Magnetic susceptibility study of Ce in PbCeA (A=Te,Se, S)

The magnetic susceptibility of Pb_1-xCe_xA (A=S, Se and Te) crystals with Ce³⁺ concentrations 0.006≤x≤0.036 was investigated in the temperature range from 2 K to 300 K. The magnetic susceptibility data was found to be consistent with a ²F_5/2 lowest manifold for Ce³⁺ ions with a crystal-field splitting Δ=E(Γ₈)−E(Γ₇) of about 340 K, 440 K and 540 K for Pb_1-xCe_xTe, Pb_1-xCe_xSe, and Pb_1-xCe_xS, respectively. For all the three compounds the doublet Γ₇ lies below the Γ₈ quadruplet which confirms the substitution of Pb²⁺ by Ce³⁺ ions in the host crystals. The observed values for the crystal-field splitting are in good agreement with the calculated ones based on the point-charge model. Moreover, the effective Landé factors were determined by X-band (∼9.5 GHz), electron paramagnetic measurements (EPR) to be g=1.333, 1.364, and 1.402 for Ce ions in PbA, A = S, Se and Te, respectively. The small difference with the predicted Landé factor g of 10/7 for the Γ₇ (J=5/2) ground state was attributed to crystal-field admixture.     

First observation of electronic structure of the even parity boron acceptor states in diamond

We use electronic Raman scattering for studying the band structure of the ns$\mathrm{n}s$ boron acceptor states in diamond. For the first time, the spin–orbit splitting of these acceptor states and the 1s→ns$1s\to \mathrm{n}s$ Lyman series of transitions are observed. The spin–orbit splitting linearly increases with n number. Lyman series exhibit fine structure consisting of four bands each. The energy spacing between series is equal to ∼13 meV$\sim 13\text{meV}$. Evolution of Raman spectra of the boron-doped diamond with increasing boron concentration is shown. Mott transition is revealed in Raman spectrum. Correct values of Luttinger parameters for diamond are specified.     

C42+分子的T  e系统的Jahn-Teller效应与各向异性现象

依据Jahn-Teller效应理论与量子理论,利用群论和对称性分析的方法探讨了具有Td对称性构型的C42+分子的T  e 系统的Jahn-Teller效应与各向异性问题。构建了T  e系统的电声耦合哈密顿量,借助么正平移变换求出了系统的基态与激发态及其能量。结果发现,由于电声耦合作用的缘故,系统发生了Jahn-Teller畸变,畸变导致在系统的势能面上形成了3个具有D2d对称性的势阱。无论系统处在哪一个势阱中,系统原初三重简并的能级都将分裂为两条能级。畸变还导致C42+分子从Td对称性降低到D2d对称性,同时C42+分子的振动频率发生分解,而频率的分解致使C42+分子的各向同性遭到破坏而呈现出各向异性。     

图形化蓝宝石衬底上InGaN/GaN多量子阱发光二极管的光谱特性研究

运用电致发光(EL)和光致发光(PL)实验,分析了图形化蓝宝石衬底(PSSLEDs)和常规平面蓝宝石衬底(C-LEDs)InGaN/GaN多量子阱发光二极管的光谱特性。对比EL谱,发现PSSLEDs拥有更强的光功率和更窄的半峰宽(FWHM),说明PSSLEDs具有较高的晶体质量。其次,PSSLEDs的EL谱半峰宽随电流增加出现了更快的展宽,而这两种LED样品的PL谱半峰宽随激光功率增加呈现了基本相同的展宽变化,说明在相同电流下,PSSLEDs量子阱中载流子浓度更高,能带填充效应更强。另外,随着电流的增加,PSSLEDs和C-LEDs的峰值波长都发生蓝移,且前者的蓝移程度较小,结合半峰宽的对比分析,说明PSSLEDs量子阱中的极化电场较小。最后,对比了PSSLEDs和C-LEDs的外量子效率随电流的变化,发现PSSLEDs拥有更严重的efficiency droop,说明量子阱中极化电场不是导致efficiency droop的主要原因。     

On an efficient splitting‐based method for solving the diffusion equation on a sphere

A novel numerical approach for solving the diffusion problem on a sphere is suggested. By using operator splitting, we develop a new method that allows constructing finite difference schemes of the second and fourth approximation orders in the spatial variables. Both schemes properly ensure the balance of mass and the energy dissipation in the L₂ ‐norm. The schemes are very cheap from the computational standpoint. Numerical results demonstrate the skillfulness of the approach in describing the diffusion dynamics on a sphere. It is shown the method can directly be extended to nonlinear diffusion problems.© 2010 Wiley Periodicals, Inc. Numer Methods Partial Differential Eq 28: 331–352, 2012     

Splitting positive definite mixed element methods for pseudo‐hyperbolic equations

Splitting positive definite mixed finite element (SPDMFE) methods are discussed for a class of second‐order pseudo‐hyperbolic equations. Depending on the physical quantities of interest, two methods are proposed. Error estimates are derived for both semidiscrete and fully discrete schemes. The existence and uniqueness for semidiscrete schemes are proved. © 2010 Wiley Periodicals, Inc. Numer Methods Partial Differential Eq 28: 670–688, 2012     

非简并p型Hg1-xMnxTe单晶(x>0.17)的负磁电阻机理研究

研究磁性半导体中负磁电阻产生机理对正确理解载流子与磁性离子间的sp-d磁交换作用 是非常重要的.通过变温(10---300 K)磁输运和变温(5---300 K)磁化率实验研究了一系列不同Mn含量 非简并p型Hg_1-xMn_xTe单晶(x>0.17)的负磁电阻和顺磁增强效应. 实验结果表明其负磁电阻与温度的关系和磁化率与温度的关系基本一致, 两者都包含一个呈指数型变化的温度函数exp(-K/T).根据磁性半导体的杂质能级理论, 非简并p型Hg_1-xMn_xTe单晶在低磁场范围内出现负磁电阻效应的主要物理机理 为外磁场的磁化效应使得受主杂质或受主型束缚磁极化子的有效电离能减小.     

AlGaN/GaN量子阱中子带的Rashba自旋劈裂和子带间自旋轨道耦合作用研究

首先把本征值方程投影到导带的子空间中, 进而得到AlGaN/GaN量子阱中第一、二子带的Rashba自旋劈裂系数(α ₁, α ₂)和子带间自旋-轨道耦合系数η₁₂. 然后自恰求解薛定谔方程和泊松方程计算了不同栅压的量子阱中的α ₁, α ₂和η₁₂, 并分别讨论了量子阱阱层、左右异质结界面和垒层对它们的贡献. 结果表明可以通过栅压来调节自旋-轨道耦合系数, 子带间自旋轨道耦合系数η₁₂比Rashba自旋劈裂系数α ₁, α ₂小, 但基本在同一数量级.     

Dimension splitting method for the three dimensional rotating Navier-Stokes equations

In this paper, we propose a dimensional splitting method for the three dimensional (3D) rotating Navier-Stokes equations. Assume that the domain is a channel bounded by two surfaces and is decomposed by a series of surfaces ■i into several sub-domains, which are called the layers of the flow. Every interface i between two sub-domains shares the same geometry. After establishing a semi-geodesic coordinate (S-coordinate) system based on ■i , Navier-Stoke equations in this coordinate can be expressed as the sum of two operators, of which one is called the membrane operator defined on the tangent space on ■i , another one is called the bending operator taking value in the normal space on ■i . Then the derivatives of velocity with respect to the normal direction of the surface are approximated by the Euler central difference, and an approximate form of Navier-Stokes equations on the surface ■i is obtained, which is called the two-dimensional three-component (2D-3C) Navier-Stokes equations on a two dimensional manifold. Solving these equations by alternate iteration, an approximate solution to the original 3D Navier-Stokes equations is obtained. In addition, the proof of the existence of solutions to 2D-3C Navier-Stokes equations is provided, and some approximate methods for solving 2D-3C Navier-Stokes equations are presented.