CuGeO3晶体自旋-佩尔斯态的EPR

报道了CuGeO₃单晶在96GHz频率,1 4K温度下的电子顺磁共振(EPR)实验,测量了主轴g因子.导出了Cu²⁺离子在CuGeO₃自旋佩尔斯系统中的混合d轨道基态波函数.采用近似自洽场方法计算了CuGeO₃的主轴g因子.使实验结果得到了解释.     

单晶变角EPR谱的解释I.掺Cr3+铝铵矾单晶的EPR

对本征场的计算方法作了新的分析,提出了新的计算方案,根据这方案编写了程序,并应用这一程序对掺Cr³⁺铝铵矾单晶变角的EPR谱作了解析,得到了更加可靠更为准确的自旋-Hamilton参数;D=0.04845cm^-1,g_x=g_y=1.9761,g₂=1.9752.用上述参数,对各个离子不同角度下的广义本征场计算的共振磁场与实验数据拟合很好.充分说明采用此法处理EPR的优越性.     

晶体NiF2的吸收光谱和电子顺磁共振谱的一种完全对角化计算

采用半自洽场(semi-SCF)自由Ni²⁺的d轨道波函数、点电荷-偶极子模型和Ni²⁺-6X^-(X=F,Cl,Br,I)络合物的μ-κ-α模型,建立结构参数与光谱、电子顺磁共振(EPR)谱(零场分裂D,E和顺磁g因子)之间的定量关系.利用能量矩阵完全对角化方法(CDP)和高阶微扰方法,统一解释NiF₂晶体的局部结构、吸收光谱和电子顺磁共振谱(EPR).比较两种方法计算得到的零场分裂D,E和顺磁g因子.结果表明:①高阶微扰方法算出的D,E值误差大;②能量矩阵完全对角化方法(CDP)算出的D,E值、光谱、顺磁g因子的值都与实验符合很好.     

三角对称晶场下d8电子组态的EPR参量的普遍公式及其应用

本文考虑到d⁸电子组态中所有自旋三重态和自旋单态对基态的影响,用高阶微扰法导出了d⁸电子组态在三角对称晶场下光谱和基态EPR普遍公式。发现在三角对称晶场下,d⁸电子组态离子的g_⊥ > g_‖或g_⊥ < g_‖和D > 0或D < 0是以立方对称晶场为界,晶体中顺磁离子的配体沿C₃轴伸长或压缩所致。利用所得公式计算了NiCl₂和NiSiF₆·6H₂O晶体的EPR参量,其结果与实验吻合较好。     

卷积差方法在过渡金属离子EPR谱中的应用

用卷积差方法提高EPR谱的分辨率,可以从多种过渡金属离子的迭加谱中直接测量出不同离子的波谱参数a_R、a_⊥、g_R和g_⊥,该方法还可提高各向异性g因子的测量精度.     

立方对称晶场中6S(3d5)态离子的磁相互作用及其自旋哈密顿参量的微观起源

基于完全对角化方法(complete diagonalization method, CDM), 研究了⁶S(3d⁵)态离子在立方对称晶场中的磁相互作用,分析了自旋哈密顿参量(a, g,Δg)的微观起源.研究中除了考虑研究者通常考虑的SO(spin-orbit)磁相互作用外,同时考虑了SS(spin-spin),SOO(spin-other-orbit),OO(orbit-orbit)磁相互作用.研究表明：⁶S(3d⁵)态离子在立方对称晶场中的自旋哈密顿参量起源于五种机理,即SO机理,SS机理,SOO机理,OO机理以及SO-SS-SOO-OO联合作用机理.文中研究了五种机理的相对重要性,结果表明：SO机理与SO-SS-SOO-OO联合作用机理在五种机理中最为重要.尽管SS,SOO,OO磁相互作用单独作用时对自旋哈密顿参量的贡献很小,但它们的联合作用SO-SS-SOO-OO机理对自旋哈密顿参量的贡献非常可观.此外研究表明：零场分裂参量a主要来自纯自旋四重态及自旋二重态与自旋四重态联合作用的贡献,而Zeemang(或者Δg)因子主要来自纯自旋四重态的贡献.纯自旋二重态对自旋哈密顿参量a与g(或者Δg)的贡献为零.在我们所选择的晶场区域,发现下列关系始终成立：a>0,a(-|Dq|)<a(|Dq|),g(-Dq)=g(Dq),a(-Dq,-ξ_d,B,C)=a(Dq,ξ_d, B,C),Δg(-Dq,-ξ_d, B, C)=Δg(Dq,ξ_d, B, C).作为本文理论的应用,研究了四种典型的Mn²⁺掺杂晶体材料,即Mn²⁺:KZnF₃,Mn²⁺: RbCdF₃,Mn²⁺: MgO,Mn²⁺: CaO,理论与实验测量符合很好. 关键词： 自旋哈密顿参量 6S(3d⁵)态离子')" href="#">⁶S(3d⁵)态离子 磁相互作用 完全对角化方法(CDM)     

外磁场对(Ga，Mn)As有效g因子的影响

利用时间分辨Kerr旋光技术测量低温下稀磁半导体Ga_0.937Mn_0.063As中光注入极化载流子的自旋进动信号,并观察到自旋极化载流子的有效g因子值随外磁场的增强而增大的反常现象.这归结于磁场导致局域化空穴转化为非局域化空穴,从而使自发磁化强度增强,有效g因子值增大.基于此物理图像,进一步给出了(Ga,Mn)As的有效g因子与外磁场的关系式. 关键词： 时间分辨Kerr旋光测量 Zeeman效应 Ruderman-Kittel-Kasuya-Yosida模型     

计算晶体CdCl2:Ni2+的电子顺磁共振谱的完全对角化和高阶微扰方法

采用半自洽场自由Ni²⁺的d轨道波函数和点电荷-偶极子模型,建立局部结构、光谱与电子顺磁共振(EPR)谱(零场分裂D和顺磁g因子)之间的定量关系.利用完全对角化方法(CDP)和高阶微扰方法,统一解释CdCl₂:Ni²⁺晶体的局部结构、光谱和电子顺磁共振谱(EPR),并比较两种计算方法得到的结果.     

InAs量子点中自旋-轨道相互作用下电子自旋弛豫的参量特征

本文在处理InAs单电子量子点哈密顿模型时,将自旋-轨道(SO)相互作用作为微扰项,计算在Fock-Darwin本征函数下SO相互作用的矩阵元,利用其对能级和波函数的二阶修正,并且考虑新的能级对g因子和有效质量m^*的影响,计算得到在声子协助下电子的自旋弛豫率Γ的表达式.给出了InAs量子点中声子协助的电子自旋弛豫率Γ对于限制势频率ω₀、温度T、纵向高度z_{0关键词： 自旋弛豫率 自旋-轨道(SO)相互作用 InAs量子点 Fock-Darwin本征函数}     

CaBa-铝酸盐玻璃中Cr4+谱线宽度随温度的变化

测量了15~300K温度范围内57.5%Al_1.5O-35%CaO-7.5%BaO玻璃中四价铬的发射光谱.这种材料中铬离子的能级处于Tanabe-Sugano图上弱场范围中,最低的激发态是³T₂,发射谱是一个宽带.按照单频近似理论拟合低温下的光谱,得到³T₂能级的零声子线位置E_zp=8400cm^-1,声子能量tω=320cm^-1,黄昆因子S=358.尽管单频近似能够较好地描述低温下的线形,发射光谱宽度随温度的变化却与单频近似理论的结果不符.讨论了这种差别的原因,认为可能的解释是与激发态耦合的声子能量大于与基态耦合的声子能量.     

Study on the local structure of (CrO6) complex in garnet crystals by optical and EPR spectrum

The local lattice structure distortions for YAG and YGG systems doped with Cr³⁺ have been investigated by the d³ configuration complete energy matrices which contain the Zeeman energy besides the electron–electron interaction, the trigonal crystal field as well as the spin–orbit coupling interaction. The local lattice structure parameters R and θ of (CrO₆)⁹⁻ complex are determined for Cr³⁺ in YAG and YGG systems, respectively. The calculated results show that the local lattice structures have expansion distortions, which almost tend to the same after distortions. Meanwhile, the EPR parameter D, g factors (g_||, g) and optical spectrum of these systems have been interpreted uniformly by quantitative calculation. It is shown that the effect of the orbit reduction factor k on g factors (g_||, g) cannot be ignored.     

Diffusion of W on A W(211) plane

The diffusion of W on a (211) plane of a W field emitter has been re-examined by means of the fluctuation autocorrelation method. Diffusion along channels yielded E = 16.8 ± 0.5 kcal, D₀ = (3 ± 1) × 10⁻⁵ cm² s⁻¹. For diffusion across channels E =6.6 kcal, D₀ = 4 × 10⁻⁹cm² s⁻¹ at T < 752 K, and E = 24 kcal, D₀ = 5 × 10⁻⁴ cm² s⁻¹ at T > 752 K. The results for diffusion along channels yield E and D₀ values intermediate between recent results by Wang and Ehrlich [Surf. Sci. 206 (1988) 451] using field ion microscopy (E = 19 kcal, D₀ = 7.7 × 10⁻³ cm² s⁻¹) and Tringides and Gomer [J. Chem. Phys. 84 (1986) 4049], using the same method as the present work but a larger slit (E = 13.3 kcal, D₀ = 7 × 10⁻⁷ cm² s⁻¹). The results for cross channel diffus good agreement with those of Tringides and Gomer below 752 K, where these authors stopped. The new high temperature results suggest that the channel wall exchange mechanism postulated by Tringides and Gomer for cross channel diffusion at low T gives way to diffusion by climbing over the channel walls with higher E but also higher D₀ above 752 K. Possible reasons for the discrepancies between these three sets of results and the absence of cross channel diffusion in the work of Wang and Ehrlich are briefly discussed.     

Simulations of migration, fragmentation and coalescence of non-wetting fluids in porous media

A model based on invasion percolation was used to simulate the migration on a non-wetting fluid through a porous medium filled with an immiscible wetting fluid under the influence of a gradient such as that provided by gravity. The migrating fluid clusters undergo both fragmentation and coalescence. The fragment size distribution obtained from two-dimensional simulations in which the gradient g is slowly increased from 0 can be represented by the scaling form N_s(g)s^-2ƒ(s|g|^-z where z=1+(D−1)ν(ν+1). Here D is the fractal dimensionality of invasion percolation, with trapping, and ν is the ordinary percolation correlation length exponent.     

Theoretical studies of spin-Hamiltonian parameters for Ni ions in CsMgX3 (X=Cl, Br, I) crystals from the two-mechanism model

In this paper, the high-order perturbation formulas of spin-Hamiltonian (SH) parameters (g factors g, g and zero-field splitting D), including both the crystal-field (CF) and for the first time charge-transfer (CT) mechanisms, are established for 3d⁸ ions in trigonal octahedral clusters. By using these formulas, the SH parameters of Ni²⁺ ions in CsMgX₃ (X=Cl, Br, I) crystals are calculated. The results are consistent with the experimental values. The calculations suggest that the sign of Q^CT (Q=Δg, Δg or D, where the g-shift Δg_i=g_i−g_e, g_e≈2.0023 is the value of free-electron) due to CT mechanism is the same as that of the corresponding Q^CF due to CF mechanism, and the relative importance of CT mechanism (characterized by Q^CT/Q^CF) increases with the increasing atomic number of ligand X. So, for the 3dⁿ ML_m clusters with ligand having large atomic number, the reasonable theoretical explanations of all SH parameters should take both CF and CT mechanisms into account. The defect structure of (NiX₆)⁴⁻ impurity centers in CsMgX₃:Ni²⁺ crystals is also considered in our model.     

Optical absorption, disorder and the Anderson transition

The optical gap, E_g, of amorphous indium-oxide films is measured as a function of static disorder near the metal-insulator transition. On the insulating side of the transition the optical gap obeys a scaling relation, ΔE_g = -E_*Δg where E_* is of the order of the Fermi energy of the given sample and g≡K_Fl. These results are ascribed to the continuous shift of the mobility-edge in the conduction band with disorder.     

Resummations with renormalon effects for the hadronic vacuum polarization contribution to the muon (g−2)

The hadronic vacuum polarization contribution to the muon (g−2) value is calculated by considering a known dispersion integral which involves the R_e⁺e⁻(s) ratio. The theoretical part stemming from the region below 1.8 GeV is the largest contribution in our approach, and is calculated by using a contour integral involving the associated Adler function D(Q²). In the resummations, we explicitly take into account the exactly known renormalon singularity of the leading infrared renormalon in the usual and in the modified Borel transform of D(Q²), and map further away from the origin the other renormalon singularities by employing judiciously chosen conformal transformations. The renormalon effect increases the predicted value of the hadronic vacuum polarization contribution to the muon (g−2), and therefore diminishes the difference between the recently measured and the SM/QCD-predicted value of (g−2). It is also shown that the total QED correction to the hadronic vacuum polarization is very small, about 0.06%.     

Diffusion of silicon in Fe-based amorphous and crystalline alloys

The segregation rate of silicon was measured in three different Fe-based amorphous and crystallized alloys with different silicon contents: 3.5, 5 and 9 at%. Analysis of the segregation kinetics yielded the diffusion activation energies E, as well as the frequency factors D₀. A linear dependence was found between In D₀ and E. In general, the D₀ and E values were lower for the amorphous specimens than for the crystalline ones, were independent of silicon content and are explained in terms of an oversaturated concentration of structural defects. In the crystalline specimens, diffusion behaviour was influenced by silicon content near the solubility limit of silicon in iron.