bluuebunny/crossref_metadata_2025 huggingface dataset:
Stochastic Liouville Equation Model for Nonperiodic Systems and Finite Temperatures
Authors: Čápek V. , Szöcs V.
Published: July 2007

Theoretical background leading to the recently proposed generalization of the stochastic Liouville equation model of the excitation transfer to nonperiodic systems and finite temperatures is reformulated here using the time‐convolutionless generalized master equations. In the lowest order and for linear coupling to phonons, the Haken‐Strobl‐Reineker parametrization becomes acceptable after a short initial time‐interval following the creation of the excitation, but with time‐dependent parametrization, the theory applies to arbitrarily short time‐intervals. For separable initial conditions, the time development of the excitation is calculated numerically for onedimensional models describing the dynamics of the excitation near traps, trap‐luminescence etc. provided that the time‐development in the initial time interval is negligible. The equations correctly provide non‐equal asymptotic site‐occupation probabilities for non‐equal sites if the excitation lifetime is infinite.
Phonons and the Electron‐Phonon Interaction in Multi‐Layer Systems
Authors: Fomin V. M. , Pokatilov E. P.
Published: July 2007

A theory of the potential due to the slow polarization field is developed for multi‐layer systems with an arbitrary number of layers. The general expression of the potential is specialized for three‐ layer and periodic systems. As result of diagonalization of the energy of the polarization vibration field, the bulk and surface vibrations are separated and the spectrum of their eigenfrequencies is determined both, for systems with a finite number of layers (inparticular, for a layer of a heteropolar semiconductor between a substrate of an ionic crystal and a homopolar dielectric medium) and for periodic systems. Finally, the exact electron‐phonon interaction Hamiltonian for multilayer systems is obtained in the second quantization representation.
Evaluation of the First‐ and Higher‐Order Volume and Pressure Derivatives of Dielectric Constants of Alkali Halide Crystals
Authors: Dutt N. , Agrawal G. G. , Shanker J.
Published: July 2007

An analysis of first and higher order volume and pressure derivatives of low frequency or static dielectric constant is presented for sixteen alkali halide crystals with NaCl structure using seven different potential forms for the short range overlap repulsive energy. The potential parameters are calculated using recent values of van der Waals potentials and taking proper account of the thermal contribution derived from consistent experimental ultrasonic data. Calculated values of volume derivatives of dielectric constant and optic mode Grüneisen parameters are compared with available experimental data. The results obtained from some potential forms present distinctly better agreement with experiment in comparison of others. The usefulness of such potential forms is demonstrated in predicting the higher order pressure derivatives of dielectric constants of ionic crystals.
Some Remarks on the Random Field Ising Model on a Lattice
Authors: Nattermann T.
Published: July 2007

It is suggested that domain wall roughening due to random fields in lsing‐like systems is different for lattice and continuum models. It is shown quite generally, that this is incorrect for dimensions d ≦ 3; on a sufficiently large scale the scale dependence of the wall roughness and the interface tension are identical for both types of models. This may have consequences for metastability and hysteresis effects.
Acoustic and Optical Deformation Potentials in Cubic IV‐VI Compounds
Authors: Enders P.
Published: July 2007

Acoustic and optical deformation potentials (DP) in cubic IV‐VI compounds are calculated by diagonalizing the p‐model Hamiltonian including finite lattice distortions at the L‐ and T‐points of the Brillouin zone. A very pronounced and even non‐monotonous dependence is found of some DP upon the very lattice deformation and, most surprisingly, Ξ2(L) < 0 for the optical DP. This may explain the wide variance of experimental data for different samples and experimental conditions.
Localized Impurity Level and Carrier Concentration in Self‐Intercalated TiS2 Crystals
Authors: Inoue M. , Koyano M. , Negishi H. , Ueda Y. , Sato H.
Published: July 2007

The a‐ and c‐axis resistivities and Hall coefficients of self‐intercalated IT‐CdI2, type layered crystals of TiS2, are measured over the temperature range 1.5 to 300 K. The temperature dependence of the carrier concentration at low temperatures T < 150 K can be explained by a simple model which takes into account both, the host Ti 3d conduction band and a localized impurity level Ei due to excess Ti atom. The position of Ei is found to lie by about 5 meV above the Fermi energy. The self‐intercalated Ti atoms become ionized impurity scattering centers as Ti4+ and Ti3+ ions, whose relaxation times are calculated to give a good fit to the observed residual resistivity vs. carrier concentration curve.
Effect of Lattice Anharmonicity on Specific Heat of Alkali Alloys
Authors: Soma T. , Higuchi H. , Kagaya H.‐Matsuo
Published: July 2007

Using the expression by Trivedi in the high‐temperature limit with nearest‐neighbour central‐force interaction, the anharmonic contributions to the specific heat of the alkali alloys are studied theoretically. The concentration x‐dependence of the anharmonic coefficient for the specific heat A, defined by CΩ/3Nk = 1 + AT, is calculated for CS1−xKx, CS1−xRbx, and Rb1−xKx solid solutions.
Structural Phase Transformamtion and the Equation of State of CsCI, CsBr, and CsI Crystals
Authors: Narain J. , Dwivedi N. K. , Agrawal G. G. , Shanker J.
Published: July 2007

The structural phase transformation of CsCl crystals under the effect of high temperature is investigated using an interionic potential model which takes account of repulsive interactions up to second neighbours and of van der Waals (vdW) interactions between dipole‐dipole and dipole‐ quadrupole. It is found that the transition temperature at which the CsCl crystal transforms from B2 (CsCI) to B1 (NaCl) structure can be predicted correctly only if larger values of vdW potentials are used in calculations. The same potential parameters are used to predict the high pressure equation of state for CsCl, CsBr, and CsI crystals. The use of overlap integrals in the Born‐Mayer potential form yields good agreement between theory and experiment for the high pressure compression data.
Defect Clusters and Subcascades. I. The Distribution of Mean Free Paths of PKA and Splitting Function
Authors: Melker A. I. , Romanov S. N. , Tarasenko N. L.
Published: July 2007

A theory of displacement cascade splitting is developed. The free path distribution of PKA is obtained in which inelastic energy losses are included. On this basis an equation for the number of subcascades per PKA is suggested.
Copuling of a Structural and a High‐Spin‐Low‐Spin Transition in MnAS1−xPx Compounds
Authors: Bärner K. , Gmelin E.
Published: July 2007

Unusual temperature dependences of the orthorhombic distortion η, of the hs fraction γ, and of the specific heat capacity cp suggest a coupling between the high‐spin‐low‐spin and the structural transitions of MnAs1−xPx crystals. A mutual dependence of the coupling constants and the static order parameters is assumed and its effect on η, γ, and cp is evaluated.
X‐Ray Spectroscopic Studies of Azurite Mineral
Authors: Hemachandran K. , Chetal A. R.
Published: July 2007

The K‐absorption of copper in azurite and in some copper systems is studied using a Gauchois‐type X‐ray spectrograph. It is established that copper is in the divalent state and behaves as a cation in azurite. The two structures, B and C, observed in the Cuk edge of the mineral are assigned to the transitions 1s → 2a2u and 1s → 3eu on the basis of the molecular orbital theory.
Parametrization of Crystal Field Spectra of Mn2+ in ZnSe and ZnS
Authors: Biernacki S. W.
Published: July 2007

A new parametrization scheme is proposed of the optical spectra of Mn2+ in ZnSe and ZnS considering the symmetry dependent deformation of the radial wave function and the dependence of one electron energies on spin orientations. It is found that the covalent bonding between d states of symmetry t2 and e with ligand states gives the main contribution to the splitting of the free ion terms in a crystalline environment.
Influence of Local Environment on Bound Excitons and Bound Excitonic Mqlecules in III‐V Alloys. II. Numerical Results for GaxIn1−xP:N and the Role of Disorder Topology for the Optical Spectrum
Authors: Müller H. ‐J.
Published: July 2007

The binding energy, the oscillator strength, and the broadening of bound excitons and bound excitonic molecules in GaxIn1−xP:N are calculated considering an x‐dependent multi‐valley band structure, the mutual particle interaction, the isoelectronic nature of the impurity, and the influence of disorder in the local environment. A satisfactory agreement with available experimental data is obtained. The results for the spectra of GaAs1−xPx:N and GaxIn1−xP:N prove the relevance of the disorder topology for the description of the shape of the spectra.
Dielectric tails in K2ZnCl4: No evidence for an intrinsic chaotic state
Authors: Nattermann T.
Published: July 2007

It is shown, that the increasing dielectric tail found recently for decreasing impurity concentration Ni in the incommensurate system K2ZnCl4 does not indicate the existence of an intrinsic chaotic state. Using a simple model for the pinning of solitons by impurities (but more realistic than those used previously in this context) it is shown, that the dielectric tails grow with growing soliton density ns but with dropping Ni. The precise dependence on Ni depends on the pinning mechanism (i.e. weak or strong pinning).
The structural disorder model: Pressure induced transitions in the semiconductors Si and Ge
Authors: Dixit P. K. , Vaid B. A. , Sharma K. C.
Published: July 2007

The structural disorder model, recently proposed by the authors to explain the thermodynamic properties near the transitions of first order, is generalized to include the pressure induced transition in the semiconductors Ge and Si. The calculated values show at least a in order of magnitude agreement with the experimental data.
Calculation of thermal expansion and phonon frequency shift in deuterated naphthalene
Authors: Jindal V. K. , Kalus J.
Published: July 2007

A calculation of the implicit shift to the phonon energies for phonons in deuterated naphthalene at q = 0 is presented, the “explicit shift” having been already described in an earlier paper. With this the calculation of the shift in the phonon energies due to temperature becomes complete and consistent, ready for direct comparison with the measured results of the shift obtained by neutron scattering experiments. The results for the total calculated shift in the phonon energies, arising from both, the explicit anharmonic terms and the implicit (i.e. the volume dependent) shift are presented and compared with the experimental neutron scattering results. The calculations of thermal expansion, compressibility, and the Grüneisen constants which naturally enter the calculation of the implicit shift, are also described and a comparison with the experimental neutron scattering results of these also is made. All the results are very satisfactory, strengthening the faith in the assumption for the model of the molecular crystals.
Electromigration in niobium. A finite‐cluster‐model study
Authors: Brand M. G. E. , Lodder A.
Published: July 2007

The windforce acting upon a host atom and the impurities Ta, Cr, and Ni in niobium is calculated in a finite cluster model. In this model all strong and multiple scattering effects up to lmax = 2 are preserved. Special attention is given to the influence of the vacancy, the cluster size, and of charge transfer. A positive windforce is found, in accordance with experiment, so that this appears to be not directly related to a hole current contribution, contrary to what is believed commonly.
CDW‐SDW transition in the extended hubbard model
Authors: Zhong Jian , Zhang Kaiyi , Chao K. A. , Micnas R. , Robaszkiewicz S.
Published: July 2007

The ground state phase diagram of the extended Hubbard model for arbitrary electron density is investigated with the broken‐symmetry Hartree approximation. It is found that for two‐sublattice orderings, only the charge‐order and the antiferromagnetism exist without the mixed phase.
Detailed low‐field magnetic properties of rare‐earth ion states in cubic crystal fields
Authors: Fischer G. , Herb A.
Published: July 2007

The effect of a cubic crystal field on rare‐earth ions is calculated and presented in a graphical form representing the individual magnetic moment and Van Vleck susceptibility of the lowest‐lying sub‐state, for J = 3.5; 4; 4.5; 6; 7.5; 8. This is a practical guide for analyzing the moderate‐field part of the magnetization. The results are given for the three principal directions. In order to analyze susceptibility measurements, the calculated Curie constant (or the Van Vleck susceptibility) of the fundamental multiplet is also represented.
The second‐order correction to field‐electron‐emission formulae for an extended temperature range
Authors: Workowski C. J.
Published: July 2007

Corrected formulae for the total energy distribution, the emission current density, and the inversion temperature are derived under the condition that the field‐electron emission takes place from a free‐electron metal. The corrections relate to the series truncation approximating the WKB phase integral inherent in the analytic approximation of the electron tunneling probability. The assumed approximation for the phase integral takes into account not only the zero and first order terms, present in the existing theory, but also the quadratic term. The expression for the total energy distribution, obtained on this basis, is in typical circumstances valid for field emission in the electron energy range of |ε| ≦ 1.5 eV with respect to the Fermi energy. The accuracy of the approximations used is also discussed.
Nondipole radiation of electrons at planar channeling
Authors: Baier V. N. , Katkov V. M. , Strakhovenko V. M.
Published: July 2007

The nondipole radiation of electrons is considered for any shape of the interplane potential. A concrete analysis and comparison with the radiation of positrons are carried out for a potential of the „inverse parabola”︁ type. It is shown that for the description of the radiation of particles with energy e ε ⪅ 10 GeV in the region of the maximum of the spectral distribution it is possible to take into account the few first harmonics of the motion only. This substantially simplifies the calculation, especially for the potentials with complex shape. The diagrams which illustrate the radiation spectrum as a function of the angular width and of the direction of beam incidence in a thin crystal, are depicted. A detailed comparison of the results with available experimental data is made.
Stopping power of atoms near metal surfaces at grazing incidence condition
Authors: Kato M. , Ohtsuki Y. H.
Published: July 2007

The energy loss of slow atoms is studied from the viewpoint of the indirect excitation of low‐energy electron–hole pairs, i.e., the excitations of electron–hole pairs through the electron exchange process from the metal to the projectile's atomic states, and vice versa. For the slow atom, v ≪ vF (v and vF are the velocity of the projectile and the Fermi velocity, respectively), electrons have enough velocity for response, thus the atomic states are not well defined due to the screening effect and the electron exchange processes. By constructing the model Hamiltonian which describes such effects from first principles the stopping power at grazing incidence condition, especially for the Cs surface, is calculated.
Static polarizability and dipolar surface plasmon of small metal particles. II. Including the lattice structure
Authors: Bao Tran Thoai Duy
Published: July 2007

The frequency of the dipolar surface of small particles is calculated using the sum rule techniques due to Lushnikov et al. The effect of surface diffuseness of electron density is included. The screening of the electrons is described within the Thomas‐Fermi approximation. The lattice structure and the lattice relaxation through the introduction of pseudopotentials are taken into account. The ground state charge density is obtained from a variational estimate of the total energy of the clusters based on the local density functional formalism. The surface plasmon frequency is red‐shifted from its classical value.
Luminescence et transition non radiative 3T1u → 3A1u dans le luminophore BaS:Bi3+
Authors: Asano Par S. , Nakao Y. , Yamashita N. , Matsuyama I.
Published: July 2007

Emission and excitation spectra of BaS:Bi3+ phosphors are measured at 300, 80, and 6 K. I n the excitation spectra the A and C excitation bands are observed. In the emission spectra only one band is observed which is assigned to the transition 3A1u → 1A1g on the basis of the measurement of the time‐resolved emission spectra and the decay constant of the phosphorescence. The diffused reflection spectra and the magnetic effect on the phonon structure of the emission band are also measured at 80 and 4.2 K, respectively. The former is compared with the excitation spectra. The reason why the emission band 3T1u → 1A1g cannot be observed at low temperatures is explained by the fact that the probability of the tunnel effect 3T1u → 3A1u is larger than that of the luminescent transition 3T1u → 1A1g.
The realization of the generalized transfer equation in a medium with fractal geometry
Authors: Nigmatullin R. R.
Published: July 2007

It is shown that in a medium representing an example of “Koch's tree”‐type fractional structure the diffusion process is described by a generalized transfer equation in partial derivations. Such a structure can serve as a model of a porous medium where the diffusion process takes place. The geometry of an inhomogeneous medium can serve as the dicisive factor in the explanation of the “universal response” phenomenon. A range of frequencies is found where such “superslow” diffusion process can be observed.
Dynamical model for the vibrations of the hydrogen halide crystals
Authors: Higgs J. F. , Zeng W. Y. , Anderson A.
Published: July 2007

A force constant model is developed and applied to the vibrations of the hydrogen halide crystals, HBr, HCl, and HF, in their ordered phases. Fundamental frequencies are calculated and compared to those observed by infrared and Raman spectroscopy. It is found that two bending forces, representing electrostatic interactions, are necessary, one of which partially cancels elastic forces for certain modes. Variations of force constants with interatomic distances and comparisons of their values for the three crystals are briefly discussed.
Thermodynamic analysis of the Anderson‐Grüneisen parameters
Authors: Dhoble Aruna , Verma M. P.
Published: July 2007

Thermodynamic equations connecting the Grüneisen and the Anderson‐Grüneisen parameters r, q, δT, and δS with experimentally determinable quantities are used to determine the values of these parameters at room temperature 295 K. The results so obtained are discussed in the light of the currently accepted theoretical and experimental values of these quantities.
On the defecton statistics in quantum crystals
Authors: Pushkarov D. I.
Published: July 2007

The defecton statistics in quantum crystals is treated, and a new method for determining commutation relations is proposed. Defectons related to defects of a different kind (vacancies, impurities, interstitials) are considered in crystals both of the Bose‐type (4He) and Fermi‐type (3He). The kinematic interaction is discussed.
Quantum theory of free‐carrier absorption in quasi‐two‐dimensional semiconducting structures
Authors: Giner C. Tballeeo , Antón M.
Published: July 2007

The quantum theory of free carrier absorption in quasi‐two‐dimensional structures like thin films, layered heterojunctions, and inversion layers is generalized to the cases when the carriers are scattered by polar optical phonons, piezoelectric phonons, and nonpolar optical phonons. The obtained results are compared with those of the quantum theory of free‐carrier absorption in a bulk semiconductor and it is found that the absorption coefficient increases when the width of the layer or thin film decreases in all the cases.
Effect of thin space‐charge layers on exciton reflectance
Authors: Kiselev V. A. , Novikov B. V. , Cherednichenko A. E. , Ubushiev E. A.
Published: July 2007

Resonance reflectance in semiconductors in the frequency region of exciton transitions depends strongly on characteristics of the near‐surface space‐charge layers. It is shown by numerical computation that the majority of the exciton reflection lineshapes observed on CdS earlier may be explained by the presence of a thin (10 to 100 nm) space‐charge layer with a relatively high (104 to 105 V/cm) surface electric field. Various treatments of surfaces alter charges on and below them thus modifying the electric field distribution. The latter causes changes in the exciton reflectance. Transformations of the exciton lineshapes under the action of illumination and electron bombardment are discussed in detail for the case of CdS. The lineshapes show drastic variations with expositions of both influences. In a single experiment one may observe all of the anomalies typical for the thin space‐charge layers.
Charge transfer satellites in X‐ray photoelectron spectra of La2CuO4
Authors: Viswanathan B. , Madhavan S. , Swamy C. S.
Published: July 2007

The displacements and intensity of charge transfer (oxygen to lanthanum) satellites of lanthanum 3d, 4d, and 4p levels are found to be different for La2O3 and La2CuO4, while they are the same for other ABO3 perovskites and La2O3. This difference is caused by the increased possibility of „mixed configuration”︁ for lanthanum ions in La2CuO4 due to d2z2 level of half of copper ions intersecting the Fermi level. The effect of the changes in the geometry of the environment of the cations is also reflected in the asymmetric nature of the O(ls) peak in La2CuO4 which is known to contain different types of MO bonds.
Calculated low energy electron total current spectra for the A1(111) surface
Authors: Smith A. E. , Lynch D. F.
Published: July 2007

Results of low energy electron diffraction calculations using the scattering matrix method are presented for the incident energy range 0.5 to 40 eV for the (111) A1 face and a comparison is made with reported measured total current spectroscopy results. It is concluded that the structure of the experimental spectra is determined by elastic diffraction effects and that the TCS technique provides information on the mean inner and absorption potentials in the very low incident energy region.
Hot nuclear fluorescence in the LiI crystal
Authors: Haas M. A.
Published: July 2007

Resonance scattering of γ‐radiation by Li nuclei is considered in a LiI crystal. In this crystal hot nuclear fluorescence is the main scattering process a t energies of ≈ 477 keV, whereas at a fixed scattering angle the spectral distribution of the scattered quanta depends essentially on the direction of the incident beam. Calculations are made for the orientational effects expected in the case of backward‐scattered quanta registered by a resonant detector. It is shown that the signal of such a detector as a function of mutual orientation of the crystal and the incident beam has sharp (of ≈6° width) maxima of a reasonable intensity in the [100] and [111] directions. The connection between the obtained angular characteristics, the details of the relaxation process in the crystal lattice, and the specific form of the interatomic potential are discussed.
Variances in molecular magnetic susceptibilities of monoclinic crystals
Authors: Aly A. A. , Ibrahim I. H. , Abdeen A. M. , Abdel‐Gawad M. M.
Published: July 2007

Expressions are obtained for the variances of the molecular magnetic susceptibilities and anisotropies in the case of monoclinic crystals. The molecular magnetic susceptibilities, anisotropies, and their variances for some organic compounds (monoclinic crystals) are calculated refered to the molecular orientations and their inclinations on the crystallographic axes. These molecular magnetic susceptibilities are compared with those obtained using the molecular inclination determined by X‐ray analysis.
Nonlinear optics of metal surface
Authors: Brodskii A. M.
Published: July 2007

The possibilities of formation of optical solitons moving along a metal surface have been assessed. The experimentally observed effects of anomalous field enhancement near metal surface are explained as resulting from formation of such solitons.
Self‐consistent theory of the electronic structure of inversion layers. II. Quantum effects and the electronic properties of MIS structures
Authors: Übensee H. , Paasch G. , Zöllner J.‐P.
Published: July 2007

In part I a new method was described for the self‐consistent calculation of electron and hole densities, band bending, and subband energies in inversion layers of MIS structures. This method is of the numerical simplicity of the classical calculation but the results obtained with this method deviate only slightly from those ones obtained from explicit solutions of the Schrödinger equation. Here the new method is used to investigate the influence of quantum effects in the inversion layer on electronic properties of MIS structures. Since the latter usually are calculated classically the method is compared even with the classical one. The classical method yields in special cases good results for the calculation of MIS structures. The deeper reasons for them are shown and where the classical method is no longer applicable.
Determination of the orientation distribution function from pole figures in arbitrarily defined cells
Authors: Pawlik K.
Published: July 2007

Practical problems of the reproduction of the orientation distribution function (ODF) from pole figures (PFs) using discrete methods (with special attention paid to Imhof's method,) are analysed. A new variant of the iteration method for the determination of the ODF in arbitrarily defined size of cells in the orientation space, is suggested. The special case, in which the centro‐symmetrical equivalency of the PFs is induced by the elements of proper rotations in crystal symmetry, is considered.
Quantum‐mechanical calculations for hydrogen in niobium and tantalum. II. Diffusion coefficients
Authors: Klamt A. , Teichler H.
Published: July 2007

Results of quantitative theoretical investigations are presented concerning the diffusion coefficients of H and D in Nban Ta. They are based on the quantum theory of the diffusion of light interstitials and take into account the lattice‐configuration dependence of the hydrogen tunneling integrals and the effects of adiabatic saturation of the transition rate. Thecalculations make use of a semiempirical hydrogen‐host‐lattice interaction potential which is adapted to experimental data from outside the diffusion phenomena. The resulting theoretical values for the diffusion coefficients agree well with the experimental observations.
Defect reactions in electron‐irradiated α‐Fe111 studied by means of PAC measurements
Authors: Golczewski J. , Maiee K. , Frank W.
Published: July 2007

Defect reactions in electron‐irradiated α‐Fe111In were studied by means of the perturbed‐angular‐correlation (PAC) technique. There is no indication of a mutual annihilation of freely migrating Stage‐IE defects and Stage‐III defects trapped at 111 In probes. This is as expected from the two‐interstitial model and provides strong evidence against the one‐interstitial model for α‐Fe.
The curie temperature of an anisotropic heisenberg ferromagnet with mixed spins
Authors: Iwashita T. , Uryû N.
Published: July 2007

For the anisotropic Heisenberg ferromagnet with mixed spins of S = 1/2 and S = 3/2 and of S = 1/2 and S = 2, the Curie temperature TC is calculated with the use of pair model approximation. Assuming an anisotropic bilinear exchange interaction J between nearest neighbors of different spins and a uniaxial single‐ionic anisotropy D‐term for the spins of S = 3/2 and S = 2, the behavior of Tc as a function of these parameters J and D is investigated for some types of the spin system with various values of the anisotropy parameter α of the exchange interaction.
On participation of medium oscillations in wannier exciton motion
Authors: Myasnikov E. N. , Druzhinin A. E. , Popov A. P.
Published: July 2007

The effect of quantum polarizable‐medium motion on relative and translational motion of the Wannier nonlocalized exciton (NLE) is investigated. It is shown that the polarization admixed to the internal motion of electron‐hole pair does (since each of the two particles is involved in both types of motion) participate in the external exciton motion which may bear the quantum character. It is pointed out that in the vicinity of k = m1/m2≪ 1, where m1(2) is the effective electron (hole) mass, the polarizing NLE for αh 3⪅ (αh being the coupling constant between the hole and LO‐phonons) is energetically more favourable than the self‐trapped exciton (STE).
Electron Gas heating under spin‐flip Raman scattering conditions in n‐InSb
Authors: Studenikin S. A. , Skok E. M.
Published: July 2007

Spin‐flip resonance induced magnetoresistance is studied of n‐type InSb in quantising magnetic fields. The sample is held at 2 K in magnetic fields up to 1.3 T. Double‐differentiation techniques are used to detect weak signals. It is shown that magnetoresistance changes because of electron gas heating, additionally the heating of phonons must be taken into account as well. Simultaneous measurements of the spin‐flip Raman gain and photoconductive response make it possible to determine the energy relaxation time τε ≈ 0.9 × 10−6 s which remains approximately constant in the magnetic fields.
Lattice dynamics of F.C.C. metals
Authors: Thakur V. K. , Singh T. N.
Published: July 2007

A theoretical model of the lattice dynamics of face centered cubic crystals is developed. The potential energy of a face centered cubic metallic crystal is considered due to (i) ion‐ion and (ii) ion‐electron interactions. The contribution to ion‐ion interaction is evaluated applying the valence force field. The contribution to the potential energy from ion‐electron interaction is considered through the screened Coulomb potential. The theoretical model developed is employed to compute the phonon dispersion curves for copper, silver, and gold. Computed phonon frequencies at 48 non‐equivalent points are usedto interpret specific heat and Debye characteristic temperature. The agreement between the calculated and experimental results is fairly good.
Specific heat of Nb‐Doped RuO2 single crystals
Authors: Mertig M. , Pompe G. , Hegenbarth E.
Published: July 2007

The low temperature specific heat of RuO2 single crystals is investigated up to a Nb content of x = 4.5 at% by means of the microcalorimetric ac method. The electronic part of the specific heat gives information about the alteration of the density of states at the Fermi energy D(εF) in dependence on the Nb content. The density of states at the Fermi energy of the undoped sample is D(εF) = 30.0 (cell spin Ryd)−1. The observed increase of D(εF) up to a Nb content of 4.5 at% is smaller than 6%. It is checked, whether a rigid band model explains the observed results. Characteristic changes in the phonon contribution of the specific heat will be discussed, too.
Semiempirical calculation of oxygen vacancy in vitreous silica
Authors: Sokolov V. O. , Sulimov V. B.
Published: July 2007

Electronic properties of an oxygen vacancy in solid silicon dioxide are investigated by a semiempirical LCAO/MO method (MINDO/3) in a molecular cluster approximation. The importance is demonstrated of taking into account the relaxation of the nearest atomic environment of the oxygen vacancy. One‐electron energies and wave functions, conformation parameters, and ESR electronic g‐factors are calculated for a number of charge states of the oxygen vacancy.
Absorption and uniaxial stress experiments in the B, C, and d' Bands of Pb2+ centres in KBr, RbBr, KI, and RbI
Authors: Schmitt K.
Published: July 2007

The optical absorption and the stress‐induced dichroism of the Pb2+ centre in KBr, RbBr, KI, and RbI are studied in the spectral range of the B, C, and d' bands. The splitting of the degenerate electronic states and the stress‐induced configuration interaction are analysed. In addition the assignments of the absorption bands in KI and Rbl, proposed by Tsuboi are confirmed.
Tunnelling in k‐space application to degenerate valence bands
Authors: Dargys A. , Rudolph A. F.
Published: July 2007

Hole tunnelling between light and heavy mass bands in a homogeneous semiconductor due to strong electric fields is analyzed in the framework of the spherical and degenerate at k = 0 bands with spin‐orbit interaction neglected. It is found that in k‐space intense transitions between bands occur in a ring‐shaped volume, whose symmetry axis is parallel to the electric field. At high fields, of the order of 30 kV/cm, the average diameter of the ring, where hole tunnelling is most intense, becomes smaller than the diameter of the optical phonon sphere. As a result, before the collision with an optical phonon, the ballistically moving hole experiences velocity modulation. Some possible experimental situations which would allow to discriminate the hole tunnelling in the degenerate bands from the collision dominated processes, are discussed briefly.
Theoretical study of the gradual chemical transition at the Si‐SiO2 interface
Authors: Hübner K. , Klinkenberg E.‐D. , Stern A.
Published: July 2007

Ball‐and‐sticks cluster models for the Si(111)–SiO2 and the Si(100)–SiO2 interregion are built. Oxygen constituents are represented by model elements realized with the help of cardan links, which permit a variable oxygen bridging angle already during the building procedure. The atomic positions are refined by means of a modified Keating potential. The numerical analysis indicates that the width of the chemical transition between Si and SiO3 has a value of approximately 1 nm and also depends on the substrate orientation. The resulting oxygen profile reveals an asymmetric form. The calculated distribution of the elastic energy has a maximum at a distance of 0.6 nm from the Si surface and is mainly caused by rings with less than six members. The resulting structure of the transition region supports the random‐bonding model for the statistical distribution of its tetrahedral Si‐SiyO4–y constituents (y = 0,…, 4). Theoretical scattering data permit to compare the model structures with corresponding results of X‐ray scattering experiments.
Raman and infrared studies of tetramethylammonium tetrachlorozincate
Authors: Tang S. H. , Looi E. C. , Radhakrishna S.
Published: July 2007

Raman and IR studies for the ferroelectric crystal (N(CH3)4)2ZnCl4, is reported. From these studies the Raman lines observed are assigned and the local site symmetry of ZnCl4, is determined.
EPR spectra of single crystal bis(glycine) calcium (II) dichloride tetrahydrate with copper(II) ion
Authors: Subramanian P. , Hariharan N.
Published: July 2007

Single crystals of bis(glycine) calcium(II) dichloride tetrahydrate (GCaCl) are grown with Cu2+ dopant. The observed spectra in all three planes show the fact that the paramagnetic ions enter substitutional position. The Cu2+ ion entering the site of calcium ion has coordination of eight oxygen atoms in a distorted dodecahedral arrangement. The ion experiences an orthorhombic crystalline field. Molecular orbital coefficients are determined for this complex and a comparison is made with dodecahedral metal complexes. The unpaired electron resides in the dxy orbital. The metal‐ ligand σ‐bond is stronger and hence shows the strong covalent nature of metal‐oxygen.

Bis(Glyzin)‐Kalzium(II) dichloridtetrahydrat (GCaCl)‐Einkristalle werden mit Cu2+‐Dotierung gezüchtet. Die beobachteten Spektren in allen drei Ebenen zeigen die Tatsache, daß die paramagnetischen Ionen Substitutionsplätze einnehmen. Das Cu2+‐Ion, das den Kalziumplatz besetzt, hat eine Koordination von acht Sauerstoffatomen in einer gestörten Dodekaederanordnung. Das Ion ist einem rhombischen Kristallfeld ausgesetzt. Molekülbahnkoeffizienten für diesen Komplex werden berechnet und ein Vergleich mit Dodekaedermetallkomplexen durchgeführt. Das ungepaarte Elektron besetzt das dxy‐Orbital. Die Metall‐ ligand σ‐Bindung ist stärker und zeigt so die starke kovalente Natur der Metall‐Sauerstoff‐Bindung.
X‐Ray K‐Absorption Study of Copper in Malachite Mineral
Authors: Hemachandran K. , Chetal A. R.
Published: July 2007

The shape and chemical shift of the Cu K‐absorption edge in malachite mineral are studied by using a Cauchois type bent crystal X‐ray spectrograph. The oxidation state of copper is established as two in the mineral. The peaks A, B, and C observed in the absorption edge are explained on the basis of molecular orbital theory (MOT).
Optical Properties of Multi‐Layer Structures. I. Polaritons
Authors: Fomin V. M. , Pokatilov E. P.
Published: July 2007

A theory of polaritons is developed for multi‐layer structures with an arbitrary number of layers. On the basis of the solutions of Maxwell equations with the boundary conditions taken into account the dispersion relations of s‐ and p‐polarized polaritons are obtained for multi‐layer structures and, in particular, for periodic structures. The classification of polaritons is made by the character of a spatial distribution of the electric and magnetic fields as well as by the change of the fields in a period of the structure (spatially decreasing and extended). A new type of polaritons is found in multi‐layer structures, viz. spatially decreasing polaritons. The decrease coefficients and decrements of the localized polaritons are calculated for superlattices GaAs/Ga1−xAlxAs.
Theoretical Study of the Gradual Chemical Transition at the SiSiO2 Interface. II. Electronic Density of States Calculations
Authors: Hübneb K. , Stern A. , Klinkenberg E.‐D.
Published: July 2007

Calculations of the electronic density of states at the Si‐SiO2 interface performed with the help of the cluster‐Bethe‐lattice method are presented. A cluster is constructed, which realizes the semiconductor‐insulator transition between a Bethe lattice of Si atoms and an SiO2 Bethe lattice within three atomic SiOx layers with average x values of 0.33, 1.17, and 1.67. The resulting densities of states are compared with corresponding results for bulk SiOx and the static effective charges of all the cluster atoms are calculated. It is shown that an intermediate‐range order (Si‐Si chains and rings) strongly influences the position of the valence‐band edge and, therefore, the variation of the width of the gap in dependence on the chemical composition x across the Si‐SiO2 inter‐region. The defect levels resulting from dangling bonds of Si atoms with different backbond configurations and from a peroxy bridge and a peroxy radical are investigated. An influence of structural percolation effects on the dangling‐bond levels is shown. Further microscopic origins of interface states are discussed.
The Gryromagnetic Factor of Conduction Electrons in Silver, Gold, Palladium, and Platinum
Authors: Schober C. , Kurz G. , Wonn H. , Nemoshkalenko V. V. , Antonov V. N.
Published: July 2007

For the gyromagnetic factor of the conduction electrons in metals a rigorous relativistic theory is developed generalizing Roth's theory, within which the Pauli formalism is used. In a first test calculation the g‐shift is calculated for Ag, Au, Pd, and Pt in spherical approximation. The calculations yield a negative g‐shift for Ag and a positive g‐shift for Au, Pd, and Pt in agreement with the experimental results.
On the Concept of Intermediate One‐Particle States in Finite Chains. A Self‐Consistent Field Study
Authors: Liegener C.‐M. , Biczó G. , Godzik A.
Published: July 2007

Ab initio self‐consistent field calculations are performed on finite chains of hydrogen atoms and other model systems to test the prediction of a quantum‐size effect, namely the arising of intermediate one‐particle states. The calculations confirm earlier conjectures concerning the appearance of intermediate states, not only at the simple Hückel, but also at the self‐consistent field level of approximation. Furthermore, the stability of intermediate states with respect to perturbations is studied.
Surface Excitations on Small Metal Particles by Fast Electrons
Authors: Bao Tran Thoai Duy
Published: July 2007

Inelastic scattering of fast electrons by isolated small metal particles is studied within the hydro‐dynamic model. The energy loss probability for multipole surface modes is calculated. Numerical calculations for rs = 2 jellium are carried out for different parameters: fast electron energy, electron impact parameter, radius of the partide, and energy loss.
Dielectric Dispersion in Tris‐Sarcosine Calcium Chloride (TSCC)
Authors: Pawlaczyk Cz. , Unruh H.‐G. , Petzelt J.
Published: July 2007

Dielectric dispersion of TSCC single crystals of three different qualities is investigated in the frequency range 102 to 6 × 109 Hz in the close vicinity of Tc. Up to three dispersion regions are found where only in the highest frequency one the results are nearly sample independent. They can be roughly fitted to a Debye law where the relaxation frequency obeys the classical critical slowing‐down law fε = A(T  Tc) with A = 0.23 cm−1 K−1 and Tc = 130.5 K for 130.7 K < < T < 131.4 K. The results are connected to the far infrared soft‐mode dispersion observed by Kozlov et al. and analyzed using the two‐coupled‐mode model. Although the phase transition is driven by the displacive soft‐mode coordinate, close to Tc a strong mixing with a pseudospin relaxing coordinate takes place. The discussion concerning the character of the phase transition in TSCC can be concluded stating that the dynamical origin of the instability leading to the phase transition is overwhelmingly of the displacive type. However, due to the disorder present in the paraelectric structure, the soft‐mode eigenvector becomes temperature dependent near Tc and at Tc it consists of an equal mixture of both the mode coordinates.
Infrared Lattice Vibration, Dielectric Dispersion, and Lattice Dynamics of BaFCl
Authors: Sieskind M. , Ayadi M. , Zachmann G.
Published: July 2007

The reflectivity of single crystals of BaFCl is measured in the wave number range from 30 to 5000 cm−1 at room temperature using a Fourier transform infrared spectrometer. The recorded reflection spectra are evaluated by means of the classical oscillator model and the Kramers Kronig analysis in order to get the TO and LO frequencies and the optical constants. The calculated effective dynamical charges of the involved ions are found to be in good agreement with the results obtained using a shell model.
Precise Measurement of the Free Electron g‐Factor in InSb
Authors: Vdovin A. V. , Skok E. M.
Published: July 2007

The dependence of g‐factor of free electrons in n‐InSb on magnetic field and concentration is investigated by the spin‐flip Raman scattering gain method (SFRS method). The correct values of g‐factor at the conduction band edge g0 = −51.55 ± 0.02 and dg/dH (H ∥︁ [100]) = (2.06 ± ± 0.02) (I/T) are obtained by extrapolation of these values to zero field and concentration. The value of g0 agrees well with the data obtained by electron spin resonance (ESR) method (g0 = = −51.53). The g‐factor anisotropy coefficient γ = (0.095 ± 0.004) (1/T) is measured at H = = 0.9434 T. The values m*/m0 = 0.0135 ± 0.0001, EP = (24.55 ± 0.2) eV, EQ = (17.8 ± 1) eV, E'P = (6.0 ± 3.8) eV, F = −2.0 ± 0.4 and N1 = −0.04 ± 0.03 are obtained by using the parameters: Δ = (0.803 ± 0.005) eV and Eg = (0.2368 ± 0.0002) eV.
Bisolitons in a Molecular Polymer Chain
Authors: Ristovski Lj. , Davidović‐Ristovski G. S. , Ristić V.
Published: July 2007

A molecular chain in which two types of tight‐bound excitons are excited, is considered in the continuum approximation. The exciton‐exciton and exciton‐lattice interactions are taken into account. The strong exciton‐lattice coupling causes the appearance of autolocalized excitons, viz. solitons. In the case considered two types of interacting solitons can appear. The soliton‐soliton interaction causes the creation of a bound state, the bisoliton, which propagates along the chain, as a free particle‐like autolocalized excitation with an interior degree of motion. The bisoliton effective mass and energy are determined and analysed.
Dynamical Model for the Lattice Frequencies and Crystal Field Splittings of Carbon Disulphide
Authors: Higgs J. F. , Anderson A.
Published: July 2007

A simple force constant model is used to calculate the normal mode frequencies and eigenvectors of the carbon disulphide crystal. By adjustment of three intramolecular and four intermolecular parameters, good agreement with spectroscopic data is obtained for the lattice mode frequencies and for the crystal field splittings of the molecular modes.
Temperature Dependence of Resonance Splittings in Molecular Pairs. Comparison of Optical Experiments and Theoretical Results for the Phenazine Triplet State
Authors: Reineker P. , Winkler R. G. , Port H.
Published: July 2007

The temperature dependence of the resonance splitting is calculated for pairs of translationally equivalent and inequivalent molecules in a molecular crystal using a canonical transformation method. The model Hamiltonian takes into account the excitonic transfer matrix element and linear local coupling between excitons and both acoustic and optical phonons. The calculations are successfully applied to optical data obtained for triplet excitons in phenazine.
The F+‐Centre in Alkali Oxides of Antifluorite Structure. a Model Potential Numerical Calculation
Authors: Kassim H. A.
Published: July 2007

Absorption energies of the F+‐centre in Li2O and other alkali‐oxides of antifluorite structure are calculated numerically using the point ion and model potentials incorporating core repulsion based on the modified Bartram, Stoneham and Gash pseudopotential as proposed by Matthew and Green. Other effects such as electronic polarization and ionic distortion are also considered. The results obtained are in good agreement with the experimentally assigned value for the band peak position and with the recent variational calculations by Ong on the same systems.
Negative Momentum Relaxation Rate and Transport in Polar Semiconductors
Authors: Dimoulas A.
Published: July 2007

The possibility of a negative momentum relaxation rate by absorption of polar optical phonons in a non‐degenerate semiconductor is examined. Charge density wave propagation is predicted as a result of this. The wave sets up an average dc field in which the electrons respond in such a way that a dc current independent of the external field flows. This implies that a persistent current could flow in the solid.
Momentum‐Dependent Dielectric Response of Strongly Heterogeneous Materials with Anisotropic Components
Authors: Drechsler S. L. , Bobeth M.
Published: July 2007

An effective medium approach (CPA) for calculating the static wave‐number‐dependent effective dielectric function of strongly heterogeneous composites with randomly oriented anisotropic components is presented, where the composite is supposed to consist of a random arrangement of homogeneous regions (grains) with known material properties. Final formulae governing the effective dielectric function at arbitrary wave numbers are given for spherical and cylindrical grain shapes. In the long‐wavelength limit the general case of ellipsoidal shape is considered and a marked dependence of the effective permittivity on the eccentricity is obtained for moderate and large anisotropy.