高阶阈值上电离的量子电动力学理论

用非微扰量子电动力学理论研究一个由再散射产生的高阶阈值上电离（ATI）.利用形式散射理论给出了高阶ATI谱的解析形式，并且讨论了在高阶ATI中不同ATI通道的干涉效应和光电子以不同角度入射时的高阶ATI谱. 关键词： 阈值上电离 再散射 跃迁概率     

利用双色激光场下阈上电离谱鉴别H3^2+两种不同分子构型

我们最近证明,利用红外和深紫外双色激光场,SF6分子的结构信息可以通过其电离谱上的相干条纹获得[arXiv,1912.08499(2019)].在本文中,我们利用该方法考察了两种不同几何结构的分子离子H32+ 在激光场中的直接阈上电离(ATI)过程.通过与单色激光场中电离谱的比较发现,双色激光场的电离谱可以分辨分子的不同几何结构.由相干条件导出的公式可以很好地解释直接ATI动能谱和动量谱中的干涉条纹.此外,还发现通过改变分子核间距或改变激光强度可以改变电离谱的形状.由此可以推断,双色激光场诱导的ATI谱具有鉴别分子不同构型的能力,对复杂分子的几何结构成像具有一定的参考意义.     

Neutralization and Detachment in H^＋-H^- Collisions

The cross sections for neutralization and detachment in H^＋-H^- collisions in the energy range from 1.0 to lOO keV/u are calculated using the two-centre atomic orbital close-coupling （TC-AOCC） method. The results are compared with the available experimental and theoretical data. It is found that the neutralization cross section agrees well with the experimental data by Schon et al. [3. Phys. B 20 （1987） L759] and Melchert et al., [J. Phys. B 32 （1999） L139] especially at low energies. However, for the detachment process, our calculated cross section lies between the experimental data by Melchert et al. and by Peart et al. [J. Phys. B 9 （1976） 3047] for the energy below 15keV/u. Above this energy, our result is smaller than the two experimental data. It is worth pointing out that there exists a large difference between these two experimental data and it is difficult to judge which data is more accurate. Therefore, a high-precision measurement for detachment cross sections is expected to resolve this discrepancy and to test the theoretical calculations.     

阈上电离过程中光电子角分布的精细结构

应用非微扰散射理论并考虑自发辐射 ,研究了阈上电离过程中光电子的角分布。由于自发辐射的影响 ,电子的角分布具有精细结构 ,成功地解释了Nandor等人的实验观测。     

First principles analysis of the MgAl2O4:Ni absorption spectrum

Analysis of the energy-level scheme and absorption spectrum of the Ni²⁺ ion in MgAl₂O₄ was performed. The recently developed first-principles approach to the analysis of the absorption spectra of impurity ions in crystals based on the discrete variational multi-electron (DV-ME) method [K. Ogasawara, et al., Phys. Rev. B 64 (2001) 115413) was used in the calculations. The method is based on the numerical solution of the Dirac equation; no phenomenological parameters are used in the calculations. As a result, complete energy-level scheme of Ni²⁺ and its absorption spectra were calculated, assigned and compared with experimental data on the ground and excited state absorption spectra. Numerical contributions of all possible electron configurations into the calculated energy states were determined. By performing analysis of the molecular orbitals population, numerical contributions of the oxygen 2p- and 2s-orbitals into the 3d molecular orbitals were determined.     

Raman Investigation of BaWO4-II Phase under Hydrostatic Pressures up to 14.8GPa

The BaW04-17 phase is synthesized at 5.0 GPa and 610~C with a cubic-anvil apparatus and identified by XRD. Raman scattering measurement is carried out to investigate the phase behaviour of a pure BaW04-Ⅱ phase （space group P21/n, Z = 8） under hydrostatic pressures up to 14.8 GPa at ambient temperature. In each spectrum recorded for this phase, 27 Raman modes are observed, and all bands shift toward higher wavenumber with a pressure dependence ranging from 3.8 to 0.2 cm- 1/GPa. No pressure-driven phase transition occurs in the entire pressure range in this study. Our results indicate that the previously reported high pressure phase of Ba WO4 at pressure above about 10 GPa and room temperature （Errandonea et al. Phys. Rev. B 73（2006）224103） is not the BaW04-Ⅱ phase.     

Above-threshold ionization photoelectron spectrum from quantum trajectory

Many nonlinear quantum phenomena of intense laser-atom physics can be intuitively explained with the concept of trajectory. In this paper, Bohmian mechanics (BM) is introduced to study a multiphoton process of atoms interacting with the intense laser field: above-threshold ionization (ATI). Quantum trajectory of an atomic electron in intense laser field is obtained from the Bohm-Newton equation first and then the energy of the photoelectron is gained from its trajectory. With energies of an ensemble of photoelectrons, we obtain the ATI spectrum which is consistent with the previous theoretical and experimental results. Comparing BM with the classical trajectory Monte-Carlo method, we conclude that quantum potential may play a key role to reproduce the spectrum of ATI. Our work may present a new approach to understanding quantum phenomena in intense laser-atom physics with the image of trajectory.     

Molecular-orbital X-rays from 1 GeV 208Pb + 208Pb and 209Bi + 209Bi collisions

We have measured the spectra of continuum X-rays above the characteristic K lines for 4.5 to 4.8 MeV/N ²⁰⁸₈₂Pb → ²⁰⁸₈₂Pb, Pb → Bi, Bi → Pb and Bi → Bi collisions. Above ≈400 keV X-ray energy the spectral shape and intensity agree roughly with calculations of Kirsch et al. for the 1sσ molecular-orbital (MO) X-ray spectrum from Pb-Pb. Deviations from the theory below ≈400 keV suggest transitions to other MO's.     

高阶CIP数值方法及其在相关物理问题中的应用

利用函数的高阶空间导数值构建其高次插值,得到高阶CIP(Constrained Interpolation Profile)数值算法,并在此基础上模拟研究等离子体物理中著名的伏拉索夫-泊松(Vlasov-Poisson)方程相关物理问题.高阶CIP数值方法具有更高数值精度,从而可以在同等精度的情况下减少计算格点数,加速数值计算速度.     

Crystallization kinetics study of Pb4.3Se95.7 chalcogenide glass using DSC technique

Differential scanning calorimetry (DSC) technique was used to study the kinetics of amorphous to crystalline transformation in Pb_4.3Se_95.7 chalcogenide glass. Non-isothermal measurements were performed at different heating rates (5-60 K/min). The activation energy of crystallization was determined by analyzing the data using Matusita et al. method. A strong heating rate dependence of the activation energy was observed. The isoconversional methods of Kissinger-Akahira-Sunose (KAS) and Vyazovkin confirm that the activation energy of crystallization is not constant but varies with the degree of crystallization and hence with temperature. This variation indicates that the transformation from amorphous to crystalline phase in Pb_4.3Se_95.7 is a complex process involving different mechanisms of nucleation and growth.     

On the room-temperature ferromagnetism in (ZnO)0.98(MnO2)0.02

Room-temperature ferromagnetism (RTFM) is investigated in the polycrystalline bulk (ZnO)_0.98(MnO₂)_0.02 samples prepared by a modified solid-state sintering route. Successive sintering of a sample was carried out in air at different temperatures in the range of 400-1000 °C. The study of magnetization and phase-investigation in the sample was carried out after each sintering step. The progressive suppression of impurities and the consequent reduction in RTFM is clearly observed in the samples with increase in the sintering temperature up to 800 °C. The subsequent successive sintering of the (ZnO)_0.98(MnO₂)_0.02 sample up to 1000 °C yields fully paramagnetic sample exhibiting wurtzite structure. The studies support the conjecture (Kundaliya et al., Nat. Mater. 3 (2004) 709 [18]) that RTFM in this system has an origin related to a randomly distributed impurity phase produced by local dissolution of ZnO and MnO₂.     

Solitary-waves and low temperature conductivity in the 1-D compounds K2Pt(CN)4X0.3−3.2H2O (X = Br, Cl)

We report careful conductivity measurements on KCP(Br) and KCP(Cl) in the low temperature region. We find that below 50 K, the activation energy lowers to a value which is inconsistent with the Peierls gap.According to Rice et al.'s theory and by correlation with recent NMR data, we suggest that this behaviour is due to current carrying solitary waves. A decomposition of the conductivity shows that solitons should be the main transport mechanism below 40 K in both the compounds.     

Temperature dependence of the reflectance spectrum of (TMTSF)2ClO4

The near-infrared and visible reflectance spectrum was measured on (TMTSF)₂ClO₄ single crystal at various temperatures in the range of 30K–290K. The reflectance spectrum polarized parallel to the stacking axis was analyzed by Drude model, giving the results that the band width 4t is about 1 eV and m¹_p/m is about 1.3. The band parameters obtained here were almost the same as those of (TMTSF)₂PF₆ reported by Jacobsen et al.     

Intelligibilities of 1-octave rectangular bands spanning the speech spectrum when heard separately and paired

There is a need, both for speech theory and for many practical applications, to know the intelligibilities of individual passbands that span the speech spectrum when they are heard singly and in combination. While indirect procedures have been employed for estimating passband intelligibilities (e.g., the Speech Intelligibility Index), direct measurements have been blocked by the confounding contributions from transition band slopes that accompany filtering. A recent study has reported that slopes of several thousand dBA/octave produced by high-order finite impulse response filtering were required to produce the effectively rectangular bands necessary to eliminate appreciable contributions from transition bands [Warren et al., J. Acoust. Soc. Am. 115, 1292-1295 (2004)]. Using such essentially vertical slopes, the present study employed sentences, and reports the intelligibilities of their six 1-octave contiguous passbands having center frequencies from 0.25 to 8 kHz when heard alone, and for each of their 15 possible pairings.     

Gd2CuO4的远红外反铁磁共振理论

提出一个适用于奈耳温度6.4K以下,Gd₂CuO₄的远红外反铁磁共振理论.理论预言的结果与Kaplan等的实验符合. 关键词：     

Investigations of zero-field splitting and defect structure for the tetragonal FeK-OI center in KTaO3 crystal

By using the defect structure data (characterized by the coordinates of impurity center) obtained from the shell model and the density functional theory in the generalized gradient approximation (GGA) corresponding to two supercell sizes, the zero-field splitting D of the tetragonal -O_I center in KTaO₃ crystal is calculated from the high-order perturbation formula based on the dominant spin-orbit coupling mechanism. The calculated results suggest that the sign of zero-field splitting D is negative and the defect structure data obtained from GGA method are more reasonable. Compared with that corresponding to the smaller supercell size, the calculated D value based on the GGA coordinates corresponding to the larger supercell size is closer to the observed value, suggesting that the GGA coordinates obtained from the larger supercell size are more accurate.     

Electronic structure of a thermoelectric material: CsBi4Te6

We have calculated the electronic structure of CsBi₄Te₆ by means of first-principles self-consistent total-energy calculations within the local-density approximation using the full-potential linear-muffin-tin-orbital method. From our calculated electronic structure we have calculated the frequency dependent dielectric function. Our calculations shows that CsBi₄Te₆ a semiconductor with a band gap of 0.3 eV. The calculated dielectric function is very anisotropic. Our calculated density of state support the recent experiment of Chung et al. [Science 287 (2000) 1024] that CsBi₄Te₆ is a high performance thermoelectric material for low temperature applications.     

First-principles calculations of the electronic and optical properties of In6S7 compound

The electronic structure and the optical properties of In₆S₇ crystal are calculated by the first-principles full-potential linearized augmented plane wave method (FP-LAPW) using density functional theory (DFT) in its generalized gradient approximation (GGA). The calculated band structure shows that the In₆S₇ is a semiconductor with a direct band gap in good agreement with experimental studies. Furthermore, the dielectric tensor and the optical properties, such as absorption coefficient, refractive index, extinction coefficient, energy-loss spectrum and reflectivity, are derived and analyzed in the study.     

Rescattering effect in above-threshold ionization processes

The Keldysh-Faisal-Reiss (KFR) theory for Above-Threshold Ionization (ATI) phenomenon is generalized to include the effect that ionized electrons return to the vicinity of the ion core and rescatter with it. The theoretical calculation of such rescattering effects for the ground state of hydrogen under linearly polarized laser light yields good agreement with recent findings in ATI experiments.     

Magnetic structure of geometrically frustrated compound Co2Cl(OH)3 determined by proton NMR

The magnetic structure of a geometrically frustrated system Co₂Cl(OH)₃ is determined by comparing the observed proton NMR spectrum with numerical calculations based on various magnetic models. The best fit is obtained with a model that the magnetic moments of Co²⁺ ions in the triangular plane are parallel to the principal axis of local crystal field and those of Co²⁺ ions in the kagome lattice plane are randomly disordered in the a-b plane, which nearly bisects the angle between the principal axis of the local field and a line pointing towards the body center of the tetrahedron. The coexistence of the ferromagnetic order in the triangular plane and the random disorder in the kagome plane is consistent with the results of measurements by Zheng et al. However, the magnetic moments of Co²⁺ ions are not directed towards the body center of the tetrahedron as characteristic in the “spin ice” magnetic structure. Furthermore, the Co²⁺ ions in the triangular plane have a smaller magnitude of magnetic moment than those in the kagome plane. Thus, our result suggests that the transition metal compound Co₂Cl(OH)₃ is different from the “spin ice” in magnetic structure, although it is similar to rare-earth pyrochlores in crystal structure.