum processor and/or quantum memories.     

自旋轨道耦合系统中的自旋流与自旋霍尔效应

作为自旋电子学的重要研究内容,如何在固态系统中产生、操控以及探测自旋流引起了研究人员的广泛兴趣.基于自旋轨道耦合的自旋霍尔效应为在非磁性半导体中产生自旋流提供了一种有效途径.然而,在具有自旋轨道耦合的系统中,自旋流并不守恒.如何理解这点并恰当地表述相应的连续性方程,成为自旋输运研究的基本问题之一.本文主要综述自旋轨道耦合系统中自旋流与自旋霍尔效应方面的研究进展.引入SU(2)规范势后,自旋流满足协变形式的连续性方程,该方程保证了SU(2)Kubo公式在不同规范固定下的自洽性.利用SU(2)场强张量,可以直接得到自旋密度和自旋流在SU(2)外场中受到的白旋力,该力在只有U(1)磁场时对应于Stern-Gerlach力.由于依赖杂质散射的外在自旋霍尔效应很难被利用,内在自旋霍尔效应的概念被提出:在非磁半导体中,U(1)电场会诱导出自旋流并导致系统边缘处的自旋积累.自旋霍尔效应已经在半导体和金属材料中被观察到.虽然在干净的二维电子气中自旋霍尔电导率是一普适常数e/8π,但杂质对它的影响却引起了人们的高度关注.通过引入退相干效应,自旋霍尔效应中杂质效应的一些令人困惑的理论结果,则得到清晰的解释.此外,本文还将介绍具有层间隧穿的双层二维电子气中的自旋输运现象.在能量简并点附近,自旋霍尔电导率和隧穿白旋电导率均会出现共振现象.当两层间的杂质势强度存在差异时,隧穿自旋电导率随门压的变化曲线呈现出非对称性,显示出自旋二极管效应.     

自旋轨道耦合系统中的自旋流与自旋霍尔效应

作为自旋电子学的重要研究内容,如何在固态系统中产生、操控以及探测自旋流引起了研究人员的广泛兴趣。基于自旋轨道耦合的自旋霍尔效应为在非磁性半导体中产生自旋流提供了一种有效途径。然而,在具有自旋轨道耦合的系统中,自旋流并不守恒。如何理解这点并恰当地表述相应的连续性方程,成为自旋输运研究的基本问题之一。本文主要综述自旋轨道耦合系统中自旋流与自旋霍尔效应方面的研究进展。引入SU(2)规范势后,自旋流满足协变形式的连续性方程,该方程保证了SU(2)Kubo公式在不同规范固定下的自洽性。利用SU(2)场强张量,可以直接得到自旋密度和自旋流在SU(2)外场中受到的自旋力,该力在只有U(1)磁场时对应于Stern-Gerlach力。由于依赖杂质散射的外在自旋霍尔效应很难被利用,内在自旋霍尔效应的概念被提出:在非磁半导体中,U(1)电场会诱导出自旋流并导致系统边缘处的自旋积累。自旋霍尔效应已经在半导体和金属材料中被观察到。虽然在干净的二维电子气中自旋霍尔电导率是一普适常数e/8π,但杂质对它的影响却引起了人们的高度关注。通过引入退相干效应,自旋霍尔效应中杂质效应的一些令人困惑的理论结果,则得到清晰的解释。此外,本文还将介绍具有层间隧穿的双层二维电子气中的自旋输运现象。在能量简并点附近,自旋霍尔电导率和隧穿自旋电导率均会出现共振现象。当两层间的杂质势强度存在差异时,隧穿自旋电导率随门压的变化曲线呈现出非对称性,显示出自旋二极管效应。     

Influence of impurity-induced spin-orbit scattering on persistent spin helix

The persistent spin helix discovered in intrinsic spin-orbit coupled systems previously is reexamined using the motion equations of Green's functions by considering the effect of extrinsic impurity-induced spin-orbit coupling. We find both the intrinsic and extrinsic spin-orbit couplings can increase the excitation energy of spin helix. They together can reduce drastically the lifetime of the spin helix, making it severely departure from the ideal infinite value. The effect of impurity density on spin helix is also analyzed. The results may be helpful to understand experimental measurements on spin helix.