bluuebunny/crossref_metadata_2025_split huggingface dataset:
Quantum Theory of Thermopower in Quasi‐Two‐Dimensional Semiconductor Quantum Well Structures
Authors: Kubakaddi S. S. , Mulimani B. G. , Jali V. M. 
Published: July 2007

AbstractA quantum‐mechanical theory for the thermopower in quasi‐two‐dimensional semiconductor quantum well structures, using the density matrix approach, is developed. Expressions for thermopower are obtained, both, when the temperature gradient is applied parallel and perpendicular to the plane of the layer forming the quantum well. The expressions obtained for the longitudinal configuration agree with those obtained from the conventional Boltzmann transport equation in relaxation time approximation.
Magnetic Order in Intermediate Valence Systems
Authors: Nolting W. , Ramakanth A. 
Published: July 2007

AbstractA „hybridized”︁ s—f model is used in order to investigate the possibility of a coexistence of ferromagnetism and intermediate valence in systems which fluctuate between a magnetic and a nonmagnetic 4f configuration. The Curie temperature Tc, is determined, the local magnetic f‐moment mf, the valence nf and the static susceptibility χ as functions of the f‐level position Ef, the hybridization V, the s—f exchange g, and the Bloch bandwidth W for semiconducting as well as metallic 4f systems. It is found that electronic fluctuations destablize the local moments, but enhance the coupling between them. This leads to a Tc‐maximum just in the intermediate valence phase. Many results remarkably depend on, how the gap between the 4f‐level and the lower band edge (or Fermi‐edge) is closed, by a shift of the f‐level towards the conduction band (alloying!) or by a respective broadening of the band (external pressure!). Striking differences between semiconducting and metallic 4f‐systems are observed, while qualitatively similar behaviour is found for systems with ferromagnetic and systems with antiferro magnetic s—f exchange coupling. Magnetic phase diagrams in terms of Ef, W, V, and conduction band occupation n are derived and discussed. Qualitative agreement is found with recently performed experiments on systems like EuO, EuRh3B2, CeNixPt1−x, Ce(Rh1−xOsx)3B2,‥.
Continued‐Fraction Approximation for the Inverse Brillouin Function
Authors: Katriel J. 
Published: July 2007

AbstractThe first nine coefficients in the continued‐fraction representation of the inverse Brillouin function are obtained. The approximation thus generated is demonstrated to be of sufficient accuracy over the whole physically interesting range, in contrast with the corresponding power series. Possible applications of the inverse Brillouin function in non‐iterative molecular field theory as well as to the construction of the effective Hamiltonian, using the experimentally determined temperature dependence of the magnetization, are pointed out.
59Co NMR and Nuclear Magnetic Relaxation Study of the Magnetic Superconductor Y9Co7
Authors: Figiel H. , Barata A. C. , Guimarães A. P. 
Published: July 2007

AbstractThe magnetic superconductor Y9Co7 presents in its structure magnetic and non‐magnetic Co atoms. A search is made of the 59Co NMR lines attributed in the literature to magnetic Co atoms, with negative results. For the strong 59Co NMR line arising from nuclei of non‐magnetic Co atoms the relaxation times T1 and T2 versus temperature are measured directly at 6.5 and 9.0 MHz. A linear dependence on temperature is observed for 1/T1 which can be attributed to interactions with conduction electrons. 1/T2 is not linear with temperature, an effect that is related to the temperature dependence of the magnetization.
Short‐Time Behaviour of the Transverse Auto‐Correlation Function of the 1D XY‐Model
Authors: Farias G. A. , Gonçalves L. L. 
Published: July 2007

AbstractThe dynamics of the spin 1/2 one‐dimensional XY‐model in a transverse field is considered. The short‐time behaviour of the auto‐correlation function 〈S(t) S(0)〉 for the closed chain is obtained numerically by considering the exact results known for the open chain which are given in terms of Pfaffians. The bulk auto‐correlation is identified with the correlation 〈S(t) S(0)〉 for the open chain, and this identification is shown to be valid up to a characteristic time Jt ≅ 20. It is also shown, as expected, that the boundary effects are more pronounced for fields smaller than the exchange constant (h < |J|) and in the low temperature limit. The results are obtained for different temperatures and field strengths, and the numerical convergence is discussed in each case.
Raman and Infrared Spectra of YAsO4
Authors: Pradhan A. K. , Choudhary R. N. P. , Wanklyn B. M. 
Published: July 2007

AbstractSingle crystals and polycrystalline specimens of YAsO4 are prepared by flux method and solid‐state reaction, respectively. Crystal and powder Raman and infrared spectra at 300 K and crystal Raman spectrum at 77 K of YAsO4 are taken to study the internal and external vibrations of AsO4−3 ions. It is found that lattice vibrations with k = 0 associated with the tetrahedra of YAsO4 are similar to that of DyAsO4 and SmAsO4. The Raman spectrum at 77 K shows slight shifting of phonon lines to higher frequencies due to the decreasing anharmonic interactions of the vibrations. Similarly softening of one of the force constants (f4) at 77 K in comparison to that of 300 K was observed. Different dosages of X‐ray irradiation produces a very little effect to create defects in the YAsO4 crystals.
Static Structure Factor of Non‐Simple Liquid Metals Bi, Ga, Sb, and Sn
Authors: Zou Xian‐Wu , Jin Zhun‐Zhi , Shang Ya‐Jun 
Published: July 2007

AbstractA simple theoretic expression for the static structure factor a(Q) of non‐simple liquid metals is presented, based on the hard sphere cluster model. This expression is a superposition of two Ash‐croft‐Lekner expressions with weight factors representing the atomic percentage of each type of clusters. The structure factors of liquid Bi, Ga, Sb, and Sn are computed. The calculated results are in good agreement with experiments over the entire range of momentum space.
Ionic Conductivity of Magnesium and Aluminium Doped Sodium Chloride Crystals
Authors: Deb S. K. , Bandyopadhyay S. , Neogy C. , Nag A. 
Published: July 2007

AbstractThe electrical conductivity of magnesium and aluminium doped sodium chloride crystals are measured at 1 kHz as a function of temperature from 275 to 730°C with the help of an ac bridge. The results show that, unlike divalent defects, the conductivity of aluminium doped crystals is lower than those values of the pure crystals in the extrinsic range, suggesting strong association between the aluminium ion and the created cation vacancies.
On the Determination of Interaction Parameters from Correlations in Binary Alloys
Authors: Maysenhölder W. 
Published: July 2007

AbstractThe determination of interaction parameters from correlation functions in binary alloys is discussed by means of high‐temperature expansions for the correlations. The inherent nonlinearity of this „inverse problem”︁ of statistical mechanics leading to non‐unique solutions is emphasized. The formulation includes pair and triplet interactions. Some results of a specific „inverse Monte Carlo calculation”︁ are criticized. The paper provides a collection of formulae, especially for probabilities and correlations, which should prove useful for clarifying the subject.
Vibrational Properties of Hydrogen in Proton‐Implanted Silicon
Authors: Tatarkiewicz J. , Winer K. 
Published: July 2007

AbstractSome aspects of the infrared absorption spectra of crystalline silicon containing implanted hydrogen or deuterium are interpreted on the basis of simple atomic cluster calculations. It is shown that the vibrational properties of the implanted ions can be understood solely by taking into account the effect of the host silicon network on the local impurity vibrations.
Lattice Vibrational Contribution to the Bulk Properties of Si and Ge
Authors: Kagaya H.‐Matsuo , Shoji N. , Soma T. 
Published: July 2007

AbstractThe lattice vibrational contributions to the bulk properties of Si and Ge are studied in the dynamical treatment using higher‐order perturbation. The internal energy, Helmholtz free energy, thermal pressure from lattice vibrational term, and the temperature dependence of elastic constants are quantitatively obtained.
The Pair Correlation Function and Mott Transition in Two‐Component Fermi Systems
Authors: Schmidt M. , Röpke G. 
Published: July 2007

AbstractMany particle theory is applied to describe the properties of nonideal two‐component Fermi systems as, e.g., the electron—hole plasma in highly excited semiconductors. Density corrections to thermodynamic properties as the equation of state and the pair correlation function are considered. Starting with a separable model potential the T‐matrix is calculated analytically. Two models for density dependent two particle properties (binding energy, scattering phase shifts) are compared, simulation by variable potential parameters without account for Pauli blocking and explicite inclusion of Pauli blocking. The continuity of thermodynamic functions if the system undergoes a Mott transition and the importance of Pauli blocking for the compensation of Bose singularities are discussed. The borderline for the onset of Bose condensation in the continuum of scattering states is presented.
γ‐Quantum Resonance Scattering in a Plane‐Parallel Isotropic Layer
Authors: Mkrtchyan A. R. , Gabrielyan R. G. , Martirossian A. H. , Grigoryan A. Sh. 
Published: July 2007

AbstractThe problem of non‐coherent γ‐quantum scattering is investigated in the medium taking the multiple scattering into account. Two models of the elementary process of scattering of the resonant γ‐quanta by the nuclei are discussed. It is shown that in case of large values of the quantum reemission probability or a large effective thickness, the problem cannot be limited only to the quantum single scattering approximation.
Magnetic Properties of the Ising Ferromagnet of Large Spin with Biquadratic Exchange Interaction and Uniaxial Anisotropy
Authors: Iwashita T. , Uryǔ N. 
Published: July 2007

AbstractFor an Ising ferromagnet with S = 5/2, the magnetization 〈Sz〉 and the Curie temperature TC are calculated using the pair model approximation. Assuming bilinear and biquadratic exchange interactions (J and J′) between nearest‐neighboring pair of spins and uniaxial single‐ionic anisotropy D for each spin, the behaviors of 〈Sz〉 and TC as functions of these exchange parameters and the uniaxial anisotropy parameter are investigated for an Ising ferromagnet on crystal lattices of various types.
Optical Properties of Al Films within and beyond the Effective‐Medium Approximation
Authors: Jungk G. , Schultze V. 
Published: July 2007

AbstractThe complex dielectric function of slightly differently prepared polycrystalline Al films is determined ellipsometrically for photon energies hω between 1 and 4 eV. The results can be explained by symmetrical and asymmetrical EMA for hω ≧ 1.8 eV through the incorporation of Al2O3. Below 1.8 eV significant discrepances occur due to resonantly enhanced electric fields in nonspherical Al grains surrounded by a dielectric.
The role of single collisions in the process of scattering and stopping of 200 to 400 keV protons in thin gold foils
Authors: Bednyakov A. A. , Iferov G. A. , Kadmenskii A. G. , Naumova N. M. , Zhukova Yu. N. 
Published: July 2007

AbstractThe trajectories of 200 to 400 keV protons in 5 to 18 nm thick gold foils are simulated by means of Monte‐Carlo calculations. The impact‐parameter distributions of ion–atomic collisions at different emission angles are obtained. The impact‐parameter distributions of the mean energy transfered to the atom at given emission angles are calculated. The angular dependence of the mean energy loss is also calculated. By fitting the latter with experiment the impact‐parameter dependence of the energy transfer in a single collision is obtained.
Interrelationship between higher‐order elastic constants and pressure derivatives of dielectric constants for ionic crystals
Authors: Srivastava G. M. S. , Sinha R. K. , Shanker J. 
Published: July 2007

AbstractAn interrelationship between the pressure derivatives constants and higher‐order elastic constants is investigated. Some useful relations connecting the first‐ and second‐order pressure derivatives of dielectric constants, third‐ and fourth‐order elastic constants, and bulk modulus and its pressure derivatives are obtained. A numerical application of these relations in the case of alkali halide crystals yields results which are found to be in good agreement with available experimental data. The utility of the mathematical expressions reported in the present work is demonstrated by calculating the pressure derivatives of dielectric constants.
GaAs–AlGaAs quantum well of compositional graded interface in the envelope function approximation
Authors: López‐Gondar J. , Rodriguez‐Coppola H. , Pérez‐Alvarez R. 
Published: July 2007

AbstractAnalytical expressions for the energy levels of a GaAs–AlGaAs quantum well with compositional graded interfaces are reported. The results for the first conduction and valence levels are compared with those obtained using a tight binding method. Good agreement between both the methods is obtained when the thickness of the graded layer is small enough. The method developed here can be straightforwardly extended to other structures of compositional graded layers. The results obtained for the energy levels when the well thickness is large and the layers of compositional graded material are small enough show that the usual abrupt interface approximation is valid to a great extent.
Dissipative effects of the interaction of crystal lattice surface with medium
Authors: Ya. Vetrov S. , Shabanov V. F. 
Published: July 2007

AbstractThe processes of dissipation due to the crystal interaction of lattice with medium are taken into account using the friction forces. The methods of discrete lattice dynamics shows that the dissipative forces induce surface waves of new type which penetrate deeper to crystal and damp weaker than the waves existing without dissipation. The possibilities to discover and use the obtained surface vibrations are considered. Besides it is shown, that the accounted dissipation leads to essential modification of known surface waves: their frequency and damping is renormed, penetration to crystal decreases, at intensive enough dissipation the surface waves become aperiodic surface motions of different types. The estimations of surface vibration damping are given for contacts of crystal with gas and liquid.
A study of the electronic structure of Fe1−xCox alloys by a polarized positron annihilation
Authors: Szuszkiewicz S. 
Published: July 2007

AbstractThe results from the angular correlation curves measured for Fe1–xCox ordered alloys with and without a magnetic field are presented. The average numbers of the 4s‐like and 3d‐like electrons per alloy atoms as well as the average numbers of the d‐like electrons in majority and minority spin bands are determined as function of Co concentration.
To the theory of two‐magnon absorption of light by surface collective excitations in the singlet–triplet ferromagnets
Authors: Seidov Yu. M. , Suleimanov A. M. 
Published: July 2007

AbstractBy the multi‐time Green's function method the light absorption by surface excitations in the singlet–triplet ferromagnets is investigated using the pseudospin formalism. The possibility of two‐magnon absorption of light on the surface of the singlet‐triplet ferromagnets is shown. It is estimated that the absorption of light by the surface of singlet–triplet ferromagnets is due to the simultaneous emission of two surface magnons in different branches of the spectrum of the singlet–triplet ferromagnets.
Energy levels of triply ionized praseodymium in BiLiF4 crystals
Authors: Schultheiss E. , Scharmann A. , Schwabe D. 
Published: July 2007

AbstractThe energy level scheme of Pr3+ in BiLiF4 is investigated by means of polarized absorption and emission spectroscopy on single crystal samples at various temperatures. Vibronic lines appearing in the spectra are identified according to the q = 0‐phonons of the host coupling to electronic levels.
Analysis of the electrical conduction in CdHgTe crystals
Authors: Dziuba Z. 
Published: July 2007

AbstractThe electrical conduction versus magnetic field in p‐like CdHgTe samples at 77 K is investigated by analysing the conductivity tensor components. The electrical conduction is mainly due to electrons in the conduction band and low‐mobility carriers in an impurity band. In the investigated samples CdxHg1–xTe with the composition x ≈ 0.17 the concentration of electrons in the conduction band is higher than the intrinsic one and in samples with the composition close to HgTe the concentration of electrons in the conduction band is equal to or lower than the intrinsic one. The model of a half‐filled impurity band situated close to the bottom of the conduction band is proposed to account for the concentration of electrons in the conduction band.
Modifications of the hopping conductivity due to long‐range coulomb interactions
Authors: Goedsche F. 
Published: July 2007

AbstractThe conductivity law derived by Efros and Shklovskii for variable‐range hopping (VRH) in the presence of long‐range Coulomb interaction is modified to take into account new numerical results for the density of single‐particle states (DOS) within the Coulomb gap. The characteristic temperatures appearing in this modified VRH law, including limiting temperatures for the applicability of VRH, are expressed in terms of DOS parameters, localization length and dielectric constant. The results are compared with experimental studies in crystalline and amorphous semiconductors.
Electronic properties of liquid SbSe and BiSe alloys
Authors: Satow T. , Uemura O. , Matsumoto K. , Okamura S. 
Published: July 2007

AbstractThe electrical conductivity (σ), the magnetic susceptibility (χ), and the thermoelectric power (S) of liquid SbSe and BiSe alloys are measured as function of composition in the temperature range from the melting point to about 1000 °C. On adding Se to Sb and Bi σ indicates a rapid fall and χ has a sharp maximum of diamagnetism at the stoichiometric composition of M2Se3 in both the systems. A reversion of the sign of S is observed around the composition of Sb2Se3 in liquid SbSe alloys, while S in liquid BiSe alloys remains negative over a wide composition range including Bi2Se3. The calculated value of g (the ratio of real and free electron density of states at the Fermi level) using the observed values of σ begins to decrease in the vicinity of 50 at% Se and drops sharply at the concentration of 60 at% Se in both systems. Electronic properties obtained are discussed in the light of current transport theories employed in liquid semiconductors.
Many‐body effects in antiferromagnetic 4f‐systems
Authors: Bulk G. , Nolting W. 
Published: July 2007

AbstractA many body approach is presented for the electronic excitation spectrum of an antiferromagnetic semiconductor with ABAB‐sublattice structure. By use of the s–f model the sensitive dependencies of the quasiparticle density of states (Q‐DOS) on the temperature T, the carrier concentration n, and the effective coupling constant g/W is derived and discussed. The electronic spin polarization per sublattice is a direct consequence of this Q‐DOS‐behaviour. It increases for higher band occupations, lower temperatures and stronger couplings g/W. The lower edge of the quasi‐particle spectrum shifts with increasing n to higher energies showing for fixed n rather small blue shifts as function of decreasing temperature.
Dynamics of phonon‐assisted optical interband processes in semiconductors
Authors: Stahl A. , Frank D. 
Published: July 2007

AbstractThe influence of the electron–phonon interaction on the dynamics of the electronic band edge is studied within the framework of the recently developed coherent wave approach. The applications being considered are the dynamics of an indirect band‐to‐band transition and the dissipative influence of spontaneous lattice vibrations on polariton propagation. The relation to the theory of spontaneous and induced light scattering is established.
Temperature dependence of the elastic constants for solids of cubic symmetry.Application to Germanium and Silicon
Authors: Toupance N. 
Published: July 2007

AbstractThe extension of the finite strain expansion of the Mie‐Grüneisen equation (taking into account the elastic constants in the reference configuration up to the fourth‐order) is used to derive the temperature dependence of the volumetric compression and of the second‐order elastic adiabatic moduli of cubic solids. Numerical results are given for germanium and silicon and compared to experimental data. Finally, the second pressure derivative of these constants is estimated at zero pressure and 300 K.
The exact solution of the real square‐lattice‐gas system
Authors: Szász A. 
Published: July 2007

AbstractThe square‐lattice‐gas model is calculated exactly by a special process. This model previously had no exact solution because it requires a general solution of the square‐lattice‐Ising model with external magnetic field, which also to‐date does not have an exact solution. In the present calculation an exact solution to the square‐lattice‐model is obtained in a form that does not require the solution of the external field contained in the Ising model.
The 7,7′, 8,8′‐tetracyano‐p‐quinodimethanide salt of the N‐n propyl quinoxalinium cation — its structure, conductivity, and triplet spin excitons
Authors: Firlej L. , Graja A. , Rajchel A. , Woźniak K. , Krygowski T. M. 
Published: July 2007

AbstractA new organic semiconductor (N‐n propyl quinoxalinium)+ (7,7′,8,8′‐tetracyano‐p‐quinodimethanide)2− is synthesized and characterized by elemental analysis and X‐ray diffraction. The electrical dc conductivity, the thermoelectric power as well as the ESR spectra are reported and discussed. The crystal is of triclinic symmetry. TCNQ moieties stack plane‐to‐plane, in stoichiometric groups of four; adjacent columns from sheets interleaved by the cations. The charge transport properties are discussed in terms of a one‐electron semiconductor model with low temperature behaviour controlled by electrically active impurities. The ESR spectra are interpreted by the model of Q 1‐D mobile triplet excitons; it is consistent with the charge localization found by bond lengths analysis and assumed by the model of the electrical transport.
A semi‐empirical approach to the bulk properties of copper
Authors: Craig B. I. , Smith P. V. 
Published: July 2007

AbstractA semi‐empirical method suitable for d‐band metals is presented. This method is an extension of the Chadi scheme which has been successfully applied to semiconducting systems. In this scheme the electronic structure is determined by the Slater‐Koster matrix method. For metals careful attention has to be now given to the dependence of the diagonal matrix elements upon the neighbouring atomic positions. The new method is applied to the calculation of several properties of copper, such as the bulk modulus, elastic constants and phonon frequencies, and shown to produce good agreement with the experimental values.