bluuebunny/crossref_metadata_2025 huggingface dataset:
Dynamics of Liquid Na0.5K0.5Alloy
Authors: Jain K. C. , Gupta N. , Saxena N. S.
Published: July 2007

An effort is made to study the motion of effective atoms in liquid Na0.5K0.5alloy in terms of velocity autocorrelation function, power spectrum, and mean square displacement analogous to the single particle motion in liquid metals employing the model developed by Glass and Rice in quasi crystalline approximation. The motions of effective atoms are also studied through the collective excitations by computing the longitudinal and transverse phonon frequencies. The results of collective excitations are in good agreement with the molecular dynamics (MD) results. Besides, results of thermodynamical properties such as isothermal bulk modulus and Debye temperature are also presented. The computed values are in good agreement with the results obtained by other theoretical calculations.
Remarks on the Thermodynamics of Sintering of Ceramics
Authors: Skala L. , Kenkre V. M. , Weiser M. W. , Katz J. D.
Published: July 2007

In the microwave sintering of some materials a rapid increase of their density is observed in a relatively small temperature range of about 100 K. This may be viewed as a transition from a metastable low density state to a more stable state with a density close to the maximum theoretical density. A thermodynamic description of this transition similar to the Landau theory of phase transitions is suggested and applied to the sintering of boron carbide and alumina.
Tight‐Binding Description of Surface States in Semiconductors
Authors: Kasandrov S. Yu.
Published: July 2007

A matrix Green's function technique is used to find the surface band structure of the zincblende‐type semiconductors. A crystal is described by a tight‐binding Hamiltonian with interactions between nearest neigbours. The exact analytical expressions for the transfer matrices at the centre of the surface Brillouin zone are obtained and existence conditions of the surface states are discussed.
Collective Charge‐Density Excitations in Generalized Fibonacci Semiconductor Superlattices
Authors: Zhong J. X. , You J. Q. , Yan J. R.
Published: July 2007

The plasmon properties of generalized Fibonacci type I and type II semiconductor superlattices are studied by a dynamical‐map method. It is shown that the plasmon spectra are Cantor‐set‐like, i.e. the spectra are self‐similar and the gaps in the spectra are densely distributed.
Calculation of the Free Energy and the Pair Correlation Functions of Disordered Binary Alloys by the Method of Collective Variables
Authors: Yukhnovskii I. R. , Gurskii Z. A. , Chushak Ya. G.
Published: July 2007

The expressions of the free energy and the pair correlation functions for random binary alloys are obtained by means of the method of collective variables. The advantages of a new approach are discussed. The theory is exemplified by numerical calculations of the K‐Cs system properties. The calculated phase diagram is in agreement with the results obtained by other authors and with the experimental data. The analysis of the Fourier transform of the binary correlation function shows that the KcCs1−c alloys are similar to ideal solid solutions at high temperatures (T ≧ 300 K). As the temperature decreases, the deviation from the ideal solution increases. The short‐range order parameter at the first coordinate sphere is calculated.
Effect of Non‐Parabolic Band on the Scattering Rates of Free Electrons in High Purity Semiconductors at Low Lattice Temperatures
Authors: Ghorai A. K. , Bhattacharya D. P.
Published: July 2007

The scattering rates of the free electrons in a semiconductor depend upon the energy band structure of the material. No semiconductor possesses a parabolic energy band. The acoustic scattering rate of the free electrons for a non‐parabolic and band is well known for the high lattice temperatures when the scattering is effectively elastic. But when the lattice temperature is quite low ( <20 K) the scattering process becomes inelastic. The effect of the band non‐parabolicity on the acoustic and the piezoelectric scattering rates of the free electrons is investigated here under the condition when the lattice temperature is low. The same effect on the piezoelectric scattering rates at high lattice temperatures is also obtained here. Numerical calculations are carried out at different lattice temperatures for Si which has a low value for the non‐parabolicity factor and for InSb which has quite a high value for the same factor. The results are interesting and prompt one to take up further investigation.
Generalized Explicit Dispersion Relation for a Gyrotropic Waveguide
Authors: Matyáš M.
Published: July 2007

A generalized explicit dispersion relation for a gyrotropic waveguide in the longitudinal configuration is derived. The solution is valid for waveguides whose anisotropy can be described by the permittivity and permeability tensors in diagonal form.
Far‐Infrared Spectra of Crystalline Antimony Tri‐Iodide and Arsenic Tri‐Iodide
Authors: Anderson A. , Campbell J. A.
Published: July 2007

Far‐infrared spectra of SbI3 and AsI3 in both single crystal and powder form at 20 K are reported. Principal features are identified through the predictions of a group theoretical analysis and by comparison with Raman data. Tentative assignments of the six infrared active modes are proposed. Certain anomalies are attributed to a partial breakdown of the molecular interpretation of the spectra and to the importance of interionic effects, especially for SbI3.
Optimal Density of States in the Fourier Space (k‐Space)
Authors: Schulz M. , Handrich K.
Published: July 2007

The orthogonality relations for a crystalline lattice are invalid for an amorphous solid. Therefore it is reasonable to determine a basic set, lying in the neighbourhood of the orthogonal system. A minimum problem, whose solution determines the optimal density of states in thek‐space, is formulated.
Spin Collective Oscillations in Two‐Dimensional Charged Fermi Liquids
Authors: Ahmad M. , Gladysz S. J.
Published: July 2007

Starting from the transport equation for spin magnetization the transverse dynamic spin susceptibility is calculated in terms of the Landau two‐dimensional Fermi liquid parameters Bl. The formula allows to estimate the dispersion relation of spin waves with arbitrary l and the oscillator strength of the modes with l = 0, 1. The possibility of experimental determination of the parameters Bl with higher l is discussed.
The Einstein relation in quaternary alloys under different physical conditions
Authors: Ghatak K. P. , Mondal M.
Published: July 2007

The Einstein relation for the diffusivity—mobility ratio of the carriers in quaternary alloys is studied, taking the In1−xGaxAsyP1−y lattice matched to InP, by using the three‐band Kane model in bulk specimens, magnetic quantization, cross‐field configurations, and the low‐dimensional quantum confined structures of the same material under various quantization of band states by formulating the respective electron energy spectra. The same ratio is plotted with different physical variables in all the cases and the theoretical results are in agreement with the suggested experimental method of determining the Einstein relation in degenerate materials having arbitrary dispersion laws. In addition, the corresponding well‐known results of parabolic semiconductors are obtained from our generalized expressions as special cases under certain limiting conditions.
Semi‐ab initio tight‐binding band‐structure calculations of χ(3) (− 3ω; ω, ω, ω) in C, Si, Ge, SiC, BP, AIP, AlAs, AlSb, GaP, GaAs, GaSb, InP, InAs, and InSb
Authors: Moss D. J. , Ghahramani E. , Sipe J. E.
Published: July 2007

A full band‐structure calculation is made of the dispersion, anisotropy, and magnitude χ(3) for optical third harmonic generation (THG) in C, Si, Ge, SiC, BP, AIP, AlAs, AlSb, GaP, GaAs, GaSb, InP, InAs, and InSb. The calculation is performed using a semi‐ab initio tight‐binding band‐structure technique and standard perturbation theory within the random phase approximation and neglect of local field corrections. The sign of χ(3) (0) is positive for all materials, consistent with experimental results from the literature. Trends are investigated in the periodic table in the structure of χ(3), and shown that the structure in most materials is dominated by 3ω resonances with either the E0 or E1 optical peaks, with the E2 critical points typically making a negligible contribution to χ(3).
On Extreme Dynamic Parameters of a Powerful Ion Beam–Metallic Target System
Authors: Boiko V. I. , Kishkin V. P. , Shamanin I. V.
Published: July 2007

A model for the interaction of a power ion–beam a metallic target is briefly discussed. It is taken as a base for simulating numerically the interaction of a 1.5 MeV proton beam with an aluminium target at current densities up to 1.5 MA/cm2. The magnitudes of pressure applied to the target and recoil impulse of plasma scattered from the irradiated surface are found to tend to saturation. It is found that a heavy fraction present in the light ion beam diminishes the efficiency of providing the beam energy for a target.
Exciton Effects in the Reflectance Spectra of Mixed Lead Halides PbCl2xBr2(1 −x)
Authors: Certier M. , Erguig H. , Lumbreras M.
Published: July 2007

The reflectance spectra of orthorhombic single crystals of PbCl2xBr2(1 − x) (0 ≦ x ≦ 1) are studied in the spectral range between 3.5 and 4.8eV at 293, 95, and 39K. The strong peaks observed in these isomorphic solid solutions are attributed to cation exciton transitions. The fine structure of these exciton peaks is observed as a function of temperature and solid composition x. The coefficient of temperature dependence varies nearly linearly with composition for PbBr2 (x = 0), PbClBr (x = 0.5), and PbCl2 (x = 1). The variation of the singlet exciton peak with the fractional composition x shows two different regions: one for 0 ≦ x ≦ 0.5 and another one for 0.5 ≦ x ≦ 1.
Space‐Charge‐Limited Currents at High Electric Fields
Authors: Grekov E. V. , Sukhorukov O. G.
Published: July 2007

The steady‐state space‐charge‐limited current at high electric fields in an insulator or high‐resistance semiconductor with traps is analyzed theoretically. Poole‐Frenkel carrier emission from traps is considered. The analysis of the space‐charge centroid yields a current–voltage characteristic in analytical form. These results are compared with experimental data on the conductivity of Si3N4 films. The obtained characteristic gives a good fit to the observed relation between the current and the film thickness. The trap density in Si3N4 is determined to be (5 to 8) × 1018 cm−3.
Superconducting Transition Point in Dilute U and Be Solutions in V
Authors: Tiwari M. D.
Published: July 2007

The Green's function technique is applied to study theoretically the changes in phonon specific heat and transition temperature of V due to introduction of heavy (U) and light (Be) impurities. Changes in force constants (radial and angular), in mass and in volume are taken into account. The anharmonic effects due to large impurity motions are accounted for within the quasiharmonic approximation and the relaxations of the V neighbours of an impurity are also included. The electron–phonon and electron–impurity interactions are discussed. The calculated results are in good agreement with the experimental results for both the properties.
Reorientational Motion of NH4 Ions in (NH4)2SbF5 Quasielastic Neutron Scattering Study
Authors: Mukhopadhyay R. , Goyal P. S. , Rao K. R.
Published: July 2007

(NH4)2SbF5 has orthorhombic structure at room temperature. It has two crystallographically inequivalent NH4 ions in the unit cell. Neutron quasi‐elastic scattering study is made of reorientational motion of NH4 ions in this salt. Experiments are carried out at 300, 180, and 160 K in the wave vector transfer region of 10 to 23 nm−1. Measured ratio of elastic to quasi‐elastic intensity as a function of wave vector transfer suggests that the two NH4 ions have similar reorientation times measurable within the time window of the spectrometer namely, in the range of 3 to 75 ps. The average form factor A(Q) and the average reorientation time, τ = (10 ± 3) ps, associated with the two NH4 ions are obtained. Broadening of the elastic peak is not seen at 180 or 160 K. This suggests that at these temperatures the value of τ is more than 75 ps.
Dynamics of Liquid Metals
Authors: Gupta N. , Jain K. C. , Saxena N. S.
Published: July 2007

Single particle motion and collective excitations for group IIA elements (Mg, Ca, and Sr) are presented at their respective melting temperatures. The theory developed by Glass and Rice in static harmonic well approximation is applied for the study of the dynamical variables. Three independent theories viz. theory of amorphous solid, Hubbard and Beeby approach, and a model approach given by Bhatia and Singh are applied to study the collective excitations in terms of longitudinal and transverse phonon frequencies in these metals. Besides, some thermodynamic properties are computed. It is observed that the theories of Takeno and Goda and Hubbard and Beeby describe collective excitations in these liquid metals in close agreement whereas the model approach of Bhatia and Singh underestimates the phonon frequencies.
Investigation of the Role of Excited States in the Impurity Breakdown Development
Authors: Danilchenko B. A. , Komirenko S. I. , Rozhko S. Kh.
Published: July 2007

I–U characteristics of n‐Ge:Sb samples with impurity concentrations of Nd = 2 × 1016 cm−3 are of S‐shape at the temperature of liquid He. The depth of the NDC‐region increases with lowering the temperature and with application of uniaxial stress along the 〈111〉 direction. This fact is explained within the framework of the “three‐level” mechanism of the impurity breakdown. Nonequilibrium ballistic phonons ionise excited states of impurity atoms abundantly populated in pre‐breakdown fields, and cause the development of breakdown, that approves the model discussed.
Ground State Energy of an Exciton Coupled to Acoustic Phonons in 2D Nonpolar Crystals
Authors: Xiao Jing‐Lin
Published: July 2007

Some properties of an exciton both, strongly and weakly coupled with acoustic phonons via the deformation potential in 2D nonpolar crystals are studied. The effective Hamiltonian of the surface exciton is obtained by the method of a linear‐combination operator and a simple unitary transformation. The self‐trapping energy and the effective electron–hole interaction potential of an exciton may be written as a series α(α), the first term being proportional to α1(α2) the coupling constant.
Structural and Dynamical Properties of Solid Solutions of BaF2 and GdF3. An EPR Study
Authors: Den Hartog H. W.
Published: July 2007

Results of EPR experiments on solid solutions of barium and gadolinium fluoride in the temperature range 300 to 900 K are presented. At room temperature the Gd‐ions are located predominantly at trigonal sites. If the temperature is increased, the interstitial fluoride ions are found to dissociate from the dipolar complexes, and cubic Gd‐centers are formed. The transition of the Gd‐ions from the trigonal symmetry to the cubic one occurs in qualitatively the same temperature region for GdF3 concentrations between 0 and 4 mol%. For low Gd‐concentrations and moderate temperatures the widths of the cubic EPR lines vary only slightly with increasing temperatures. The widths of these lines increase rapidly with T at high temperatures. The increasing linewidths are associated with the increasing avarage mobility of the interstitial fluoride ions present in the crystals. For heavily doped samples the distance between the Gd‐centers is small. Consequently, the EPR lines of the cubic Gd‐ions are broadened due to the rapid jumps of the highly mobile interstitial fluoride ions of nearby dipoles.
Spin‐1 Random‐Bond Transverse Ising Model with Competing Interactions
Authors: Yang Chuan‐Zhang , Zhong Jia‐Lin , Jiang Xue‐Fan
Published: July 2007

The longitudinal magnetization, the transverse magnetization, and the order parameter y of the spin‐1 random‐bond transverse Ising model with competing interactions on a diamond lattice are discussed within the framework of the effective‐field theory. The phase diagrams of the system are obtained. The possible reentrant phenomena displayed by the system and the influence of random parameters α and p̄ on the behavior of the system are investigated.
An Extended Polarizable Point Ion Model for Schottky Defects
Authors: Banhatti R. D. , Murti Y. V. G. S.
Published: July 2007

The polarizable point ion model for Schottky defects is extended to include the effects of induced quadrupoles in region 1. Schottky defects in AgCl are studied using this model. It is found that it is important to include induced quadrupole moments in any theoretical treatment of charged point defects in ionic crystals. Quadrupolar deformations make sizable contribution to the defect energy which ranged from −0.2 to −0.4 eV in the case of the cation vacancy over the range of anion quadrupole polarizabilities studied. The work further points to the relative significance of chlorine ions in respect of the quadrupole distortions.
γ‐Fe Precipitation in Cu97Fe3 and Cu75Au24Fe1
Authors: Klein J. , Campbell S. J. , Aubertin F. , Gonser U. , Schneeweiss O.
Published: July 2007

A series of isothermal and isochronal heat treatments (300 to 800 °C; 0 to 92 h) is used to compare the precipitation of f.c.c. γ‐Fe in Cu97Fe3 with that in Cu75Au24Fe1 as determined by room temperature Mössbauer spectroscopy. The precipitation process is similar in both systems with up to 90% and 70% of the Fe in Cu97Fe3 and Cu75Au24Fe1, respectively, being precipitated in the form of γ‐Fe. Low temperature measurements (15 K) in zero and applied magnetic fields (5.3 T) on γ‐Fe in the Cu75Au24Fe1 sample show magnetic behaviour similar to that of the familiar low moment, low atomic volume γ1‐state of Fe rather than the high moment γ2‐state expected of this matrix of high atomic volume.
Effect of Scattering Center Correlation on the Conductivity of Disordered Metals
Authors: Parish J. L.
Published: July 2007

The effect of scattering center correlation on the conductivity of two‐dimensional disordered metals, is found.
Magnetophonon Resonance on Three Types of Carriers in p‐InSb
Authors: Ugrin Yu. O. , Sheregii E. M.
Published: July 2007

For the first time in a single experiment the magnetophonon resonances of three types of carriers in p‐InSb are investigated: light holes (MPR1), heavy holes (MPRh), and electrons (MPRe). From the temperature shift of the ground series (most intensive ones) of MPR1 and MPRh the valence‐band parameters of the band structure as function of temperature are calculated. The investigation completed allows for the first time to identify nonearlier observed two‐phonon transitions in p‐InSb, alongside with an additional series of peculiarities: a satellite of the main MPRh series peaks at weak magnetic fields. The comparison of MPRh of two samples with different mobilities of heavy holes lead to the observance of a distortion in the period of the transverse field of the main MPRh series in the sample of less mobility of heavy holes.
Neutron Scattering Studies of C6H12 and C6D12 Cyclohexane under High Pressure
Authors: Mayer J. , Urban S. , Habrylo S. , Holderna K. , Natkaniec I. , Würflinger A. , Zajac W.
Published: July 2007

The results of inelastic neutron scattering (INS) and neutron diffraction (ND) studies of both, C6H12 and C6D12 cyclohexane under hydrostatic pressure (up to 3.7 × 108 Pa) and in the temperatures down to 160 K, are reported. All the solid phases (three in C6H12 and four in C6D12) are well seen in the INS and ND experiments. The lattice vibration spectra strongly depend on the crystal phase, on the applied pressure, and on the isotopic substitution. In view of the complementary Raman spectroscopy results (under atmospheric pressure) it is concluded that the molecular dynamics plays a decisive role in the mechanism of the consecutive phase transitions in cyclohexane.
Band Structure and Nonlinear Optical Susceptibilities of Proustite (Ag3AsS3)
Authors: Dovgii Ya. O. , Kityk I. V.
Published: July 2007

Theoretical and experimental investigations are made of the band structure of proustite (Ag3AsS3). The calculation is performed using the tight‐binding method. As scale factors in the corresponding secular equation the experimental results of VUV‐reflection are used in the spectral region 2 to 30 eV. The contribution of different electronic states to the electronic bands are obtained. From the calculated band energy structure and infrared spectra the influence of the cluster vibrations on the nonlinear susceptibilities is estimated and the contribution of the electronic and ionic part to the electrooptical tensors is separated.
Electron Polarization in Quantum Wells with Uniform Electric Field
Authors: Ilaiwi K. F. , Tomak M.
Published: July 2007

The polarization of a quantum electron confined in square, parabolic, and triangular quantum wells is calculated numerically. The aim of the present calculations is to compare the results for various geometries.
Phonon‐Polaritons in Isotropic Ferromagnets II. Polaritons Due to Magnon‐Phonon Excitations
Authors: Dimitriev O. P. , Lozovskii V. Z. , Getsko O. M.
Published: July 2007

The possibility of phonon‐ and magnon‐polaritons coupling in the volume and on the surface of a polar ferromagnetic isolator is theoretically investigated. Conditions under which excitations of new type waves, magnon‐phonon polaritons, occur are found. It is shown that the properties of these waves may be efficiently guided by applied magnetic fields, which can be used to make new devices in the infrared.
Magnetic Properties and Structure of (CrxAl1‐x)2O3 Solid Solutions
Authors: Viktorov V. V. , Evdokimov I. V. , Fotiev A. A.
Published: July 2007

Statistical homogenity of (CrxAl1‐x)2O3 solid solutions is investigated. It is shown, that there may be distinguished the region of statistical regularities and regions where prevail the clusters of two, three, and four chromic ions (III). The formation mechanism of solid solutions mentioned is proposed.
Theoretical Investigation of Auger Recombination in PbSnTe Structures
Authors: Lemke F. , Mocker M.
Published: July 2007

An approximate analytical formula of the Auger rate is developed, describing the rate in dependence on the dimension parameter v with v = 3, 2, 1 for bulk, quasi‐two‐dimensional, and quasi‐one‐dimensional structures, respectively. The main influence to the Auger coefficient is due to the increased effective gap in low‐dimensional structures, leading to an increased activation energy and therefore in lead chalcogenides to a reduced Auger rate compared to the bulk. The effects of anisotropy and of the changed matrix elements modify this main effect in such a way, that Auger recombination in some special planes and directions is more effective than in others.
Local Electric Field Gradients in Anionic and Cationic Positions of Cesium Perchlorate
Authors: Tarasov V. P. , Meladze M. A. , Kirakosyan G. A. , Shvelashvili A. E. , Buslaev Yu. A.
Published: July 2007

Polycrystalline CsClO4 is studied over the range from 95 to 440 K by 35Cl and 133Cs NMR in the field B0 = 7.04 T. From the analysis of the lineshape the quadrupole coupling constant CQ and the asymmetry parameter η at the nuclei 35Cl and 133Cs are determined. The temperature dependence of CQ is linear for both the nuclei with a negative temperature coefficient. A sharp break of η(133Cs) at 342K is due to the change in the relative values of the tensor components qij of the electric field gradient on 133Cs. The temperature dependence of qij is considered in relation to the anisotropy of the thermal expansion and a numerical evaluation of the thermal expansion coefficient is made.
Anharmonic Effects in the Thermal Diffuse Scattering of X‐Rays
Authors: Tsarkov A. G. , Tsirelson V. G.
Published: July 2007

The thermal diffuse scattering (TDS) of X‐rays in the anharmonic one‐phonon and harmonic two‐phonon approximations is considered. The complete expression for the one‐phonon intensity of X‐rays is derived by perturbation theory and presented for a polyatomic crystal in the high‐temperature limit. The method of evaluating the corrections of the X‐rays intensities for the thermal diffuse scattering is given and the importance taking into account the anharmonic effects in the one‐phonon scattering for KZnF3, CsCl, and YBa2Cu3O7−δ crystals at room temperature is discussed. Anharmonic TDS‐effects achieve considerable magnitudes for soft (acoustic) anharmonic crystals as CsCl.
Evidence of Tetrahedral and Octahedral Aluminum Coordination in Rare‐Earth Aluminates
Authors: Landron C. , Badets M. C. , Douy A. , Coutures J. , Coutures J. P. , Daniel P. , Flank A. M.
Published: July 2007

The local order around the aluminum atoms in a series of rare‐earth aluminates with perovskite and garnet structure is characterized by X‐ray diffractometry and by near K‐edge X‐ray absorption. The aluminate samples are elaborated by an original sol‐gel technique. The Al XANES spectra contain features which appear to be similar to those recorded on other aluminum fluorites with similar structure. In both systems, K edge clearly demonstrat a structure showing the octahedral metal–oxygen coordination for the perovskite stoichiometry and a mixture of tetrahedral and octahedral coordination for the garnet stoichiometry.
Void Sink Strength in H.C.P. Materials
Authors: Grande N. Smetniansky‐De , Tomé C. N. , Savino E. J.
Published: July 2007

The strength of a void in h.c.p. lattices for the trapping of vacancies and interstitials is calculated. An analytic solution for the diffusion equation of point defects is used. The resulting expressions can be introduced in rate theory models, for simulating the performance of nuclear reactor components. The effect of a stress field on the anisotropic diffusion of vacancies and interstitials is studied. A discrete lattice approximation is used for calculating the elastodiffusion tensors. The dependence of the void sink strength on the anisotropy diffusivity ratio, Dc/Da, is studied. It is concluded that the anisotropy in the diffusion plays a fundamental role in the behaviour of spherical sinks.
Quadratic Force Constant of a Cleaved Jellium and Its Relation to Quadratic Response Functions of the Homogeneous Jellium
Authors: Streitenberger P. , Ziesche P. , Kaschner R.
Published: July 2007

Rigorous expressions are derived yielding the quadratic force constant B of a jellium interface in terms of the quadratic density‐potential response function and the quadratic dielectric function, respectively, of the homogeneous jellium. For the quadratic dielectric function an exact formula including quadratic exchange and correlation corrections is obtained. B is calculated analytically within the local density approximation and numerically within the gradient expansion method using different values of the bulk density. The connection of the linear and quadratic force constants with the jellium cleavage fracture strength and the fracture strength separation is discussed.
Band Structure and Charge Density Distribution of Cubic Face‐Centred TlI Single Crystals
Authors: Dovgii Ya. O. , Kityk I. V. , Kolinko M. I. , Krochuk A. S. , Franiv A. V. , Zamorskii M. K.
Published: July 2007

For the first time self‐consistent band‐structure calculations of TlI single crystals (space group O) are performed using nonlocal pseudopotentials. The method is described briefly. The contributions of the different band states to the charge density distributions are estimated. Correlations between the band dispersion, valence electron mobility, and charge density distribution are outlined. The origin of the different bands is defined and the total density of states is calculated.
Quantum Mechanical Properties of a Thin Cylinder. I. The Density of Electronic States
Authors: Makar M. N. , Ahmed M. A. , Awad M. S.
Published: July 2007

The electronic density of states is calculated in the case of a hollow metallic cylinder placed in a uniform magnetic field. The oscillatory features are estimated when the magnetic field intensity is weak. This shows rapid changes in the density of states on the contrary of the case of fields of intermediate densities where the effect is quite small.
Functional Integrals in the Strong Coupling Regime and the Polaron Self‐Energy
Authors: Efimov G. V. , Ganbold G.
Published: July 2007

A general method of representation of functional integrals in the strong coupling regime is developed. This method is applied to the computing of polaron ground state energy at large coupling constant.
Fine Structure of Quasi‐Bound Acceptor States in Germanium Induced by Magnetic Field
Authors: Palkin A. M. , Shegai O. A.
Published: July 2007

The energy spectrum of quasi‐bound states of shallow acceptors in pure p‐Ge is investigated experimentally by the method of far‐infrared (FIR) laser magnetospectroscopy. A fine structure of quasi‐bound states is observed which is connected with the removal of degeneracy of the total angular momentum parallel to the magnetic field. Additional peaks found in the photoconductivity spectrum are refered to the impurity combined resonance.
pf‐Hybridization and the Crystal Fields in RBa2Cu3O7—δ
Authors: Kuz'min M. D. , Popov A. I. , Zvezdin A. K.
Published: July 2007

Mechanisms are considered, which form the crystal field (CF) acting on rare earth ions (REI) in the high‐Tc superconductors RBa2Cu3O7—δ. The electrostatic component of the CF is calculated using the point‐charge model. A significant contribution to the CF is brought in by pf‐hybridization and is taken into account on the basis of a two‐centre approximation using Slater‐Koster parameters. A new parameterization of the hybridization contribution to CF is proposed, which is based on utilizing two parameters — the energies Eσ and Eπ of the σ‐ and π‐bonds in the pair R3+−O2−. Proceeding from the analysis of the experimental data, it is shown that for all compounds studied thus far (R = Nd, Dy, Ho, Er, Tm) a universal relation holds between these two parameters, Eσ ≈ 2.9Eπ, which enables to reduce the number of disposable parameters of the theory.
Intrinsic Broadening of F‐Electron Energy Levels Due to Phonon Mediated Hybridization of the Electronic States
Authors: Lagos M. , Monreal Mc. R. , Rogan J.
Published: July 2007

In a first step the temperature dependent lineshapes of F‐center optical features are obtained analytically from the usual small‐polaron theory and Condon approximation. Though the calculation may be considered already standard, it is improved in putting emphasis in retaining the full spectrum of lattice modes and in keeping control of the accuracy of the approximations. Although the latter is shown to be better than 0.1% for F‐centers the theory fails in giving the temperature dependent shifts of the spectral features and the difference between the emission and absorption linewidths. A parameter‐free test of the so obtained results with experiment shows good agreement, but significant deviations are also observed. Refining the theory it is shown that, in order to fully account for the optical properties of F‐centers, one has to go beyond the current treatments, drop the Condon approximation, and consider the splitting of the F‐electron energy levels due to phonons induced hybridization of the electronic states. The temperature dependence of the band shifts is calculated in this way, obtained excellent agreement with experiment. It is concluded that F‐centers have appreciable intrinsic structure which may be of interest for further experimental investigation.
Optical Properties of Anionic Gold Centers in CsBr and CsI Crystals
Authors: Shimanuki S. , Kawai T.
Published: July 2007

Optical studies are for the first time performed on Au− centers in Cs‐halides. Absorption spectra above 90 K and emission and excitation spectra down to 13.9 K are investigated for CsBr:Au− and CsI:Au− crystals. In both the crystals four absorption bands exist called D1, C, B, and A and two emission bands called B′ and A′ in the order of decreasing energy. In CsBr, a luminescence resembling α emission known in other alkali systems is also observed, but it seems not to be peculiar to Au− centers because of its dependence on the thermal treatment of the specimens. The King‐Van Vleck factors, λ, which are obtained by analyzing the optical data are 2.5 (CsBr) and 2.2 (CsI), which are larger than unity as in the case of all other alkali halides: Au− so far investigated.
Short‐Range Order and Solid Solution Hardening
Authors: Blanter M. S. , Ya. Fradkov M.
Published: July 2007

A Monte‐Carlo simulation is made of the short‐range order in TaO with oxygen—oxygen long‐range strain‐induced potential with the exception of the first coordination shell. In a wide temperature range short‐range order of cluster type is discovered. On the basis of dislocation‐obstacle interaction models the start stress of (1/2)〈111〉{110} screw dislocations in the solid solution with clusters is calculated. Cluster nucleation leads to solution hardening.
Some Conditions of Ferromagnetic Liquid Crystal Existence
Authors: Buivydas M.
Published: July 2007

The possibility of the existence of the ferromagnetic liquid crystal based on analogy between electric and magnetic phenomena is considered. Nematic and smectic liquid crystalline states and symmetry conditions are discussed. The most common case — hypothetical ferromagnetic‐ferroelectric liquid crystal (FFLC) and some of the field effects on it are described based on Landau free energy expression.
The Magnetic Phase Diagram of the Emery Model within the Hartree‐Fock Approximation
Authors: Saalmann U. , Hayn R.
Published: July 2007

The Hartree‐Fock approximation is applied to investigate the ferromagnetic, antiferromagnetic, and paramagnetic phases of the Emery model. The phase diagram in dependence on copper correlation and hole doping is calculated by comparing the total energy in the one‐dimensional case. The transition from the antiferromagnetic to the paramagnetic phase with increasing doping is only found for relatively small values of the correlation. In the other cases a transition to ferromagnetism is obtained.
The Ion Charge Fluctuation Effect on Impurity Depth Distributions for High‐Energy Ion Implantation. The Backward Transport Equation‐Based Simulation
Authors: Burenkov A. F. , Komarov F. F. , Fedotov S. A.
Published: July 2007

A model of high‐energy ion implantation is formulated with allowance for fluctuations of the charge state of ions and the corresponding backward transport equation for post‐implantation spatial distributions of an impurity. Simulation results of experiments concerned with boron ion implantation into silicon by numerical solving the backward transport equation are reported. It is shown that the account of ion charge fluctuations in the high‐energy range leads to an increase of the range straggling of the implanted impurity and provides a better agreement with the experiment than the traditional methods of modelling based on the use of the Monte‐Carlo method or the backward transport equations.
Positron Annihilation Angular Correlation Studies in GaSb
Authors: Panda B. K. , Mahapatra D. P. , Padhi H. C.
Published: July 2007

Two‐photon angular correlation lineshapes along [100] and [111] crystallographic directions of GaSb are reported. The theoretical calculations of the lineshapes are carried out employing the pseudopotential band model for the calculation of the electron wavefunction. The positron wavefunction is evaluated under the point core approximation. The calculated lineshapes and their anisotropies are in good agreement with the experimental data.
Optical Determination of Carrier Concentration and Mobility in p and n Bulk GaSb by Infrared Reflectivity Spectral Analysis
Authors: Mezerreg A. , Llinares C. , Montaner A.
Published: July 2007

Infrared reflectivity measurements are made on both, n and p bulk GaSb at 300 K to determine carrier concentration and mobility of the material by using a least‐square fit on a non‐linear model to experimental data after their transfer from spectrometer to a compatible computer in ASCII code. For n‐type GaSb a method is proposed for calculating density and mobility of carriers from plasma frequency and carrier scattering time given by the fit, taking into account contributions of both, Γ and L band electrons to conductivity. Good agreement is obtained between density and mobility given by reflectivity and those given by Hall measurements for density range 1.2 × 1017 to 3 × 1018 cm−3.
On the FMR Theory of Metallic Amorphous Ferromagnets
Authors: Fraitová D.
Published: July 2007

The formulae for dispersion relations, together with formulae for the surface impedance, skin depth, wavelength, and inflection linewidth are discussed, for the ferromagnetic resonance (FMR) in parallel configuration in amorphous alloys. The importance of the FMR cross‐over effect is pointed out.
A New Type of Domain Wall Excitation in Magnetic Systems
Authors: Talim S.
Published: July 2007

A 2π domain wall excitation is studied in a magnetic system. The domain walls studied before by other authors are different because in theses works the spin rotates by an angle of π in the domain wall. In 2π domain walls the spins rotate by an angle of 2π and the problem is described by a double sine‐Gordon equation, which has a richer dynamics than the conventional sine‐Gordon equation.
The 4T1(F) → 4A2(F) Luminescence of the Co2+ (d7) Impurity Centre in Zinc Selenide Crystals
Authors: Goetz G. , Schulz H.‐J.
Published: July 2007

The 4T1(F) → 4A2(F) transition of Co2+ (d7) ions in ZnSe is detected by its emission at T ≈︁ 4 K. The no‐phonon line at v̄ = 5558 cm−1 is demonstrated to coincide with the inverse absorption transition. The luminescence shows medium coupling to ZnSe lattice vibrations. An exponential decay with a time constant τ = 100 μs is recorded. A rich fine‐structure is displayed by the 4T1(P) ← 4A2(F) absorption studied for comparison. Qualitatively, it can be described by spin–orbit and Jahn‐Teller interaction. Finally, the properties of two additional emission bands present in the 4200 to 5600 cm−1 region are illustrated, one of them dominated by a no‐phonon line at 5471 cm−1. Capture of a hole by a neutral donor is discussed as a possible interpretation of a broad luminescence band peaking near 4600 cm−1.
Reflectivity Spectra of YBa2Cu3O7−x in the 0.6 to 6.1 eV Range Evidence for Excitonic Absorption
Authors: Nag A. , Neogy C. , Ghosh B. , Joarder R. , Deb S. K.
Published: July 2007

Reflectance measurements at room temperature (298 K) on ceramic YBa2Cu3O7−x in the spectral range 0.6 to 6.1 eV and subsequent Kramers‐Kronig analyses of the spectra indicate the presence of excitations at 1.0, 2.1, 3.6, and 5.7 eV. It is argued that there is enough evidence to consider the 1.0 and 2.1 eV excitations as excitons.
Induced Radiation from a Relativistic Electron Beam in Periodic Structures
Authors: Baryshevskii V. G. , Batrakov K. G. , Dubovskaya I. Ya.
Published: July 2007

The spectral‐angular distribution of an induced X‐ray parametric quasi‐Cerenkov radiation (PXR), generated by a relativistic particle in periodic structures, is derived for different diffraction geometries. The possibility of experimental observation of such radiation is discussed.
Direct Observation of the Discommensuration in the Nearly Commensurate Charge‐Density Wave Phase in 1T‐TaS2 by Scanning Tunneling Microscopy
Authors: Ohta H. , Takase T. , Komiya Y. , Miyamoto H. , Mishima S. , Okada T. , Nomura K.
Published: July 2007

The charge‐density wave (CDW) structure of the nearly commensurate phase of 1T‐TaS2 is studied with scanning tunneling microscopy (STM). The hexagonal domain structure is observed in the CDW superlattice at room temperature. It is assigned to the discommensuration (DC) network. The domain size is about 8 nm and the width of domain walls is of the order of 3 nm. The observed structure agrees well with the DC model proposed by Nakanishi and Shiba. The DC structure is easily destroyed by disorder of the CDW lattice in the neighboring region.
Interaction between Excitons and Electrons in ZnSe1−xSx Epilayers under High Excitation
Authors: Guan Z. P. , Zheng Z. H. , Zhang J. H. , Lu Y. M. , Fan G. H. , Fan X. W.
Published: July 2007

Excitonic properties are investigated of ZnSe1−xSx epilayer fabricated on GaAs substrate by a Ap‐MOCVD. Luminescence, excitation, and time‐resolved spectroscopy are employed to study the interaction between excitons and electrons at 77 and 300 K. Under pulsed N2 laser excitation it is found that the peak shift of the near band edge emission are more large, especially at room temperature. This is due to the fact that the bottoms of the conduction bands are filled at the higher temperature, so the carriers from the exciton‐exciton scattering must occupy higher energy levels. Therefore a shift of the peak towards lower energy is expected.
Coulomb Interaction and Polaronic Exciton States in Compositional Superlattices
Authors: Beril S. I. , Pokatilov E. P. , Kalinovski V. V.
Published: July 2007

The general theory of Wannier‐Mott polaron excitonic states is developed using the Pekar‐Fröhlich Hamiltonian of electron‐phonon interaction in a periodic structure consisting of alternating pairs of two different polar semiconductor layers, such as compositional superlattices (SL). The effects of dynamical screening of electron‐phonon interaction by inertial polarization are examined in two limiting cases, namely in the Haken limit with Rex > Ri and in the Meyer limit with Rex < Ri,; Rex, Ri, are the exciton and polaron radii of electron (i = e) or hole (i = h). For the first time the renormalization of the optical vibration spectrum is taken into account, and the exact potential of electron‐hole interaction is used to calculate the size dependent exciton binding energy. The theory is employed to calculate the binding energy of exciton states in GaAs/AlxGa1−xAs superlattices.
Role of Bulk d‐Electrons in the Formation of Ultraviolet Photoelectron Spectra for a Number of 4d‐Metals
Authors: Kormilets V. I. , Belash V. P. , Klimova I. N. , Sorokina M. F. , Shirokovskii V. P.
Published: July 2007

The contribution of bulk electron crystal states to the ultraviolet photoelectron spectra (UPS) is studied for the following 4d‐metals: molybdenum, rhodium, palladium, and silver. The discrepancy between the calculated curves of bulk contribution to the UPS and the experimental UPS curves is found to increase, when going from the elements at the end of 4d‐period to the elements closer to its beginning. This regularity appears to be connected with the decrease in the d‐electron localization in the above‐mentioned sequence of elements, which is demonstrated by the calculations. Comparison of the calculated bulk contribution to the UPS with the experimental UPS allows to distinguish those peaks in the UPS of molybdenum and rhodium, which are most likely due to the surface electronic structure.
The Diagram Technique for Calculation of Transport Constants of Random Inhomogeneous Materials. I. The AC Effective Conductivity
Authors: German A. I. , Chaikovskii I. A.
Published: July 2007

Diagram methods are applied for evaluating the ac effective conductivity σ*(ω) of a disordered semiconductor (e.g., a highly doped compensated semiconductor, a composite, etc.). Expressions for σ*(ω) are obtained in a number of approximations — the cumulant approximation, the self‐consistent moment approximation, and the effective medium approximation. For a random binary mixture which consists of two materials with conductivities σ1 and σ2, the dependences of real and imaginary parts of σ*(ω) on the frequency ω of the external electric field, volume fraction x of the most conducting material and the ratio of the conductivities σ2/σ1 are presented for all approximations mentioned. For a metal‐insulator mixture (σ2 = 0) on the onset of percolation the cumulant and effective medium approximations predict the following behaviour of σ(ω): σ(0) ∼ (x — xc)t, σ(ω) ∼ ωs, here t = 1, s = 1/2. The results, obtained for σ(ω) are compared with those of computer simulation in the model of fully penetrating spheres (Balberg and Binenbaum). The cumulant approximation is in good agreement with the computer results.
Optical and Electrical Investigations of n‐Type Bi2Se3 Single Crystals
Authors: Stordeur M. , Ketavong K. K. , Priemuth A. , Sobotta H. , Riede V.
Published: July 2007

Bi2Se3 single crystals were prepared in the electron concentration range from 1.8 × 1019 to 5.6 × 1019 cm–3. At room temperature experimental values are given for the specific electrical resistivity, for the Hall and Seebeck coefficients, and the ir‐plasma reflectivity spectra were measured in the wave number range from 300 to 4000 cm–1. For the first time it was found that not only the resistivity and the plasma reflectivity but also the thermopower show a distinct anisotropy perpendicular and parallel to the trigonal c‐axis, whereas the Hall effect is isotropic. In terms of a one‐carrier, one‐valley conduction band model with elliptical isoenergy surfaces and a nonparabolic dispersion the anisotropy of the thermopower can be explained in the extrinsic range by an anisotropic mixed scattering mechanism on acoustic phonons and ionized impurities in the relaxation time approximation. In this frame a quantitative, consistent interpretation is reached for all experimental data. The calculated values for the high‐frequency dielectric constant, the carrier density, the Fermi level, the parameter of nonparabolicity, the mean optical relaxation times, the effective masses and the drift mobilities are given.
Energy‐Dependent Excitonic Injection of Charge into Anthracene Crystals
Authors: Strzelecka B. , Godlewski J. , Kalinowski J.
Published: July 2007

Steady‐state exciton‐injection currents (EIC) as a function of electric field and temperature are measured in anthracene crystals upon energy‐selective excitation within the S0→ S1transition. The current for each given absorption coefficient decreases as the excitation energy (ℏω) passes through the high‐energy wing and is swept downward the low‐energy wing (Urbach tail) of the absorption band, demonstrating that the flux of excitons reaching the injecting contact is energy dependent. The maximum absorption at the S0→ S1transition establishes a demarcation energy ℏω0. Above ℏω0only diffusion of mobile (band) excitons (S) is an injection‐determining process, below ℏω0thermal activation of localized states (St) becomes an unavoidable step in the S‐exciton creation process, diminishing the effective flux of S‐excitons reaching the contact. An analysis of the dependence of the activation energy on the localization energy ℏω0— ℏω of primarily excited Ststates indicates that EIC are the sum of a singlet exciton‐injection contribution and a triplet exciton‐injection contribution, the triplets being produced via iniersystem crossing transitions from S and Ststates. A theoretical description of excitonic processes underlying charge injection is presented and applied to the experimental results. Agreement between theoretical predictions and experiment is good if the frequency factor for the thermally activated St→ S excitation is assumed to be ≈︁ 109s–1.
Strong Non‐Adiabatic Interactions and Phase Transitions in Conductive Jahn‐Teller Crystals
Authors: Kiselev A. A. , Liaptsev A. V.
Published: July 2007

A model of a conducting crystal composed of quasi‐molecules with D4hsymmetry and with nearly degenerate A1gand B1gstates is considered. The model Hamiltonian includes intramolecular strong non‐adiabatic interactions, which are non‐diagonal with respect to the electronic quantum numbers and linear (Jahn‐Teller type) and quadratic (Renner‐type) in the vibrational coordinates. The model Hamiltonian is analysed with the help of the mean field method. It is shown that the non‐adiabatic electron‐phonon interaction causes a structural phase transition which splits the degenerate vibrational mode involved in the interaction, the minimum frequency of the lower branch decreasing when the temperature decreases. For the electrons the two‐band BCS equation follows from the calculation, the interaction constant being multiplied by the average number of low‐frequency phonons.