bluuebunny/crossref_metadata_2025_split huggingface dataset:
Vibrational dynamics of Pd80Si20 glass
Authors: Prasad A. , Jain K. C. , Saxena N. S. 
Published: July 2007

AbstractThe vibrational dynamics of Pd80Si20 glass has been studied at room temperature in terms of the phonon eigenfrequencies of longitudinal and transverse modes employing the theoretical formulations of Hubbard and Beeby as well as of Takeno and Goda. The effective interatomic pair potential in this glass is obtained using the experimental partial pair correlation functions and the hypernetted chain (HNC) equation. Long wavelength limits of the phonon modes are then used to get information on the elastic and thermal properties of the system. It has been found that the theoretical results of these properties as computed through Hubbard and Beeby's method are in good agreement with the available experimental results.
Self‐consistent green's function approach to dissipative two‐state system
Authors: Chu H. Y. , Ye Z. , Umezawa H. 
Published: July 2007

AbstractWe study the properties of a dissipative two‐state fermionic system embedded in a phonon bath at zero temperature. In contrast to the traditional path‐integral and canonical transformation approaches, we propose a self‐consistent Green's function approach. Our results show that the mean field theory overestimates the polarization of the system. To justify our approach, we consider a simplest case in which there is only one phonon mode. This simple model can be ‘exactly’ diagonalized. We find that the results from the self‐consistent Green's function approach agree well with the quantum mechanical diagonalization results.
Empirical tight‐binding band structure of zinc‐blende nitrides GaN, AIN, and BN
Authors: Ferhat M. , Zaoui A. , Certier M. , Khelifa B. 
Published: July 2007

AbstractThe electronic band structure and density of states for zinc‐blende nitrides GaN, AIN, and BN are reported using an sp3s* tight‐binding method. The large band gap found for these compounds is analyzed in terms of chemical and volume deformation effects. The calculated ionicity agrees with the Phillips scale and shows a strongly ionic character for GaN and AIN, while BN is found more covalent.
Phase diagram of three fermionic chains: A renormalization‐group study
Authors: Arrigoni E. 
Published: July 2007

AbstractThe weak‐coupling phase diagram of a system of three coupled spin 1/2 chains (at zero temperature) is studied as a function of fermion density and of transverse single‐particle hopping by means of a renormalization‐group analysis. We identify different phases with a different behavior of the renormalization‐group flow and interpret the effect of relevant couplings in terms of the associated bosonized Hamiltonian. A frustrated (gapped) magnetic spectrum in a large region about and at half filling is obtained in the unphysical case of periodic boundary conditions in the direction transverse to the chains. The expected spin phase diagram (as also observed in the Sr2Cu3O5 ladder compounds) is instead obtained when open transverse boundary conditions are considered. In particular, the spin modes are ungapped in a wide region about half filling and at half filling down to a critical value of the transverse hopping t⟂. A Mott transition as a function of ⟂ is thus present at half filling.
Analysis of transient phenomena in GaAs within the metastable model
Authors: Santic B. , Radic N. , Desnica U. V. , Fillard J. P. 
Published: July 2007

AbstractTransients of the diode capacitance Cd, optical absorption coefficient α, and EPR signal in GaAs are studied within the framework of the metastable model. The spectral behavior of transients is studied theoretically in the 0.9 to 1.3 eV range. It is shown that the occupancy factor F (electron occupancy of EL2 defect) plays an important role in the observation of the characteristic ‘fingerprint’ signals. It significantly influences both the amplitude and the shape of the transient as well as its spectral behavior. A novel way for the determination of the value of F from the experimental results is proposed. It is discussed why the variation of F among the samples leads to the sample dependence of the results which is frequently experimentally observed. The appearance of ‘non‐quenchable’ and ‘EL2‐like’ defects is also discussed. The experimentally observed results can be modeled even with the assumption of a constant value of σ* (capture cross section for the metastable transition). The light flux intensity and the time of illumination should be specified for a meaningful comparison of various experimental results.
Surface effects on excitons in n‐period CdMnTe/CdTe superlattices
Authors: Afif K. , Diouri J. 
Published: July 2007

AbstractThe binding energy EB of Wannier excitons in N‐period CdMnTe/CdTe superlattices including or not a step discontinuity in the potential barrier at the interface and with varying N as well as well width is calculated by a variational method. The calculation is performed in the framework of the effective mass approximation for both heavy‐hole and light‐hole excitons. The results obtained show that EB is sensitive to those three parameters in the limit of short dimensions of the structure.
Phase diagrams of the spin‐3/2 transverse ising model with random interactions
Authors: Kerouad M. , El‐Atri A. , Ainane A. , Saber M. 
Published: July 2007

AbstractThe transverse spin‐3/2 Ising model with random interactions is studied using an effective field method within the framework of a single‐site cluster theory. The effective field equations are derived using a probability distribution method based on the use of generalized Van der Waerden identities, that account exactly for the single‐site kinematic relations. A model is adopted in which the nearest‐neighbour exchange couplings are described by the probability distribution law: P(Jij) = p δ(Jij‐J) + (1‐p) δ(Jij‐aJ). The critical temperature at which the longitudinal magnetization vanishes is studied as a function of p and the transverse field strength. The thermal variation of the longitudinal and transverse magnetizations and higher‐order magnetization moments are also studied.
Magnetism of the Rh13 cluster
Authors: Yang Jinlong , Deng Kaiming , Xiao Chuanyun , Wang Kelin 
Published: July 2007

AbstractThe electronic structure of the 13‐atom Rh cluster is studied with the structure model optimized by Estiu and Zerner using the discrete variational local‐spin density‐functional method. The magnetic moment per atom of the cluster is calculated to be 0.54μB, in good agreement with experimental measurements (0.48±0.13)μB. It confirms our previous assumption that the structural distortion of the Rh13 cluster from a perfect icosahedron to its ground state geometry decreases its magnetic moment and makes the theoretical calculation close to the experimental measurement.
Theoretical interpretation of the temperature dependence of zero‐field splitting of Ni2+ in NiSiF6 · 6 H2O
Authors: Peng Long‐Cai , Wu Ping‐Feng , Zhou Kang‐Wei 
Published: July 2007

AbstractBy use of a trigonal crystal‐field model and by means of the eigenvalues and eigenvectors of a d8 (C) ion, a unified calculation is given for the spectral fine structure, the EPR parameters (D, 9|, 9⟂), and the EPR absorption condition (H,v) of Ni2+ ions in NiSiF6· 6H2O at different temperatures. The theoretical results agree well with the findings. It is shown that the trigonal field parameter v, which describes the splitting degree of the t2g orbitals in a trigonal field, has approximately a linear temperature dependence, v (cm−1) = 117.3 + 0.4898 T (K). This is shown to be the physical mechanism of the temperature dependence of the zero‐field splitting parameter D. The theoretically predicted EPR absorption conditions (H,v) and a very slight temperature dependence of the g‐values also agree very well with the findings.
Spontaneous polarization behaviour in ferroelectrics
Authors: Wojtczak L. , Zasada I. 
Published: July 2007

AbstractThe spontaneous polarization behaviour in the vicinity of the ferro‐paraelectric phase transition is discussed. The experimental results for ferroelectrics are analyzed in the case of pyroelectric function investigations. The description in terms of the two‐point scaling hypothesis is then applied in order to explain the tail of the polarization in the paraelectric phase. The critical exponents are evaluated. The Curie temperature determined from experimental data above or below the temperature for the maximum of the pyroelectric function is considered in the model assuming that the fixed point can be related to one of the stability points for the ferro‐ or paraelectric phase, respectively. In the model presented the temperature hysteresis seems to be a natural phenomenon because of the phase transition point whose position results from the competition between fluctuations in the ferro‐paraelectric phase coexistence interval.
Electronic and vibronic structure of the nonplanar organic charge‐transfer salt m‐BDNT‐PF6
Authors: Dong J. , Yakushi K. , Yamashita Y. , Imaeda K. , Inokuchi H. 
Published: July 2007

AbstractThe monoclinic form of BDNT‐PF6 (m‐BDNT‐PF6) is characterized as a pseudo‐one‐dimensional half‐filled Hubbard system from the electrical conductivity, magnetic susceptibility, and single crystal optical spectra. m‐BDNT‐PF6 undergoes a spin‐Peierls transition at about 150 K. The lattice dimerization was confirmed by the evolution of the vibronic modes at low temperature. The small polaron binding energy of this compound, which was estimated through the analysis of the vibronic modes, is smaller than those of TTF, TCNQ, or CA. Hubbard parameters U and t were obtained to be 0.8 and 0.13eV by analyzing the charge‐transfer band. The optical and magnetic data are consistent with each other.
Photoluminescence spectra of CdTe/CdMnTe quantum well structures in an external magnetic field
Authors: Aguekian V. F. , Ashenford D. E. , Lunn B. , Koudinov A. V. , Kusrayev Yu. G. , Zakharchenya B. P. 
Published: July 2007

AbstractThe investigation of the photoluminescence spectra of CdTe/CdMnTe quantum well structures proves that the exciton localization efficiency is governed by temperature, external magnetic field, and excitation energy. The polarization of the luminescence in a magnetic field suggests that the impurity related luminescence band is due to the recombination of electron states situated near the interface.
Atomic charges in RBa2Cu3O7 superconductor lattices. Electronic structure of the copper atoms
Authors: Masterov V. F. , Seregin P. P. , Nasredinov F. S. , Seregin N. P. , Sagatov M. A. 
Published: July 2007

AbstractThe effective atomic charges for all sites of the RBa2Cu3O7 lattices have been found using our Mössbauer data withthe 67Cu(67Zn),133Ba(133Cs), 155Eu(155Gd) isotopes, our calculations of the lattice electric field gradient (EFG) at the lattice sites, as well as the 17O NMR data available in literature. The charges show holes placed in the chain oxygen sublattice mainly. The Cu2+ Sternheimer factor has been estimated and the Cu2+ valence EFG in YBa2Cu37 has been found. The z‐axes of the total, lattice, and valence EFG tensors for Cu(2) coincide with the crystal axis c. For Cu(1) they coincide with the axes b, a, and a, respectively.
Orthogonalizing of core bloch states for crystalline copper
Authors: Syrotyuk S. V. , Ye. Kynash Yu. 
Published: July 2007

AbstractThe orthonormalized core Bloch states for crystalline copper have been obtained by means of the unitary rotation matrix. This matrix depends on anoverlap matrix which is evaluated on non‐orthogonal core Bloch functions. We evaluate the orthogonalization matrix in two ways. The first one consists in evaluation of the orthogonalization matrix exactly by iteration. The second approach is perturbative. The comparison of the numerical results of these two approaches allows us to conclude that the orthogonalization of core Bloch functions for crystalline copper should be done by means of aunitary rotation matrix, which is evaluated up to fifth order with respect to the overlap matrix.
Additive double gate analysis in photoinduced current transient spectroscopy: Application to cuprous oxide
Authors: Rakhshani A. E. , Khan W. I. , Mathew X. 
Published: July 2007

AbstractPhotoinduced current transient spectroscopy, in its conventional doublegate version, has been used extensively in the characterization of deep levels in semiinsulating materials. The analysis of the digitally captured transient signals by the post capture double gate method is a parallel technique with much more advantages. One of the drawbacks of the latter is, of course, the excessive time needed to capture data with a high signal‐to‐noise ratio. We have shown that the capturing time can be chosen tobe relatively low and the signal‐to‐noise ratio can be improved by a post capture data analysis referred to as the additive double gate analysis. The usefulness of this approach is demonstrated by the results obtained, for the first time, on high resistivity films of cuprous oxide. Thetechnique leads to the identification and measurement of the parameters of a few deep levels. The apparent activation energies of these levels are 0.33, 0.47, 0.49, and 0.59 eV. The corresponding capture cross sections are 2 × 10−17, 7 × 10−12, 1 × 10−15 (7 × 10−13), and 4 × 10−15 cm2, respectively.
Comparison between the endor data of different superoxide ions in alkali halides
Authors: Van Doorslaer S. , Callens F. , Maes F. , Boesman E. , Bouden D. 
Published: July 2007

AbstractThe ENDOR data of O−2 in RbBr and KBr are compared with the ones in KCl for which two different types of O−2 ions were reported earlier. Interactions with the nearest neighbour alkali ions could be detected. The corresponding hyperfine and nuclear quadrupole coupling tensors were determined. For all cases, the ENDOR spectra could be explained in terms of a monovacancy model, i.e. the O−2 ion is replacing a single halide ion. One of the O−2 defects in KCl was found to be completely analogous to the ones found in KBr and RbBr. The second type of O−2 ion is also replacing a single halide ion and is believed to be perturbed by a nitrogen impurity.
Luminescence of Pb2+ and energy transfer from Pb2+ to rare earth ions in silicate oxyapatites
Authors: Lin Jun , Su Qiang 
Published: July 2007

AbstractThe Pb2+ luminescence in a series of silicate oxyapatites Me2(Y, Gd)8(SiO4)6O2, Me4Y6(SiO4)6O(Me = Mg, Ca, Sr) is reported and discussed in relation to the crystal structure. The maximum wavelengths of the excitation (1S03P1) and emission (3P1−1S0) bands of Pb2+ are independent of the Me:Y ratio (2:8 or 4:6), but they have lower energies in MgY‐oxyapatites than in CaY‐ and SrY‐oxyapatites. The Stokes shift of Pb2+ luminescence amounts to 11100 to 11400 cm−1, which does not depend strongly on the host composition. There exists a mutual energy transfer between Pb2+ and Gd2+ in Sr2Gd8(SiO4)6O2. At last, the dependence of the energy transfer efficiency of Pb2+−Sm3+, Tb3+, Dy3+ in Sr2(La, Gd)8(SiO4)6O2 and Ca2(Y, Gd)8(SiO4)6O2 on their doping concentrations was studied in more detail.
Spectroscopic characteristics of color centers produced in a LiF crystal surface layer by microwave discharge
Authors: Ter‐mikirtychev V. V. , Tsuboi T. , Konyzhev M. E. , Danilov V. P. 
Published: July 2007

AbstractWe have studied the absorption and luminescence spectra of color centers in a LiF crystal surface thin layer which are produced by low energy electrons from a secondary electron emission microwave discharge. The intensityratio of the absorption band due to the F2 color center to the band due to the F center was observed to be much higher than the ratio of these color centers produced in the whole bulk crystal. It was found that the F−2 center is produced in a thin layer through a selective two‐step photoionization of F2 color center by irradiation with the 514.5 nm Ar+ laser line. A mechanism of colorcenter formation in the thin layer is discussed.
Effective cubic nonlinear response of a coated granular composite medium
Authors: Liu Xin‐yu , Li Zhen‐ya 
Published: July 2007

AbstractAn approximate expansion method is developed to study the bulk effective response of a nonlinear dielectric granular composite. The system considered here is composed of some grains with the same structure and properties (linear cores and cubic nonlinear concentric shells) randomly distributed in a linear host. An approximate method is invoked for deducing the effective nonlinear susceptibility of such a system. As we introduce a structural parameter λ representing the thickness of the coating shell, we discuss the influence of this structural parameter on the bulk effective nonlinear response in the whole system. Through adjusting both the dielectric properties of each component and the structural parameter, we can obtain the enhancement of the effective nonlinear response of the system. Our solutions are valid and useful to deal with a nonlinear dielectric system with a small volume fraction of nonlinear grains.
Calculation of tensor constants for quasicrystal aggregates
Authors: Divinski S. V. , Dnieprenko V. N. , Zheng Wen‐Chen 
Published: July 2007

AbstractAn approach for calculating the tensor constants of single quasicrystals by the data on textured aggregates of structure elements has been proposed. The distribution of the structure elements on orientation has been approximated by a model function that describes well a broad spectrum of possible textures ranging from a single orientation to the fully isotropic distribution. The anisotropy of two‐rank and four‐rank tensor properties has been analysed for decagonal quasicrystals. The melt‐spun textured decagonal quasicrystals have been found to reveal an appreciable anisotropy of physical properties even in the ribbon plane.
A comparative study of birch and kumar equations of state under high pressure NaCl as an example
Authors: Kumar M. , Bedi S. S. 
Published: July 2007

AbstractA comparative study of the Birch and Kumar equations of state is presented to demonstrate their validity for a wide range of pressure, viz. from atmospheric pressure up to the structural transition pressure. It is found that these equations of state are equally good in the low pressure range anddeviations occur under the effect of high pressures. The comparison demonstrates that the results obtained by the Kumar equation of state are in better agreement with the experimental data as compared with the Birch equation of state. The application of Kumar's equation of state is also discussed at high temperatures, viz. from room temperature up to the melting temperature. The good agreement between theory and experiment demonstrates the validity of the Kumar equation of state recently proposed for the entire range of pressure and temperature.
Effects of confined longitudinal optical phonons on the binding energy of the impurity in a quantum well
Authors: Moukhliss S. , Sayouri S. , Fliyou M. 
Published: July 2007

AbstractThe effects of the confined LO phonon‐electron interaction on the binding energy of shallow donors confined in a GaAsGa1−xAlxAs quantum well are investigated. The barrier potential height is taken into account. Using the variational method of Lee‐Low‐Pines, we find that the effect of this interaction is negligible for very narrow quantum wells. For thick quantum wells, the polaronic contribution is quite large.
Two‐point conductivity tensor of nonmultilayer magnetic systems
Authors: Sheng L. , Gu R. Y. , Xing D. Y. , Dong Jin‐ming 
Published: July 2007

AbstractThe transport properties of nonmultilayer magnetic systems are described in terms of a semiclassical Boltzmann equation. Interfaces are modeled asthin mixed interlayers so that both bulk impurity scattering and interface scattering are included in a position‐dependent relaxation time. Theresulting expression for the two‐point conductivity tensor is in accordance with that derived from the real‐space Kubo formula, indicating a close connection between the semiclassical method and the quantum approach.
Electronic transmission coefficient for solid‐state structures with spatially variable anisotropic electronic effective mass
Authors: Kupka M. 
Published: July 2007

AbstractThe method for calculating the electronic transmission coefficient for elastic electronic transport through a layered structure with spatially variable anisotropic effective mass and one‐electron potential energy is proposed. In this method, the transmission coefficient is evaluated by means of a certain matrix quantity assigned to any region of the sample. Thismatrix is determined by functional shapes of the reciprocal effective mass tensor and a one‐particle potential energy in a given region as wellas by the energy and group velocity of an incident electron. As an example, the transmission coefficients are calculated for a triple‐barrier structure as well as for a structure obtained by replacing the inner potential barrier by an anisotropic conductive layer.
X, l, and γ lines in low temperature photoluminescence spectra ofal0.47Ga0.53As0.035Sb0.965 alloys
Authors: Tronc P. , Mani H. , Maciejko R. , Reid B. , Leroux M. , Lazzari J. L. , Segura‐fouillant C. 
Published: July 2007

AbstractIn Al0.47Ga0.53As0.035Sb0.965 layers nearly lattice‐matched to GaSb(100) substrates, the X, L, and Γ optical transitions have energies close to each other. By varying the temperature of the samples and the power of the laser beam, one can separatethe contribution of every transition in the photoluminescence spectra and measure the different transition energies versus temperature. The experiments provide very accurate measurements of the difference between the above transition energies and, together with X‐ray double diffraction measurements, show the existence of fluctuations of composition within the alloy.
Two‐photon absorption and magnetoabsorption of P excitons in β‐ZnP2
Authors: Engbring J. , Fröhlich D. , Schepe R. , Spitzer S. , Arimoto O. , Nakamura K. 
Published: July 2007

AbstractElectronic transitions in biaxial β‐ZnP2 are studied by two‐photon absorption. The anisotropy of the crystal leads to a large energy splitting of the P excitons. The energy shift of the P excitons and Landau transitions are observed in a magnetic field up to 6T. We present a theory which describes the anisotropic P excitons in a magnetic field. The analysis of the experimental data allows the determination of the anisotropic dielectric constants and effective masses of the valence and conduction bands.
Raman scattering in 2‐Amino‐5‐Nitropyridine‐L‐(+)‐Tartrate single crystals
Authors: Oussaïd M. , Kemiche M. , Becker P. , Carabatos‐nédelec C. , Watanabe O. 
Published: July 2007

AbstractSingle crystals of 2‐amino‐5‐nitropyridine‐L‐(+)‐tartrate (ANPT) have been studied by Raman scattering and infrared absorption at room temperature and at 10 K. The crystal ofmonoclinic symmetry space group P21 (C22) undergoes no detectable structural phase transition between these two temperatures. The room temperature spectra were compared with those of parent compounds in order to propose a tentative assignment of the observed vibrational modes. Particular attention was paid to the hydrogen bond modes.
BaTiO3 crystal structure phase transition caused by the Jahn‐Teller effect and the model of like‐hydrogen molecule‐ion (H)
Authors: Zhang Duan‐Ming , Yu Bo‐Ming , Li Yuan , Zhang Xin‐Yu , Lai Jian‐Jun , Li Hua 
Published: July 2007

AbstractBy utilizing the Jahn‐Teller effect, we discuss the structural phase transition of BaTiO3 crystals. By taking into account the simple model of the like‐hydrogen molecule‐ion (H) and the effective point charge, we compute the structural paraelectrical‐ferroelectrical phase transition temperature Tc of BaTiO3. The theoretical value obtained is in good agreement with the experimental results.