bluuebunny/crossref_metadata_2025 huggingface dataset:
The Dependence of the Density of States Tail on the Random Potential Statistics
Authors: Klochikhin A. A. , Kühn O. , Ogloblin S. G.
Published: July 2007

The problem of the long‐range correlated random potential in a dielectric disordered system is studied by means of numerical solution of the saddle point equation. The obtained frequency dependence of the density of states displays the Halperin‐Lax behaviour at a correlation length small compared with the De'Broglie wavelength, it shows the Gaussian decreasing in the opposit limit and a relatively narrow region of a cross‐over Urbach‐like regime. The reasons are given in behalf of a predominant role of the fluctuations with the smallest correlation length possible for the system.
On the Electronic Structure of Small NiP Clusters
Authors: Stepanyuk V. S. , Szász A. , Katsnelson A. A. , Grigorenko B. L. , Farberovich O. V.
Published: July 2007

A self‐consistent electronic‐structure calculation for small NiP clusters is performed. There is no charge transfer from P to Ni. It is shown that the cluster effects are important in the mesoscopic ranges.
Dynamics of the Pseudo‐E ⊗ ε Jahn‐Teller Hamiltonian. A Quantum Optical Approach
Authors: Lais P. , Kraus M.
Published: July 2007

New dynamical aspects are investigated of the pseudo‐E ⊗ ε‐Jahn‐Teller Hamiltonian (PJTH). A close relation is found between the PJTH and the Jaynes‐Cummings model in quantum optics. After using a continued fraction method for the diagonalization of the Hamiltonian the exact eigenfunctions are used to investigate some aspects of the dynamics. A rotating wave approximation is introduced which makes the problem exactly solvable. The results of the two approaches are compared.
Calculation of the Normal‐State Resistivity for High‐Tc Superconductors
Authors: Schiller W. , Weschke K.
Published: July 2007

Using the method of force‐correlation functions the electrical resistivity is calculated for the anharmonic model of high‐ Tc superconductors with structurally unstable lattices. This model contains the interaction between electrons and strong anharmonic ion vibrations. The influence of this interaction on the temperature dependence of the electrical resistivity in the normal conducting phase is discussed in the case of weak scattering. The results are compared with experimental and theoretical investigations on YBaCuO compounds.
Energy Spectrum and Elementary Excitation Damping in the Structurally Disordered Ising Model in a Transverse Field
Authors: Vakarchuk I. A. , Tkachuk V. M.
Published: July 2007

The elementary spin excitations in the structurally disordered anisotropic Heisenberg model are investigated by the two‐time temperature Green function method. The Ising model in a transverse field is considered as a special case of an anisotropic model. An equation is obtained for the excitation spectrum and damping, caused by scattering of the excitations on the structure fluctuations. The asymptotics of damping in the long‐wave limit and the critical temperature at which the excitation spectrum gap turns to zero are investigated.
The Optical Properties of Impurity Center Short‐Range Potentials in a Magnetic Field
Authors: Sinyavskii E. P. , Safronov E. Yu.
Published: July 2007

The impurity absorption of light and the luminescence on bound states in solid matter under magnetic fields are studied using the model of zero‐radius potential. The absorption constant K(Ω), at various configurations of the magnetic field intensity,H, and electric field intensity, E, is calculated. The results obtained for K(Ω) and the dependences of the electron binding energies on the short‐range potential on H are compared with experimental data in multivalley semiconductors. The peculiarities of the frequency dependence of the spectral intensity of radiation ϕ(Ω) are discussed. It is noted that ϕ(Ω), as a function of frequency Ω, at great H has an oscillatory character.
Boundary Conditions in Case of Electromagnetic Wave Absorption
Authors: Kudykina T. A.
Published: July 2007

Boundary conditions for electromagnetic waves in absorbing media are obtained. The fact is taken into account, that in absorbing media the electric induction has two components: one in phase with the electric field of the incident wave and the other – out of phase by π/2. The Maxwell boundary conditions for each component gives equations enough to determine the amplitudes of all excited waves in the range of exciton resonance and of all waves, charge, and current densities in the band‐to‐band excitation range. For TM‐waves the analogue of Snellius' law is obtained in the case of absorbing media. TE‐waves Snellius' refraction law is valid in case of absorbing media too. In both the cases the reflectivity depends upon absorption and in the limit of great absorption (χ → n, where n, χ are the indexes of refraction and absorption, respectively) tends to unity.
Short‐Range Order in Superstructures
Authors: Rempel A. A. , Gusev A. I.
Published: July 2007

Regions of allowed values of short‐range order parameters are calculated for ordered A2t–1B alloys and non‐stoichiometric interstitial Me2tX2t–1 (t = 1, 2, 3, and 4) compounds. A relationship is established between the short‐and long‐range order parameters as a function of solid‐solution composition and superstructure type. Suggestions are made about possible formation mechanisms of various superstructures.
An Evaluation of Structural and Transport Properties of Molten Potassium–Rubidium Alloy
Authors: Rao R. V. Gopala , Bandyopadhyay U.
Published: July 2007

In comprehensive investigations the perturbation treatment of the Lebowitz equation with a square well attractive tail is utilised to calculate the partial and total structure factors at different atomic fractions of potassium in the potassium–rubidium melt. Further the Bhatia‐Thornton correlation functions are evaluated. Using the direct correlation function in the long‐wave limit, the isothermal compressibilities are calculated through the Kirkwood‐Buff equation. The partial structure factors are then utilised to calculate the self‐diffusion coefficients using the linear trajectory approximation due to Helfand.
Incorporation and Aggregation Properties of Bismuth Ions in KCl Crystals
Authors: Nistor S. V. , Stoicescu Gh. , Mateescu C. D.
Published: July 2007

The optical absorption spectra of bismuth doped KCl crystals, grown by the Bridgman method in reactive atmosphere, reveal the presence of both Bi3‐ and (BiO)+ centers in variable ratios. The ratio changes along the crystal axis and depends on the chemical form of the dopant and its initial concentration. The shape, intensity, and peak positions of the optical spectra are sensitive to the thermal history of the crystal, reflecting the aggregation/dissolution of the centers. An apparent third‐order reaction is observed to govern the early stages of the Bi3+ aggregation, with an activation enthalpy of 0.60 eV, in good agreement with earlier results of diffusion and ionic conductivity measurements.
Dynamical Correlations in Liquid Sodium
Authors: Jain K. C. , Gupta N. , Pratap A. , Saxena N. S.
Published: July 2007

The theory developed by Glass and Rice is used to study the atomic motions in liquid sodium in terms of the velocity autocorrelation function, power spectrum, and mean square displacement at 373 K. The interatomic pair potential for liquid sodium at the melting temperature is obtained by using Ashcroft's pseudopotential theory with the dielectric function of Vashishta and Singwi. Results of these calculations are compared with the results obtained by Miranda and Tora from molecular dynamics at 373 K. These results of dynamical variables obtained by the theory of Glass and Rice show a good agreement with the molecular dynamics results for liquid sodium. Besides, calculations are also done for the coherent behaviour of liquid sodium in terms of the dynamical structure factor S(k, ω). Quasi dispersion curves derived from the peak positions of the longitudinal current‐current correlation function ω2S(k, ω)/ω−2 against k, are in good agreement with experimental phonon dispersion results of Cocking for liquid sodium.
Fermi Surface Charactertics of Palladium
Authors: Ahuja R. , Solanki A. K. , Auluck S.
Published: July 2007

The Fermi surface of palladium is calculated using the linear muffin tin orbitalmethod in the atomic sphere approximation. The calculations demonstrate the need to include relativistic corrections for a good representation of the Fermi surface. Calculations are performed including the f‐band potential parameters and by increasing the number of k points in the Brillouin zone summation. With the view to ascertain which exchange‐correlation potential is appropriate for Fermi surface work calculations are made using a number of exchange‐correlation potentials. The calculations indicate that the Slater Xα exchange with α = 0.75 provides the best agreement with the experimental Fermi surface data. Using this exchange the electron velocities and mass enhancement factor are calculated for the various sheets of the Fermi surface. The results are compared with the experimental data and with available theoretical calculations.
Self‐Consistent Theory of Delocalization
Authors: Olemskoi A. I.
Published: July 2007

The Anderson delocalization theory is constructed by analogy with the microscopic theory of superconductivity, where the square‐rooted ratio of the number of the bound sites to the total number of the impurity sites plays the role of an order parameter and the shift from the band center plays the role of a conjugate field. The spectrum dependence of the effective interaction parameter is shown to lead to anomalous behaviour of a system (2 + δ transition, where δ = 0 is the addition due to a logarithmic factor).
Configuration Interaction and Crystal Field Splitting of the Cu2+ Ion in D2d and D3h Symmetry
Authors: Gomathy V. , Basu C. , Ghosh U. S.
Published: July 2007

The effect of interaction of excited electronic configurations 3d84s, 3d84d, and 3d84f with the ground 3d9 configuration on the crystal field splittings of the Cu2+ ion in Cs2CuCl4 having D2d symmetry and in [Cu(NH3)2]Ag(SCN)3 having D3h symmetry is investigated. The amount by which the crystal field splittings of the Cu2+ ion in these two systems are affected by the various mechanisms of configuration interaction are estimated within the framework of crystal field theory using Richardson's wave functions for the radial integrals.
Regular Algorithm for the Solution of the Inverse Problem in Mössbauer Spectroscopy
Authors: Voronina E. V. , Ershov N. V. , Ageev A. L. , Babanov Yu. A.
Published: July 2007

Generalizing the regular solution algorithm the inverse problem of Mössbauer spectroscopy is proposed for obtaining the distribution function of the hyperfine interaction parameters from the spectrum. By model calculations it is shown that the algorithm is stable with respect to statistical noise and errors in the spectrum parameters. It is noticed that the algorithm is applicable strictly only to objects which properties can be described by a continuous distribution of one of the hyperfine interaction parameters. The condition of the normalization is introduced as an additional criterion of the correctness of the solution. There is a possibility of investigating the spectra with paramagnetic components. The algorithm may be applied to an analysis of both, poorly resolved and well resolved spectra.
Magnetic Properties of Pd3Fe
Authors: Maksimović G. D. , Popović Z. S. , Vukajlović F. R. , Vuletić K.
Published: July 2007

The Stoner model of ferromagnetism in combination with self‐consistent linear muffin‐tin paramagnetic calculations are used for the investigation of magnetic properties of the Pd3Fe compound. Very good agreement is obtained with previous more complicated spin‐polarized calculations and experiments.
Qualitative and Quantitative Differentiation of Paramagnetic Anion‐Antisite‐Related Spectra in GaAs
Authors: Goltzené A. , Schwab C.
Published: July 2007

The electron paramagnetic resonance spectra related to the anion antisite in GaAs may be sorted out into two groups according to their behaviour under photoexcitation and microwave saturation. This qualitative separation is quantitatively supported by different values for the central hyperfine constant and for the component linewidth of the quadruplet spectrum usually modeled by an isolated As defect. These observations lead to reinvestigate the initial extrapolation, based on the isolated PGa centre in GaP, which results in the identification of the former quadruplet. It supports the existence of several antisite‐related defects likely differing by their first shell as in GaP.
On a Simplified Analysis of the Magnetic Susceptibilities of Electrons in Ultrathin Films of Non‐Parabolic Semiconductors in the Presence of a Quantizing Magnetic Field
Authors: Ghatak K. P. , Mondal M.
Published: July 2007

An attempt is made to formulate simplified expressions of the dia‐and paramagnetic susceptibilities of electrons in ultrathin films of non‐parabolic semiconductors under strong magnetic quantization, taking n‐CdGeAs2 as an example. It is found, on the basis of a newly derived magneto‐dispersion relations of ultrathin films, that both the susceptibilities oscillate with increasing film thickness and increase with increasing electron concentration in the quantum limit. In addition the corresponding results for the three‐band Kane model, two‐band Kane model, and parabolic energy bands are derived as special cases of our generalized expressions.
The Dielectric Function and Reflectivity in KDP‐Type Ferroelectrics
Authors: Wesselinowa J. M.
Published: July 2007

A Green function technique is developed to study the real and imaginary parts of the dielectric function ε(k, E) for KDP‐type ferroelectrics below and above Tc. The dependence of the numerically calculated ε(k, E) on energy E and temperature T is discussed. Using the Kramers‐Kronig analysis the refractive index n, the absorption index χ and reflectivity R are obtained for T = 120 and 300 K and are found to be in very good agreement with the experimental data for KDP.
Stable States and Ordering in Chalcogenide Vitreous Semiconductors
Authors: Maslyuk V. T.
Published: July 2007

A chemical‐structural scheme of the stable state construction in amorphous semiconductors is proposed. Proceeding from the thermodynamic considerations the stable states, energy level diagram, and the temperature features of their population are determined. The feasability of a given approach for the description of induced structural transformations in chalcogenide vitreous glasses (ChVG) is illustrated by Müller's additivity principle.
Study of Lithium Interaction with Lattice Defects in Silicon
Authors: Myakenkaya G. S. , Gutsev G. L. , Afanaseva N. P. , Evseev V. A. , Konopleva R. F.
Published: July 2007

A theoretical and experimental study is carried out on the behaviour of the Li donor impurity in the Si lattice with vacancy‐like (V) radiation‐induced defects. The electronic and geometrical structure of the cluster Si4H12 + Li4 simulating the V + Li4 complex in Si is calculated by the discrete variational Xα‐method. It is found that the cubic tetrahedral configuration of the complex is geometrically stable where the 8t2 state near the edge of the valence band is completely populated. The principal possibility of passivation of the V‐type defects by Li atoms is checked experimentally on n‐ and p‐Si samples with a Li concentration of ≈ 1017 cm−3 irradiated by reactor neutrons at fluences of 1.6 × 1015, 4 × 1015, and 3.4 × 1016 cm−3. The temperature dependences of the conductivity, Hall constant, and mobility are measured. It is shown that at high Li atom concentrations considerably in excess of the concentration of the dopant and radiation‐induced defects the electrical characteristics of the irradiated Si restore to the original level which is in agreement with the calculations on the passivation of the Li atoms by the V‐states in Si.
Charge Asymmetry in the Dependence of Stopping on Impact Parameter
Authors: Balashova L. L. , Kabachnik N. M. , Kondratev V. N.
Published: July 2007

The charge asymmetry effects in the dependence of electronic energy loss on impact parameter are studied theoretically. Allowance for some corrections to the calculations made in terms of the first‐order perturbation theory is shown to result in a dependence of stopping on projectile charge sign. Corrections for binding‐energy variations and for Coulomb deflection are allowed for in the case of stopping on inner shells of atoms. A correction for electron cloud polarization is allowed for in the case of valence electrons. Particular calculations are carried out in case of proton and antiproton stopping by Si atoms. The antiproton energy loss proves to exceed the proton energy loss in case of low values of impact parameters, and vice versa in case of high values of impact parameters. As the projectile velocity increases, all the corrections decrease, thereby resulting in that the impact parameter dependences of the proton and antiproton stoppings become in practice identical.
Activation Process Model
Authors: Tavgin V. L. , Stepanov A. V.
Published: July 2007

An attempt is made to produce an activation process model. The physical essence of the given model is different from that of the known activation model. The proposed model is based on following assumptions: 1) in the elementary activation interaction act the potential energy of moving atoms changes discretely or quantizes: the elementary activation act appears to be a series of quantum subsystems occurring in sequence (those subsystems may also be defined as identical harmonic oscillators); 2) an idempotent energy exchange between infrared radiation and interaction atoms causes their discrete translational motion, the process is characterized by absorption and subsequent emission of oscillation energy quantum series produced by atoms. The first principles in accordance with the model give formula, which describes the average energy of the translationally moving atoms participating in the elementary activation act. As an application of the model the formulae of solid state atomic diffusivity are derived as well as constants of first‐order chemical reaction rate. It is pointed out that the model may be applied to interpret superionic conductivity effect and atom or molecule tunnelling.
On the Kinetics of Decomposition of Dilute Al—(Zn, Mg) Alloys
Authors: Schmelzer J.
Published: July 2007

A theoretical explanation is given of typical features of the phase separation kinetics in dilute Al—(Zn, Mg) alloys. It is shown that the experimental results can be interpreted as a decomposition in the first non‐asymptotic stage of Ostwald ripening.
Tachyons in a Crystalline Structure
Authors: Günther H.
Published: July 2007

A class of solutions is discussed of sine‐Gordon equation applied to dislocations in solids which do not admit an interpretation in terms of particles. The energy density for these states propagates faster then the characteristic velocity of the sine‐Gordon equation. Hence they will be called tachyons. The possibility for their physical reality reflects an internal relativity of simultaneity in the crystalline solid on the basis of standards for the measurement of space and time which are inherently related to the lattice structure. Tachyons cannot be used for transmitting signals. They should, however, play a role for the quantized sine‐Gordon equation. A general symmetry relation between particle solutions and tachyon solutions of sine‐Gordon equation can be formulated with the help of a generalization of Seeger's π‐transformation.
Analysis of Far Infrared Spectra Showing Bulk and Surface Phonon‐Polaritons in CdTe Epilayers on GaAs Substrates
Authors: Dumelow T. , El Gohary A. R. , Maslin K. A. , Parker T. J. , Tilley D. R. , Ershov S. N.
Published: July 2007

A theoretical interpretation is given of far infrared measurements by dispersive Fourier transform spectroscopy (DFTS) and attenuated total reflection (ATR) spectroscopy on two semiconductor samples, each consisting of a CdTe epitaxial layer deposited by plasma MOCVD on a GaAs substrate. In each case calculation gives a very good description of the measured spectra. The DFTS measurements reveal both the CdTe and GaAs reststrahlen bands, which lie in well‐separated spectral ranges. At frequencies above the CdTe reststrahlen band, where the CdTe layer behaves effectively as a dielectric film, interference between the beams reflected from the top and bottom of the layer leads to striking structure in the phase spectrum. ATR measurements are made in both p and s polarisation, and it is shown that a p‐polarised surface polariton is detected in the CdTe reststrahlen band, and both p‐ and s‐polarised guided waves are detected in the GaAs reststrahlen band. The frequency of the s‐polarised guided mode is found to vary with layer thickness, and both techniques provide a sensitive probe of the layer thickness.
Electronic Properties and Crystal Structure of a Methylthio Substituted Naphthalene Cation Radical Salt: (DMbTN)3(ClO4)2
Authors: Söderholm S. , Hellberg J. , Krzystek J. , Olovsson G. , Olovsson I. , von schütz J. U.
Published: July 2007

The crystal structure, the conductivity, and the magnetic properties of the monoclinic cation radical salt 2,7‐dimethoxy‐3,6‐bis(methylthio)naphthalene‐perchlorate [(DMbTN)3(ClO4)2] are presented. The stack of DMbTN molecules consists of triads which make the salt semiconducting, σ(300 K) ≈ 10−4 S/cm, with a band gap of 0.6 eV. In spite of the low conductivity the susceptibility is very high, about 0.27 spins/complex. This is due to the presence of significant correlation effects, causing the coupling between the spins to be antiferromagnetic with J = 56 meV. Because of the trimerization of the DMbTN stack the primary spin excitations are thermally activated triplet spin excitations of the Wannier type. The electrical and magnetic properties for T ⪅ 200 K are governed by the presence of deep defect levels in the band gap. The ESR linewidth is unusually narrow, about 1 G at 300 K, for an ion‐radical salt containing sulphur, this implies that the spin density on the sulphur atoms is very low.
The Electronic Structure of Alkaline‐Earth Oxides. IV. CaO and SrO Ground State in the Crystalline Cluster Approach
Authors: Lobatch V. A. , Rubin I. R. , Sobolev A. B.
Published: July 2007

The electronic structure of CaO and SrO in the ground state is calculated in terms of the crystalline cluster approach. Calculations for 27‐atom clusters at different ratios between muffin‐tin sphere radii show that in both crystals the charge configuration is similar to that obtained earlier for MgO: Mg2+ ‐O− plus one electron, distributed in the interstitial region. Such distribution of the electronic density is interpreted in terms of the theory of resonance scattering on the anion effective potential.
Examination of the Electronic Structure of Pd1−xNix Alloys by Positron Annihilation
Authors: Dęb⊙wska E. , Rudzińska‐Girulska J.
Published: July 2007

The entire concentration range of α‐phase Pd1−xNix alloys is studied by angular correlation of the positron annihilation radiation method at room temperature and at 90 K. The number of nearly free and d‐itinerant electrons as well as interstitial electron density against x are calculated. The increase in d‐itinerant electron number at low temperature as compared to room temperature results is possible to be the reason of the onset of ferromagnetism for the alloys with x ≦ 0.20. The electron redistribution model valid for Pd‐noble metal alloys is not confirmed for PdNi alloys. The big difference in interstitial electron densities for Pd and Ni is consistent with “common‐band” structure of PdNi alloys.
Josephson Tunneling Critical Current between Superconductors with Charge‐ or Spin‐Density Waves
Authors: Gabovich A. M. , Moiseev D. P. , Shpigel A. S. , Voitenko A. I.
Published: July 2007

The temperature dependences are calculated of the critical current Ic across a symmetrical tunnel Josephson junction between superconductors with partial electron spectrum dielectrization. The dielectric pairing is considered to be either singlet (charge‐density wave) or triplet (spin‐density wave). The dependences of the superconductivity gap Δ and Ic on T do not differ substantially from the well‐known Mühlschlegel and Ambegaokar‐Baratoff curves. The current Ic falls rapidly when the dielectric gap ∑ increases and the ratio ν ≡ Nnd(0)/Nd(0) decreases. Here Nnd(Nd) is the electron state density on the non‐dielectrized (dielectrized) Fermi surface section. The values jc of the critical current density for the bulk Josephson samples of ceramics BaPb1−xBixO3 with x = 0.15, 0.25, 0.3, and current—voltage characteristics of the tunnel type are measured. The quantity jc drops sharply when x increases, i.e. when the dielectrization degree increases (ν decreases).
Acoustic Second Harmonic Generation in Magnetized High Resistivity Piezoelectric Semiconductors. Effect of Nonuniform Electric Field Intensity and Carrier Concentration
Authors: Dey (Bose) M. , Ghosh S.
Published: July 2007

The acoustic second harmonic generation in transversely magnetised nondegenerate piezoelectric semiconductors in the presence of an electrostatic field in the direction of the wave propagation is studied theoretically. Even in trap‐free semiconductors the electrostatic field and the carrier concentration inside the sample are taken as nonuniform. It is found that the relative flux of second harmonic gets enhanced due to this nonuniformity; whereas application of magnetostatic field reduces it. Numerical estimations are made for n‐CdS at room temperature.
Study of Frustrated Ising Ferrimagnets
Authors: Li Mai Suan
Published: July 2007

It is shown that at low magnetic fields the paramagnetic—spin glass transition temperature Tg(H) of Ising ferrimagnets may be proportional to H2/5 for certain parameters of the model. From the calculations follows that a jump of the magnetocaloric effect at the compensation point Tk decreases with inceasing frustration. The influence of disorder on the discontinuity in the entropy at Tk is also discussed.
The Dynamics of the Domain Boundaries and Soft Lattice Mode in SbSI Crystals
Authors: Burlakov V. M. , Kiselev S. A. , Petukhov V. N. , Anikiev A. A.
Published: July 2007

The temperature dependence of the heat capacity of SbSI crystals in the ferroelectric phase is measured both, in the adiabatic and continuous temperature scanning regimes. The anomaly of the heat capacity in the temperature scanning regime is observed near 262 K. On the basis of the anomaly dependence on the temperature scanning rate it is concluded that this anomaly is caused by the movement activation of the domain boundaries. By the position of the anomaly maximum and its width the activation energy E0 = 0.014 (TC − T) eV/K (Tc = 298 K; Curie temperature) and the oscillation frequency of the domain wall at the pinning center μ = 3.2 × 109 Hz are determined. The manifestation of the increase of the mobility of domain boundaries in the temperature dependence of the soft ferroelectric mode is discussed.
Localization and Resonance Transmission of Light Waves in a One‐Dimensionally Disordered Dielectric. Polarization Effects
Authors: Kosobukin V. A.
Published: July 2007

Using a diagrammatic self‐consistent approach the problem of Anderson localization is treated for photons with different polarizations in a layered random dielectric. The diffusion coefficient and localization length are calculated for photons. Two types of anomalies are found whose manifestation is a divergency of the localization length. One of the anomalies, which originates in the total transmission of light through scatterers, is peculiar to both (s and p) polarizations. Another anomaly associated with the Brewster effect is a feature of p‐polarized waves only.
A Correlation Study of Small Potassium Cationic Clusters
Authors: Altekar S. D. , Ray A. K.
Published: July 2007

Fourth‐order many body perturbation theory is used to investigate the properties of small potassium cationic K (2 ≦ n ≦ 7) clusters. Detailed electronic structures of these clusters are studied. Stabilities from the points of view of binding and fragmentation energies are discussed and, wherever possible, results are compared with published data in the literature.
Preliminary Studies on the Stabilities of Three Types of Ordered Structures in the A(BB)O3 System
Authors: Wang Qiang , Gu Binglin , Zhang Xiaowen
Published: July 2007

Three types of ordered domains, i.e., 1/2〈111〉, 1/2〈110〉, and 1/2〈100〉 superlattice structures, are observed, and the experimental results show that the 1/2〈111〉‐type ordered structure is much more stable than the other two. The eight‐point cluster variation method is established firstly and then the second and third neighbour interactions are taken into account. Based on the method, the phase diagrams as a function of reduced temperature (kT/J) and composition (x) are obtained and the stabilities of various ordered structures are analyzed. Theoretical results well explain the experimental observations.
Mori Approach to the Dynamics and Thermodynamics of Tunneling Centers
Authors: Junker W. , Wagner M.
Published: July 2007

An extended 2‐site model is considered for phonon‐assisted quantum diffusion which beyond the conventional coordinate coupling also embodies a momentum coupling initiated by the nonadiabatic behaviour of the tunneling particle. The Mori vector formalism is used to derive the fundamental Green functions, which govern both, the thermodynamics and the diffusive process. The formalism is established in such a manner that it satisfies the lowest four sum rules. Closed expressions are derived for the internal energy and the specific heat and the temporal behaviour is also discussed.
Fundamental Vibrations in Pb5(GeO4)(VO4)2 Crystals
Authors: Anachkova E. , Gospodinov M. , Nikolov A. , Svestarov P. , Petkov N. , Markov Yu. , Limonov M. , Bruchman G.
Published: July 2007

A group‐theoretical analysis of the vibrational spectrum of lead‐germanate vanadate crystal is presented, extended with some remarks concerning positional disorder observed in the new X‐ray study of this crystal. Raman spectra of the crystal studied are compared with the theoretical results as well as with infrared and Raman spectra of similar compounds.
Cohesive Energies, Equation of State, and Thermoelastic Properties of Mixed Alkali Halide Crystals
Authors: Dixit S. , Niwas R.
Published: July 2007

The cohesive energies and equations of state describing the pressure‐volume relations are studied for nine systems of mixed alkali halide crystals for the entire range of composition. The Harrison analytical potential form for the overlap repulsive energy derived from quantum mechanical considerations is used to describe the nearest neighbour as well as next neighbour interactions. The long‐range electrostatic and the short‐range van der Waals interactions are also considered in the potential model. The thermoelastic properties such as the Grüneisen parameter and its volume derivative, isothermal and isentropic Anderson parameters are also calculated and reported. The results are discussed and compared with experimental data.
Magnetotransport Properties and Subband Structure of the Two‐Dimensional Electron Gas in the Inversion Layer of Hg1−xCdxTe Bicrystals
Authors: Kraak W. , Kaldasch J. , Gille P. , Schurig Th. , Herrmann R.
Published: July 2007

The electronic and magnetotransport properties of conduction electrons in the grain boundary interface of p‐type Hg1−xCdxTe bicrystals are investigated. The results clearly demonstrate the existence of a two‐dimensional degenerate n‐type inversion layer in the vicinity of the grain boundary. The observed quantum oscillations of the magnetoresistivity result from a superposition of the Shubnikov‐de Haas effect in several occupied electric subbands. The occupation of higher subbands is presumable depending on the total carrier density ns of the inversion layer. Electron densities, subband energies, and effective masses of these electric subbands in samples with different total densities are determined. The effective masses of lower subbands are markedly different from the band edge values of the bulk material, their values decrease with decreasing electron density and converging to the bulk values at lower densities. This agrees with predictions of the triangular potential well model and a pronounced nonparabolicity of the energy bands in Hg1−xCdxTe. At high magnetic fields (B > 10 T) it is experimentally verified that the Hall resistivity ϱxy is quantized into integer multiplies of h/e2.
Equilibrium and Kinetics of Ion Exchange in Zinc Selenide Single Crystals
Authors: Aleksanyan A. O. , Ganshin V. A. , Korkishko Yu. N. , Fedorov V. A.
Published: July 2007

The process of ion‐exchange Cd2+ ⇄ Zn2+ in ZnSe single crystals is studied for the first time. A mixture of K2SO4Na2SO4ZnSO4 is used as doping melt. It is shown that the CduZn1−uSe solid solution formed in the surface region of the crystal as a result of the ion exchange has zinc‐blende structure at all values of u and is regular. The thermodynamical and diffusion‐kinetic parameters of exchange and diffusion stage of the process in the temperature range from 400 to 500 °C are determined.
Role of Electron‐Phonon Interaction Induced Hybridisation in Spin Included Mixed‐Valence Phenomena
Authors: Ghosh S. C. , Ghosh N. K. , Sarkar R. L.
Published: July 2007

The phenomenon of valence transition is investigated on the basis of a model which incorporates the electron‐phonon interaction induced hybridisation between f and d bands. Finite temperature specific heat, magnetic intersite spin correlations are also studied. It is shown that strong EP interaction makes the first‐order transition possible. A comparison is also made with results obtained previously.
Non‐Relativistic and Scalar‐Relativistic LAPW Electronic Energy Bands of (001) Cu Films
Authors: Dubrovskii O. I. , Kurganskii S. I. , Rubtsova L. A. , Wolf G. W.
Published: July 2007

The band structures of 1‐, 3‐, and 5‐layer f.c.c. (001) Cu films are calculated using the linearized augmented‐plane‐wave method both, in the non‐relativistic and the scalar‐relativistic modification. The one‐electron potential of the Kohn‐Sham equation, constructed using the film “muffin‐tin” approximation is the same for both the cases. The account of relativistic effects is shown to result in the nearly homogeneous ≈ 16 mRy shift of the energy spectrum towards lower energies.
Calculation of the Normal‐State Thermal Conductivity of the Lattice for High‐Tc Superconductors
Authors: Schiller W. , Weschke K.
Published: July 2007

Starting from the method of inverse linear response theory the thermal conductivity of the lattice is calculated for the anharmonic model of high‐Tc superconductors with structurally unstable lattices. This model describes the interaction between strong anharmonic ion vibrations and the electron system. The contribution of this interaction and a contribution due to the structure of the anharmonic model determine the properties of the lattice thermal conductivity. The influence of both scattering mechanisms on the temperature behaviour in the normal‐conducting phase is considered. Results for different parameters of the anharmonic model are discussed and compared with experimental investigations on YBaCuO compounds.
Transport with Microscopic Inhomogeneities. Residual Resistivity Dipole, Landauer Formula, and the Three‐Dimensional Impurity Case
Authors: Lenk R.
Published: July 2007

A superposition method for the density matrix of stationary transport processes is developed where an arbitrary perturbation is superimposed on a weakly scattering background. Additional scatterers, areal perturbations of the grain boundary type and/or geometrical confinements in wires or films are candidates for applications. In the present paper an arbitrarily strong added scatterer is treated whose linear size remains small compared with the mean free path within the background. This problem is solved for a one‐channel quantum wire and for the three‐dimensional bulk. In both cases the evolving residual resistivity dipole (RRD) is determined. Already existing results are confirmed, generalized, and complemented by the inclusion of oscillatory density terms. A comparison of both the cases demonstrates the decisive role played by the topology of the problem. Within the scope of a completely formalized nonclassical transport theory, the internal mechanism producing the RRD is analysed. In this way it is shown that the voltage drop due to an added scatterer is given correctly, in the one‐channel case, by an expression of the (R/T)‐type quite similar to the original Landauer formula (LF). This derivation of a modified LF abandons the concept of dissipative reservoirs and ideal leads. The physical difference between ideal and resistive leads yields different results, too. These agree completely only for a sharp Fermi energy while, in the general case of finite temperatures, non‐negligible energy dependences destroy the full equivalence of both approaches.
Drag Effects in Semiconductors with Position‐Dependent Band Structure
Authors: Istrate Mariana , Istrate S.
Published: July 2007

In a semiconductor with position‐dependent band structure if on take into account the drag effects, the expressions for the kinetic coefficients contain terms in addition to those corresponding to the conventional components for such semiconductors. These expressions are developed for a nondegenerate and a degenerate semiconductor, in the case of a phonon—phonon drag. The relations can be used for a variety of materials including graded band gap semiconductors, graded heterojunctions and others.
Spin‐1 Exchange Interaction Model of Ferromagnetism
Authors: Chaddha G. S. , Singh J.
Published: July 2007

Effects of biquadratic exchange on the low temperature behaviour of magnetisation, Curie temperature, and zero field susceptibility at high temperatures are investigated in the case of a spin‐1 Heisenberg ferromagnet. The Green function technique with mixed Callen and RPA decoupling approximations is utilized. Some invalid results and drawbacks of earlier treatments are noted.
Interband Resonance Raman Scattering in p‐Type Semimagnetic Semiconductors in Quantizing Magnetic Field
Authors: Gashimzade F. M. , Ismailov T. G. , Nadirzade R. S.
Published: July 2007

The electron Raman scattering in the wide‐gap semimagnetic semiconductor p‐Cd1−xMnxTe in a quantizing magnetic field is studied. Expressions in analytical form for the differential effective cross section depending on frequency shift are obtained. The possibility of determination of exchange parameters from experiment is shown.
Evidence for Order Parameter Spatial Fluctuations in TlGa(Se1−xSx)2 Crystals by Raman Spectroscopoy
Authors: Burlakov V. M. , Anikiev A. A. , Yakheev M. R.
Published: July 2007

Raman spectra of the ferroelectric layered crystals TIGa(Se1−xSx)2 are studied for concentrations x = 0, 0.05, 0.15 over a wide temperature range. The contribution of the order parameter spatial fluctuations to the spectral line parameters is defined by comparing the concentration dependence of the low‐frequency integral intensity to that of the splitting of a doubly degenerated hard mode at ≈ 55 cm−1. Large spatial fluctuations of the order parameter are assumed to be caused by the presence of an order–disorder component in the ferroelectric instability of the layered crystal. The order—disorder component is thought to be related to a narrow one‐dimensional soft phonon band.
Temperature Dependence of the Oxygen Absorption Band in ZnTe: O
Authors: Slusarenko V. , Burki Y. , Czaja W. , Berger H.
Published: July 2007

Absorption measurements are made as function of temperature for the isoelectronic trap ZnTe: O. This spectrum is well separated from the intrinsic absorption and from the absorption due to other impurities. The spectra can be semiquantitatively understood using a model developed for AgBr:I. The temperature dependence of the absorption due to LO‐phonon cooperation is given by ∼e−γT2 where γ can be derived from the value for AgBr:I. The fine structure of the absorption is explained and the spectral symmetry between emission and absorption is discussed in detail. The electron—phonon coupling (Huang‐Rhys factor) is found to be different for different phonon modes and smaller in absorption than in emission for optical modes but the inverse is true for accoustic modes.
Lattice Dynamics and Phonon Dispersion in the Narrow Gap Semiconductor Bi2Te3 with Sandwich Structure
Authors: Kullmann W. , Eichhorn G. , Rauh H. , Geick R. , Eckold G. , Steigenberger U.
Published: July 2007

The extremely anisotropic bonding properties of the narrow gap semiconductor bismuth telluride (Bi2Te3) with sandwich structure is studied by inelastic neutron scattering. In combination with lattice dynamical shell model calculations, new information is obtained on the complex bonding forces of this sandwich structured V–VI semiconductor. The sandwich character leads predominantely to three‐dimensional bonding behavior. No characteristic two‐dimensional lattice properties can be observed.
Analysis of Ionic Radii, Second Neighbour Interactions, and Electronegativity Difference for Ionic Crystals
Authors: Singh B. P.
Published: July 2007

Values of ionic radii are determined using the additivity rule and experimental information on X‐ray diffraction and electron density measurements for NaCl crystals. The calculated values of ionic radii are found to produce the nearest‐neighbour interionic separations close to the experimental values in I–VII, II–VI, and III–V compounds. In order to demonstrate the suitability of the calculated radii the interionic distances in tri‐atomic compounds are also predicted. The second‐neighbour overlap repulsive interactions and electronegativity differences are discussed in terms of ionic radii. The calculated radii are found to correlate very well with the electronegativity differences.
Isostructural γ‐α Transition in Metallic Cerium as a Mott Transition
Authors: Ionova G. V. , Nikolaev A. V.
Published: July 2007

The isostructural γ–α phase transition of Ce is studied by means of FLAPW band calculations carried out for four different electronic structures of Ce. The calculated results support the picture of a 4f localized‐itinerant transition at the γ–α transition.
Resonant Polaritons
Authors: Kaganov M. I. , Shalaeva T. I.
Published: July 2007

Polariton properties are investigated near the frequences where dielectrical and magnetic susceptibilities simultaneously turns into zero or to infinity. Such polaritons are called resonant polaritons. A specific frequency impedance dependence and anomalous anisotropy of the reflection coefficient are predicted.
Fermi Surface and Mass Enhancement Factor for Niobium
Authors: Solanki A. K. , Ahuja R. , Auluck S.
Published: July 2007

Calculations of the extremal areas of Fermi surface orbits in the transition metal niobium (Nb) are presented using the ab initio linear muffin tin orbital method in the atomic sphere approximation and including the combined correction terms. Self‐consistent calculations are performed using various exchange‐correlation (XC) potentials. The Xα exchange‐correlation potential (with α = 0.75) gives the best agreement with the experimental data. The anisotropy of the Fermi velocity of electrons at the Fermi surface and the mass enhancement factor are also calculated using this XC potential. These are compared with the experimental data and recent theoretical calculations.
Self‐Consistent Calculation of Density of States in Impure Semiconductors
Authors: Grill R.
Published: July 2007

Using the Kadanoff‐Baym Green's function formalism the density of states function is calculated. The calculation is performed for the heavy hole band and screened charged impurity scattering in the Born approximation. The results are shown for p‐HgCdTe semiconductor. It is argued that a qualitative change of the band near the edge is essential for a band occupation.
Auger Recombination via Defects in Tellurium
Authors: Mazur Yu. I. , Rubo Yu. G. , Snitko O. V. , Strikha M. V.
Published: July 2007

Auger process including a bound electron and two free holes proved to be the dominant recombination path in tellurium at low temperatures (T < 50 K). The experimental value of the Auger constant is C = 1.6 × 10−28 cm6 s−1. The theoretical model considering the tellurium band structure explains the experimental data qualitatively and gives an order of magnitude value for the lifetimes of excess carriers.
Theory of Transport Phenomena in Ferromagnetic Semiconductors with Superlattice Produced by Coherent Light Beams
Authors: Semchuk A. Yu. , Grechko L. G. , Ogenko V. M.
Published: July 2007

The present paper deals with the effect of a superlattice of non‐equilibrium electrons and magnons on transport phenomena in ferromagnetic semiconductors (FMSC). Such superlattices are formed by coherent light beams (CLBs). A general expression is derived for an additional current in FMSC, caused by the presence in FMSC of superlattices of the carrier concentration, electric field strength, electron, and magnon temperatures. The field dependence of the electrical conductivity of FMSC on superlattices is investigated.
Non‐Resonant Microwave Absorption in N = 3 Phase of BiPbSrCaCuO High‐Temperature Superconductor
Authors: Owens F. J.
Published: July 2007

A detailed study is made of the temperature and magnetic field dependent properties of the non‐resonant microwave absorption in granular composites of the N = 3 phase (Tc = 110 K) of the high‐temperature supercondutor Bi2−xPbxSr2CaN−1CuNO4 + 2N using an EPR spectrometer. The magnetic field value of the center of the line and the width of the line depend on the magnitude of the previously applied dc magnetic field and the direction of sweep of the field. The position and width also change with temperature. It is shown that the theory of Xia and Stroud for the electromagnetic response of superconducting current loop in an increasing magnetic field, assuming a Boltzmann distribution of loop areas in the granular composite, can account for the shape of the derivate and the temperature dependence of the intensity of the derivative of the absorption. The change of the magnetic field position and linewidth with temperature and field can not be accounted for by the theory. These effects are argued to be a result of the flux trapping behavior of the sample.
Ensemble Averaged Moments and Autocorrelation of the Actual Static Factor
Authors: Schulz M. , Handrich K.
Published: July 2007

For various problems of disordered systems one needsmore information, than that contained in the staitc structure factor S(k). Therefore, and actual static structure factor s(k) is defined, which is connectted to the static structure factor S(k) by the average S(k)=〈s(k)〉. The correlation function 〈s(k)s(k′)〉, all moments 〈s(k)n〉, and the probability distribution of s(k) are determined.
Estimation of the Leading Order Anharmonic Parameters from Available Thermodynamic Data
Authors: Mulargia F. , Quareni F.
Published: July 2007

A procedure is presented to estimate from available thermodynamic data the leading order anharmonic coefficients, their volume derivatives, and the quasi‐harmonic terms in the framework of perturbation theory of lattice dynamics to the fourth order in the Hamiltonian. It consists of fitting the theoretical expressions of three functions of compressibility, heat capacity, and thermal expansion to experiment particularly tailored to minimize the effect of experimental errors. The capability of the procedure to produce stable and accurate results is tested through an application to NaCl. NaCl is chosen because of the large number of available independent data, which allows to study in detail the effect of external as well as internal errors. Accurate estimates are found to be possible. Referred to the 300 K volume and on the basis of all available data, the resulting leading order anharmonic parameters of NaCl are A2=(4.6 ± 0.6) x 10−4 J mol−1 K−2, dA2/d In V=(9 ± 4) x 10−4 J mol−1 K−2, while the quasiharmonic parameters are 〈ω〉=(6.8 ± 0.2) × 1026 s−2, 〈γi〉=1.57 ± 0.01, 〈γiωi2〉=(1.2 ± 0.1) × 1027 s−2.