bluuebunny/crossref_metadata_2025_split huggingface dataset:
Vibronic Spectra and the Dynamic Jahn‐Teller Effect of Cubic ZnS:Cu2+
Authors: Maier H. , Scherz U. 
Published: July 2007

AbstractNear infrared absorption and emission spectra due to the transitions 2T2 ↔ 2E of the Cu2+ ion in cubic ZnS have been measured at 4K. The distinct vibronic sidebands of the absorption spectrum exactly correspond to various critical point energies of TA, TO, and LO lattice modes, whereas the structure of the luminescence spectrum cannot be interpreted in terms of lattice phonon satellites. A dynamic Jahn‐Teller interaction in the 2T2 ground state being in the same order of magnitude as static lattice spin‐orbit splitting and phonon energy is shown to produce this deviation from the mirror symmetry. Weak and strong coupling approximations in the cluster limit have been extended to include vibronic states with up to six E‐modes.
Nonlocal Xα‐Exchange for s‐ and d‐Electrons in Transition Metals
Authors: Karsch P. , Rennert P. 
Published: July 2007

AbstractStarting from Hartree‐Fock expressions a nonlocal exchange potential of the Xα‐type for transition metal valence electrons is calculated, respresented by different values αs and αd. No fitting parameter was introduced. Whereas αs remains nearly constant within one period αd increases nearly linearly with the number of d‐electrons. The dependence on the chosen atomic configuration and the influence of pressure were investigated. For Cu the energy bands mere calculated. They agree well with fitted local calculations.
Spin–Lattice Relaxation (SLR) of Paramagnetic Centres in the Vicinity of Off‐Central Ions
Authors: Vikhnin V. S. , Deigen M. F. , Shanina B. D. 
Published: July 2007

AbstractThe SLR mechanism of paramagnetic centres in the vicinity of off‐central ions due to the modulation of spin‐Hamiltonian constants by transitions between ground‐state multiplet (GSM) and excited‐state multiplet (ESM) is observed. These transitions are induced by interaction with phonons. The situation is investigated when the internal fields in crystal influence essentially the GSM. Agreement with experimental results for FA(Li)‐centres in KCI is obtained.
Galvanomagnetic Properties of HgTe in Strong Magnetic Fields
Authors: Dziuba E. Z. 
Published: July 2007

AbstractResults of measurements are presented of the Hall coefficient and conductivity in undoped samples of HgTe in the temperature range 4.2 to 300 K and magnetic fields up to 30 kG. The results are explained using a three‐carrier model of conductivity in conduction band states, valence band states, and impurity states. The temperature dependence of the electron concentration and the contribution to the electrical conductivity of “heavy” carriers are determined.
The sd Bond and the Localized Magnetic Moment in the Solid Solutions of Transition Metals
Authors: Galperin F. M. , Kizheav F. G. , Shvedkov V. I. 
Published: July 2007

AbstractThe role of the sd bond is considered in the formation of the magnetic moment of the 3d‐transition elements dissolved in 4d‐metals. It is shown that in consequence of the sd bond the Coulomb interaction of the 3d‐electrons on an impurity atom is reduced by about 15 to 20% in comparison with a free atom.
Wavelength‐Modulated Absorption Spectra of Pseudodirect Bandgap A2B4C Compounds
Authors: Babonas G. , Ambrazevičius G. , Grigoreva V. S. , Neviera V. , Šileika A. 
Published: July 2007

AbstractThe wavelength‐modulated absorption spectra of ZnGeP2, ZnSiAs2, ZnSiP2, and CdSiP2 chalcopyrite crystals have been investigated with polarized light in the region of the absorption edge at 77 and 300 °K. Structures due to the pseudodirect optical transitions derived from indirect ones in sphalerite have been observed. The valence band structure and the relative location of the energy levels in the conduction band of the pseudodirect‐band gap A2B4C compounds have been determined.
Investigation of the Infrared‐Active Lattice Vibration in SrCl2
Authors: Droste R. , Geick R. 
Published: July 2007

AbstractSrCl2, single crystals were grown by the Czochralsky method. Their reflectivity at 300 K and transmission at 4.2 K were measured for frequencies from 10 to 930 cm−1 and 10 to 150 cm−1, respectively. The reststrahl band found in the reflection spectrum has been analyzed by means of a classical oscillator model. In addition, a Kramers‐Kronig analysis was performed since a satisfactory fit could not be achieved with the classical model. The frequencies of the TO‐mode and the LO‐mode were determined to be 138 and 233 cm−1, respectively. A pronounced shoulder on the reststrahl band was observed as is also the case for CaF2, BaF2 etc. Its origin is discussed in terms of multi‐phonon processes. The results of the transmission measurements show that SrCl2, is transparent in the far infrared up to 110 cm−1 where the lattice absorption starts at 4.2 K.
A Simple Tight‐Binding Model Applicable to Calculations of the Band Structure of Amorphous Germanium
Authors: Henderson D. 
Published: July 2007

AbstractA simple semi‐empirical tight‐binding model applicable to germanium is presented which takes into account the effects of rotation of the dihedral angle and of bond distortions. The effects of rotation of the dihedral angle are taken into account by including all interactions between nearest‐neighbors, the effects of distortions in bond angles by means of a two‐center approximation together with the properties of spherical harmonics, and the effects of distortions in bond‐length by fitting the matrix elements to the sophisticated band calculations of Herman et al. not only for crystalline Ge at the observed density but also for uniformly compressed and dilated crystalline Ge. Comparison of the results of this model with sophisticated calculations for various polymorphs of Ge shows that this model is, at very least, qualitatively satisfactory and should be useful in band structure calculations for amorphous Ge.
Temperature Dependence of the Cyclotron Resonance Absorption of Electrons in AgBr
Authors: Baxter J. E. , Ascarelli G. 
Published: July 2007

AbstractThe temperature dependence of the cyclotron mass and mobility of electrons in zone‐refined AgBr has been measured from 5 to 22 °K. The electron mobility, measured at 55 GHz, approaches 6 × 105cm2/Vs at 5 °K (ωc τ ≈︁ 30). The measurements indicate that there are two types of zone‐refined AgBr the difference arising from the relative electron and hole trap densities. The bulk of our experiments were performed on material where the electron traps are dominant. In this material the mass change with temperature is exponential with an activation energy (95 °K) nearly equal to the binding energy of the n = 2 bound state of the electron traps. The same 95 °K activation energy is also observed in the temperature dependence of the mobility. The exponential temperature dependence of both the mass and the mobility can be explained as arising from a resonant scattering of the electron by the traps with the aid of a virtual phonon. The AgBr where the hole traps dominate, on the other hand, shows a linear temperature dependence of the effective mass that is in agreement with what is expected of an electron moving in a polarizable continuum.
Interaction between a Vacancy and Impurity Atoms
Authors: Masuda K. 
Published: July 2007

AbstractThe vacancy‐impurity interaction energy is calculated on the Wolff‐Clogston model using the Hartree‐Fock approximation. It is suggested that if a bound state exists below the band bottom and if most of the excess electrons are localized at the impurity sites, the interaction energy tends to become negative. There is a qualitative agreement between the theory and the experimental results in Fe base alloys with 3d‐transition metal impurities. The interaction due to the magnetic origin inherent in the host metal structure is also taken into account using the simple Stoner model.
LCAO MO Treatment for Electronic Structure of Deep Levels in Semiconductors — S+Donor in Silicon
Authors: Shimizu T. , Minami K. 
Published: July 2007

AbstractThe energy and wave function of the ground state of the S+donor in silicon are calculated by empirical LCAO MO method. The donor state is simulated by a cluster of a S+ion and 274 silicon atoms surrounding it. The interaction and overlap integrals determined by Al‐strup and Johansen are used which fit the bands of silicon calculated by LCAO method to those of OPW calculation. The ground state is known to be totally symmetric, so that only the totally symmetric energy states are calculated. The fact enables to take the large cluster. The calculated MO coefficients agree rather well with those estimated from ENDOR data. Extended Hückel theory is found to be unsuccessful in describing the donor state in this case.
Polarized Optical Reflection Spectra of the Highly Anisotropic Organic Semiconductor TEA(TCNQ)2
Authors: Brau A. , Brüesch P. , Farges J. P. , Hinz W. , Kuse D. 
Published: July 2007

AbstractFrom polarized reflection spectra of TEA(TCNQ)2 single crystals at room temperature, quantitative values of the complex dielectric function ε(ω) and the optical conductivity σ(ω) in the range from the far infrared to the ultraviolet have been derived. The polarization of the vibrational bands almost exclusively parallel to the highly conducting direction suggests strong interaction of conduction electrons with intramolecular TCNQ vibrations.
Electron–Phonon Interaction in the Photoluminescence of CdTe
Authors: Gippius A. A. , Panossian J. R. 
Published: July 2007

AbstractThe intensity of electron‐phonon coupling in the optical transition (characterized by the value of parameter N in the formula of relative intensity of phonon replicas, In = IoNn/n!; n = 0, 1, 2, …) was studied as a function of the ionization energy E1 of the luminescence centres in CdTe. It was found that N = 76 (eV−2) E. This dependence is in agreement with the results of the theory assuming bound carrier coupling with LO‐phonons for deformation potential coupling.
A Theory of Two‐Exciton Light Absorption in Antiferromagnetic Dielectrics
Authors: Gaididei Yu. B. , Loktev V. M. 
Published: July 2007

AbstractThe light absorption in antiferromagnetic dielectrics by the creation of two Frenkel excitons in the crystal is considered. It is shown that the absorption lines accompanied by the formation of bound states split into three perpendicularly polarized components. The form of the absorption spectrum both in the presence and absence of bound states for different polarizations of incident light, as well as the ratio of the intensities of the components are found. The object of the investigation is a crystal with a body‐centered orthorhombic lattice.
The Dislocation Loop in an Anisotropic Medium and Its Interaction with an Interstitial Atom
Authors: Meissner N. , Savino E. J. , Willis J. R. , Bullough R. 
Published: July 2007

AbstractSeveral explicit expressions for the distortion field of an elliptical dislocation loop in a general anisotropic medium are presented. These are used to evaluate the interaction energy between an interstitial dislocation loop in copper and a nearby interstitial atom. The interstitial atom is represented by either a simple spherical inclusion or by realistic Kanzaki forces for its dumb‐bell configuration. The effects of both the microscopic anisotropy of the point defect and of the elastic anisotropy of the body on the form and magnitude of the interaction energy is thus exposed.
The H2O− Centre in KCl: An F‐Like Paramagnetic and Paraelectric Defect
Authors: Rusch W. , Seidel H. 
Published: July 2007

AbstractESR, ENDOR, optical, and electrooptical investigations of the H2O− centre and its deuterated versions in KCl are reported. The centre is produced by photochemical reactions in a KCl: OH− crystal. It can be considered as an F centre perturbed by an embedded water molecule: optical absorption bands at 2.40 and 2.09 eV are similar to the F band in energy and width; the hyperfine interaction constants of the surrounding nuclei are only changed up to 20%. The C2v, axis of the water molecule lies in one of the eight {lll) directions. Reorientation occurs below 7 K as a one‐phonon process, above 15 K by thermal activation with δE = 0.025 eV. Above 30 K motional averaging results in an ENDOR spectrum of cubic symmetry. An electric field induces strong dichroism in the optical absorption bands due to partial alignment of the H2O molecules. The effective electric dipole moment is 0.31 eÅ. The hyperfine interaction constants of the protons and of nearest neighbours can be calculated with fair agreement by a model wavefunction formed by orthogonalization of the F‐centre wavefunction to the H2O molecular orbitals.
Improved Perturbation Treatment of Bound‐State Problems with Special Applications to the Exciton
Authors: Pollmann J. 
Published: July 2007

AbstractThe Hamiltonian H0 + Hp for a perturbed bound state problem is separated in a self‐consistent way into a new exactly solvable part H0v and a new perturbation Hvp. Perturbation theory on H Hpv leads in many cases to a better converging result compared to Hp Especially the calculations of the phonon‐ and anisotropy‐influence on the bound exciton states compare satisfactory with experimental data and with results of involved variational methods. This good agreement is achieved by a partial summation of important parts of all higher order perturbation terms of Hp, without using any free parameters.
Sur le facteur de structure du gallium liquide Par
Authors: Badiali J. P. , Regnaut C. 
Published: July 2007

AbstractLe facteur de structure du gallium liquide diffère, dans la zone du pic principal, de celui que l'on peut construire à l'aide du modèle des sphères dures. A cette différence peut‐ětre associée une fonction indépendante de la structure et de la température. En identifiant cette fonction à une variation de potentiel interionique, on montre à l'aide d'un modèle approché, que le pseudopotentiel peut jouer un rǒle déterminant dans la structure du gallium liquide, comme l'ont suggéré Heine et Weaire.
Magnetic Structure of CsCoCl3 at 4.2 °K
Authors: Melamud M. , Pinto H. , Makovsky J. , Shaked H. 
Published: July 2007

AbstractThe compound CsCoCl3 is paramagnetic at room temperature and belongs to the space group D−P63/mmc with two formula units per unit cell (CsNiCl3 type structure). The neutron diffraction of CsCoCl3 powder and single crystal samples were studied as a function of sample temperature. A transition to antiferromagnetism was found at TN = 21.5 °K. The magnetic structure determined from the diffraction pattern at 4.2 °K is collinear and consists of ferrimagnetic ab planes stacked antiferromagnetically along the c‐axis with spins parallel to the c‐axis. The magnetic moment consistent with the diffraction at 4.2 °K is (3.0 ± 0.3) and (2.3 ± 0.3) Bohr magnetons per Co2+ ion according to the powder and single crystal data, respectively. The magnetic unit cell is the hexagonal H‐cell (a = √3a0, c = c0) with six formula units per unit cell. This structure belongs to the magnetic space group P63′/m′cm′ (III‐ P63′/m′cm′). The powder and single crystal data show that the magnetic structure near TN is different from the magnetic structure at 4.2 °K.
Thermally Activated Unpinning of Dislocations from Point Obstacles in Terms of a Non‐Equilibrium Transition‐State Theory
Authors: Frank W. , Frydman R. 
Published: July 2007

AbstractThe wide‐spread treatment of thermally activated unpinning of dislocations from point obstacles in terms of the absolute rate theory is criticized. In particular, doubts are raised about the validity of the assumption that a thermodynamic equilibrium distribution is established between the equilibrium state of a pinned dislocation and its saddle‐point configuration. In analogy to Rice's dynamical theory of diffusion an alternative approach to dislocation unpinning is suggested, which does not make use of this assumption and which furthermore accounts for unpinning transitions by‐passing the saddle‐point configuration.
Infrared Absorption in Microcrystals of MgO
Authors: Lagarde P. , Nerenberg M. A. 
Published: July 2007

AbstractThe absorption coefficient of small crystals of the NaCl structure is calculated following a microscopic approach: a perturbed Green's function formalism with a change of the force constants of the ions at the surface of the microcrystals. Theoretical and experimental results are compared for the case of MgO samples.
Inverse Raman Effect by Polaritons in LiIO3 Single Crystals
Authors: Kneipp K. , Werncke W. , Ponath H. E. , Klein J. , Lau A. , Thuys Chu Dinh 
Published: July 2007

AbstractFirst experimental observation of inverse Raman scattering (IRS) from polaritons are reported. The IRS frequency shifts measured in LiIO3 crystals using different scattering geometries are discussed and compared with SRS experiments. Using extraordinary continua and ordinary laser fields, the polaritons associated with the 769 cm−1 El‐phonon shift to 595 cm−1. In addition in this scattering geometry an absorption at 860 cm‐I was detected, due to a polariton in the upper dispersion branch. It is shown that the polariton absorption frequencies in IRS can be determined as in SRS from “undamped” quasi ‐momentum conservation laws. The IRS absorption coefficient for polaritons has a Lorentzian form. In some scattering geometries in anisotropic crystals, IRS and SRS can result in different polariton frequencies for the same fixed laser polarization; especially large polariton shifts in SRS are accompanied by small shifts in IRS and vice versa.
The Flow Stress of the Flux Line Lattice and the Magnetization Curve of Low‐x Type II Superconductors
Authors: Essmann U. , Schmucker R. 
Published: July 2007

AbstractIn low‐x type II superconductors there exists a long range attractive interaction between flux lines. This leads to a step B0 in the magnetization curve at Hc1. Experimental results frequently deviate from the ideal behaviour. The deviations are caused by the necessity to perform a plastic deformation of the intruding flux line lattice in order to accommodate the specimen geometry, and by flux line pinning. It is shown that both mechanisms lead to a finite slope of the magnetization curve near Hc1. The flow stress of the FLL and the volume pinning force may be obtained from magnetization measurements.
Optical Mode Gammas, Pressure Derivatives of Elastic and Dielectric Constants, and Stability of Rutile‐Structure Fluorides in the Rigid Ion Approximation
Authors: Striefler M. E. , Barsch G. R. 
Published: July 2007

AbstractThe microscopic Grueneisen parameters of all optical modes at zero wave vector, and the pressure derivatives of the elastic and dielectric constants of the difluorides XF, (X = Mg, Mn, Fe, Co, Ni, Zn) have been calculated from a rigid ion model with an effective ionic charge and with first and second nearest neighbor Born‐Mayer‐type central force short range interaction. The parameters of the model were previously determined from zero pressure values of the optical frequencies and elastic constants. The calculated values agree quite well with the few available experimental data. Several optical mode frequencies and elastic constant eigenvalues have negative pressure coefficients, which reflects and is related to the presence of several high pressure phases.
Crystal Field Calculations of Nd3+ Ions in Scheelites with D2d Symmetry
Authors: Kumar V. , Dass N. , Chandra K. 
Published: July 2007

AbstractCrystal field calculations of the temperature dependent principal and mean magnetic susceptibilities, μeff, and the Schottky specific heat have been considered over the temperature range 10 to 400 °K in Nd3+: PbMoO4 and Nd3+: CaWO4 systems with D2d point symmetry at the crystal ion site. The spectroscopic splitting factors, Curie constants, and the extra entropy associated with Schottky anomaly are compared with available experimental data.
Theory of Lattice Thermal Conductivity of Anharmonic Crystals with Impurities. (II). Interference Effects
Authors: Altukhov V. I. , Zavt G. S. 
Published: July 2007

AbstractThe interference of the anharmonic and impurity scattering of phonons is investigated. In particular, a general formula is obtained for the resonant scattering of phonons by impurities taking into account the inelastic channel which is responsible for the temperature dependence of the total cross‐section of impurity scattering. It is found that the anharmonic scattering is decreased by interference effects. The latter is connected with the finite life‐time of the phonons scattered by impurities. The case of resonant scattering of phonons by isotopic defects is considered in detail.
A Theory Accounting for Electron–Phonon Interaction in a Compositionally Disordered System
Authors: Böttger H. 
Published: July 2007

AbstractAn incorporation of the electron–phonon interaction into the current theoretical concept of electronic states in disordered solids is investigated on the basis of a simple model of a compositionally disordered solid. In particular a single‐site approximation including contributions of the electron–phonon interaction is discussed.
A Theoretical Analysis of Cation Diffusion in Potassium Azide
Authors: Danemar A. G. , Royce B. S. H. , Welch D. O. 
Published: July 2007

AbstractA theoretical analysis has been made of the temperature dependence and anisotropy of the self‐diffusion of tracer potassium ions in KN3. A vacancy mechanism is assumed, and the effects of correlation on diffusion are examined. An approximate analytic expression is obtained for the correlation factor, and its validity is determined by comparison with more accurate numerical calculations. The temperature dependence of the elements of the diffusion tensor including correlation is evaluated, making use of theoretical values of the migration energy of cation vacancies, and the role of correlation in determining the crystallographic anisotropy of cation diffusion is discussed. Comparison is made to available experimental data.
Electroreflectance Spectra of AlxIn1−xSb Alloys
Authors: Isomura S. , Prat F. G. D. , Woolley J. C. 
Published: July 2007

AbstractThe preparation of homogeneous samples of AlxIn1–xSb alloys from a stoichiometric melt is considered. A slow horizontal Bridgman method with ingots encapsulated in liquid B2O3 has been used to provide samples suitable for optical reflectance measurements and details of the variation of composition with position along the ingot are given. Electroreflectance measurements, using the electrolyte technique, have been made on samples cut from cross sectional slices, and the variation of the transition energy with composition has been determined for the E0, E0 + Δ0, E1 and E1 + Δ1 peaks. The experimental values of E0, Δ0 and Δ1 as a function of x are compared with the previously proposed theoretical equations based on the concept of interband mixing due to disorder of the lattice, and the significance of some of the energy parameters in these equations is discussed.
Electron–Lattice Interaction in Gallium Selenide
Authors: Schmid Ph. , Voitchovsky J. P. 
Published: July 2007

AbstractIn the layered semiconductor GaSe, the interaction of holes with non‐polar, fully symmetric, optical phonons governs both the Hall mobility of the carriers and the temperature shift of the direct energy gap. The results are in agreement with theory and indicate that the interaction of charge carriers with acoustic phonons is rather weak.