Zero-field splitting parameters and local structures for tetragonal Cr2＋ centers in Cr2＋-doped ZnSe semiconductors

The inter-relation between zero-field splitting （ZFS） parameters and local lattice structures of the （CrSe4）6 clusters in ZnSe semiconductors has been established by using the complete diagonalization （of the energy matrix） method. On the basis of this, the local lattice distortions, the ZFS parameters D, a, F and the optical spectrum for Cr2＋ ions doped into ZnSe are theoretically investigated, and the contributions of the spin singlets have been taken into account. The calculated ZFS parameters are in good agreement with the experimental values. From our calculations, the tetragonal distortion parameters AR = 0.091A and Aθ = 4.28° of Cr2＋ in ZnSe are acquired, and the results suggest that there exists a tetragonal expansion distortion for the local lattice structure of （CrSe4）6- clusters in ZnSe crystals. The influence of the spin singlets on ZFS parameters is also discussed, indicating that the contributions to ZFS parameters a and F cannot be ignored.     

A complex first-principles study of the L2,3-edge XANES spectra and crystal field effects for divalent 3d ions in cubic ZnS

A detailed first-principles analysis of the L_2,3 X-ray absorption near edge structure (XANES) spectra, crystal field strength 10Dq, covalent effects and molecular orbitals (MO) position for all divalent 3d ions from Sc²⁺ to Cu²⁺ in cubic ZnS is performed in the present paper. The calculations were done in the framework of the first-principles fully relativistic discrete variational multi-electron (DVME) based on numerical solution of the Dirac equation with the local density approximation. As a result of the performed calculations, the L_2,3 XANES spectra for all considered ions were calculated and assigned in terms of the electron configurations involved into the absorption transitions; fairly good agreement with available experimental data for Ti²⁺, Mn²⁺, Fe²⁺, Co²⁺ and Ni²⁺ is demonstrated. Experimental XANES spectra for Sc²⁺, V²⁺, Cr²⁺, Cu²⁺ not reported previously were also calculated for the sake of completeness of the present study to enable a systematic analysis of all calculated results for the whole series considered. It was shown that the L₃ and L₂ bands shift to the higher energies on increasing a 3d ion atomic number. In addition, the separation between the L₃ and L₂ bands, the crystal field strength 10Dq and mixture between the 3d ion and sulfur wave functions increase along the considered series, from Sc²⁺ to Cu²⁺. On the other hand, all orbitals of the 3d ions systematically lower down in the same direction. The above formulated trends were confirmed by the experimental data on the crystal field splittings and nephelauxetic effect.     

Local electronic structures at selected sites of intermetallic perovskites Mn3MeX (Me=divalent metal,X=N,C)

Summary We have measured the XANES (X-ray absorption near edge structure) spectra on the manganese and metal MeK-edges of the intermetallic perowskites Mn₃MeX (X=N, Me=Mn, Cu, Zn, Ga, Sn; X=C, Me=Ga, Sn) to investigate the distribution on the partial density of the empty states. The information on the local electronic structure at the two differents sites, obtained from the spectra in the first 10 eV above the onset, is discussed in terms of one-electron band model. The relative shape changes in the spectra between the different compounds are explained by the different magnitude of hybridization between the electronic states of different atoms and/or the filling of the empty band by the electrons supplied by the substituted metal. Moreover, information about the local geometrical structure has been obtained from the (10÷50) eV range of the spectra.

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Riassunto La distribuzione della densità parziale degli stati vuoti nelle perovskiti intermetalliche Mn₃MeX (X=N, Me=Mn, Cu, Zn, Ga, Sn; X=C, Me=Ga, Sn) è stata studiata mediante spettroscopia XANES (X-ray absorption near edge structure) alle soglieK del Mn e del metallo Me. Le informazioni sulla struttura elettronica locale di entrambi i siti, ottenute dall’analisi dei primi 10 eV degli spettri XANES, sono discussed in termini di un modello proposto. Il cambiamento relativo della forma negli spetttri dei diversi composti è posto in relazione alla differente ibridizzazione tra stati di atomi diversi e/o dal riempimento degli stati della banda vuota con elettroni forniti dal metallo sostituente. Sono state anche ottenute informazioni sulla struttura geometrica locale analizzando gli spettri nell’intervallo da 10 a 50 eV.

     

Three-Party Quantum State Sharing of an Arbitrary Unknown Two-Qubit State Based on Entanglement Swapping and Bell-State Measurements

We propose a scheme for sharing an arbitrary unknown two-qubit state among three parties by using a four-qubit cluster-class state and a Bell state as a quantum channel. With a quantum controlled phase gate （QCPG） operation and a local unitary operation, any one of the two agents has the access to reconstruct the original state if he/she collaborates with the other one, whilst individual agent obtains no information. As all quantum resource can be used to carry the useful information, the intrinsic efficiency of qubits approaches the maximal value. Moreover, the present scheme is more feasible with present-day technique.     

Electron Dispersion in Liquid Alkali and Their Alloys

Ashcroft＇s local empty core （EMC） model pseudopotential in the second-order perturbation theory is used to study the electron dispersion relation, the Fermi energy, and deviation in the Fermi energy from free electron value for the liquid alkali metals and their equiatomic binary alloys for the first time. In the present computation, the use of pseudo-alloy-atom model （PAA） is proposed and found successful. The influence of the six different forms of the local field correction functions proposed by Hartree （H）, Vashishta Singwi （VS）, Taylor （T）, lehimaru-Utsumi （IU）, Farid et al. （F）, and Sarkar et al. （S） on the aforesaid electronic properties is examined explicitly, which reflects the varying effects of screening. The depth of the negative hump in the electron dispersion of liquid alkalis decreases in the order Li --→ K, except for Rb and Cs, it increases. The results of alloys are in predictive nature.     

B~0-B~0 Mixing in Local Gauged Baryon and Lepton Numbers

Using the effective Hamiltonian method, we analyze the B0-B0 mixing in the extension of the standard model （SM） where baryon number and lepton number are local gauge symmetries. The numerical results indicate the correction from the extra particles to the mass difference ArnB is significant. There is a 60% enhancement compared to the SM prediction for AraB at most, which agrees with the current experimental result.     

Electron states scattering off line edges on the surface of topological insulator

We study the local density of states （LDOS） for electrons scattering off the line edge of an atomic step defect on the surface of a three-dimensional （3D） topological insulator （TI） and the line edge of a finite 3D TI, where the front surface and side surface meet with different Fermi velocities, respectively. By using a S-function potential to model the edges, we find that the bound states existed along the step line edge significantly contribute to the LDOS near the edge, but do not modify the exponential behavior away from it. In addition, the power-law decaying behavior for LDOS oscillation away from the step is understood from the spin rotation for surface states scattering off the step defect with magnitude depending on the strength of the potential. Furthermore, the electron refraction and total reflection analogous to optics occurred at the line edge where two surfaces meet with different Fermi velocities, which leads to the LDOS decaying behavior in the greater Fermi velocity side similar to that for a step line edge. However, in the smaller velocity side the LDOS shows a different decaying behavior as x-1/2, and the wavevector of LDOS oscillation is no longer equal to the diameter of the constant energy contour of surface band, but is sensitively dependent on the ratio of the two Fermi velocities. These effects may be verified by STM measurement with high precision.     

Classification of Bipartite and Tripartite Qutrit Entanglement Under SLOCC

We classify biqutrit and triqutrit pure states under stochastic local operations and classical communication. By investigating the right singular vector spaces of the coefticient matrices of the states, we obtain explicitly two equivalent classes of biqutrit states and twelve equivalent classes of triqutrit states respectively.     

Anomalous Scaling of Surface Growth Equations with Spatially and Temporally Correlated Noise

Based on the scaling idea of local slopes by Lopez et al. [Phys. Rev. Lett. 94 （2005） 166103], we investigate anomalous dynamic scaling of （d ＋ 1）-dimensional surface growth equations with spatially and temporally correlated noise. The growth equations studied include the Kardar-Parisi-Zhang （KPZ）, Sun-Guo-Grant （SGG）, and Lai-Das Sarma-Villain （LDV） equations. The anomalous scaling exponents in both the weak- and strong-coupling regions are obtained, respectively.     

Two-Step Deterministic Remote Preparation of an Arbitrary Quantum State

We present a two-step deterministic remote state preparation protocol for an arbitrary qubit with the aid of a three-particle Greenberger-Horne-Zeilinger state. Generalization of this protocol for higher-dimensional Hilbert space systems among three parties is also given. We show that only single-particle yon Neumann measurements, local operations, and classical communication are necessary. Moreover, since the overall information of the quantum state can be divided into two different pieces, which may be at different locations, this protocol may be useful in the quantum information field.     

Electronic structure of formamidinium ions in lead triiodide perovskites

Perovskite formamidinium lead triiodide (FAPbI₃) is a very promising photovoltaic material. Unfortunately, perovskite FAPbI₃ converts to a hexagonal phase at ambient conditions. Herein we study the electronic structure of both perovskite and hexagonal FAPbI₃ films using soft X‐ray absorption near edge structure (XANES) and density functional theory. We find that the C and N 2p states of FA hybridize with the Pb, I states at the conduction band minimum in hexagonal, but not perovskite, FAPbI₃. We also demonstrate that C K‐edge XANES can be used to investigate shifts in the valence band in other organic‐inorganic hybrid perovskites.

Graphical summary of the electronic structure and C K‐edge XANES in both perovskite and hexagonal FAPbI₃ highlighting our findings.     

Local coordination geometry around Cu and Cu ions in silicate glasses: an X-ray absorption near edge structure investigation

We present an X-ray absorption near edge structure (XANES) study on Cu⁺ and Cu²⁺ ions in silicate glasses at the Cu K-edge, aimed to determine the geometry of the local structure around the metal. This study is based on the comparison between experimental data and theoretical calculations made in the framework of multiple scattering theory. The XANES signals relative to several clusters are simulated on the basis of known crystalline structures involving Cu⁺ and Cu²⁺ ions in silicate matrices. Concerning the Cu²⁺ in glass, the simulations suggest the presence of a square coordination of oxygen atoms around the absorber, with a possible presence of metal ions in the second shell. As for the Cu⁺ ions, the metal clustering is excluded and a linear O-Cu-O coordination is evidenced. Received 30 April 1999     

Fast local reconstruction by selective backprojection for low dose in dental computed tomography

The high radiation dose in computed tomography （CT） scans increases the lifetime risk of cancer, which becomes a major clinical concern. The backprojection-filtration （BPF） algorithm could reduce the radiation dose by reconstructing the images from truncated data in a short scan. In a dental CT, it could reduce the radiation dose for the teeth by using the projection acquired in a short scan, and could avoid irradiation to the other part by using truncated projection. However, the limit of integration for backprojection varies per PI-line, resulting in low calculation efficiency and poor parallel performance. Recently, a tent BPF has been proposed to improve the calculation efficiency by rearranging the projection. However, the memory-consuming data rebinning process is included. Accordingly, the selective BPF （S-BPF） algorithm is proposed in this paper. In this algorithm, the derivative of the projection is backprojected to the points whose x coordinate is less than that of the source focal spot to obtain the differentiated backprojection. The finite Hilbert inverse is then applied to each PI-line segment. S-BPF avoids the influence of the variable limit of integration by selective backprojection without additional time cost or memory cost. The simulation experiment and the real experiment demonstrated the higher reconstruction efficiency of S-BPF.     

Ab initio calculation and synchrotron X-ray spectroscopy investigations of tin oxides near the Sn <Emphasis Type="Italic">L</Emphasis><Subscript>3</Subscript> absorption edges

The results of theoretical and experimental investigations of the electron-energy structure of the conduction band of tin oxides have been presented. The Sn L ₃ X-ray absorption near-edge fine structure (XANES) has been calculated for the first time for single crystals of metallic tin and tin monoxide, as well as for the orthorhombic and tetragonal phases of tin dioxide, using the linearized augmented plane wave (LAPW) method. The fine structure of the XANES spectra has been compared with the specific features of the energy distribution of the local partial densities of states of the tin compounds under investigation. A joint analysis of the results of the simulation and the experimental X-ray synchrotron Sn L ₃ XANES spectra of commercial bulk samples of metallic tin and tin oxides SnO and SnO₂ has been carried out.     

Europium-151 Mössbauer spectroscopic and XANES investigation of europium-exchanged Y-zeolite

Eu³⁺ in ca. 10 wt% europium-exchanged Y-zeolite is partially reduced by treatment in hydrogen at 600°C to Eu²⁺. The reduction of Eu³⁺ is more readily achieved in Y-zeolite than in europium(III) oxide. The discrepancy in the extent of reduction as revealed by¹⁵¹Eu Mössbauer spectroscopy and near edge X-ray absorption fine structure (XANES) is associated with any difference in the recoil free fractions of Eu²⁺ and Eu³⁺ which may exist at 298 K and the enhanced sensitivity of the XANES to changes in the europium oxidation state.     

Evaluation of thermal resistance constitution for packaged A1GaN/GaN high electron mobility transistors by structure function method＊

The evaluation of thermal resistance constitution for packaged A1GaN/GaN high electron mobility transistor （HEMT） by structure function method is proposed in this paper. The evaluation is based on the transient heating measurement of the A1GaN/GaN HEMT by pulsed electrical temperature sensitive parameter method. The extracted chip-level and package-level thermal resistances of the packaged multi-finger A1GaN/GaN HEMT with 400μm SiC substrate are 22.5 K/W and 7.2 K/W respectively, which provides a non-invasive method to evaluate the chip-level thermal resistance of packaged A1GaN/GaN HEMTs. It is also experimentally proved that the extraction of the chip- level thermal resistance by this proposed method is not influenced by package form of the tested device and temperature boundary condition of measurement stage.     

A Complex Higher-Dimensional Lie Algebra with Real and Imaginary Structure Constants as Well as Its Decomposition

A new Lie algebra G of the Lie algebra sl（2） is constructed with complex entries whose structure constants are real and imaginary numbers. A loop algebra G corresponding to the Lie algebra G is constructed, for which it is devoted to generating a soliton hierarchy of evolution equations under the framework of generalized zero curvature equation which is derived from the compatibility of the isospectral problems expressed by Hirota operators. Finally, we decompose the Lie algebra G to obtain the subalgebras G1 and G2. Using the G2 and its one type of loop algebra G2, a Liouville integrable soliton hierarchy is obtained, furthermore, we obtain its bi-Hamiltonian structure by employing the quadratic-form identity.     

Transport properties of a binary mixture of CO2-N2 from the pair potential energy functions based on a semi-empirical inversion method

The potential energy snrface of a CO2-N2 mixture is determined by using an inversion method, together with a new collision integral correlation [J. Phys. Chem. R@ Data 19 1179 （1990）]. With the new invert potential, the transport properties of CO2-N2 mixture are presented in a temperature range front 273.15 K to 3273.15 K at low density by employing the Chapman-Enskog scheme and the Wang Chang-Uhlenbeck de Boer theory, consisting of a viscosity coefficient, a thermal conductivity coefficient, a binary diffusion coefficient, and a thermal diffusion factor. The accuracy of the predicted results is estimated to be 2% for viscosity, 5% for thermal conductivity, and 10% for binary diffusion coefficient.     

Global Structure Stability of Riemann Solution of Quasilinear Hyperbolic System of Conservation Law in Presence of Boundary： Shocks and Contact Discontinuities

In this paper, we investigate a class of mixed initial-boundary value problems for a kind of n × n quasilinear hyperbolic systems of conservation laws on the quarter plan. We show that the structure of the pieeewise C^1 solution u = u（t, x） of the problem, which can be regarded as a perturbation of the corresponding Riemann problem, is globally similar to that of the solution u = U（x/t） of the corresponding Riemann problem. The piecewise C^1 solution u = u（t, x） to this kind of problems is globally structure-stable if and only if it contains only non-degenerate shocks and contact discontinuities, but no rarefaction waves and other weak discontinuities.