bluuebunny/crossref_metadata_2025_split huggingface dataset:
Temperature Dependence of Optical Absorption near the Structural Phase Transition of Potassium Nitrate
Authors: Kawashima R. , Katsuki K. , Suzuki K. 
Published: July 2007

AbstractThe electronic properties of a KNO3 crystal near the structural phase transition are investigated by observing ultraviolet absorption spectra. The spectra show an anomalous temperature dependence near the transition point Ttr. The anomalous behaviour of the exponential absorption tails in the spectra is observed and discussed phenomenologically in relation to anomalies in the dielectric constant and lattice constant of KNO3.
On the Calculation of the Pressure Dependence of the Transverse Optical Mode Frequency of Cubic Ionic Crystals
Authors: Batana A. , Faour J. 
Published: July 2007

AbstractDue to the lack of experimental measurements of the Grüneisen parameter γt = − ∂ In ωt/∂ In V at T → 0 K, this magnitude is calculated for salts of f.c.c. and b.c.c. structures using different models and low and room temperature experimental data. In general, for each salt, similar results are obtained with all models, being slightly larger those given by the shell model. When low temperature data are used the values are similar to the room temperature experimental data available.
Invariant Harmonic Oscillator Functions. I. The Cubic Groups Td, O, and Oh
Authors: Wöhlecke M. , Scherz U. , Maretis D. K. 
Published: July 2007

AbstractExcited energy states of quantum mechanical two‐ or three‐dimensional harmonic oscillators are of interest in Jahn‐Teller calculations and rotational tunneling systems. A general method is given to calculate symmetry adapted oscillator functions by numerical computation. The basic relations are formulated in the occupation number representation. Therefore advantage of group properties like isomorphism and direct product groups can be taken easily. Results are given for two‐ and three‐dimensional irreducible representations of the cubic groups Oh, O, and Td.
The Nucleation Fields of Uniaxial Ferromagnetic Crystals
Authors: Kronmüller H. 
Published: July 2007

AbstractIt is shown that in crystals of hexagonal or tetragonal symmetry the nucleation field, HN depends on the orientation of the easy magnetic direction with respect to the c‐axis. For an easy direction parallel to the c‐axis HN depends for K1 > 4K2 exclusively on the first anisotropy constant, K1, whereas for oblique easy directions the maximum nucleation field for (−) (K1 + Kd) = K2 is governed exclusively by K2, and is given by 2K2/Ms.
Application of the Density‐Functional Formalism to Bound Polarons
Authors: Röseler J. 
Published: July 2007

AbstractCalculating the ground state energy of the bound polaron with the help of the density‐functional formalism high quality results are found for all α and R. Beside the usual energy functional of the electronic density a new energy functional without self‐energy contributions can be constructed, allowing to prove quantitatively the applicability of the local density approximation if electron–phonon interaction is included. Furthermore, the validity of the parametrized formula for the exchange‐correlation energy of a homogeneous e–h plasma in polar semiconductors is confirmed by the calculations. Comparing both energy functionals new insights are obtained with respect to the structure of these functionals.
Self‐Consistent Theory of the Electronic Structure of Inversion Layers. I. A New Method Using the Modified Local Density Approximation
Authors: Übensee H. , Paasch G. , Zöllner J.‐P. , Fiedler Th. , Gobsch G. 
Published: July 2007

AbstractA new method is described for the self‐consistent calculation of electron and hole densities, band bending, and subband energies in inversion layers of MIS‐structures. This method makes use of new and simple expressions for carrier densities which take into account the influence of the interface semiconductor–insulator within a modified local density approximation. The method allows for an accuracy which is comparable with that one of explicit self‐consistent solutions of the Schrödinger equation for inversion layers. But it is of the numerical simplicity of the classical method. This gives the possibility to calculate electronic properties of MIS‐structures in much more detail than before. In part I the method is described and its advantages for modelling MIS‐structures are shown. In part II the influence is discussed of quantum effects in inversion layers on electronic properties of MIS‐structures in comparison with classical calculations for various semiconductors in a wide range of temperature and doping concentration.
Mode Grüneisen Parameters for Long‐Wave Phonons of III‐V Covalent Compounds under Pressure
Authors: Soma T. , Kagaya H.‐Matsuo 
Published: July 2007

AbstractThe elastic shear constants C44 and C′ = (C11 ‐ C12)/2 of GaAs, GaSb, InAs, and InSb under pressure are studied theoretically using the presented binding force and the local Heine‐Abarenkov model potential. The pressure derivatives dC44/dP and dC′/dP decrease under compression from the experimental data at low pressures. Then, the Grüneisen parameters of the individual modes of long‐wave phonons under pressure are obtained in the [100], [110], and [111] directions.
T = 0 Magnetic Polaron in f‐Systems with Antiferromagnetic s‐f Exchange
Authors: Nolting W. , Dubil U. 
Published: July 2007

AbstractThe s‐f model is used for investigating ferromagnetic f‐systems with an antiferromagnetic s‐f exchange interaction between conduction electrons and localized magnetic f‐moments. Particularily the electronic excitation spectrum is discussed for the exactly solvable limiting case of an empty conduction band at T = 0, and that via physical quantities such as the one‐electron spectral density, the quasiparticle density of states, and the electronic selfenergy. The ↑‐spectrum is simple, consisting of one single, only rigidly shifted band. The ↓‐spectrum, however, is built up by two quasiparticle subbands of quite different physical meaning. The gap between them closes if the Bloch band width exceeds a critical value. The ↓‐spectral density consists of one low‐energy δ‐peak and a relatively broad, high‐energy scattering part, which results from magnon emission processes. The dependence on model parameters and the distinction from f‐systems with ferromagnetic s‐f exchange is discussed in detail.
Critical Behaviour of the Ising Model with a Transverse Field
Authors: Wesselinowa J. M. 
Published: July 2007

AbstractA Green's function technique is developed to study the Ising model with a transverse field. The order parameter and the longitudinal susceptibility are determined. The critical exponents β and γ are numerical calculated for different dimensional lattices. Using the scaling laws, α, δ, η, and v are obtained too. The critical exponents are in very good agreement with other theoretical results and with the experimental data.
Two‐Dimensional Properties of n‐Inversion Layers in InSb Grain Boundaries under High Hydrostatic Pressure
Authors: Kraak W. , Herrmann R. , Nachtwei G. 
Published: July 2007

AbstractMagnetotransport properties of n‐inversion layers in grain boundaries of p‐InSb bicrystals are investigated under high hydrostatic pressure up to 103 MPa. A rapid decrease of the carrier concentration in the inversion layer is observed when hydrostatic pressure is applied. A simple model taking into account the pressure dependence of the energy band structure of pure InSb is proposed to describe this behaviour.
Free Carrier Absorption in n‐Type Indium Selenide
Authors: Mari B. , Segura A. , Chevy A. 
Published: July 2007

AbstractInfrared absorption of n‐type indium selenide is studied in the 2.5 to 50 μm spectral range at 300 °K. Lattice absorption peaks are observed between 25 and 50 μm. Tin‐doped samples with an electron concentration higher than 1016 cm−3 exhibit free carrier absorption for λ larger than 10 μm. The experimental results are interpreted by the quantum theory of free carrier absorption. Quantitative account of absorption coefficients is given by introducing homopolar optic phonon and ionized impurity scattering.
The Coulomb Correlations and the Electric Field Local Heterogeneities on the Proton Conductivity of Hydrogen Bonded Chains
Authors: Krasnogolovets V. V. , Tomchuk P. M. 
Published: July 2007

AbstractThe hydrogen bonded chain conductivity is considered without the assumption of small concentration of the charge‐carriers (excess proton) in the small polaron model. The current density expression is derived considering Coulomb correlations and electric field local heterogeneities. The case of a space‐charge‐limited proton current is considered.
Resonatorless Optical Bistability of CdS Reconsideration of Transient Effects Due to Lattice Heating
Authors: Rossmann H. , Henneberger F. 
Published: July 2007

AbstractResults of laser pulse transmission measurements are presented. Introducing a variable optical delay between exciting and probing pulse the relaxation behaviour of induced optical nonlinearities in the spectral region around the An = 1‐exciton resonance is investigated. Optical bistability reported earlier is supported. Crystal lattice heating and nonstationarity due to long‐living extrinsic effects are observed, too, but are of minor importance.
Valence Band Investigations of GaS by Means of Polarized X‐Ray Emission Spectra
Authors: Dräger G. , Czolbe W. , Schulz E. , Simunek A. , Drahokoupil J. , Kucherenko Yu. N. , Nemoshkalenko V. V. 
Published: July 2007

AbstractThe polarized K‐emission valence band spectra of the layer compound GaS are measured for both the components, Ga and S. For Ga spectra Johanm‐type and double crystal spectrometers are used. All spectra are calculated by the self‐consistent pseudopotential band structure method and also by the Xα‐scattered‐wave cluster calculation. The calculated and measured spectra are compared and discussed.
Continuity Chords of Bands and Band Structure of Semiconducting Compounds with TlSe‐Type Structure
Authors: Gashimzade F. M. , Guliev D. G. 
Published: July 2007

AbstractAll the simple band representations of the space group D are constructed. Using the concept of band representation and continuity chord, developed by Zak, it is shown that for semiconducting compounds with TlSe‐type structure it is possible to extract some useful information about the character of localization of basic functions, belonging to the same band, i.e. in fact about the nature of the chemical bond responsible for the observed band structure. In particular, from the comparison with a calculated band structure of the ternary semiconducting compounds with TlSe‐type structure, it is shown that the lower four valence bands correspond to s‐states of chalcogen atoms. Two following valence bands correspond to s‐states of three‐valent cations. Then, a large group of ten valence bands is produced by pz‐states of chalcogen atoms and px−, py−, Pz−states of three‐valent cations.
Hybrid Pairing and Heavy Fermions
Authors: Schuh B. 
Published: July 2007

AbstractIf the d–f exchange interaction is taken as the driving attractive interaction for a non‐phonon hybrid pairing mechanism one gets results of surprising significance for heavy Fermion superconductors: a transition temperature one order of magnitude smaller than the single ion Kondo temperature, a large critical field initial slope, and a huge specific heat jump, whereas the ratio of the gap at zero temperature to kTc has the BCS value 3.53. Except for the relation between Tc and the Kondo temperature these statements remain to be true for any other hybrid pairing interaction of the same form.
Dielectric Properties of Trans‐Polyacetylene. I. The Macroscopic Longitudinal Dielectric Function of a Peierls‐Fröhlich Semiconductor of Commensurability 2 within RPA
Authors: Drechsler S. L. , Bobeth M. 
Published: July 2007

AbstractThe macroscopic longitudinal wave‐vector‐ and frequency‐dependent dielectric function (MLDF) of a Peierls‐Fröhlich semiconductor with one electron per site is calculated within the 3D‐approach of Lee and Kivelson based on the Su‐Schrieffer‐Heeger model. Local field and exchange effects as well as overlap terms in the calculation of the matrix elements of the charge density are neglected. Conditions for the occurrence of an interband plasmon are presented, which are fulfilled in trans‐(CH)x. Special attention is paid to the q‐dependence of the MLDF and the influence of the interchain hopping.
Multiple‐Quantum Transitions and Optical Excitation Processes in the EPR of Mn2+ in ZnS
Authors: Backs I. , Stösser R. , Lieberenz M. 
Published: July 2007

AbstractMicrowave induced resonances of multiple‐quantum transitions, observed by the EPR method, are described for the system ZnS:Mn. From the anisotropy of the resonance lines, the EPR signal intensity‐microwave power dependence and the theoretical and practical intensity ratio of one‐and multiple‐quantum transitions it is concluded that the resonances are due to double‐and triple‐quantum transitions. Under certain experimental conditions a phase inverted EPR line is observed. Some irregularities are observed in the manganese EPR spectrum for the samples used. This is an optical excitation following microwave saturation, a different saturation dependence of the various fine structure transitions, a deviation of the occupation numbers from thermal equilibrium and of the fine structure line intensity from the theoretical ratio.
Mössbauer Absorption Spectra under Continuous Localized Diffusion
Authors: Afanasev A. M. , Sedov V. E. 
Published: July 2007

AbstractThe problem of the Mössbauer lineshape broadening due to the diffusion of the Mössbauer atom in an arbitrary drift potential is reduced to a solution of the Schrödinger equation of the quantum mechanics. The spectral shape can be obtained in explicit form provided an exact solution of the quantum problem is known. By means of this method the diffusion analogues of the quantum oscillator and the Coulomb atom are considered and analytical expressions for the respective spectra are derived. The temperature dependence of the intensity of the unbroadened spectral component is shown to be related with the form of the arbitrary “diffusional” potential by a simple law. The temperature curves of the mean‐square Mössbauer atom displacement resulting from this relation show the nontrivial behaviour at each value of the wave vector of absorbed γ‐quanta even in the simplest case of anharmonical oscillator. Under certain choice of the parameters the temperature trend of these curves may simulate the phase transitions.
EPR of Cu2+ in Barium Formate Single Crystal
Authors: Chand Prem , Upreti G. C. , Umar M. , Singh R. J. 
Published: July 2007

AbstractResults of an X‐band (≈ 9.3 GHz) EPR study of Cu2+ doped barium formate single crystal at RT and at LNT show that Cu2+ enters the host lattice at substitutional Ba2+ sites as well as at an interstitial site. Both the copper (II) complexes show a low symmetry and low site symmetry effects are evident in EPR at RT. The g and A tensors are non‐coaxial at RT for both the copper complexes, however, they become coaxial at LNT. From experimental EPR data the ground state orbitals are obtained and discussed. The ground states are found to be mainly d with some admixture of d. From the observed g‐value the energy splitting of the d‐orbitals of the metal ion are also obtained. The angular behaviour of EPR spectra is in conformity with the symmetry class of the host crystal as determined by X‐rays.
The Magnetic Hyperfine Field for 119Sn Atoms in GdMnSi Intermetallic Compound Zero Contribution from 3d Moments
Authors: Delyagin N. N. , Krylov V. I. , Mujiri G. T. , Nesterov V. I. , Reiman S. I. 
Published: July 2007

AbstractThe magnetic hyperfine interaction for 119Sn impurity atoms in the GdMnSi host has been studied by Mössbauer spectroscopy. The hyperfine field for Sn atoms at 5 K is Bhf = (−27.6 ± 0.3) T. The temperature dependences of Bhf and magnetization are practically identical. As follows from the comparison of the results to data for GdCoSi host and an analysis of the satellite structure of the spectrum in Gd0.95Y0.05MnSi host, the contribution to the transferred hyperfine field from 3d moments in GdMnSi vanishes. Both experimental results and obtained empirical function of the radial dependence of the gadolinium contribution to Bhf emphasize the short‐range nature of the hyperfine interaction for Sn impurity atoms in Gd‐based magnetic alloys.
Many‐Body Theory for the Dense Exciton Gas of Direct Semiconductors. III. Response of the Many‐Exciton System on an Externally Driven Light Field
Authors: May V. , Boldt F. , Henneberger K. 
Published: July 2007

AbstractThe nonlinear response of a dense exciton gas in a platelet on an externally driven field is discussed using non equilibrium Green's function technique. A generalized Boltzmann‐equation of excitons containing many‐particle corrections in the diffusion‐, drift‐ and collision‐term is derived. Using a relaxed distribution (Boltzmann‐distribution) and an unrelaxed distribution (macro‐occupation) of ls‐excitons a bistability in exciton density as well as in the transmitted light intensity is obtained for a nearly resonant and stationary applied pump‐field of intensity 0.1 and 10kW/cm2, respectively. The bistability is obtained as a pure excitonic effect below the Mott‐transition.
Influence of Real Structure in the Interfacial Region on the Maxwell‐Wagner Effect Spherical Void in a Ionic Crystal
Authors: Poźniak J. 
Published: July 2007

AbstractTheoretical calculations of the Maxwell‐Wagner polarization are performed by considering thermodynamic equilibrium conditions. The model applied consists of a spherical void inside an ionic matrix of NaCl type containing charge carriers (cation and anion vacancies) subjected to the action of an external dc electric field. Accurate analytical solutions obtained for the stationary state describes i) the distribution of the charge carriers in the vicinity of void and ii) the distribution of potential and electric field both, inside the void and in the crystal matrix.
New Aspects in the Theory of Impact Ionization
Authors: Ziep O. , Mocker M. , Keiper R. 
Published: July 2007

AbstractThe field induced change of the electron states causes avalanche processes already below the usual ionization threshold. For the calculation of the impact ionization coefficient αI the field influence of the corresponding microscopical rates has to be considered especially below the characteristic threshold energy due to higher occupation numbers. A comparison of the calculated values αI with experimental data in GaAs raises essential questions concerning the validity of the used stationary transport models.
Electron‐Spin‐Resonance Study of Co2+ and Ni+ Centers in AgCl(Cu, Co, Ni)
Authors: van Robbroeck L. , Goovaerts E. , Schoemaker D. 
Published: July 2007

AbstractSingle crystals of AgCI doped with Co2+, Ni2+, and Cu2+ are studied by means of electron spin resonance. As‐grown AgCI crystals contain three different Co2+ centers: called Co2+(cub), Co2+‐ (ortho) and Co2+(tetra) corresponding to centers in which a substitutional Co2+ ion is either unperturbed, or perturbed by a nearest or by a next nearest cation vacancy. Ultra violet illumination at 50 K produces Ni+ and Cu2+ centers and converts the Co2+(cub) centers to Co+ centers which are stable up to 80 K. The thermal decay of the latter enhances the Ni+ concentration. Above 160 K the Ni+ centers are thermally unstable and contribute to the decay of the Cu2+ centers. It is concluded that the presence of Co2+ ions supresses the darken ability of AgCI which is enhanced by the Ni2+ impurity.
Impurity Induced Energy Transfer in a Linear Polymer Chain
Authors: Čabrić B. , Ristovski L. J. , Davidović G. 
Published: July 2007

AbstractA molecular polymer chain with a substitutional isotopic impurity is considered and the process of the energy transfer from the impurity to the host molecule on account of the exciton‐phonon interaction is investigated. The probability of this energy migration process is determined and numerically analysed.
A Theoretical Model of Ferroelectrics Exhibiting One, Two, or Three Curie Points
Authors: Piekara A. H. 
Published: July 2007

AbstractA theory is presented for a ferroelectric crystal which is composed of two subsystems. In each of the subsystems there exist different interactions between the own elements as with the foreign ones. Even for simple ferroelectrics with a suitable nonlinearity of the argument of tgh there exists a thermal hysteresis for Ps.
On the Effects of Localized States and Tunnel Charge in Thin Insulating Films
Authors: Campabadal F. , Aymerich‐Humet X. 
Published: July 2007

AbstractTunneling barrier modifications produced by the charge of localized states in thin SiO2 films and by the charge due to the electron tunnel penetration into the barrier are analysed by means of the Green's function formalism. The charge density distribution at each energy, the modification of the electric field at the insulator, and the barrier height are obtained at equilibrium and under biasing conditions. It is shown that there exists a thickness d0 such that for d > d0 the charge inside the insulator is due to the localized states whereas ford d < d0 the tunnel charge predominates. Moreover, in the latter case, it is shown that in SiO2 films the electric field enhancement can be so large as to make the external electric field needed for breakdown lower than expected, in accordance with the anomalous breakdown values experimentally observed in the literature. An analysis of the transient charge localization in the oxide is also performed.
Polycrystalline Simple Average of Mechanical Properties in the General (Triclinic) Case
Authors: Ganster J. , Gems D. 
Published: July 2007

AbstractFor the general (triclinic) case the complete numerical values of the decomposition coefficients (d.c.) are given, necessary to calculate averaged mechanical properties (fourth rank tensors) from the single crystal compliance S (Reuss model) or stiffness C (Voigt model) and the generalized Fourier coefficients Cmmt of the orientation distribution function. With the help of a group theoretical approach many symmetries of the dc are found. This leads to a considerable reduction of numerical data. It is shown that only CTmmiwith l ‐ 0, 2, 4 are needed, i.e. that the simple mechanical average is not affected by ghost phenomena and depends only on certain features of the texture.
Solution Enthalpies of Aliovalent Defects in Alkali Halides
Authors: Bandyopadhyay S. , Deb S. K. 
Published: July 2007

AbstractThe solution enthalpies of some monovalent, divalent, and trivalent defects in some alkali halides are calculated following the standard procedure of minimising the total lattice energy change numerically, as a function of the relaxation of the nearest neighbours, when the defect cation occupies a substitutional position. The energies considered are electrostatic, dipole, dipole–dipole, and repulsive. It is found that inclusion of dipole–dipole energy helps to avoid the polarisation catastrophe problem for divalent and trivalent defects. The Born‐Mayer repulsive parameters of the aliovalent defects are obtained from the charge density overlap method. Thus it is shown that a single method is capable of yielding positive values of solution enthalpies for all the aliovalent defects considered.
Hartree‐Fock Approximation in the Scattering Wave Method. K‐Absorption of Ionic Crystals in the Single‐Scattering Formalism (XANES and EXAFS)
Authors: Bugaev L. A. , Vedrinskii R. V. 
Published: July 2007

AbstractThe scattering wave (SW) method is generalized for the case of Hartree‐Foek atomic potentials in ionic crystals. An earlier developed scheme of these crystal potential construction is used to obtain photoelectron scattering phase shifts. X‐ray absorption near edge structure (XANES) and extended fine structure (EXAFS) of crystals NaCl, KCl, NaF are then calculated in the single‐ scattering approximation of the SW‐method. The approach used permits to obtain EXAFS of ionic crystals with high accuracy and also the main features of their XANES.