bluuebunny/crossref_metadata_2025_split huggingface dataset:
Mixed Valence Phase Transition in Ferromagnets
Authors: Valkov V. V. , Ovchinnikov S. G. 
Published: July 2007

AbstractThe electronic phase transitions in ferromagnetic semiconductors connected with redistribution of electrons between localized and band states due to s‐d Coulomb and exchange interactions and hybridization is investigated. There are several regions on the phase diagram of the system at T = 0 with integral or mixed valence. The temperature behaviour is determined by the ground state and the transition between different valence state may be smooth as well as sharp.
Effective Pair Potential and Thermodynamic Properties of Liquid Noble Metals
Authors: Joarder R. N. , Rao R. V. Gopala 
Published: July 2007

AbstractThe variational method associated with the Gibbs‐Bogolyubov inequality in the thermodynamic perturbation method allows the determination of the thermodynamic properties of liquid noble metals. The interionic potentials are generated from the energy‐wave‐number characteristics obtained from a model pseudopotential in conjunction with the dielectric response function of the interacting electron gas. The variation of the packing density with volume and temperature shows a relatively hard core pseudoatom and it is shown that under pressure, along the melting line, the packing density actually increases for noble metals unlike the simple metals. In addition, the results compare favourably with experiments as well as the calculations of Moriarty based on Harrison's generalised transition metal pseudopotential.
Equation for the Melting Curve of Solids under High Pressure
Authors: Boguslavskii Yu. YaL 
Published: July 2007

AbstractSimon's equation of the melting curve is obtained using the Clausius‐Clapeyron equation in the linear approximation of the pressure dependence of the melting entropy and the volume change at the melting point. The constants in Simon's equation are calculated in this approximation for the alkali metals Li, Na, K, Rb, Cs and also for hydrogen, H2, and argon. It is shown that one can obtain the constants of Simon's equation in a pressure range which is wider than the region of the thermodynamical validity of Simon's equation by averaging the values of the constants determined in different points of the melting curves. The constants obtained by this manner agree well with the experimental data.
Spin–Orbit Interaction in Superexchange with Orbital Degeneracy. I. Coupling Coefficients and Operator Algebra for the Chain 0* ⊂ SU2
Authors: Blaszak M. 
Published: July 2007

AbstractBecause the spin–orbit splitting in the strong crystal field approximation leaves more degeneracy than that expected from the group theory, all considerations should be extended from one symmetry group to the chain of groups. The nΓγ and nΓ symbols for octahedral spinor group O* and the njΓ and njΓ symbols for the chain O* ⊂ SU2 are introduced. Irreducible operator sets for both groups are defined and the connections between them are found. The connection between operators from associated spaces for the O* group is found also.
Electron‐Energy‐Loss Spectroscopy of Different Al2O3 Modifications. I. Energy Loss Function, Dielectric Function, Oscillator Strength Sum Rule and the Quantity ϵ2E
Authors: Tews W. , Gründler R. 
Published: July 2007

AbstractUsing 40 keV electrons electron‐energy‐loss measurements are performed on amorphous, polycrystalline γ‐ and α‐Al2O3 thin films. From the electron‐energy‐loss spectra measured in the energy range up to 40 eV the energy‐dependent energy loss function Im(–ϵ−1) is derived. The dielectric function, optical constants, and neff(E) are computed using the Kramers‐Kronig analysis and wellknown formulae. The quantity ϵ2E is compared with a simple joint density of states model.
Coherent Motion of Triplet Excitons in Molecular Crystals with Two Differently Oriented Molecules per Unit Cell. Application to the Charge Transfer Crystal Anthracene/Tetracyanobenzene
Authors: Schmid U. , Reineker P. 
Published: July 2007

AbstractThe dynamics of triplet Frenkel excitons moving coherently in a molecular crystal is investigated by a model calculation. The model assumes that the crystal has two differently oriented molecules per unit cell and that the interaction between the molecules in different crystal directions is strongly anisotropic. The Hamiltonian of the model consists of an electronic and a spin part. The first part contains the excitation energy of the electron‐hole pair and the interaction matrix element for the coherent exciton transport. The second part comprises the Zeeman energy of the triplet spin and the fine‐structure terms of the differently oriented molecules. The eigenvalue problem is solved for parameters of anthracene/tetracyanobenzene in the case of zero and high magnetic fields. In zero field the experimentally observed doublet structure of the ODMR lines can be explained, in high field especially the ESR line positions for several orientations of the crystal in the field are discussed.
Thermoluminescence of Coloured Alkali Halides
Authors: Murti Y. V. G. S. , Sucheta N. 
Published: July 2007

AbstractA rigorous analysis of the thermostimulated luminescence of several irradiated alkali halide crystals is presented. The accuracy of the fitting of glow curves to theoretical models is examined with the help of a statistical chi‐square test and the applicability of the different physical models is discussed.
Electron–Hole Correlation Effects on Donor–Acceptor Pairs
Authors: Kartheuser E. , Babcenco A. , Evrard R. 
Published: July 2007

AbstractThe effect of the electron–hole correlations on the effective mass electronic states of donor–acceptor (DA) pairs in polar semiconductors is investigated. Variational calculations are carried out and compared with previous theoretical work in the case of GaP and ZnSe. Analytic expressions for the energy, charge density, and pair distribution function of DA pairs are obtained as a function of the pair separation R. It is shown that whereas the energy and the charge distribution of a DA pair are only slightly affected by the electron–hole correlations, the pair distribution function shows a strong enhancement at short electron–hole distance.
Modified Self‐Scattering Procedure for Monte‐Carlo Simulation of Hot Electrons
Authors: Kozlov V. A. , Nefedov I. M. 
Published: July 2007

AbstractThe generalization of the self‐scattering procedure of the electron trajectory simulation in semiconductors for the arbitrary scattering rates w(p, p′) from the state with momentum p to p′ is suggested. In the method proposed instead of the total scattering rate per unit time v (p) = f w(p, p′) d3p′ the random function ξ(p) with the average value 〈ξ(p)〉 = v(p) is introduced. Such simulation procedure corresponds to the calculation of v(p) along the simulated trajectory by means of the Monte‐Carlo method. The comparison of the commonly employed self‐scattering procedure with the suggested one is performed.
Infinite Range Ising Models with a Tricritical Point
Authors: Lee B. S. 
Published: July 2007

AbstractTwo infinite range Ising models are solved exactly using a microcanonical ensemble in the longrange order parameter. Classical tricritical points exist for both models. The first model involving two‐spin and four‐spin terms is relevant to the compressible Ising model. The other model is the infinite range version of the Blume‐Capel spin‐one Ising model. In both the cases the exact free‐energy functions calculated are examples of exact classical Landau free‐energy functions with tricritical point behaviour.
Symmetries of Luminescent Centers in NaCl:Pb2+ Excited in the A‐Absorption Band
Authors: Benci S. , Fermi F. , Reverberi R. 
Published: July 2007

AbstractPolarized luminescence measurements are used to study the luminescent characteristics of NaCl:Pb2+ excited into the A‐absorption band. For the E1 = 4.01 eV emission it is found that the luminescent centers have tetragonal and trigonal symmetries due to the Jahn‐Teller effect that allows the coexistence of tetragonal and trigonal minima on the 3T1u APES while the E2 = 3.29 eV emission band is due to aggregates of impurities in the {111} planes with trigonal symmetry. The charge compensating vacancy associated to the impurity gives a meaningless effect on the luminescence polarization and its position cannot be ascertained.
Theory of Non‐Radiative Multiphonon Capture Processes. Solution of Old Controversies
Authors: Peuker K. , Enderlein R. , Schenk A. , Gutsche E. 
Published: July 2007

AbstractThe solution is given for long persisting controversial problems in the theory of non‐radiative multiphonon capture of free carriers. Taking the adiabatic wave functions as basic states for the perturbational treatment of the transition probability particular attention is focused on the correct determination of the transition matrix elements. In this framework it is shown that to first order in the non‐diagonal matrix element of the electron‐lattice interaction all approaches developed so far (Condon approximation, non‐Condon approximation, static approximation, etc.) lead to the same result, in contradiction to statements in the literature. In particular, the reason is found why earlier results for the transition rate within the adiabatic and Condon approximation are much too small. The static approximation is shown to be the lowest approximation to the adiabatic approach.
Shallow Acceptors in Cadmium Telluride
Authors: Molva F. , Chamonal J. P. , Pautrat J. L. 
Published: July 2007

AbstractThe photoluminescence spectroscopy of undoped CdTe crystals provides information on two acceptors which are the main contaminants of as‐grown crystals. These acceptors called y and z have their respective ionization energies at 147 and 108 meV. A complete series of two hole replicas is observed for y and only one for z. These acceptors are believed to be due to Cu and Ag impurities. Backdoping experiments with Li and Na give rise to new transitions. From the conduction band–acceptor level transitions, the ionization energies are respectively obtained to 57.8 and 58.8 meV. In the case of Li, some extra‐lines are tentatively identified as phonon interacting two‐hole transitions.
Derivation of the Scattering Model for Josephson Effects from the Ginzburg‐Landau Equations
Authors: Orlowski M. C. L. 
Published: July 2007

AbstractThe scattering model for the Josephson effects as proposed some years ago is rigorously derived from the Ginzburg‐Landau equations. Along these lines the validity of the scattering model and new aspects of the present derivation are discussed. The derivation exhibits the relevance for the fermionic character of the Cooper electrons in the weak‐link situation. Attention is called to the possible application of this model in field theories for dual string.
Micromagnetic Theory of Phase Transitions in Inhomogeneous Ferromagnets. V. Magnetic Phase Transition of Amorphous Fe10Ni70B16P4
Authors: Meyer R. , Kronmüller H. 
Published: July 2007

AbstractThe static magnetization curves and the dc susceptibility of amorphous Fe10Ni70B16P4 are measured in the low temperature region and in the vicinity of the critical region up to fields of μ0H = 1 T. The behaviour near the Curie temperature is found to obey critical material laws with critical indices: β = 0.44 ± 0.02; γ = 1.63 ± 0.07; δ = 4.82 ± 0.20, and the ferromagnetic Curie temperature TC = (191.1 ± 0.1) K. The critical indices satisfy the static scaling law γ = β(δ – 1). The exponent γ is found to apply over a wide temperature range of T – TC ± 100 K. The existence of this extended critical region is attributed to the correlation between temperature dependent spin clusters and the static fluctuations of the exchange interactions.
Cohesion, Phase Transition, Elastic and Dielectric Properties of Group IV Semiconductors
Authors: Ghosh A. , Banerjee L. K. , Basu A. N. 
Published: July 2007

AbstractBased on the energetics of bond formation and a statistical model analysis of the electronic charge density deformation in a covalent crystal the existence of an effective three‐body interaction is suggested between the particles in a lattice. In addition to describing the different properties of group IV semiconductors the present model together with the idea of the structure dependence of potential parameters provides a satisfactory description of the polymorphic phase transition of these substances.
Relaxation and Optical Processes in Impurity Centres with Two‐Well Adiabatic Potential
Authors: Kulagin S. A. , Osadko I. S. 
Published: July 2007

AbstractThe theory of interwell and intrawell relaxation is developed. Numerical calculation of appropriate transition propabilities is realized. It shows relaxation dependence on temperature and two‐well system parameters. On the basis of the same theory two specific experimental effects (the appearance of “multiplets” in quasi‐line spectra and “hole‐burning”) are analyzed.
Equation of State of SiGe Solid Solution
Authors: Soma T. , Iwanami H. , Matsuo H. 
Published: July 2007

AbstractThe equation of state of the SiGe solid solution is studied using the previous electronic theory based on pseudopotentials. The calculated results for the Si1−xGex solid solution are not monotonous as function of x, and show the softening of the crystal under compression in comparison with those of pure Ge.
Isoelectronic Impurity Te in CdS1−xSex Mixed Crystals
Authors: Goede O. , Heimbrodt W. 
Published: July 2007

AbstractIn hexagonal CdS1−xSex amalgamation‐type mixed crystals the isoelectronic impurity Te is studied as a function of the composition x in the range 0 ≦ x ≦ 1 by emission and excitation measurements at 4 and 77 K. The binding energies of excitons bound to isolated Te impurities and nearest‐neighbour Te pairs are found to decrease strongly with increasing x. For x ⪆ 0.85 isolated Te cannot bind an exciton and, therefore, in CdSe only Te pairs lead to bound impurity states. The measured relaxation energies and halfwidths of the corresponding emission and excitation bands yield information on the x‐dependence of the electron‐phonon interaction for both types of impurities. The experimental results are discussed on the basis of a simple potential‐well model using variational calculations.
Effect of Size Quantization on the Electronic Heat Capacity in Ultrathin Films of Non‐Parabolic Semiconductors
Authors: Ghatak K. P. , Ghosh K. K. , Mukherjee H. M. , Chakravarti A. N. 
Published: July 2007

AbstractAn attempt is made to investigate the effect of size quantization on the electronic heat capacity in ultrathin films of Kane‐type non‐parabolic semiconductors. It is found, taking n‐InSb as an example, that the heat capacity corresponding to a given carrier concentration per unit area increases considerably with decreasing film thickness. The heat capacity corresponding to a given film thickness is also observed to increase with increasing carrier concentration. Besides, humps are seen to appear in the variation of the heat capacity with film thickness as a direct consequence of energy quantization along the direction normal to the film.
Thermal Dissociation Energy of F‐Centers in Alkali Halides
Authors: Dalal M. L. , Sivaraman S. , Murti Y. V. G. S. 
Published: July 2007

AbstractThe electrolytic coloration process is employed to obtain the mobility of F‐centers in KI, KBr, KCl, and NaCl crystals by measuring the drift velocity of the color cloud, during its withdrawal as function of temperature. The motion of the color cloud is timed between two previously marked lines and the field was also measured between them. An optical arrangement is used to project the crystal on a screen. The thermal dissociation energy EF is deduced for all these crystals which comes out to be 2.33, 2.66, 2.88, and 2.45 eV for KI, KBr, KCl, and NaCl crystals, respectively. The variation of the ratio of the fields (Uun/Ucol) in the colored and uncolored regions is also studied with temperature. A Mollwo‐Ivey type of relation is also tried between EF and various physical properties of the crystals, from the extrapolation of which the hS value for NaI is deduced which agrees very well with the reported value, where hS is the Schottky defect formation energy.
On the Lineshape of the Conduction Electron Spin Resonance in Thick Metallic Samples under the Anomalous Skin‐Effect Conditions
Authors: Ustinov V. V. , Khusainov D. Z. 
Published: July 2007

AbstractThe influence is investigated of quantum effects caused by the comparability of the effective de Broglie wavelength of the electron and skin depth, on the conduction electron spin resonance lineshape in thick metallic samples under anomalous skin‐effect conditions. The dependence of the asymmetry parameter of the line of derivative of the power absorbed with respect to the magnetic field (A/B ratio) on the value of the parameter A equal to the ratio of effective de Broglie wavelength of the electron and double skin depth is calculated.
Covalent Contribution to the Bond Energy of Phases with Ll2 Structure
Authors: Bogdanov V. I. , Ruban A. V. , Fuks D. L. 
Published: July 2007

AbstractThe Brillouin‐Wigner pseudopotential perturbation theory is used for calculating multi‐ion interaction effects contributing to the mixing energy and the total bond energy of phases with Ll2 structure. It is shown that these contributions are of the same order as the mixing energy itself and they must be taken into account in theoretical investigations of the order–disorder phase transition temperature. Numerical results for some alloys with Ll2 structure are presented and the phase transition temperatures for Cu3Au and Au3Cu are discussed.
Calculated Low Frequency Phonon Dispersion in Anthracene‐d10
Authors: Chaplot S. L. , Pawley G. S. , Dorner B. , Jindal V. K. , Kalus J. , Natkaniec I. 
Published: July 2007

AbstractA model is presented for the low frequency lattice vibrations in anthracene‐d10, which involve the molecular external vibrations and certain internal distortions, namely the butterfly and twisting motions. The calculated phonon dispersion relation is compared with experimental results from neutron coherent inelastic scattering, Raman scattering, and infrared absorption.
The Γ‐Point Band Structure Parameters of CdxHg1−xSe (x ≦ 0.1) Mixed Crystals from Thermomagnetic Measurements
Authors: Iwanowski R. J. 
Published: July 2007

AbstractMeasurements of thermoelectric power as a function of magnetic field, α(H), at 30 and 100 K in undoped n‐CdxHg1−xSe (x = 0.05; 0.10) mixed crystals are performed. Electron effective mass at the Fermi level vs. carrier concentration is determined. The fitting of theory to the experimental m(n) dependences leads to the verification of certain band structure parameters. In particular, a modified E0, (x, T) dependence for CdxHg1−xSe in the range T ≦ 100 K is proposed. Additional argument for the modified E0(x, T) dependence is given on the basis of the longitudinal Nernst‐Ettingshausen effect (Δα∞) measurements at 30 K. The theory, which includes the most important scattering mechanisms, gives much better agreement with the experiment when applying the new values of disorder scattering parameters V and W in calculations.
Composition Dependence of the Electron Fermi Surfaces Tilt in Bi1−xSbx Alloys (0 ≦ x ⪅ 0.22)
Authors: Braune W. , Fellmuth B. , Kubicki N. , Herrmann R. 
Published: July 2007

AbstractThe composition dependence of the Fermi surfaces tilt out of the basal plane in Bi1−xSbx alloys (0 ≤ x ⪅ 0.22) is determined by investigating the anisotropy of the propagation of magnetoplasma waves in the Voigt configuration B ⊥ C2 ∥ k. In the semimetallic phase (0 ≤ x ⪅ 0.07) no change is observed whereas in the semiconducting phase (0.07 ⪅ x ⪅ 0.22) a strong composition dependence is obtained, which is marked distinctly especially near the semimetal‐semiconductor phase transitions (at x ≈ 0.07 and x ≈ 0.22) and in the composition region 0.15 < x < 0.18. The dispersion relation of the charge carriers, which is based on the deformation theory, connects the characteristics of the Fermi surfaces with the sub‐lattice displacement, the rhombohedral shear, and the spin–orbit coupling. A first analysis indicates that those composition dependences of these quantities which may cause the complex change of the charge carrier spectrum found are more complicated than assumed till now.
On Superconductivity in Narrow‐Band Alloys
Authors: Beckmann A. , Kolley E. , Kolley W. 
Published: July 2007

AbstractTwo different approaches to disordered superconductors are examined to derive a random contact model on the basis of nonlocal electron‐phonon coupling. The formalism, aimed at transition metal alloys in the weak‐coupling regime, takes into account both, the finite‐range pairing interaction, and the intraatomic Coulomb repulsion of the tightly bound electrons. The superconducting transition temperature of AcB1−c alloys is calculated for the nonmagnetic and magnetic cases.
A Double Chain Approximation to the Ising Model
Authors: Plascak J. A. , Silva N. P. 
Published: July 2007

AbstractTo calculate thermodynamic properties of the anisotropic Ising model, a double chain approximation (DCA), based on Bogolyubov's variational procedure, is presented. The critical temperatures are compared to those obtained by the usual mean field approximation (MFA), the linear chain approximation (LCA), and the exact or series results, when existing. A fitting of the spontaneous polarization and the dielectric constant data for the quasi‐one‐dimensional ferroelectric crystal PMDP (PbDPO4) is also made.
Effect of Surface Polarization on the Absorption Spectrum of an F‐Center
Authors: Mijangos R. R. , Marin J. L. , Clark A. , Navarro A. , Mejía C. Ruíz 
Published: July 2007

AbstractThe effect of surface polarization on the ground state of an Fs center in NaCl and KCl is studied. The energy of this state is calculated by perturbative and variational methods. The F band position of this center is obtained also, for some alkali halides, by first order perturbation. It is found that these effects are, in general, small.
Temperature Dependence of the Phonon Spectra of β‐AgI
Authors: Kostadinov I. Z. , Binh Vu Thi 
Published: July 2007

AbstractThe temperature dependence of the far infrared absorption of β‐AgI is calculated. The increasing occupation of higher energy minima by Ag+ ions leads to the appearance to two low energy phonon lines with frequencies of 38 cm−1 and 85 cm−1, respectively, discussed lately by Brafman and Vardeny. The current calculations taking into account the hopping kinetics for the pseudospin variables lead to an infrared conductivity similar to that observed by Funke and Jost. The activation energy of 75 K is in good agreement with the temperature dependence of the infrared conductivity discussed by Burns, Dacol, and Shafer.
Spin Glass and Superantiferromagnet in the Site Diluted Ising Model on the Frustrated Square and F.C.C. Lattices with First‐ and Second‐Neighbor Interactions
Authors: Katsura S. , Fujiki S. , Suenaga T. , Nagahara I. 
Published: July 2007

AbstractThe diluted Ising model of the frustrated square and face‐centred cubic lattices with first‐ and second‐neighbor interactions are considered by the square‐cluster approximation. Phase boundaries between the paramagnetic and ordered (ferromagnetic, superantiferromagnetic (antiferromagnetic states of the second kind in f.c.c.) and spin glass) phases are obtained. The result explains qualitatively the experiment on MnpCd1–pTe.