bluuebunny/crossref_metadata_2025 huggingface dataset:
Lattice Dynamics of the Force Constant Defect System Pd0.95Ru0.05
Authors: Maliszewski E. , Sosnowski J. , Bednarski S.
Published: July 2007

The lattice dynamics of a Pd0.95Ru0.05 single crystal is investigated at room temperature. The phonon dispersion relations along the directions [100], [110], and [111] are measured using the inelastic neutron scattering technique. The seven‐neighbour Born‐von‐Kármán model is fitted to the experimental branches and the force constants and elastic constants are calculated. The phonon frequency shifts, Δω(q), and the self‐energy functions, Σj (q, ωj(q)), are determined. From the comparison of the self‐energy functions for 5 and 10 at% Ru contents in Pd matrix the evolution of the self‐energy with the Ru concentration is clearly seen.
Dynamics of Electric Field Screening in Semi‐Insulating ZnSe
Authors: Astratov V. N. , Furman A. S. , Ilinskii A. V. , Repin S. M.
Published: July 2007

The dynamics of the screening of an external electic field in semi‐insulating ZnSe is studied. It is found that this dynamics exhibits two different regimes depending on the crystal temperature and the conditions of the preliminary illumination: expansion of the single homogeneous depletion layer or formation of numerous space charge layers of alternating sign. All these results are described within a simple model allowing for two types of deep centers with different recharging times.
On the Electronic Structure of Phosphorus in Nickel
Authors: Stepanyuk V. S. , Katsnelson A. A. , Kozlov A. V. , Farberovich O. V. , Szász A. , Kojnok J.
Published: July 2007

The electronic density of states of the NiP amorphous system is calculated in a self‐consistent way from first principles, using a KKR Green's‐function method with a single perturbed muffin‐tin potential in a periodic lattice.
Unthreshold Impact Ionization by Virtual Electrons in Semiconductors under Streamer Discharge Excitation
Authors: Voitikov S. V.
Published: July 2007

Impact ionization of semiconductors under ultrafast electric‐field excitation at the streamer discharge front is theoretically investigated. It is shown that impact ionization is initiated by virtual electrons and is of unthreshold character unlike the known mechanisms of impact ionization in quasi‐stationary field. Amplitudes and probabilities of the interband transitions are calculated. The lack of threshold conditions permits the momentum transmitted at impacts between particles to be very small which results in the increase of interband transition probabilities and concentrations of non‐equilibrium carriers of charge. It is also shown that with increasing velocity of discharge propagation the intensity of ionization by virtual electron impact essentially increases, and the carrier concentrations achieve 10(16.5 ± 1.5) cm−3.
Cyclotron Resonance of a Magnetopolaron in a Polar‐Crystal Slab at Finite Temperatures
Authors: Wei Bao‐hua , Gu Shi‐wei
Published: July 2007

Taking into account the interaction of an electron with both, bulk longitudinal‐optical (BO) and surface‐optical (SO) phonons, the cyclotron resonance of a magnetopolaron in a polar‐crystal slab at finite temperatures is investigated by using the generalized Larsen perturbation‐theory method. The temperature dependence is studied of the cyclotron resonance mass of a magnetopolaron in the resonant region of the GaAs slab.
Superconductivity in the Extended Hubbard Model
Authors: Bulka B. R.
Published: July 2007

The extended Hubbard model on a square lattice is considered in the framework of the mean‐field formalism. A detailed analysis of the stability of the superconducting state of the s‐ and the d‐type symmetry is performed for different band filling. Special attention is focused on the state with mixed sd‐type symmetry, which may occur at an intermediate strength of interactions.
Fluctuations of the Molecular Field in the Two‐Ion Model for Temperature‐Induced Metamagnets
Authors: Rudziński W. , Onyszkiewicz Z.
Published: July 2007

A special quartic spin model of spontaneous metamagnetism, proposed by Onyszkiewicz is considered involving dipole‐octopole interaction between two neighbouring ions. The thermodynamic properties of this model are investigated, using the high‐density expansion method in the approximation including Gaussian fluctuations of the molecular field. The free energy, the magnetization, the octopole parameter as well as mean squares of fluctuations are calculated for A → F metamagnets. The results are then compared with those obtained by the molecular field approximation. Moreover, a comparison of the results with those obtained earlier for the so called four‐ion model confirm effectiveness of the two‐ion model also in such refined procedure as the Gaussian fluctuation approximation.
A New Random Surface Fractal for Applications in Solid State Physics
Authors: Hermann H.
Published: July 2007

A new random surface fractal is developed. The construction is based on a Boolean model with spherical primary grains. The radii of the grains follow a distribution that can be approximated by a power‐law in the limit of small radii. The fractal dimension is estimated according to the Minkowski‐Bouligand definition. Volume fraction and two‐point correlation function of the fractal are derived exactly.
Shear Moduli of Macroisotropic Cubic Polycrystalline Materials
Authors: Sisodia P. , Dhoble A. , Verma M. P.
Published: July 2007

The effective shear moduli of the perfectly disordered polycrystalline cubic solids are determined by solving the well known cubic equation. The solids include perhaps all the cubic crystals for which single crystal elastic constant data are available at present. It is observed that the effective shear modulus can be empirically expressed as a simple function of the anisotropy parameter A and that a justification for such an expression can be derived from the cubic equation itself. It is further observed by analysing the cubic equation that (a) considering the shear modulus G to be independent of the bulk modulus B one would obtain bounds for G even narrower than the Hashin‐Shtrikman bounds and (b) that the VRH mean is quite close to the self consistent shear modulus for all the cubic solids.
Self‐Trapped States of Amide I Excitations in the Hydrogn‐Bonded Chain of Peptide Groups
Authors: Ichinose S.
Published: July 2007

A theory is proposed of interactions of the Amide I excitation with lattice distortions in the hydrogen‐bonded chain of peptide groups. By studying the classical equations of motion, exact one‐soliton solutions are given in the case of the continuum limit. It is shown that the moving acoustic soliton may capture the Amide I excitation. On the other hand, the longitudinal sound velocity is slightly decreased due to the coupling between them. The nonlinearity of the hydrogn‐bond generates thus both a self‐trapping mechanism for Amide I excitations and an acoustic soliton formation for lattice vibrations.
Calculation of Bond Parameters and of Nonlinear Optical Susceptiabilities in Quartz‐Homeotypic MXO4Crystals
Authors: Engel G. F. , Defregger S.
Published: July 2007

The Phillips‐van Vechten (PV) dielectric theory extended to multibond compounds is used to calculate the homopolar and heteropolar energy gaps, the susceptibilities, and the ionicities of bonds in the quartz homeotypic crystals MPO4(M = Al, Ga, and Fe) and MAsO4(M = Al and Ga). Based on these results, a bond charge calculation of nonlinear optical susceptibilities is performed. Trends within the MXO4crystal class including SiO2and GeO2are discussed.
A Weakly‐Bonded Polaron in Semiconductors with a Degenerate Valence Band Edge
Authors: Gifeisman Sh. N. , Koropchanu V. P. , Pasechnik O. F.
Published: July 2007

A polaron is considered which is bonded on a shallow acceptor near a Γ8 degenerate valence band edge. With the assumption that the polaron binding energy of the impurity centre is far smaller than the optical phonon limiting energy, an expression is obtained for the effective Hamiltonian of an impurity‐phonon system, and the ground and first excited state energy in a number of AIIBVI and AIIIBV compounds is calculated A comparison with both, the experiment and results of other papers is also made. It is shown that, if degeneration of the valence band is taken into account, the energy gap between the ground and first excited states becomes considerably lower as compared to the simple hydrogen‐like model near a non‐degenerate band.
Magneto‐Optics of Excited States of the Donor–Exciton Complex in CdS A Proof for the Excited‐Hole‐States Model
Authors: Puls J. , Henneberger F. , Gutowski J. , Hönig T. , Mikhailov G. V.
Published: July 2007

A model for excited electronic states of exciton–impurity complexes in uniaxial II–VI semiconductors is extended to the case of an applied magnetic field. This allows to prove its validity for the donor–exciton complex (Do, X) in CdS by performing magneto‐optics of the excitation resonances of its I2 recombination line. The experiments confirm the interpretation in terms of transitions into p‐ and d‐like excited‐hole states of this complex given previously. g‐values and diamagnetic shifts are explicitly deduced and compared with the model predictions. Applications to respective complexes in other II–VI compounds are discussed.
Transport Phenomena in Mixed‐Valence Zero‐Gap Semimagnetic HgFeSe Semiconductors
Authors: Kuleev I. I. , Lyapilin I. I. , Karyagin V. V.
Published: July 2007

On the basis of the nondegenerate Anderson model for mixed‐valence impurities an expression is found for the electrical conductivity taking into account the radical change of the energy spectrum and damping of conduction electrons resulting from the hybridization of s and d electrons and background scattering mechanisms. It is shown that within the framework of the developed theory the anomalous change in the mobility of electrons observed in HgFeSe as a result of varying iron content can be explained without recourse to the idea of formation of the Wigner crystal from Fe3+ ions at low temperatures.
Pyroelectric Effect and Dielectric Constant in Deuterated Betaine Calcium Chloride Dihydrate
Authors: Ribeiro J. L. , Chaves M. R. , Almeida A. , Müser H. E. , Albers J. , Klöpperpieper A.
Published: July 2007

The dielectric constant and pyroelectric effect in deuterated betaine calcium chloride dihydrate single crystals (DBCCD) are investigated. Due to the nonexistence of typical H‐bonds in the chemical structure of this compound, deuteration does not produce the important isotopic effects observed in other betaíne compounds. The results show however that deuteration can induce local lattice strains, which, at some transition points, may give rise to structural branching processes similar to those observed in normal BCCD under hydrostatic pressure. The critical regime of the spontaneous polarization at the transition to the lowest temperature ferroelectric phase is also affected by deuteration.
Effect of Manganese Impurities on the Phase Transition Sequence in BCCD
Authors: Ribeiro J. L. , Chaves M. R. , Almeida A. , Müser H. E. , Albers J. , Klöpperpieper A.
Published: July 2007

Pyroelectric and dielectric constant measurements to study the effect of Mn impurities on the phase transition sequence of betaine calcium chloride dihydrate (BCCD) were used. Mixed crystals of B(C1‐xMnx)CD are grown from solutions with molar ratios of 5 and 20% of Mn. The chemical analysis of these crystals reveals compositions corresponding to x = 0.01 and x = 0.05, respectively. Replacing Ca by an ion with a smaller ionic radius is expected to induce local strains and local electric charges. The effect of the substitutional disorder on the different modulated commensurate phases is dicussed.
Electronic Structure of the Ideal Vacancies in (Hg, Cd)Te
Authors: Erbarut E.
Published: July 2007

The localized orbital method (LOM) based upon an atomic‐like basis set and empirical pseudopotential Hamiltonian in conjunction with the Green's function method is employed for the study of electron states of ideal vacancies in (Hg, Cd)Te. This method is used for the first time for a calculation of ideal vacancies in (Hg, Cd)Te. Bloch sums are formed from Gaussian orbitals of s and p symmetry on each atomic site. A systematic study shows that an accurate description of band energies and density of states can be obtained, with the use of a minimal Gaussian set. Since the relativistic terms are neglected the weighted average of the spin splitted levels of HgTe and CdTe are used for the calculation of band energies and densities of states. The calculated ideal vacancy states are in general agreement with what is known about defect levels in (Hg, Cd)Te.
Effect of Pressure on the Charge Density Wave Transitions in η‐Mo4O11 Crystal
Authors: Ôhara S. , Koyano M. , Negishi H. , Sasaki M. , Inoue M.
Published: July 2007

Electrical resistivity ϱ versus temperature T over 4.2 to 300 K under hydrostatic pressures up to 1.2 GPa, transverse magnetoresistance, and Hall effect at 4.2 K and constant pressure are measured for a quasi‐two‐dimensional crystal of monoclinic η‐Mo4O11. Semiempirical analysis of the ϱ−T curves below the charge density wave (CDW) transition temperatures Tc1 and Tc2 shows that the temperature dependences of the CDW gap energies δ1(T) and δ2(T) follow a single universal curve, independent of applied pressures. The Shubnikov‐de Haas oscillations are also observed in these transport quantities, from which the effect of pressure on the nature of Fermi surfaces of holes and/or electrons associated with the CDW transitions is discussed qualitatively.
Magnetic Properties of Thin Films with a Gaussian Distribution of Exchange Integrals
Authors: Balcerzak T. , Mielnicki J. , Urbaniak‐Kucharczyk A. , Wiatrowski G.
Published: July 2007

Magnetic properties of thin ferromagnetic films with Gaussian distribution of the exchange integrals are investigated in the framework of the Ising model. The correlation functions corresponding to Matsudaira's third approximation are taken into account. The numerical results for phase diagrams, magnetisation, and correlation functions are presented, and in the discussion a comparison with the results obtained for the Handrich‐Kaneyoshi distribution is made.
Thermal stability of Ti41Zr41Si18 metallic glass studied by small‐angle neutron scattering
Authors: Borély S. , Smirnov L. S. , Kovneristii Yu. K. , Nartova T. T. , Tarasova O. B. , Yu. Bezzabotnov V. , Ostanevich Yu. M.
Published: July 2007

The thermal stability of amorphous Ti41Zr41Si18 alloys is studied by small‐angle neutron scattering. In as‐quenched samples inhomogeneities of 8.1 nm in radius are observed which disappeared during a low temperature (250 °C) annealing treatment. The annealing carried out a 500 °C for different times (10, 30, 60 min, and 24 h) leads to a considerable increase of the scattered intensity. Because of the interparticle correlation the dimensions of the particles must be determined by the least‐squares fitting of the total scattering cross‐section formula to the measured intensity pattern. The dimensions of the particles obtained in this way do not explain the non‐monotonous time course of the scattered intensity. Therefore it is concluded that the scattering length density of the particles, that is their composition, has changed during the high temperature annealing treatment.
Charge transfer effect on formation and binding energies of vancancy pairs in NaCl and KCl
Authors: Rao B. Srinivasa , Sanyal S. P.
Published: July 2007

Charge transfer effect on formation and binding energies of a vacancy pair in NaCl and KCl solids is investigated by using a sophisticated model potential, which includes long range many body forces. These forces have a strong influence on the relaxing ions and mechanism of polarization. The formation energy and binding energy calculated from this potential are in good agreement with experiment.
A theoretical calculation on Schottky defects in AgCl
Authors: Banhatti R. D. , Murti Y. V. G. S. , Laskar A. L.
Published: July 2007

The formation of Schottky defects in crystalline AgCl is investigated using interatomic potentials compatible with the macroscopic dielectric response of the solid with consistent van der Waals interaction coefficients. It is shown that two‐body central interactions in a point dipole model can yield satisfactory defect formation energy provided the dielectric polarization of the distorted defect crystal is adequately simulated. The calculated formation energy of the Schottky defect is 2.0 eV according to the potential that includes dipole—quadrupole van der Waals forces. The variation of the defect energy with temperature is studied in a quasiharmonic approximation.
Redistribution of relativistic electron flux in the region where the strong axial channeling instability occurs
Authors: Meshcherov B. R. , Tumanov V. I.
Published: July 2007

Measurements are made of nuclear reaction and hard bremsstrahlung yield for 50‐MeV electron motion along the silicon monocrystal axis. With the obtained data one can determine the electron flux redistribution as a function of penetration depth up to 10 μm. The scale and behaviour of this quantity allow to make a conclusion of the strong instability of particle transverse motion.
An investigation on the adhesive behaviour between transition metals titanium, niobium, tantalum, and tungsten
Authors: Li Kebin , Sun Jiansan , Liu Ling , Qi Zhenzhong
Published: July 2007

The contact adhesive energies between two transition metals (Nb, Ta, Ti, W) are measured in ultra‐high vacuum (UHV) condition. The results show that they depend on the cohesive energies of contacted materials. It is suggested that the adhesive interaction is caused by sharing of electrons between two metals and is mainly dependent on the densities of states of their d‐electrons. The value of the adhesive energies for two transition metals are in the range of 0.1 to 3.0 (eV/coupled atoms). When the samples are heated, the adhesive strength decreases drastically because of the segregations of nonmetallic impurities such as carbon, nitrogen, boron, and sulfur etc.
Lattice stability of gold
Authors: Singh G.
Published: July 2007

Numerical computations of breaking strains in uniaxially stressed perfect crystals of gold are carried out using rigorous estimation of the binding energy. The total energy of the metal consists of kinetic, exchange, and correlation energies alongwith the ion‐ion and electron‐ion interactions. The numerical values of the stress and strain confirm that both the theoretical and experimental values at failure are quite close to theoretically ultimate values.
Defect surface layer effects on the Raman intensity for collective excitations of a semi‐infinite layered electron gas system
Authors: Yang J. , Lu X. J. , Horing N. J. M.
Published: July 2007

The transfer matrix method is applied to the determination of the Raman intensity for a semi‐infinitelayered electron gas system with a defect layer at the surface. In this, the surface layer has a different electron sheet density from that of the other layers, which is the case for realistic systems. The numerical results show that the Raman intensity at the surface plasmon energy is weakend by the presence of the defect layer under the conditions of the calculation. An analytic expression for the Raman intensity of a semi‐infinite layered electron gas having a finite number of defect layers is also presented.
The effective interparticle screening and the local‐field correction in the spin‐polarized electron system
Authors: Ivliev S. V. , Sobakin V. N.
Published: July 2007

The screening properties of a system of interacting spin‐polarized electrons are investigated. The exact closed equation for the vertex function is received by a many‐particle approach and the main contribution to that function is founded on the linear approximation of the generalized screened potential. The local field factor is calculated and its strong electron density dependence is demonstrated. The compressibility is positive in a wide interval of electron densities.
Soliton states in a chain with two atoms per elementary cell
Authors: Brizhik L. S. , Eremko A. A.
Published: July 2007

The autolocalization of carriers in a chain with two atoms per elementary cell is investigated. It is shown that in the case of big differences of neighbouring atom masses the hole in the valence band corresponds to a soliton and the electron in the conduction band is in a delocalized state, if the atom with bigger mass has the higher energetic term. In the opposite case a soliton can be formed by an electron in the conduction band. The bisoliton mechanism of superconductivity is provided by hole carriers in the first case, and electron carriers in the last one.
Investigation on the characteristics of the hubbard model
Authors: Su Gang , Ge Mo‐Lin
Published: July 2007

It is shown that a simple Hubbard model obeys supersymmetry of quantum mechanics under proper conditions in the attractive and the repulsive cases. The internal SO4 symmetry of that Hubbard model is found to be spontaneously broken. By unitary transformations superconductivity is investigated for a t—J model within the n‐pairing framework, and some essential results are achieved for the superconducting state.
Raman study of LiCsSO4
Authors: Lemos V. , Silveira E. S. , Melo F. E. A. , Filho J. Mendes , Pereira J. R.
Published: July 2007

Polarized Raman spectra of single crystals of LiCsSO4 are obtained. It is found that factor group analysis isolated fails to give a consistent interpretation of the spectra. Hence, a complementary calculation, based on a group theoretical method, is employed to obtain the relative intensities for all of the internal modes. This calculation yields zero intensity for the B1g mode of the v1‐type of vibration, so that the corresponding observed band is/assumed to be the Ag symmetry mode, exclusively. Several calculated intensities result in almost negligible values for other Ag and B1g modes. This fact is particularly helpful in the analysis of experimental data thus improving assignments of the Raman bands.
Low‐Temperature Glass Properties from the Energy Spectrum
Authors: Gluzman S.
Published: July 2007

The low‐temperature behaviour is studied of the heat capacity of different glasses dependent on the elementary excitation spectrum characteristics. The spectrum relation to the “two‐level system” and to the “fractal” properties of glasses is discussed. “Roton” part of the spectrum is shown to play a major role in the processes determining the excessive heat capacity and the thermal conductivity.
Chemisorption on Alloys with Partial Ordering
Authors: Yang Z. X. , Lu W. C. , Zhang T.
Published: July 2007

One‐electron chemisorption theory and average T‐matrix approximation are used to study the chemisorption properties of binary alloys of equal concentration with long‐range order. The chemisorption energy of H atoms on Cu0.5Ni0.5 and Ni0.5Pt0.5 substrates are calculated as functions of the long‐range order. It is found that the long‐range order seems to act as the surface concentration of the alloys.
LCAO‐Calculations of the Valence Band Structure of Modified Polar Semiconductor Surfaces: Hydrogen‐, Copper‐, and Ruthenium‐Covered Gallium Arsenide (001)
Authors: Reichert B. , Jung Ch.
Published: July 2007

Results of local density first principles LCAO calculations for a 13 layer slab of free and modified As‐terminated (1 × 1) GaAs(001) surfaces are presented. The surfaces are covered by a monolayer of hydrogen, copper, or ruthenium. The surface calculation for the hydrogen covered surface gives hydrogen‐induced and GaAs surface states in agreement with angle‐resolved photoemission results within the energy range where they are found. For the systems GaAs(001):Cu and GaAs(001): Ru metal induced gap states are predicted with a density of 2 × 1015 cm−2. The calculated surface states indicate a higher Schottky barrier for the ruthenium than for the copper covered surface.
Impurity State near the Surface of Semi‐Infinite Crystals
Authors: Shen Zhong‐Jun , Yang Bao‐Cheng , Gu Shi‐Wei
Published: July 2007

The ground state energy of a shallow donor impurity near a sharp surface of a semi‐infinite crystal is studied. The energy expression of the system as the function of its position is calculated using a variational method.
EPR Measurements on the Cu2+ Ion in the High‐Tc Superconductors MBa2Cu3O7 – δ
Authors: Guskos N. , Londos C. A. , Trikalinos Ch. , Paraskevas S. M. , Koufoudakis A. , Mitros C. , Gamari‐Seale H. , Niarchos D.
Published: July 2007

EPR studies are carried out on the polycrystalline high‐Tc superconductors MBa2Cu3O7 – δ (M = La, Pr, Nd, Sm, Eu, Gd, Dy, Ho, Tm, Yb and Lu). The onset of the superconducting transition is found to occur in the temperature range of 90 to 95 K (except for LaBa2Cu3O7 – δ where Tc = 50 K and PrBa2Cu3O7 – δ which is not superconducting for temperatures above 4.2 K). In all of these compounds an EPR spectrum of Cu2+ ions in the orthorhombic local symmetry, is observed. The signal intensities are found to depend strongly on the particular rare‐earth ions of the lanthanide series which are substitutionally introduced into the host lattice of YBa2Cu3O7 – δ at Y‐ions site. “Skin effect” is suggested to be the main cause of the observed changes in the intensity of EPR signals.
Recombination Radiation of a Semiconductor in the Field of a Strong Electromagnetic Wave and a Quantizing Magnetic Field
Authors: Frolov V. V.
Published: July 2007

The parametric transformation is considered of intense electromagnetic radiation inducing the resonance‐quantum transitions of electrons in a semiconductor between the valence band edge and the conduction band edge in the presence of a magnetic field. The dependence of the power density of the radiative recombination of a semiconductor on the frequency of radiated photons and temperature is studied. It is shown that the frequency dependence may have resonance peculiarities and the position of the resonance peculiarities depends on the intensity of the exciting electromagnetic field and the magnetic field strength.
Exciton–Polariton Dispersion of Thin Anthracene Crystals in the Thickness Range of 3 to 0.1 μm
Authors: Hashimoto S. , Ohno N. , Itoh M.
Published: July 2007

The effect of crystal thickness on the exciton‐polariton dispersion of anthracene is studied by using melt‐grown crystals with thicknesses ranging from 3 to 0.1 μm. The refractive indices in the vicinity of the first‐exciton resonance are determined for the polarization E ‖ b and E ‖ a by analyzing interference fringes observed in the reflection spectra at 10 K. In contrast to the results reported previously, it is found that the dispersion property is independent of the crystal thickness at least down to 0.1 μm. A comparison of the present result with the thickness‐dependent dispersion formula is presented.
Computer Modelling of the Dynamics of Space Dislocation Ensembles. I. Non‐Elastic Dislocation Approach
Authors: Volyntsev A. B.
Published: July 2007

A mathematical model to examine the evolution of large dislocation complexes in crystals is proposed. The complexes are studied both, in the presence and after the removal of external mechanical stress. The problem is solved within the framework of continuous dislocation distribution with account of elastic long‐range interactions and thermal activation of dislocation movement.
High Pressure Structural Phase Transition in BaSe and BaTe
Authors: Rao B. Srinivasa , Sanyal S. P.
Published: July 2007

The structural phase transition due to high pressure in BaSe and BaTe is investigated for the first time using an interionic potential approach, based on the shell model formulation. The model parameters are derived using dielectric properties. The results show good agreement with experiment. The nature of the force constants at equilibrium and high pressure is discussed.
Multivalued μ‐Acoustoconductivity of Semiconductors
Authors: Bugaev A. S. , Vakser A. I.
Published: July 2007

The phenomenon of the formation of multivalued ohmic sections in volt–ampere characteristics (VAC) of semiconductors with electrons heated by sound waves is predicted. The VAC and the switching process are shown to be governed by the sound wave intensity. A possibility for the experimental realization of the studied phenomenon is discussed.
Surface Phase Diagrams of an Amorphous Ferromagnet with Surface Crystallization
Authors: Kaneyoshi T.
Published: July 2007

Surface phase diagrams of an amorphous ferromagnet with surface crystallization are studied by the use of the effective‐field theory with correlations. It is proposed that the surface crystallization of an amorphous ferromagnet may be an effective method for investigating surface magnetic properties of the system with a higher surface transition temperature than that of the bulk.
Position Space Renormalization Approach to Spin‐1 Quantum Chains
Authors: Campana L. S. , D'Auria A. Caramico , Esposito U.
Published: July 2007

The spin‐1 transverse Ising chain with a single‐site anisotropy is studied by means of a real space renormalization group method which treats in a unified way the ground state and the finite temperature extension. The tricritical behaviour at T = 0 is presented and a comparison is made with previous results.
Angular Distribution of Parametric X‐Ray Radiation (PXR) in Case of Multiwave Diffraction
Authors: Dubovskaya I. Ya. , Ha Truong Ba , Hai Le Tien
Published: July 2007

A detailed investigation of PXR angular characteristics in the case of multiwave diffraction is carried out. A numerical calculation of a specific case of three‐wave diffraction is made.
Parametric Amplification of Acoustohelicon Waves in Semiconductors
Authors: Jat K. L. , Ghosh S.
Published: July 2007

The parametric amplification of acoustohelicon waves is analytically investigated in a longitudinally magnetised semiconductor of centrosymmetric nature. The threshold value of the pump electric field (EOth) and initial gain constants are obtained. The longitudinal magnetic field decreases the required magnitude of (EOth) for the excitation, whereas it increases the gain constants. Numerical analyses are performed for an InSb crystal at 77 K duly irradiated by frequency‐doubled pulsed 10.6 μm CO2 lasers. It is found that the gain constants for both the couplings (gb) and for piezoelectricity only (gp) are nearly equal and approximately 100 times higher than that for deformation potential coupling (gd).
Dispersion and Propagation of Light in Crystals in the Exciton Absorption Region
Authors: Kudykina T. A.
Published: July 2007

Analogues are obtained of Fresnel's formulas for the reflectivity and transmission of light in the exciton absorption range. Boundary conditions for electromagnetic waves in absorbing media obtained in a previous paper and following from them the law of light refraction are used. Calculation of the light propagation in the An = 1‐exciton absorption range in CdS crystals is in good agreement with the experiment.
A New Approach in the Optical Characterization of Amorphous Hydrogenated Silicon–Carbon Alloys
Authors: Amato G.
Published: July 2007

An expression for the imaginary part of the dielectric function for amorphous silicon–carbon alloys is assumed following previous treatments already adopted for other amorphous semiconductors like silicon, germanium, gallium arsenide, and silicon nitride. The real part of the complex dielectric function is obtained using Kramers‐Kronig analysis. The model requires the knowledge of four parameters. Suitable values of these parameters can be obtained by fitting the optical spectra of the samples. The results show that the parameters allow a deep physical insight and are strictly related to the composition of the films and to the preparation methods.
Time Resolved Spectroscopic Investigations of Pure YAIO3and Ti‐Doped YAIO3Crystals
Authors: Chosrovian H. , Rentsch S. , Grummt U.‐W.
Published: July 2007

The difference of optical densityΔD(λ, t)after light pulse excitation for Ti doped and pure YAIO3crystals is measured within 6, and 1000 ps and 10 μs and 10 s. After laser or flashlamp excitation Ti doped YAIO3crystals show a broad light induced transient absorption (LIA) between 350 to 750 nm, which consists of some independent bands. The bands are formed within a few hundreds ps and have about 103to 105times longer lifetimes as the fluorescence of Ti3+ (11 μs). Flashlamp‐spectroscopic investigations in the 10 μs region of both, Ti doped and pure YAIO3crystals show a similar spectral and temporal behaviour of absorption differences. In order to explain the experimental results the model of bound small‐polaron is used.
Scattering and Annihilation of Positrons in Magnetically Ordered Samples
Authors: Szuszkiewicz S.
Published: July 2007

Measurements are made of the angular distributions of annihilation quanta for metallic glass (CoFe)74 (MnMoSiB)26 samples. It is found that if the spins of annihilating particles are antiparallel, the number of two‐quantum annihilation acts with 3d‐like electrons increase at about 7%. The measurements are also performed for the counting rate of coincidences for tH = 0 as a function of B. A change of the counting rate with the change of the direction of the ordering of the sample indicates the change of number of scattered positrons. However the scattering depends on the electron and positron spins.
Energy Spectrum and Phonon Excitation Damping in Many‐Component Amorphous Solids
Authors: Vakarchuk I. A. , Myhal V. M. , Tkachuk V. M.
Published: July 2007

Phonon excitations in many‐component amorphous solids are treated using the Green's function method. The equation for the energy spectrum of phonon excitations is obtained. This equation takes into account the hard core in the interatomic interaction potential, the temperature dependence of phonon frequencies, and their damping, caused by phonon scattering on structure fluctuations. Zeroth approximation is considered in a space with arbitrary dimensionality. In this case it coincides with the quasi‐crystalline one. The explicit expressions for the optic and acoustic modes as well as for the longitudinal and transverse velocity of sound are obtained as example in the two‐component case. In the space of arbitrary dimension the asymptotic of damping is studied for the one‐component system in the long‐wave region. Numerical calculations of the “frequency‐wave vector” dependence are performed for some amorphous metals in the quasi‐crystalline approximation.
Effects of Disorder and Electron Correlation in Disordered Systems
Authors: Brezini A.
Published: July 2007

A disordered Hubbard model with diagonal disorder is used to examine the electron localization effects associated with both, disorder and electron–electron interaction. Extensive results are reported on the ground state properties and compared with other theories. In particular two regimes are observed: when the electron–electron interaction, U, is greater than the disorder parameter and when it is smaller.
Mean Field Renormalization Group and Path‐Integral Methods for Spin‐One Disordered Ising Model in a Transverse Field
Authors: Yang C. Z. , Song W. J.
Published: July 2007

A new approximate scheme which is combined by mean field renormalization group theory (MFRG) with the discretized path‐integral renormalization (DPIR) is employed in the study of the disordered transverse Ising model. The critical properties of random bonds spin‐one Ising systems on a d‐dimensional lattice are calculated with this new approximate scheme.
Raman Scattering in Amorphous Selenium Molecular Structure and Photoinduced Crystallization
Authors: Baganich A. A. , Mikla V. I. , Semak D. G. , Sokolov A. P. , Shebanin A. P.
Published: July 2007

Raman scattering measurements are reported for amorphous selenium. It is found that the molecular structure of a‐Se on the scale of medium‐range order differs from the structure of most inorganic glasses. A laser‐induced glass‐crystalline transition is also studied. The experimental results suggest the existence of successive phases in such transition with pronounced threshold behaviour.
Interaction of Cascade‐Generated Nonlinear Elastic Waves with Dislocation Structure Elements in Metals
Authors: Zhukov V. P. , Boldin A. A.
Published: July 2007

The collective action of spherical elastic waves generated in atomic collision cascades under ion bombardment is shown to give rise to a random force similar to white noise in the dislocation glide plane. By way of example, the behaviour of radiation‐produced perfect dislocation loops and dislocation structure segments under the action of this force is investigated. It is found that the loop depth distribution obeys the diffusion equation with a “diffusion coefficient” proportional to the ion current density J while dislocation generation due to Frank‐Read source activation can be described in the framework of first‐order phase transformation theory, with J in the role of temperature.
The Origin of Electrically Active Centers in a Near‐Coincidence Σ9 Grain Boundary in Germanium
Authors: Wang N. , Wilbrandt P. J. , Haasen P.
Published: July 2007

The electronic defect states of a near‐coincidence Σ9 tilt grain boundary (GB) in germanium is characterized by means of deep level transient spectroscopy (DLTS). An energy level at (0.52 ± 0.02) eV below the conduction band of Ge is found for 1 × 1016 m−2 defect states. The structure of this boundary, which contains GB dislocations (b = 1/9 [221] a), is further studied by high resolution electron microscopy (HREM). The dislocations are found to have many jogs (3 × 1016 m−2) which create dangling bonds. This finding may represent experimental evidence that the dangling bonds are at the origin of the electrical activity of the GB in Σ9 bicrystal.
Effective Mass of Bulk and Surface Positrons Due to Plasmon Excitation
Authors: Shindo S.
Published: July 2007

The effective mass of bulk and surface positrons is calculated. It is shown that the mass of bulk positrons is enhanced due to plasmon excitations. The effective mass of surface positrons due to surface plasmon excitations is also calculated.
The Electronic Structure of the Copper Oxide Plane within the Green's Functions Projection Method
Authors: Hayn R. , Yu. Yushankhai V.
Published: July 2007

The projection method for two‐time Green functions is used to derive a self‐consistent set of equations for the spectrum of the two‐dimensional Emery model with infinite copper correlation. In the relevant parameter region near the filling n = 1 a charge‐transfer gap is found, but in difference to the Gutzwiller approximation a finite bandwidth occurs at the transition point. The critical Δc = ϵp — ϵd at which the transition to metallic behaviour occurs is found to be approximately Δc = 2t.
Density of States and Wave Function of Excitons Localized by Alloy Potential Fluctuations in Semiconductor Solid Solutions
Authors: Gourdon C.
Published: July 2007

Using a variational wave function for excitons localized by alloy potential fluctuations, the density of localized states, the exciton localization length, and the effective Bohr radius are calculated as a function of the localization energy. Results are shown for the specific case of CdS1—xSex alloys and compared with experimental results and other previous calculations.
Supraleitung — der Weg zu hohen Sprungtemperaturen
Authors: Urland W. , Tietz F.
Published: July 2007

Mit Hilfe eines früher entwickelten „Phasendiagramms”︁ zum Verständnis von Supraleitung wird der Weg zu supraleitenden Oxocupraten mit hohen Sprungtemperaturen aufgezeigt.
Lowering of Dimensionality in Phase Transitions with Correlated and Uncorrelated Random‐Exchange or Random‐Field Ising Systems
Authors: Silva P. R.
Published: July 2007

The excess of free energy in the phase transitions of Ising systems is calculated due to the presence of quenched impurities which could generate random exchanges or random fields. Dimensionality reduction is detected in the obtained hyperscaling relation both, in the case of correlated and uncorrelated random‐exchange or random‐field Ising models.
The Magnon Excitations and Magnetic Properties of Quasi‐One‐Dimensional Organic Polymer Ferromagnets
Authors: Su Gang , Xue De‐Sheng , Li Fa‐Shen , Ge Mo‐Lin
Published: July 2007

The magnon excitations and magnetic properties of a theoretical model proposed for quasi one dimensional organic polymer ferromagnets are investigated. It is found that two non‐degenerate magnons exist in the system, and their excitations are analog with those ones in ferrites. The specific heat, magnetization, and zero‐field susceptibility of the system are also obtained, and found that the model shows some exotic behaviors.
(TMTSF)2(2,5‐DBr‐DCNQI) — A Novel Kind of CT‐Complex Electrical and Magnetic Properties Originating from Different Stacks
Authors: Söderholm S. , Von Schütz J. U. , Schaumburg G. , Helberg H. W. , Erk P. , Hünig S.
Published: July 2007

Electric and magnetic properties of the new charge‐transfer complex (TMTSF)2(2,5‐DBr‐DCNQI) are reported. The microwave conductivity is thermally activated with an activation energy of 10 meV, and the room temperature conductivity is 10−1 to 10−2 Ω−1 cm−1. The charge transport is due to hopping between TMTSF sites. The real part of the dielectric constant is unexpectedly large, 200 at 300 K, and shows a weak temperature dependence. The presence of localized charge carriers can explain the magnitude of the dielectric constant. The spin systems associated with the TMTSF and DCNQI molecules, respectively, are strongly coupled. The dominating contribution to the ESR linewidth, above 130 K, is spin‐orbit coupling. The temperature dependence of the linewidth is due to electron phonon interaction and the hopping of the charge carriers. The susceptibility is high, 8 × 10−4 e.m.u./mol at 300 K, and is dominated by the contribution from the spins associated with the DCNQI molecules. The temperature dependence is the one of an antiferromagnetically coupled one‐dimensional Heisenberg chain with an exchange interaction of about 6 K.
Photoluminescence of RbPb2Cl5
Authors: Nikl M. , Nitsch K. , Polak K.
Published: July 2007

Emission and absorption properties of RbPb2Cl5 crystals are reported for the first time at the temperature 4.2 to 300 K. The lowest energy absorption peak at 275 nm is ascribed to a cationic exciton at Pb2+ site analogically to PbCl2. Two emission bands are found peaking at 340 and 510 nm under excitation in the exciton absorption region. They are ascribed to radiative decay of the cationic exciton at two different minima of excited APES at the Pb2+ ion. A comparison of RbPb2Cl5 emission properties with those of PbCl2 and RbCl:Pb is made.
Compton Scattering Studies in ZnS and ZnSe
Authors: Panda B. K. , Padhi H. C.
Published: July 2007

59.54 keV γ‐ray Compton profiles (CP) of polycrystalline samples of ZnS and ZnSe are reported for the first time. Both the profiles scaled to lattice momentum are found to be similar except for the low momentum region where ZnS profile is more peaked. The difference in the two profiles at the low momentum region could be a core‐orthogonalisation effect which needs to be evaluated.
Strain‐Induced Magneto‐Optical Anisotropy in Semimagnetic Quantum‐Well Structures
Authors: Goede O. , Heimbrodt W. , Köpp Th. , Gumlich H.‐E. , Lunn B. , Ashenford D. E.
Published: July 2007

It is shown that the lattice‐misfit induced biaxial strain in quantum‐well structures with semimagnetic barriers leads to a significant anisotropy of the shift and splitting of the subvalence bands in the barriers by an applied magnetic field. The calculated barrier exciton energies in dependence of a magnetic field parallel or perpendicular to the sample axis are confirmed by the measured anisotropic shift of the luminescence and reflection peaks for various CdTe/(Cd, Mn)Te quantum‐well structures grown by MBE on InSb substrates. Consequences on the behaviour of the well excitons in a magnetic field are discussed.
Diffusion Constants for the Vacancy Mechanism in Mg and α‐Zr Calculation
Authors: Monti A. M.
Published: July 2007

Self‐diffusion coefficients for the monovacancy mechanism described in terms of the Arrhenius law are calculated in Mg and α‐Zr from computer simulation results. Different short‐range pair interatomic potentials which reproduce some material properties are used. Special interest is devoted to the results obtained for the α‐Zr lattice; by assuming a vacancy‐formation energy value Ef = 1.8 eV, a self‐diffusion energy value Q = 3.3 eV and a pre‐exponential factor D0 = 5 × 10−5 m2 s−1 are obtained. These numbers indirectly support some ideas proposed in the literature to understand the self‐diffusion behaviour shown by experimental results, as well as some predictions made by other authors.
Tight‐Binding Approach to the Dangling Bond Feature of Covalent Crystals
Authors: Uemura Y.
Published: July 2007

A potential function is proposed which is responsible for dangling bond generation in defect structures of covalent crystals. The defect energy is calculated by the tight‐binding method using this potential. All atoms in the defect region are relaxed in six degrees of freedom (three translations and three rotations of a tetrahedron considered at each atomic site). This method is applied to a (111) twist boundary for calculating the boundary energy and the structure. The boundary energy seems mainly to be governed by the dangling bond density which is determined by dividing the number of dangling bonds by the number of atoms included in a supercell at the interface. But in the low energy region, the dependence between them is not so simple. In the case of a low dangling bond density, the relationship between the boundary energy and the rotation angle resembles the result reported for the twist boundary in ionic crystals.
Computer Modelling of the Dynamics of Space Dislocation Ensembles II. Flexible Dislocations. After‐Effect Stages
Authors: Volyntsev A. B.
Published: July 2007

The dislocation mechanisms of spontaneous plastic flow of deformed solids after their unloading, that is the dislocation reverse mechanical after‐effect (RMA), is considered. A previous model is developed with account of dislocation flexibility and the possibility to conduct a computing experiment in the mode of preliminary loading with a fixed velocity of deformation. The evolution of structure and the RMA temperature dependence in the course of continuous heating of deformed materials is analyzed.
Fractal Analysis of Optical Domain boundaries in Y1Ba2Cu3O7−δ Single Crystals
Authors: Müller J.‐P. , Schurig Th.
Published: July 2007

Optical domains on YBaCuO single crystals can be observed under polarized light. These domains are distinguished by different orientations of twins. The arising domain boundaries have a stepped shape and can be regarded as self‐similar in a limited range of magnification. By using different methods it is possible to characterize optical domain boundaries by fractal geometry. Fractal dimensions are obtained which are a measure of the boundary roughness.
Electronic Structure of A1BiS2 Semiconducting Compounds
Authors: Soldatov A. V. , Sukhetskii Yu. V. , Lavrentiev A. A. , Gusatinskii A. N. , Gubskii A. L.
Published: July 2007

Sulphur X‐ray fluorescent K bands, X‐ray absorption near the edge structure (K‐XANES), and emission L2,3 bands are obtained in semiconducting A1BiS2 (A1 = Li, Na, K, Rb) sulphides. The electronic structure of the [BiS6]9− cluster, which is a fragment of the investigated compounds, is calculated by the self‐consistent field Xα‐scattered wave (Xα‐SW) method. On the basis of a joint analysis of X‐ray emission spectra the fine structure, the XANES data and the results of Xα‐SW calculation the energy band structure and the character of chemical bond in A1BiS2 type compounds is investigated. The origin of the anomalous increase of the energy gap in these compounds is established when the atomic number of alkaline metal increases.
On a Concept of Quasiparticles with Parastatistics
Authors: Safonov V. L.
Published: July 2007

A possibility of description of some physical models in solids in terms of quasiparticles with parastatistics is considered. These quasiparticles can be introduced both by Green's generalized second quantization and by means of a nonlinear operator transformation for Bose and/or Fermi operators. Several examples of the nonlinear transformations are given. Some physical properties of the superconducting models are discussed.