Experimental Observation of Electronic Structures of Kagome Metal YCr_6Ge_6

Using angle-resolved photoemission spectroscopy, we study electronic structures of a Kagome metal YCr_6Ge_6.Band dispersions along k_z direction are significant, suggesting a remarkable interlayer coupling between neighboring Kagome planes. Comparing ARPES data with first-principles calculations, we find a moderate electron correlation in this material, since band calculations must be compressed in the energy scale to reach an excellent agreement between experimental data and theoretical calculations. Moreover, as indicated by band calculations,there is a flat band in the vicinity of the Fermi level at the ■–M–K plane in the momentum space, which could be responsible for the unusual transport behavior in YCr_6Ge_6.     

Relativistic Multichannel Theory：Theoretical Study of C^＋ Autoionization States

Based on relativistic multichannel theory,the autoionization states of C are studied.We calculate all the autoionization states in the energy region of 193900-231700cm^-1,and the results are in good agreement with the experimental data.The energy structure we obtain will be important in the dielectronic recombination processes,which plays a key role in determining the abundance of carbon in a nebula.     

The influence from high-n dielectronic satellites to Kɑ resonance line in helium-like aluminium

Based on the multi-configuration Dirac-Fock method, this paper has made theoretical calculations for the dielectronic recombination cross-sections and the high-n dielectronic satellites to Kα resonance line in helium-like aluminium ions. It is found that high-n dielectronic satellites are seriously mixed with resonance line, which leads to a significant increase in both the apparent width and the intensity of Kα resonance line. They also induce a positional shift of Kα resonance line.     

Topological structure effect on far-infrared spectra in a GaAs/InAs nanoring

On the basis of the growth mechanism of a GaAs/InAs nanoring,we propose a fine model which reflects the confinement details of real nanoring.Through calculations of the two-electron energy and far-infrared(FIR) spectra,we find that the ring topological structure and electron-electron interaction have great influence on the FIR spectra.The two unknown transition peaks in the experiment are determined theoretically.The theoretical results are in good agreement with the experiments.     

Effect of radiation on compressibility of hot dense sodium and iron plasma using improved screened hydrogenic model with𝑙splitting

High pressure investigations of matter involve the study of strong shock wave dynamics within the materials which gives rise to many thermal effects leading to dissociation of molecules,ionization of atoms,and radiation emission,etc.The response of materials experiencing a strong shock can be determined by its shock Hugoniot calculations which are frequently applied in numerical and experimental studies in inertial confinement fusion,laboratory astrophysical plasma,etc.These studies involve high energy density plasmas in which the radiation plays an important role in determining the energy deposition and maximum compressibility achieved by the shock within material.In this study,we present an investigation for the effect of radiation pressure on the maximum compressibility of the material using shock Hugoniot calculations.In shock Hugoniot calculations,an equation of state(EOS)is developed in which electronic contributions for EOS calculations are taken from an improved screened hydrogenic model with?l splitting(I-SHML)[High Energy Density Physics(2018)2648]under local thermodynamic equilibrium(LTE)conditions.The thermal ionic part calculations are adopted from the state of the art Cowan model while the cold ionic contributions are adopted from the scaled binding energy model.The Shock Hugoniot calculations are carried out for sodium and iron plasmas and our calculated results show excellent agreement with published results obtained by using either sophisticated self-consistent models or the first principle study.     

A Calculation of Direct Radiative Recombination Cross Sections and Rate Coefficients

We calculate direct radiative recombination cross sections and rate coefficients for Be-like O^4 ,Si^10 and Na-like Fe^15 using norelativistic dipole approximation,In order to incorporate the screening effect due to the innershell electrons in the calculation,we use the distorted wave method instead of pure coulomb approximation with effective charge.The calculated cross sections and rate coefficients are in agreement with other theoretical calculations and the experimental data.     

Generation of a Super Strong Attosecond Pulse from an Atomic Superposition State Irradiated by a Shape-Optimized Short Pulse

Using a linearly polarized, phase-stabilized 3-fs driving pulse of 800 nm central wavelength shape-optimized on its＇ascending edge by its an amplitude-reduced pulse irradiating on a superposition state of the helium atom, we demonstrate theoretically the generation of a super strong isolated 176-attosecond pulse in the spectral region of 93-124 eV. The unusually high intensity of this attosecond pulse is marked by the Rabi-like oscillations emerging in the time-dependent populations of the ground state and the continuum during the occurrence of the electron recombination, which is for the first time observed in this work.     

Can non-standard recombination resolve the Hubble tension?

The inconsistent Hubble constant values derived from cosmic microwave background(CMB) observations and from local distance-ladder measurements may suggest new physics beyond the standard ΛCDM paradigm. It has been found in earlier studies that, at least phenomenologically, non-standard recombination histories can reduce the ≥4σ Hubble tension to ～ 2σ.Following this path, we vary physical and phenomenological parameters in RECFAST, the standard code to compute ionization history of the universe, to explore possible physics beyond standard recombination. We find that the CMB constraint on the Hubble constant is sensitive to the hydrogen ionization energy and 2 s → 1 s two-photon decay rate, both of which are atomic constants, and is insensitive to other details of recombination. Thus, the Hubble tension is very robust against perturbations of recombination history, unless exotic physics modifies the atomic constants during the recombination epoch.     

Momentum-space crystal in narrow-line cooling of ~(87)Sr

The discovery of the momentum space crystal based on the alkaline-earth atom ~(88)Sr in narrow-line cooling has paved the way to explore this novel physical phenomenon in other cold atom systems. In this paper, a momentum space crystal based on the fermions ~(87)Sr in narrow-line cooling of transition~1S_0–~3P_1 is demonstrated. We theoretically analyze and compare the formation principle of the narrow-line with that of broad-line cooling, and achieve the momentum space crystal in experiment. Beyond that we present a series of numerical calculations of those important parameters which influence the distribution and size of the momentum space crystal. Correspondingly, we vary the values of these parameters in experiment to observe the momentum space crystal evolution and distribution. The experimental results are in conformity with the results of the theoretically numerical calculations. These results and analyses provide a detailed supplementary study on the formation and evolution of momentum space crystal. In addition, this work could also give a guideline on atomic manipulation by narrow-line cooling.     

The effect of hydrogen on the recombination of Frenkel pair in tungsten: A theoretical insight

<正>Tungsten (W), with its primary advantages, is considered as the most promising candidate for plasma facing materials (PFMs) for the next generation of fusion devices such as ITER. However, continuous bombardment with 14.1 MeV neutron introduces Frenkel defects as the primary damage in W [1]. The Frenkel defects, composed of self-interstitial atoms (SIAs) and vacancies, can develop to extended defects such as voids and interstitial clusters, resulting in hardening, swelling and embrittlement of W, thus degrading the properties of W [2]. The recombination of SIAs and vacancies is an effective way to reduce the Frenkel defects in bulk W, which enhances the radiation resistance of W based on recent theoretical calculations [3,4]. The moving of the SIA to the vacancy could finish the recombination process through instantaneous or thermally activated way [3]. The instantaneous recombination region is an ellipse with the semi-minor axis of 5.4 ? and semi-major axis of 18 ? according to the molecular dynamics calculation [4].     

Material optimization for low scattering noise duringnonvolatile holographic recording indoubly doped LiNbO_3 crystals

Scattering noises in four kinds of lithium niobate crystals with the same double doping system, which are LiNbO3:Fe:Mn, LiNbO3:Ce:Mn, LiNbO3:Ce:Cu, and LiNbO3:Fe:Cu, are observed and compared experimentally. The results show that nonvolatile holographic recording can effectively suppress scattering noise, which mainly depends on recombination coefficients of both the shallower centers and the deeper centers. The small recombination coefficients of the shallower centers and the large recombination coefficients of the deeper centers benefit the amplification of the signal gratings and the suppression of the noise gratings. In addition, the initial seed scattering also impacts the recorded scattering noise, and the little seed scattering results in low scattering noise. The theoretical simulations are performed for confirmation. Among the four kinds of doubly doped crystals, in LiNbO3:Ce:Cu the performances of nonvolatile recording are the best with low scattering noise and high diffraction efficiency.     

Electron-mediated ferromagnetism in Fe-doped InP: Theory and experiment

We report on the electron-mediated ferromagnetism in Fe-doped InP from both first-principles calculations and experiments. Theoretically, based on the spin-polarized density functional theory within the Heyd-Scuseria-Ernzerhof (HSE03) approach, we systematically investigate the magnetic properties of Fe-doped InP and predict the existence of electron-mediated ferromagnetism. Experimentally, by diffusing Fe into the n-type InP wafer with thermal annealing at 800 C, we observe room-temperature ferromagnetism in InP:Fe, which is in agreement with the theoretical prediction.     

A Theoretical Study of Photoabsorption Cross Sections of Na^＋ 2

In the framework of quantum defect theory, we calculate photoabsorption cross sections of Na^＋ 2. Based on our calculations, there is an absorption window in the photoabsorption cross sections of Na^＋ 2. and more than one bump above the absorption window. The calculated photoabsorption cross sections provide an explanation for the abnormal bump in the experimental measurements of Hudson, which is a long-standing experimental puzzle.     

Origin and Characteristics of Blue Light Emission in Solid State Cathodoluminescence of MEH－PPV

Based on our previous study [Chin. Phys. Lett. 20 (2003) 1144] on the sofid-state cathodoluminescence from organic luminescent materials, here we study the origin and characteristics of blue light emission in solid-state cathodoluminescence of Poly [(2-methoxy-5-(2‘-ethyl-hexyloxy)phenylene vinyene] (MEH-PPV) and the dependence of each spectral peak on electric field strength. The results demonstrate that the blue spectral shift benefits from field ionization of excitons, and three regions of electric field are found, in which there are pure exciton emission, coexistence of exciton emission and radiative recombination, and pure radiative recombination.     

Comparison of Xe single bubble sonoluminescence in water and sulfuric acid

Using the equations of fluid mechanics with proper boundary conditions and taking account of the gas properties, we can numerically simulate the process of single bubble sonoluminescence, in which electron-neutral atom bremsstrahlung, electron-ion bremsstrahlung and recombination radiation, and the radiative attachment of electrons to atoms and molecules contribute to the light emission. The calculation can quantitatively or qualitatively interpret the experimental results. We find that the accumulated heat energy inside the compressed gas bubble is mostly consumed by the chemical reaction, therefore, the maximum degree of ionization inside Xe bubble in water is much lower than that in sulfuric acid, of which the vapour pressure is very low. In addition, in sulfuric acid much larger pa and R0 are allowed which makes the bubbles in it much brighter than that in water.     

First-principles study on the geometric and electronic structures and phase transition of PbZr1-xTixO3 solid solutions

With first-principles virtual-crystal approximation calculations, we systematically investigate the geometric and elec- tronic structures as well as the phase transition of lead zirconate titanate (PbZr1-xTixO3 or PZT) as a function of Ti content for the whole range of 0 ≤ x Ti ≤ 1. It can be found that, with the increase of the Ti content, the PbZr1-xTixO3 solid solu- tions undergo a rhombohedral-to-tetragonal phase transition, which is consistent with the experimental results. In addition, we also show the evolution in geometric and electronic structures of rhombohedral and tetragonal PbZr1-x TixO3 with the increasing content of Ti.     

The Binding Energy, Spin－Excitation Gap, and Charged Gap in the Boson－Fermion Model

In this paper, by applying a simplified version of Lieb‘s spin-reflection-positivity method, which was recently developed by one of us [G.S. Tian and J.G. Wang, J. Phys. A: Math. Gen. 35 (2002) 941], we investigate some general properties of the boeon-fermion Hamiltonlan, which has been widely used as a phenomenological model to describe the real-space pairing of electrons. On a mathematically rigorous basis, we prove that for either negative or positive couping V, which represents the spontaneous decay and recombination process between boson and fermion in the model, the pairing energy of electrons is nonzero. Furthermore, we also show that the spin-excitation gap of the boson-fermion Hamiltonian is always larger than its charged gap, as predicted by the pre-palred electron theory.     

Effects of Bounding Potential on High-Order Harmonic Generation with H2+

We present harmonic spectra from hydrogen molecular ions with different ionization energy Ip. By comparing the recombination matrix element from helium ions and hydrogen molecular ions, we verify that the interference effect in high-order harmonic generation originates from the recombination interference. A numerical study on recombination matrix elements in 1D shows that w = Ek ＋ Ip holds only when an exact continuum wavefunction is used, and the positions of extrema in harmonic spectra can be predicted accurately. We demonstrate that the positions of extrema in harmonic spectra are mainly affected by bounding potential dependence of the recombination interference.     

Dynamics of scalar fields in an expanding/contracting cosmos at finite temperature

This study extends the investigation of quantum dissipative effects of a cosmological scalar field by taking into account cosmic expansion and contraction.Cheung,Drewes,Kang,and Kim calculated the effective action and quantum dissipative effects of a cosmological scalar field in a recent work,where analytical expressions for the effective potential and damping coefficient were presented using a simple scalar model with quartic interactions,and the work was conducted using Minkowski-space propagators in loop diagrams.In this work,we incorporate the Hubble expansion and contraction of the cosmic background and focus on the thermal dynamics of a scalar field in a regime where the effective potential changes slowly.Given that the Hubble parameter,H,attains a small but non-zero value,we carry out calculations to the first order in H.If we set H=0,all results match those in flat spacetime.Interestingly,we must integrate over the resonances,which in turn leads to an amplification of the effects of a non-zero H.This is an intriguing phenomenon,which cannot be uncovered in flat spacetime.The implications on particle creations in the early universe will be studied in a forthcoming study.     

Ferromagnetism in Layered Metallic Fei/4TaS2 in the Presence of Conventional and Dirac Carriers

We present the microscopic origin of the ferromagnetism of Feo.25TaS2 and its finite-temperature magnetic properties.The band structures of Feo.25TaS2 are first obtained by the first-principles calculations and it is found that both conventional and Dirac carriers coexist in metallic Feo.25TaS2-Accordingly,considering the spin-orbit coupling of Fe 3d ion,we derive an effective Ruderman-Kittle-Kasuya-Yosida-type Hamiltonian between Fe spins in the presence of both the conventional parabolic-dispersion and the Dirac linear-dispersion carriers,which contains a Heisenberg-like,an Ising-like and an XY-like term.In addition,we obtain the ferromagnetic Curie temperature Tc by using the cluster self-consistent Held method.Our results could address not only the high ferromagnetic Curie temperature but also the large magnetic anisotropy in Fex TaS2.