bluuebunny/crossref_metadata_2025_split huggingface dataset:
Raman Scattering from Tunneling of Substitutional Molecules in Cubic Crystals
Authors: Dick B. G. 
Published: July 2007

AbstractRaman scattering cross‐sections for tunneling transitions of diatomic molecular or off‐center defects in cubically symmetric environments are derived for 〈100〉, 〈111〉, and 〈110〉 defects for arbitrary scattering geometry. These cross‐sections are expressed in terms of the anisotropic electronic polarizability components of the defect.
ESR and Annealing of Defect Centers Trapped in Irradiated Cadmium Chlorate
Authors: da Silva E. C. , Torriani I. C. L. , Leite N. F. , Hennies C. E. , Évora C. , Vargas H. 
Published: July 2007

AbstractBy ESR and optical absorption experiments the paramagnetic centers O, ClO2 and (ClO2Cl)− are identified in irradiated single crystal Cd(ClO3)2. The ESR spectrum and its angular dependence show that the centers have one magnetically equivalent site per unit cell. The thermal annealing of the centers show that they follow a first‐order kinetic activation process. Crystallographic data are obtained for Cd(ClO3)2 not available in the literature.
Low‐Temperature Specific Heat of VN0.74 and VN0.89
Authors: Lovtchinov V. , Mädge H. , Christensen A. N. 
Published: July 2007

AbstractThe specific heat and superconducting critical temperature of VN0.74 and VN0.89 are measured in the temperature range 1.8 < T < 20 K. The density of states at the Fermi level is determined on the basis of these results. The dependence of the density of states on the parameter of the electron—phonon interaction is discussed as well. It may be expected that increasing the N content of the mentioned compounds would lead to the intensification of the electron—phonon interaction and the increase of the density of states at the Fermi level and the critical temperature, respectively.
Charge Carrier Scattering on Neutral Centres in n‐Si
Authors: Dmitrenko N. N. , Kurilo P. M. , Litovchenko P. G. , Lutsyak V. S. , Nitsovich V. M. 
Published: July 2007

AbstractA discussion of the basic models for the calculation of the relaxation time for scattering on neutral impurities is given. A comparison is made between the experimental results of scattering of electrons on neutral oxygen atoms in n‐Si and the theoretical data obtained on the basis of three models. It is shown that an S‐partial wave approximation with a phase shift linear in the momentum, taking into account Friedel's sum rules and the many‐channel scattering in many‐valley semi‐conductors, gives a good agreement with experimental results for impurity concentrations from 1013 to 1017 cm−3 in the temperature interval 77 to 300 K.
Ionization Loss Spectra of FeS2
Authors: Kätzel W. , Berndt K. 
Published: July 2007

AbstractThe technique of energy loss spectroscopy is applied to the semiconducting compound FeS2. A comparison is made of the ionization losses with the density of unoccupied states. Taking into account other spectroscopic data the full density of states of the FeS2 valence and conduction electrons is confirmed.
Study of Lattice Instability by mm‐Wave Magnetoplasma Reflection in PbTeSnTe Compound Semiconductors
Authors: Nishi S. , Kawamura H. , Murase K. 
Published: July 2007

AbstractThe static dielectric constant ϵs in Pb1−xSnxTe (x = 0 to 0.4) single crystals is determined from a magnetoplasma reflection measurement between 4.2 and 100 K. At high temperatures ϵs increases with increasing temperature obeying a Curie law. The Curie constant is practically unchanged for different alloy composition, and the inverse static dielectric constant at 4.2 K decreases lineaarly with x, going to zero at alloy composition x = 0.35. At x = 0.40, a phase transition is observed at 20 K. The temperature dependence of ϵs is explained by anharmonic terms of lattice vibrations.
Molecular Liquid Model and Electronic Structure of Amorphous Silicon and Germanium
Authors: Halder N. C. , Shenoy S. R. 
Published: July 2007

AbstractThe atomic and electronic structure of amorphous Si and Ge are investigated by the molecular liquid model (MLM). The theoretical structure factor is calculated using simple parameters — nearest neighbor distance, packing density, and coordination number. The electronic density of states obtained with the MLM structure factor, and nonlocal energy dependent pseudopotential in second order perturbation theory, show good agreement with experimental and other theoretical results.
Theory of Absorption by Excition Polaritons in a Spatially Dispersive Medium
Authors: Nkoma J. S. 
Published: July 2007

AbstractAbsorption by normal modes of excition polaritons under normal incidence excitation is considered and an effective absorption coefficient is derived by considering the energy fluxes of the individual modes. The frequency integrated absorption in the presence of spatial dispersion is found to be a constant for large damping and approaches zero for zero damping. It is also found to oscillate for small depths due to interference of the polariton modes. Excition mass variations are also considered. The derived expressions are illustrated by parameters modelling the Is exciton of PbI2.
Discontinuous Phase Transitions Induced by Magnetic Field in a Ferromagnet such as U3X4. Application to U3As4
Authors: Kowalczyk B. 
Published: July 2007

AbstractIn the framework of a microscopic spin model which contains the fourth‐order crystal‐field anisotropy terms it is shown that the first‐order phase transitions induced by magnetic field are possible in ferromagnets such as U3X4. Using the variational method the behaviour of the system in external fields of various orientations at zero temperature is discussed. The critical field as a function of Hamiltonian parameters and the tricritical point line are found. The dependence of the magnetization on the magnetic field value is also determined. The results obtained are qualitatively consistent with the experimental data for U3As4.
Cluster MO Calculations of Electronic Structure and X‐Ray Emission Spectra of Carbide Alloys TixV1−xC
Authors: Ivanovskii A. L. , Gubanov V. A. , Zhukov V. P. , Shveikin G. P. 
Published: July 2007

AbstractResults are given of calculations of the electronic structure of TixV1−xC solid solutions within a wide range of different compositions by means of the semi‐empirical molecular orbital method in the cluster model. The calculated X‐ray emission spectra are in reasonably good agreement with experimental data.
Thermodynamical Values of a Uniaxial Two‐Sublattice Ferromagnet in a Magnetic Field
Authors: Kazakov A. A. , Litvinenko N. A. 
Published: July 2007

AbstractThe magnetization of a uniaxial two‐sublattice ferromagnet with anisotropy of the pair and oneion type in longitudinal and transverse magnetic fields is investigated using the method of parametrical two‐times Green temperature functions. The methods of calculation of the thermodynamical characteristics of the system in low‐ and high‐temperature regions are discussed.
A First Principles Model of Energetical Trap Distributions in Solids. I. The Linear Finite Defect Chain
Authors: Hamann C. 
Published: July 2007

AbstractBased on the real structure of solids a model of the finite defect chain is developed. Preserving a general validity the model allows the treatment of arbitrary potential functions containing the Coulomb potential as a case of special interest. For this potential the model leads to an analytical derivation of the exponential trap distribution, this way being physically testified for the first time.
Resonant Behaviour of X‐Ray Intensities in Metallic Nickel Near the 2p Threshold
Authors: Riehle F. 
Published: July 2007

AbstractThe Lα and Lβ lines of metallic nickel and the X‐ray isochromats recorded at quantum energies in the vicinity of these lines are reported. An X‐ray spectrum with constant energy of the final state (XCEF) is defined and yields resonance‐like intensity variations of the bremsstrahlung similar to the rare earth metals. The energy dependence of the resonances is in qualitative agreement with the model of Wendin and Nuroh showing the importance of transitions involving normally empty localised d‐states.
Theory of Absorption Profiles of Molecular Transitions in Dense Media
Authors: Paerschke H. , Süsse K.‐E. , Welsch D.‐G. 
Published: July 2007

AbstractWithin the framework of quantum theory the radiationless phase relaxation of a molecular transition in a dense medium is described by an integro‐differential equation. From the Fourier transform of this equation formulas are derived for calculating the corresponding absorption profiles. For the case that the acoustic phonons of the medium are responsible for the phase relaxation a detailed discussion of the resulting absorption profiles is given.
Comparison of Experimentally and Theoretically Determined Dipole Concentrations of NaCl:Ca++ Considering Aggregation Phenomena
Authors: Grau P. , Dubiel M. , Berg G. 
Published: July 2007

AbstractThe equilibrium state of impurity–vacancy dipoles at RT is calculated by means of experimental determined association energies of the different dipole aggregates and of the point charge approximation, respectively. A comparison with experimental results originating in dielectric loss measurements shows a good agreement, especially with the results computed by the experimentally determined energies. It is possible to quench‐in dipole concentrations higher than the equilibrium value by cooling down the samples from 600 °C. But at higher impurity content partially aggregates or precipitates are formed during this cooling process, as a comparison with the Stasiw‐Teltow association theory shows.
Electronic Excitations in Some Transition Metals and Their Oxides. Characteristic Energy Loss Measurements up to 50 eV
Authors: Frandon J. , Brousseau B. , Pradal F. 
Published: July 2007

AbstractThe characteristic energy losses suffered by a 20 keV electron beam through thin films of some transition metals (Sc, Y, Zr, Hf) and of their oxides are measured using a magnetic spectrograph up to 50 eV. The energy loss function — Im 1/ε and the complex dielectric constant are calculated. It is shown that the electron excitation spectra of metals contain two main contributions in this energy range: one due to collective excitations of the conduction electrons, the other to the excitation of inner p‐electrons. In the case of oxides the spectra display three strong structures: there are probably two collective excitations of valence electrons followed by the excitation of inner p‐electrons of the metal.
Transient Light‐Induced Spatial Gratings by Successive Optical Coherent Pulses
Authors: Shtyrkov E. I. , Nevelskaya N. L. , Lobkov V. S. , Yarmukhametov N. G. 
Published: July 2007

AbstractA new optical quantum phenomenon by interference of atomic states is discussed. The possibility of formation of induced transient gratings in a resonant medium is shown in the case when the medium is excited by two laser pulses arriving at experimental sample noncoincident in time but from different direction. The theory of such gratings is presented for detuning of the incident light from resonance. A technique is developed for observing such gratings for the 4A2–2E(Ē) transition of ruby.
Crystal‐Independent Repulsive Hardness Parameters for Alkali Halides
Authors: Shanker J. , Agrawal D. P. 
Published: July 2007

AbstractIn the present paper an analysis is performed of interionic forces in alkali halides by adopting Smith's distortion model for repulsive interactions. This model represents the repulsive potential in terms of parameters which depend only on the ions. By treating the repulsive hardness parameters ϱ to be crystal independent the cohesive energies, bulk modulus and its pressure dependence are calculated for 16 alkali halides with NaCl structure. A distinguished feature of treating the parameters as ion dependent and crystal independent is that the values of ϱ do not remain the same for cation–cation, cation–anion, and anion–anion interactions. This is a modification over the traditional Born model where a common value of ϱ is taken for all the ion pairs. To make a simultaneous fit of the cohesive energy, bulk modulus, and its pressure dependence, it is essential to consider the van der Waals interactions as well as the three‐body interactions.
Study of Excitons in SiO2. Luminescent Centres as Exciton Detectors
Authors: Trukhin A. N. 
Published: July 2007

AbstractThe spectral and temperature dependences of the quantum yield of energy transfer to a luminescent detector by an exciton are studied in SiO2. The results obtained show, that in addition to the “hot” exciton migration there is a diffusion of the relaxed exciton. The exciton structure of SiO2, consists of three states, a self‐trapped exciton, a relaxed exciton, and a resonant exciton.
Energy Gap Determination in a‐As2S3 by Means of Faraday Rotation
Authors: Van Keybus P. Den , Vanhuyse B. , Grevendonk W. 
Published: July 2007

AbstractNon‐resonant interband Faraday rotation (FR) is measured in a‐As2S3 between 480 and 850 nm in a magnetic field up to 4 T at temperatures between 4 and 300 K. Analysis of the results by means of theoretical dispersion formulae reveals an energy gap EgFR of about 3.1 eV. This value is higher than the optical gap (2.36 eV) but is in agreement with the gap determined with dispersion measurements; from literature similar FR data are found for e‐Si where FR reveals a direct gap. The temperature influence is small. From 50 to 300 K, EgFR slowly diminishes, and has a constant value below 50 K.
Gain Spectrum of an e–h Liquid in Direct Gap Semiconductors
Authors: Haug H. , Thoai D. B. Tran 
Published: July 2007

AbstractThe gain spectrum of a degenerate electron–hole plasma for direct gap semiconductors is calculated as a function of the density and the temperature of the electronic excitations. The calculation contains the collision broadening in the single‐particle self‐energies and the excitonic enhancement due to the attractive electron–hole interaction in the plasma. For the example of GaAs the numerically calculated spectrum is shown to fit the experimentally determined spectrum.
Experimental Evidence of Asymmetry of the Bound Exciton Absorption Line in GaP:N
Authors: Sokolov V. I. , Chernyaev V. V. 
Published: July 2007

AbstractThe absorption and electroabsorption spectra in GaP:N at 77, 20.4, and 4.2 K are investigated around the A‐line. The change of the electroabsorption lineshape with decreasing temperature can be understood by assuming that the A‐line is asymmetric.
Stimulated Bremsstrahlung of Electrons in a Crystalline Lattice
Authors: Jivanyan H. A. 
Published: July 2007

AbstractOn the basis of classical and quantum theories the dynamics of electron scattering on a crystalline lattice in the presence of a strong electromagnetic wave is investigated. A condition is found under which coherent energy exchange takes place between the electron and external radiation along the lattice length. It makes possible the electron acceleration in crystals and leads to the effect of an electron beam space bunching.
The Effect of Partial Charge Transfer in NMP‐TCNQ
Authors: Papatriantafillou C. 
Published: July 2007

AbstractThere appears to exist clear experimental evidence that the charge transfer in the organic salt NMP‐TCNQ is only partial, but there is ambiguity with respect to the exact value of it. In the present paper the material is considered as a realization of the one‐dimensional disordered Hubbard model, and a study is made of its electronic properties using as a parameter the degree of charge transfer in it. For small deviations from the complete charge transfer the results reduce to previously presented ones. For moderate and large deviations there appears a strong intrinsic static disorder, while other band parameters remain unchanged.
On Functional Fourier Transformation for the Hubbard Model and Similar Models
Authors: Behn U. , Weller W. 
Published: July 2007

AbstractDescribing spin ↑ ‐electrons the particle number operators ni↓ are replaced under the functional integral directly by c‐numbers vi↓(t) using a δ‐functional instead of the Hubbard‐Stratonovich transformation. The Green function of the Hubbard model is thus exactly represented as an averaged Green function of electrons moving in a stochastic potential Uvi↓(t). The probability distribution for the stochastic process v ↓ containing the many body aspect and the information about the ↓‐electrons is determined. The vi↓(t) are only allowed to jump between 0 and 1 reflecting the property of Fermion particle number operators. This exact scheme can be interpreted as a dynamically generalized alloy analogy.
The Sublattice Displacement in Zincblende‐Type Crystals. Are the Internal Atomic Displacements Identical if the Same Deformation Is Caused Mechanically and Electrically?
Authors: Suisky D. , Enderlein R. , Lange H. 
Published: July 2007

AbstractRelations are derived for the Sublattice displacements in zincblende‐type crystals if the deformation is caused purely mechanically or electrically. The ratio of the two internal displacements induced by field (d) and strain (d) is expressed in terms of characteristic crystal constants. A plot of d/d versus the internal strain parameter ζ for the various zincblende‐type materials shows a strong increase of the Sublattice displacement ratio for ζ → 1 and a change of sign at ζ = 1.
Propagation of Electromagnetic Waves for a Rotation of the Magnetic Field from the Faraday to the Voigt Configuration
Authors: Stegmann R. , Oelgart G. 
Published: July 2007

AbstractIn a semiconducting bismuth‐antimony alloy, the propagation of electromagnetic waves is observed in the frequency range between 35 and 70 GHz and for temperatures of liquid helium in the total angular range between the Voigt and the Faraday configuration. The comparison with the theoretical dispersion behaviour, where a conductivity tensor corresponding to a tripartite ellipsoidal Fermi surface is utilized, allows a qualitative understanding of the wave propagation. The influence of the redistribution effects of the charge carriers among the individual parts of the Fermi surface in a quantizing magnetic field is essential, and the inaccurate knowledge of the energy level structure makes the comparison between experiment and theory difficult.
Nonradiative and Radiative Recombination in Lead Chalcogenides
Authors: Ziep O. , Genzow D. , Mocker M. , Herrmann K. H. 
Published: July 2007

AbstractIn a wide range of temperature and doping level the small signal lifetime for Auger recombination, spontaneous emission of radiation, and for spontaneous emission of plasmons is calculated in the compounds Pb0.78Sno. 22Te and Pb0.91Sno0.09Se. In the calculation degeneracy of the carrier gas and anisotropy of band structure is taken into account. At donor concentrations ND > 1019 cm−3, recombination by emission of plasmons dominates. For ND < 5 ×1016 cm−3 radiative recombination dominates in Pb0.78. Sno22Se up to temperatures TL < 180 K, in Pb0.09Se, however, up to 230 K.
Far‐Infrared and Submillimetre Dielectric Response of (NH4)2BeF4
Authors: Petzelt J. , Volkov A. A. , Kozlov G. V. 
Published: July 2007

AbstractThe far‐infrared spectrum of the complex dielectric constant ε*(ω) of (NH4),BeF4 single crystals is measured by means of precise transmission spectroscopy (5 to 34 cm−1 region) and reflection spectroscopy (34 to 400 cm−1 region) at 90 and 300 K. The temperature dependence of ε″ (30 cm−1) revealed a disorder‐induced absorption in this region, but no other anomaly in the incommensurate phase due to amplitudon or phason absorption, confirming the order‐disorder nature of the incommensurate phase transition.
On the Lattice Dynamics of Alkali Metals
Authors: Soma T. 
Published: July 2007

AbstractThe experimentally observed dispersion curves of alkali metals are reproduced using second‐order perturbation theory and the local Heine‐Abarenkov model potential. The effect of different forms of exchange and correlation on the phonon frequency, the compressibility problem, and the crossing of dispersion curves in [001] direction are investigated.
Dispersion in Ferromagnets Interacting with Phonons
Authors: Suguna A. , Shrivastava K. N. 
Published: July 2007

AbstractConsidering the magnon‐phonon interaction it is found that there is a net reduction of Heisenberg exchange. The reduction is maximum for the magnon wave vector given by K0 = v/(2cD) where v is the sound velocity and D is just 2SJa with a0 as the lattice constant. Thus the reduction is found to depend inversely on the exchange itself. There is also a new analog of Kohn like discontinuity occuring at the magnon wave vector k8 = ½ (qm + v/cD) with qm as the maximum wave vector of the phonons. In consideration of thermal magnon scattering a kink in the magnon dispersion is thus predicted at ks. The approximate temperature dependence arising in the exchange from the magnon‐phonon coupling is discussed.
Angular and Frequency Dependence of the EPR Linewidth in a 1D Alternating System: K‐TCNQ
Authors: Alizon J. , Berthet G. , Blanc J. P. , Gallice J. , Robert H. , Thibaud C. 
Published: July 2007

AbstractA theoretical expression of the angular and frequency dependence of the EPR linewidth of K‐TCNQ is given using the alternating 1D Heisenberg model characterized by the exchange integrals J and γJ ≫ hωe with ≪ Measurements of the EPR linewidth are performed on a single crystal at high fields (0.3500 and 1.2500 T) and also at low field (0.0020 T) on crystals aligned along their c‐axes. The results obtained in these two extreme cases allow to determine the order of magnitude of the cut‐off frequency of the intrachain diffusion mechanism of electronic spins. Moreover, the results at high fields, at the two frequencies 9600 and 35000 MHz show that the observed spectral densities ψ(ω) are constant in the frequency range 9600 to 70000 MHz.
Energy Loss of Charged Particles in Crystals
Authors: Burenkov A. F. , Komarov F. F. , Kumakhov M. A. 
Published: July 2007

AbstractThe theory of charged particle energy loss by collisions as a function of impact parameter in a crystal is developed on the basis of the quantum dielectric formalism. Simple and convenient formulae taking into account the energy zone structure of crystals are obtained for nonrelativistic and relativistic particles. The relation between energy loss and local electron density is studied. For the first time it is shown strictly that the hyperchanneled particle energy loss in the axial channels is less than that in corresponding plane channels. Comparison with main experiments is presented.
Theory of Optical Absorption of Hg1–xCdxTe Solid Solutions with Account of the Contribution of Quasilocal Acceptor Levels
Authors: Mekhtiev M. A. , Ismailov T. G. 
Published: July 2007

AbstractThe calculation of the optical absorption coefficient in the presence of quasilocal acceptor levels is given. The general formula obtained in the dipole approximation is applied to Hg1‐xCdxTe solid solutions. The semimetal and semiconductor cases are considered. A comparison with the experiment for the semiconductor case is given and the values of Fermi energy, the concentration, and energy of acceptors are found.
On the Structural Transition from NaCl to CsCl Type in Alkali Hydrides
Authors: Bashkin I. O. , Dymova T. N. , Ponyatovskii E. G. 
Published: July 2007

AbstractThe solid sphere ion model is used to compare specific volumes of NaCl and CsCl phases of alkali hydrides. The transition of the NaCl to CsCl type is shown to be thermodynamically possible in K, Rb, and Cs hydrides. A phase transition is detected in KH at pressures about 40 kbar, and the T—P diagram of KH is studied. On the basis of the analysis performed, the NaCl to CsCl transition in LiH is unlikely, unless the electron configurations of the ions are changed.