bluuebunny/crossref_metadata_2025_split huggingface dataset:
Pb1−xGdxTe a New Semimagnetic Semiconductor with Rare Earths
Authors: Averous M. , Lombos B. A. , Fau C. , Ilbnouelghazi E. , Tedenac J. C. , Brun G. , Bartkowski M. A. 
Published: July 2007

AbstractPb1−xGdxTe, a new semimagnetic semiconductor, containing gadolinium as a rare earth element is synthesized. Its magnetic susceptibility, transport and optical properties are determined in the temperature range of 4.2 to 300 K using magnetic field intensities up to 6 T. The interaction between the Gd3+ ions are found to be slightly antiferromagnetic. The measured Hall mobilities of the samples with low gadolinium concentration (1 at% nominal value) are extremely high (4 × 106 cm2 V−1 s−1) at 4.2 K. They are comparable with the mobilities reported in superlattices. The large static dielectric constant of the PbTe host lattice is invoked to serve to shield out the electric fields of the ionized impurities and defects, minimizing impurity scattering. In addition, at low gadolinium concentrations, no Schubnikow‐de Haas oscillations are found although all the required conditions for them are satisfied. In this sample the Fermi level is 16.9 meV above the conduction band edge. It is argued consequently, that all the Landau levels passed the Fermi level due to the internal magnetic field induced by the rare earth ions. At higher gadolinium concentrations, 2 and 5 at%, the Fermi level moves up to 338 and 478 meV in the conduction band. Consequently, the internal magnetic field does not pre‐empt the effect of the external magnetic field. This results in the appearance of the Shubnikow‐de Haas oscillations, as expected.
Temperature and High Pressure Raman Study of M3P7 (M  Li, Na, K, Rb, Cs) Compounds
Authors: Bolduan F. , Hönle W. , Hochheimer H. D. , Henkel W. 
Published: July 2007

AbstractWe report the results of a study of M3P7 (M  Li, Na, K, Rb, Cs) compounds by Raman scattering at various temperatures and pressures in the solid state as well as in the solution. The compounds M3P7 (M  Na, K, Rb, Cs) show a first order phase transition from a crystalline to plastic crystalline state, which has already be confirmed by X‐ray, specific heat, and DTA measurements. Above the transition temperature Tc the low frequency external Raman lines vanish completely for all compounds except Li3P7, which is characteristic for a transition from a crystalline to a plastic crystalline phase. In the case of Li3P7 the external Raman modes are still present above Tc. This result combined with the results of X‐ray and DTA investigations suggests that the phase transition in Li3P7 involves a valence fluctuation within the polyanion P.
Temperature Dependence of the Raman Spectra of Calcium Oxalate Monohydrate
Authors: Duval D. , Conurate R. A. 
Published: July 2007

AbstractAnalyses of vibrational spectra and X‐ray powder diffraction data demonstrate that two phases (space groups I2/m and P21/n) coexist for calcium oxalate monohydrate between 273 and 376 K. Interpretation of the Raman spectra indicates that the I2/m‐P21/n phase transition near 320 K is analogous to the cubic‐tetragonal phase transition of NH4Cl. Unambiguous Rarnan band assignments are reported for the phase with space group I2/m. Several band reassignments are made for calcium oxalate monohydrate with space group P21/n.
First Order Raman Scattering in CdSnP2
Authors: Irmer G. , Heinrich A. , Monecke J. 
Published: July 2007

AbstractThe optical phonon spectrum of CdSnP2 and its directional dispersion is investigated by Raman scattering. The results are compared with theoretical results, ir measurements, and the phonon mode frequencies of InP, the isoelectronic analogue of CdSnP2.
Hot‐Exciton Orientation in Indirect‐Gap GaAs1−xPx Alloys
Authors: Charfi F. F. , Zouaghi M. 
Published: July 2007

AbstractResonant Raman scattering in indirect‐gap GaAs1‐xPx alloys is studied. The multiphonon scattering intensity as a function of the incident energy and polarization correlation measurements of 2LO‐phonon scattering are presented. The intensity dependence and the depolarization associated to the participation of large momentum resonant intermediate states are consistent with the hot exciton cascade model.
Quantum Effects in Accumulation Layers of Si‐SiO2 Interfaces in the WKB Effective Mass Approximation
Authors: De Castro E. , Olivo P. 
Published: July 2007

AbstractAn accurate, yet simple method is given to evaluate electric potential and quantum levels in silicon accumulation layers particularly suitable for implementation in the numerical analysis of the tunneling processes in MOS (metal‐oxide‐semiconductor) structures under general conditions. The procedure makes use of the WKB (Wentzel‐Kramers‐Brillouin) approximation for the electron wave functions: Poisson's equation is then expressed in a purely integral form solved by the Ritz method (i.e. by parametrized functions). A simplified procedure, which generalizes a one‐level model is also given. It is shown that it can give a fairly accurate estimate of the accumulation layer ground state, provided the effects of a sufficient number of subbands are taken into account.
Auger Recombination of Electrons via Deep and Shallow Acceptors
Authors: Khalfin V. B. , Strikha M. V. , Yassievich I. N. 
Published: July 2007

AbstractThe theory of Auger recombination via deep and shallow acceptors in p‐type AIIIBV semiconductors is investigated to determine the influence of free and localized carrier wave functions orthogonality. The extension of zero radius potential model to the case of several bands is used for the treatment of the deep acceptor wave function. The asymptotic wave function of the shallow acceptor for the range of the great wave vectors, and the scattering amplitude in the case of elastic scattering of the free carriers by a deep centre, are obtained, taking into account complex band structure. The results of the theory are applied to GaAs, and InGaAsP solid solutions. The rates of the various processes of Auger recombination are compared.
Quantumchemical Study of Imperfect Semiconductor Surfaces Including Step and Kink Sites
Authors: Katterle T. , Lorenz W. 
Published: July 2007

AbstractThe influence of semiconductor surface imperfections upon elementary processes of chemisorption and charge transfer is studied. Taking as simple model a silicon (111) surface with [211]‐step and kink site, chemisorption of H, OH, and H2O in different positions is investigated in TB approximation. Local and difference densities of states are calculated and adsorbate charges, relative charges of the chemisorption complexes, and adsorption energies determined.
Influence of Local Environment on Bound Excitons and Bound Excitonic Molecules in III‐V Alloys. I. Theory and Numerical Results for GaAs1−xPx:N
Authors: Müller H.‐J. 
Published: July 2007

AbstractA calculation of the local‐environment effect on nitrogen bound excitons and excitonic molecules in III‐V‐mixed crystal alloys is represented. The stochastic alloy potential is treated by means of perturbation theory, and a random distribution of As and P atoms in the appropriate sublattice is assumed. Because of special considerations concerning the concentration dependence of the averaged alloy potential the method is free of adjustable parameters. The density of states and its statistical momenta are calculated including electrons and holes simultaneously. The method is applied to GaAs1−xPx:N. Good agreement with measured bandwidths for bound excitons is obtained.
Hall Factor in p‐Ge with Anisotropic Energy Spectrum
Authors: Gutsul I. V. , Kirnas I. G. , Litovchenko P. G. , Marusyak V. I. , Nitsovich V. M. , Ostapov S. E. , Petrosyan E. E. 
Published: July 2007

AbstractBy solving the kinetic Boltzmann equation, a quasi‐momentum distribution function for charge carriers in p‐Ge is found taking into account the non‐sphericity of the constant energy surfaces of light and heavy hole bands. Account is also taken of the anisotropic carrier scattering by ionized impurities and acoustic lattice vibrations. The magnetic field and temperature dependences of the Hall‐factor rH are calculated for fields 0 < B ≦ 5 T and temperatures 77 K ≦ T ≦ = 260 K. The results calculated are compared with measured τH values obtained on oriented p‐Ge samples with free carrier concentration p ≈ 1.7 × 1014cm−3.
Three‐Body Interaction in H.C.P. Metals
Authors: Dutta B. , Sarkar S. K. , Roy D. 
Published: July 2007

AbstractThe consideration of two‐body central forces cannot explain the correct ordering of dispersion branches in the I'KM direction in many h.c.p. metals. The importance of three‐body forces in these metals is also indicated by the fact that for these metals the sum rule of Waren is not satisfied. Pseudopotential theory demonstrates that the total energy of a metal consists of an effective two‐body central interaction and a purely volume dependent part. Starting from this basis, a model expression for the energy of a metal is developed. It is shown that the interpretation of the volume strain as the local strain, as demanded by the adiabatic hypothesis, leads to an effective three‐body interaction between the ions. The model is applied to study the lattice dynamics of Mg and Be. It is found that the model predicts the correct ordering of the dispersion branches and fairly good agreement is obtained in the case of phonon frequencies and elastic data.
Spin–Phonon Excitations in Paramagnetic Crystals. Heat Transfer at High Temperatures
Authors: Kokshenev V. B. 
Published: July 2007

AbstractAn analysis is made of high‐temperature thermal conduction (above the Debye temperature) of a paramagnetic crystal in the conditions of exciting coupled spin–phonon modes. It is shown that the rearrangement of crystal spectra connected with these excitations changes drastically the character of heat carriers that may lead to considerable anomalies in the temperature behaviour of thermal conduction of a crystal formed by paramagnetic ions.
Some aspects of raman scattering in Cd3As2 single crystals
Authors: Weszka J. , Renucci M. , Zwick A. 
Published: July 2007

AbstractRaman scattering measurements in the tetragonal Cd3As2 single crystals are carried out at temperatures of 300 and 77 K. The spectra obtained are interpreted in terms of phonon‐electron and electron‐electron interactions. The features in the low‐frequency interval are due to contributions from phonon and single particle scattering. The electronic RS involving intra‐ and interband excitations is dominant at frequencies higher than 80 cm−1. The resonant enhancement of the band at 300 cm−1 arises from the incident light frequency being in the vicinity of ∑1 – ∑4.
Multiple scattering approach to the XANES theory of alkali halide crystals. I. Crystalline potential in the X‐Ray absorption spectra problem
Authors: Bugaev L. A. , Gegusin I. I. , Datsyuk V. N. , Novakovich A. A. , Vbdbinskii R. V. 
Published: July 2007

AbstractTwo schemes of the crystalline potential for the slow electron in the conduction band of alkalihalides are proposed. The first one (semiempirical) is based on the assumption that in the case of an ion in the crystal one can use the same energy dependence of logarithmic derivatives (of radial solutions at the atomic sphere radius) as in the case of the isolated ion. The modifications required consist in some potential corrections, that are due to the Madelung field as well as to the relaxation and polarization response for both, hole and electron. The second model (ab initio) suggests the straightforward solution of Poisson's equation. Both approaches are compared, so it is found that they lead to satisfactory agreement for a wide energy interval in the continuum.
Calculation of the charge carrier mobility of a size quantized semiconductor film by the energy‐loss method
Authors: Vartanian A. L. , Kirakosian A. A. 
Published: July 2007

AbstractAn energy‐loss‐method formalism applicable to a thin quantized film is developed. Within the frame of a self‐consistent field and taking into account the “imaginary” charges in the film surrounding regions the expression for a film dielectric function is derived and, in the long‐wavelength limit the analytical form of its imaginary part is found for a simple model of a size quantized film. Under the condition that the electron gas is nondegenerate and only the first subband is filled, the mobility is calculated, when an electron‐ionized impurity scattering is taken into account, and compared with the relevant Boltzmann expression.
Quantum hall effect in the inversion layer of p‐type InSb bicrystals under high hydrostatic pressure
Authors: Kraak W. , Nachtwei G. , Herrmann R. 
Published: July 2007

AbstractThe properties of a two‐dimensional electronic system in n‐inversion layers in grain boundaries of p‐InSb bicrystals are investigated under high hydrostatic pressure (up to 103 MPa) in high magnetic fields (up to 14 T). A rapid decrease of the carrier concentration in the inversion layer is observed when hydrostatic pressure is applied. At high pressures and high magnetic fields it is experimentally verified that the Hall resistivity ϱxy is quantized into integer multiplies of h/e2.
Nonlinear high‐electric‐field transport in the presence of strong laser radiation
Authors: Ziep O. , Mironov A. G. , Keiper R. 
Published: July 2007

AbstractThe Boltzmann equation is investigated in the presence of strong and time‐dependent electromagnetic fields taking into account the intra‐collisional field effect. The expression obtained for the field‐induced tail of the electron‐phonon scattering rate leads to the known results for static fields at low frequencies and includes at higher frequencies multiphoton processes.
Anderson localization on a disordered series‐parallel lattice
Authors: Zekri N. , Brezini A. 
Published: July 2007

AbstractThe Anderson localization is studied on a disordered series‐parallel lattice using a real‐space renormalization‐group transformation. Particular attention is given to the limit of strong disorder, and the numerical results for different values of the connectivity constant are presented and compared to other theories.
Three‐chain ising strip in a nonuniform field
Authors: Yurishchev M. A. , Sterlin A. M. 
Published: July 2007

AbstractThe free energy of a three‐chain Ising strip in an external field which acts either only on the system's central chain or, vice versa, only on its side ones, is found in closed analytical form by using the obvious symmetry of a Hamiltonian and the hidden algebraic symmetry of the transfer‐matrix secular equation. The behaviour of magnetization is considered for both cases.
Elliptically polarized magnon‐polaritons with longitudinal and transverse components in uniaxial ferrites
Authors: Merten L. , Kotzott B. 
Published: July 2007

AbstractIt is shown that in uniaxial ferrites magnon‐polariton waves with unusual properties exist: Concerning the magnetic vector the waves are in general elliptically polarized with a longitudinal and a transverse component. However, concerning the electric vector the waves are linearly polarized. The properties of the waves are described in detail. Besides, the corresponding magnetic reststrahlen‐bands are calculated and discussed.
Calculation of electron velocity in crystal ab initio. Results of computation by green's function method for vanadium
Authors: Shirokovskii V. P. , Shilkova N. A. , Trubitsina N. A. 
Published: July 2007

AbstractUsing the Hellman‐Feynman theorem and the perturbation theory for the matrix, an expression for the electron velocity in crystals is derived. Calculations are carried out on a mesh of 55 points in 1/48 th of the b.c.c. Brillouin zone for six energy bands of vanadium. The comparison with the data of numerical differentiation demonstrates the excellent accuracy of the technique presented. The influence of higher angular‐momentum terms in the expansion of the wave function on the velocity value is discussed.
Thallium‐belated isoelectronic bound excitons in silicon. A bistable defect at low temperatures
Authors: Conzelmann H. , Hangleiter A. , Weber J. 
Published: July 2007

AbstractDetailed investigations are reported on the luminescence spectra of thallium related isoelectronic excitons in silicon, which yield a complete picture of this most unusual luminescence system. The luminescent defect exists in two different configurations, which are able to transform into each other in the temperature range from 10 to 20 K. The stress and Zeeman experiments reveal that the low temperature configuration has trigonal symmetry, whereas the high temperature form of the center is aligned along the [100] directions. Time resolved measurements of the luminescence lines lead to a detailed model for the mechanism of reorientation. In the defect ground state the trigonal symmetry is lowest in energy. The capture of a hole or an exciton changes the relative energies in such a way that now the [100] configuration is energetically favoured.
The ligand field on dn ions in a strained corundum crystal
Authors: Lacroix R. 
Published: July 2007

AbstractThe ligand field Hamiltonian for a d electron in a transition metal doping a strained corundum crystal is worked out in the frame of a cluster model. The formulation makes explicit reference to the inner elasticity constants and allows the Hamiltonian to be used as well from the covalent point of view as in the point charge model.
Curved flux line effects in a type‐II superconducting hollow cylinder
Authors: Shehata L. N. , Refai T. F. 
Published: July 2007

AbstractMagnetic fields created by curved or straight flux lines as well as the magnetic fields within a type‐II superconducting hollow cylinder are presented for the case when an external field is applied within the hollow region. In order to verify the theoretical calculations and to measure especially the stray field an experimental set‐up is proposed that can also be used to measure the effect of a sharp edge on field intensity.
The density matrix of an infinite muffin‐tin system and mutually avoiding scattering paths
Authors: Lenk R. 
Published: July 2007

AbstractFor independent quantum particles moving in an infinite ordered or disordered array of spherically symmetric scatterers the density matrix and related quantities for the incident field are represented via the superposition of all scattered waves. The corresponding formulae contain products of two propagators which are defined for mutually avoiding scattering paths. Therefore the usual vertex effects disappear. The new formulation forms a sound mathematical base for earlier trials. It is valid also for stationary non‐equilibrium situations and can therefore be employed to construct a non‐classical transport theory.
Theory of quantum hall effect
Authors: Keeper R. , Ziep O. 
Published: July 2007

AbstractAssuming the formation of a Wigner crystal in a Q2D structure the Hall conductivity for the quantum regime is calculated. The fractional and integer values in units of e2/h are explained as related to a new correlated electron state which reflects structuring on a mesoscopic scale in real space. The results are in excellent agreement with experimental data.
Phonon density of states in amorphous Si0.5Ge0.5
Authors: Gupta H. C. , Reddy G. S. N. , Tripathi B. B. 
Published: July 2007

AbstractThe angular force model is used to investigate phonon density of states of a‐Si0.5Ge0.5 by considering only the first nearest neighbour interactions. A force constant decrease of the order of only 5% is observed when the phase changes from crystalline to amorphous system. The relevance of the obtained results to the Raman spectra is discussed.
Thermal conductivity of cooperative Jahn‐Teller E‐systems
Authors: Mutscheller W. , Wagner M. 
Published: July 2007

AbstractThe thermal conductivity of the cooperative vibronic system TmVO4 is investigated theoretically. Relaxation times are derived by means of a Mori‐Zwanzig formalism. In the calculation it is shown that the surviving phonon‐pseudo‐magnon scattering processes obeying the Ising cooperativity in the pseudo‐magnon system fully account for the anomalous behaviour of thermal conductivity in the region 0.5 Tc < T < Tc.
Inelastic incoherent neutron scattering and Raman scattering of 2,3‐dimethylnaphthalene
Authors: Kalus J. , Gerlach H. , Schleifer J. , Wörlen F. , Voss G. , Godlewska M. , Natkaniec I. , Karl N. , Prager M. 
Published: July 2007

Abstract2,3‐dimethylnaphthalene crystallizes similar to naphthalene, but with dipolar structural disorder of the acentric molecules. There are differences between the inelastic incoherent scattering spectra for differently deuterated samples (C10H6(CH3)2, C10D6(CH3)2, C10D6(CD3)2) which can be explained by the dynamics of the molecular body and the methyl‐groups. The data are taken at 20, 80, and 290 K. The results of the neutron scattering experiments are confirmed by Raman measurements for the completely deuterated sample at different temperatures. Results of theoretcal calculations are in rough agreement with the experimental data.
Resonance effects in the Raman spectrum of CdGa2Se4
Authors: Parisini A. , Lottici P. P. , Razzetti C. , Bacewicz R. 
Published: July 2007

AbstractResonance effects are observed in the Raman cross‐section of the defect chalcopyrite CdGa2Se4. The results indicate a strong resonance of the highest frequency E(LO) sphalerite‐like phonons in forbidden geometry, similar to the behaviour observed for zincblende‐like crystals. The forbidden scattering may be described through a Pröhlich intraband mechanism at the fundamental direct gap.
Surface semichanneling of molecular ions
Authors: Shulga V. I. 
Published: July 2007

AbstractComputer simulation technique is used to study the scattering of 30 keV N2 ions by the surface semichannels of a copper crystal. The specular reflection intensities of molecular and dissociated ions and the orientations of the reflected molecules are analyzed. The trajectory focusing is found to affect essentially the molecular scattering near the semichannel direction. A simple formula is obtained which relates the semichannel focusing energy directly to the interatomic potential.
The effects of defects on channeling radiation
Authors: Pathak Anand P. , Balagari Prasanna K. J. 
Published: July 2007

AbstractThe spectral features of the electromagnetic radiation emitted from relativistically fast positrons and electrons channeled along major crystallographic directions and planes are very sensitive to the interatomic potential assumed between theprojectile and the target crystal. The effects are investigated of platelets present in diamond type Ia on the channeling radiation by assuming a imple model for these defects, as seen from (100),(110), and (111) planar directions. The results arequalitatively correct and for (110) planar channel, quantitative agreement with the experimental results is also satisfactory.
A self‐consistent approximation for the random‐field ising model. Phase diagram d ≧ 3
Authors: Janiš V. 
Published: July 2007

AbstractA self‐consistent approximation is given accounting for both, the imensionality nd lattice structure effects for the free energy of the Ising model in a quenched random magnetic field. The phase diagram for the bimodal distribution of the random field is displayed.
Discreteness effects in a classical one‐dimensional antiferromagnet
Authors: Talim S. L. , Piebs A. S. T. 
Published: July 2007

AbstractPerturbation theory is used to study corrections to the sine‐Gordon soliton, in a classical onedimensional anisotropic antiferromagnet in an external field, arising from the influence of lattice discreteness. It is shown, that for TMMC, at the temperatures where most experiments have been done, the corrections are very small and can be neglected.