等离子体效应对类氦氖Kα线系电偶极辐射的影响

采用离子球模型，通过自洽求解Boltzmann方程和Poisson方程，得到类氦氖离子Kα线系的两条电偶极辐射光谱能量随等离子体环境的漂移.结果显示，Kα线系电偶极谱线随等离子体电子密度增大发生红移，红移量与等离子体电子密度有近似的正比关系；随着等离子体电子温度的降低，光谱红移对等离子体电子密度的敏感性增大.另外，所研究的两条谱线间的能量间隔随等离子体电子密度的增大而减小，减小量随等离子体电子密度的变化也呈现出近似的线性规律.值得注意的是，类氦氖Kα线系中两条电偶极谱线分别为互组合线与共振谱线，而其能量差就是1s2p(³P₁)的交换能，因此进一步发现能级中交换能将随等离子体环境变化的规律.所观察到的光谱红移和精细结构分裂在高密度等离子体中都有明显的变化，对探索高密度等离子体的诊断新方法有重要意义. 关键词： 光谱漂移 交换能 等离子体 类氦离子     

Relativistic nuclear and neutron matter at finite temperatures

Nuclear matter as well as neutron matter is studied in the framework of a relativistic nuclear field theory at finite temperature. A spectral representation for the two-point Green's function at finite temperature and finite density is constructed. The bulk properties of the interacting system are calculated in the Hartree and Hartree-Fock approach. In additionσ ³- andσ ⁴-self-interactions have been taken into account. We present and discuss the results of hot and dense matter for temperaturesT≦ 50 MeV and densitiesθ≦6θ ₀ (ρ ₀≈0.17 fm^?3) using six different model parameter sets.     

Influence of interlayer coupling and intra-layer Coulomb interaction on electronic transport in bilayer graphene

Calculations of renormalized perpendicular conductivity within Kubo formula employing single particle temperature dependent Green's function formalism for bilayer graphene has been attempted. On the basis of numerical analysis, perpendicular conductivity as a function of temperature, interlayer coupling, onsite Coulomb interaction and carrier concentration per site has been analyzed for both AA- and AB-stacked bilayer graphene. It is found that perpendicular conductivity increases with interlayer coupling and also with temperature at low temperatures while at higher temperatures, there is saturation in perpendicular conductivity. Influences of onsite Coulomb interaction and carrier concentration per site on perpendicular conductivity is just opposite to each other while onsite Coulomb energy suppresses the rate of increase of σ_⊥/σ_⊥0 with temperature, on the other hand increase in carrier density per site enhance this rate significantly. Finally, theoretically obtained results on temperature dependent perpendicular conductivity are viewed in terms of electronic transport data as well as recent theoretical works available in bilayer graphene.     

n-SiC的电子拉曼散射及二级拉曼谱研究

研究了利用离子注入法得到的掺氮n-SiC拉曼光谱. 理论线形分析表明,与4H-SiC相比,6H-SiC中LO声子等离子体激元耦合模(LOPC模)拉曼位移随自由载流子浓度变化较小. 5145nm激发光下得到的电子拉曼散射光谱表明,k位处由1s(A₁)到1s(E)的能谷轨道跃迁带来的拉曼谱6H-SiC中有四条,4H-SiC中有二条;高频6303及635cm^-1处观察到的谱线被认为与深能级缺陷有关. 最后,利用纤锌矿型结构二级拉曼散射选择定则指认了6 关键词： 碳化硅 电子拉曼散射 轨道能谷分裂 倍频谱     

Stark broadening and shift of some isolated spectral lines of singly ionised earth alkaline metals

Using aZ pinch discharge as a plasma source the profiles and shifts of some prominent ion lines of earth alkaline metals were measured and compared with Stark broadening theories and other experimental results. An electron density of 3.1 to 10.3×10¹⁶ cm^?3 was determined by the laser interferometry, while the electron temperature in the range 25100 to 34800 °K were measured from relative intensities of spectral lines. Comparison of reported experimental shifts and widths with the theories both semi-classical and quantum mechanical shows good agreement. It was also found that Griem's semi-empirical formula is useful and accurate for line widths evaluation.     

Effects of edge chemistry doping on graphene nanoribbon mobility

Doping of semiconductor is necessary for various device applications. Exploiting chemistry at its reactive edges was shown to be an effective way to dope an atomically thin graphene nanoribbon (GNR) for realizing new devices in recent experiments. The carrier mobility limited by edge doping is studied as a function of the GNR width, doping density, and carrier density by using ab initio density functional and parameterized tight binding simulations combined with the non-equilibrium Green's function formalism for quantum transport. The results indicate that for GNRs wider than about 4 nm, the mobility scales approximately linearly with the GNR width, inversely proportional to the edge doping concentration and decreases for an increasing carrier density. For narrower GNRs, dependence of the mobility on the GNR width and carrier density can be qualitatively different.     

Phase fluctuations and pseudogap phenomena

This article reviews the current status of precursor superconducting phase fluctuations as a possible mechanism for pseudogap formation in high-temperature superconductors. In particular we compare this approach which relies on the two-dimensional nature of the superconductivity to the often used T-matrix approach. Starting from simple pairing Hamiltonians we present a broad pedagogical introduction to the BCS–Bose crossover problem. The finite temperature extension of these models naturally leads to a discussion of the Berezinskii–Kosterlitz–Thouless superconducting transition and the related phase diagram including the effects of quantum phase fluctuations and impurities. We stress the differences between simple Bose–BCS crossover theories and the current approach where one can have a large pseudogap region even at high carrier density where the Fermi surface is well-defined. Green's function and its associated spectral function, which explicitly show non-Fermi liquid behavior, is constructed in the presence of vortices. Finally different mechanisms including quasi-particle–vortex and vortex–vortex interactions for the filling of the gap above T_c are considered.     

Electromagnetic volume scattering in the half-space: a moment-method analysis without Sommerfeld integrals or their approximations

Abstract

Traditionally, in moment-method analyses of electromagnetic scattering, the elements of the impedance matrix are calculated as convolutions of the basis elements with the appropriate dyadic Green's function. However, for scattering in the half-space, the vertical and azimuthal copolar terms of the Green's function require evaluation of Sommerfeld integrals which are computationally burdensome. In this paper, it is shown that, in populating the impedance matrix for the half-space problem, evaluation of Sommerfeld integrals is, in fact, not necessary. For monochromatic excitation, the plane-wave expansion of the scattered field constitutes a Fourier transform, in the horizontal plane, of a vector spectral function. This vector function results from the convolution, in the vertical dimension, of the respective angular spectra of the Green's function and the equivalent current. On application of the moment method, through the Weyl identity, the impedance-matrix elements corresponding to the singular terms of the Green's function are convolutions in the horizontal plane of spherical potentials, and Fourier transforms of scalar spectral functions. These scalar functions are derived from the basis elements and, with a judicious choice of basis, they are well behaved and of compact support, and consequently their Fourier transforms can be computed as FFTs.     

低温高压下的Na5Eu(WO4)4的发光和晶体场参数

用低温金刚石对顶砧高压显微光谱系统在20—300K低温和0—10GPa高压范围内研究了白钨矿型化学计量的基质发光晶体四钨酸铕钠Na₅Eu(WO₄)₄中Eu³⁺的发光.确定了Eu³⁺荧光谱线和能级在低温下的压力移动率.它随温度变化,表明温度和压力对Eu³⁺谱线作用不是独立无关的.按晶体场理论简化方法推导了能级的晶体场参数表达式,并按实验数据拟合出在不同低温下晶体场参数随压力的移     

Stark broadening parameters of the 381.96 nm He I line

Stark width (W) and shift (d) of the neutral helium (He I) 381.96 nm spectral line in the high lying 2p-6d transition has been measured in the optically thin linear, low-pressure, pulsed arc discharge operated in the helium at 50 000 K electron temperature and 6.1 x 10²² m^-3 electron density. These values are the first experimentally obtained W and d related to this line. Unfortunately, comparison with theoretical results is not possible due to the fact that only one existing theoretical calculations has been done at a 10¹⁹ m^-3 electron density only. We have found negative line shift (toward the blue) that agree well with existing theoretical predictions.Received: 19 February 2004, Published online: 4 May 2004PACS: 52.70.Kz Optical (ultraviolet, visible, infrared) measurements - 32.70.Cs Oscillator strengths, lifetimes, transition moments - 32.70.-n Intensities and shapes of atomic spectral lines     

Two-time Green's function method in quantum electrodynamics of high-Z few-electron atoms

The two-time Green's function method in quantum electrodynamics of high-Z few-electron atoms is described in detail. This method provides a simple procedure for deriving formulas for the energy shift of a single level and for the energies and wave functions of degenerate and quasi-degenerate states. It also allows one to derive formulas for the transition and scattering amplitudes. Application of the method to resonance scattering processes yields a systematic theory for the spectral line shape. The practical ability of the method is demonstrated by deriving formulas for the QED and interelectronic-interaction corrections to energy levels and transition and scattering amplitudes in one-, two-, and three-electron atoms. Numerical calculations of the Lamb shift, the hyperfine splitting, the bound-electron g factor, and the radiative recombination cross section in heavy ions are also reviewed.     

Das Konsistenzproblem der Greenfunktion eines A-Hyperons in Kernmaterie

An iteration procedure is derived for determining a self-consistent approximation for the one-particle Green's function in any order, starting from perturbation theory. This method is used to calculate the second Born approximation of the self energy of a Λ-particle in nuclear matter. After one iteration the approximation is nearly self-consistent. The value of the binding energy of the Λ-paiticle is only slightly decreased from the value of perturbation theory. Because of the vanishing particle density of the Λ-hyperon the quasiparticle energy depends on the square of the momentumk, the width of the spectral function is proportional tok ⁴ and the imaginary part of the self energy operator is proportional to (Ω-μ)^5/2 for Ω approaching the chemical potential μ.     

Ab-initio relativistic density functional calculations for spectral line shifts of Rb atoms in liquid helium

Accurate laser spectroscopic studies of the principal resonance transitions in Rb and Cs atoms embedded in liquid helium have shown appreciable line shifts and change in line profiles. A pilot attempt has been made here to compute ab-initio the spectral line shift of the resonance excitation lines in Rb under such a confinement. Relativistic density functional theory (RDFT) within local density approximation (LDA) has been adopted. A model cluster of fourteen helium atoms surrounding the central Rb is assumed. With an optimized radius of the cluster of 5.15 Å the RLDA estimate of the blue shift of the lowest ²S → ²P excitation line of Rb comes out to be 15.4 nm which compares very well with the experimental value of 16.4 nm.     

Das Emissionsspektrum gebundener Excitonen in Zinkoxydkristallen in Abhängigkeit von Temperatur und uniaxialer Verspannung

The recombination radiation of bound excitons in ZnO-crystals (spectral range 3,38–3,35 eV at 4.2 °K) and the adjacent phonon-assisted spectrum have been studied at temperatures between 4.2 °K and 90 °K. The phonon-assisted spectrum changes its structure at about 30 °K. With increasing temperature the exciton lines shift toward smaller quantum energies (ΔE～T ²) and their half widthH increases (H～T ²). The line shift is explained by a band gap variation due to deformation potential coupling of the holes toTA phonons. The line width is explained by broadening of an infinitely sharp line under the influence of the mean square fluctuation of thermally generated crystal deformations. The influence of uniaxial stress on the spectral positions of the lines has been studied.     

On the Cd III spectrum in a pulsed helium discharge

On the basis of the spectral line intensity relaxation during the plasma decay, fifty six spectral lines between 219 nm and 330 nm in the cadmium (Cd) spectrum were identified as Cd III (doubly ionized) or Cd IV (triply ionized) lines. The measured Stark widths of twelve, the most intense spectral lines around 315±15 nm with well defined profiles, are presented. Investigated spectral lines originate from the high lying energy levels, not classified up to now. A linear low-pressure pulsed arc was used as an optically thin plasma source. A pulsed discharge was produced in a pyrex discharge tube. Helium was chosen as the carrier gas. The cadmium atoms were sputtered from the thin cadmium cylindrical plates located in the homogeneous axial part of the discharge tube. The helium plasma was operated at electron temperatures up to 19 000 K and 1.1 × 10²³ m^-3 electron density. The stepwise ionization processes via the high lying singly ionized (Cd II) energy levels, populated well due to the Penning and charge exchange effects, provide high density of the Cd III (and Cd IV) ions in our helium plasma. The temporal evolutions of the spectral line intensities were monitored using a spectrograph and an ICCD camera as a highly sensitive detection system.     

Density Measurements from the Asymmetry of the Lyman ζ Line in a Vacuum Spark Lithium Discharge

A lithium spectrum is obtained form vacuum spark discharges using a grazing-incidence flat-field spectrometer. Hydrogen-like lines up to Lyman η are identified in the spectrum. The spectrum is analyzed, and it is found that the experimental line widths increase along the Lyman series. An asymmetry between the blue and red wings appears in the profile of the Lyman ζ line, and becomes significant in the profile of the Lyman ? line. A relatively new method is used to estimate an electron density of 1 ± 0.4 × 10¹⁸cm^?3 from the experimental degree of asymmetry between the blue and the red wings of the Lyman ζ line. This result is compared with an analysis of the experimental widths of two optically thin lines, namely, Lyman δ and Lyman ζ. In this analysis an electron density of 1.2±0.5 × 10¹⁸cm^?3 is deduced. The principal quantum number of Lyman η (n=8) is used in the Inglis-Teller formula for the last line seen before the merging of the lines with the continuum, and the estimated electron density is found to be 2.0 × 10¹⁸cm^?3 for the lithium plasma. Thus, it is demonstrated that the new method employing the asymmetry of the lineshapes in dense plasmas yields results consistent with the analysis of the widths of the lines. However, it requires obtaining the profile of just one spectral line, which is a great advantage. The reference data on the Stark broadening of the Lyman ζ line is also tabulated, which was previously unavailable in the literature.     

Slave bosons in radial gauge: A bridge between path integral and Hamiltonian language

We establish a correspondence between the resummation of world lines and the diagonalization of the Hamiltonian for a strongly correlated electronic system. For this purpose, we analyze the functional integrals for the partition function and the correlation functions invoking a slave boson representation in the radial gauge. We show in the spinless case that the Green's function of the physical electron and the projected Green's function of the pseudofermion coincide. Correlation and Green's functions in the spinful case involve a complex entanglement of the world lines which, however, can be obtained through a strikingly simple extension of the spinless scheme. As a toy model we investigate the two-site cluster of the single impurity Anderson model which yields analytical results. All expectation values and dynamical correlation functions are obtained from the exact calculation of the relevant functional integrals. The hole density, the hole auto-correlation function and the Green's function are computed, and a comparison between spinless and spin 1/2 systems provides insight into the role of the radial slave boson field. In particular, the exact expectation value of the radial slave boson field is finite in both cases, and it is not related to a Bose condensate.     

Reaction field model with free volume for the NMR chemical shift of129Xe dissolved in organic solvents

The temperature dependence of the NMR chemical shift of¹²⁹Xe dissolved in liquid alkanes is examined in the context of the reaction field model. An essential feature of the theory is the inclusion of the temperature dependence of the density of thesolvent. The theory of free volume for liquids is incorporated into the reaction field model to account for this temperature dependence. Comparison of the theory with previously reported measurements indicates the sensitivity of the¹²⁹Xe chemical shift to the free volume of liquids. Incorporation of free volume improves the agreement between measurement and theory for branched alkane solvents, and resolves the origin of the 62 ppm intercept in the plot of reaction field as a function of¹²⁹Xe chemical shift for the n-alkanes.     

Functional Integral Approach to a Many Fermion System with Bound States

The equation of state for a dense system of interacting Fermions is derived using functional integral technique. To investigate the formation of bound states, a Hubbard-Stratonovich transformation is applied which expresses the action as functional of pair fields. The evaluation of the partition function in lowest orders with respect to the pair fields leads to a result which can be interpreted as the contribution of two-particle states, accounting for density corrections as Pauli blocking and self-energy shift. Comparison is performed with results for the equation of state of hot dense matter (plasmas, nuclear matter) obtained within a Green's function approach.