bluuebunny/crossref_metadata_2025 huggingface dataset:
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

An 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

The 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

The 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

The 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

The 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

It 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

Using 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

Detailed 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

The 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

Magnetic 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

For 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

Assuming 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

The 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

The 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

2,3‐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

Resonance 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

Computer 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

The 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

A 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

Perturbation 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.
Multiphoton interband absorption of light in semiconductors in external parallel electric and magnetic fields
Authors: Katana P. K.
Published: July 2007

The coefficient of the multiphoton interband absorption of light (MPA) in semiconductors in the presence of constant external, parallel electric and quantizing magnetic fields is calculated. It is shown that the MPA coefficient has an oscillatory character and the peaks correspond to the optical transitions on Landau levels. The following particular cases are considered: multiphoton electroabsorption (MPEA) and multiphoton magnetoabsorption (MPMA).
Monte‐carlo studies of energy straggling of electrons in solids. II. Consideration of electron angular scattering
Authors: Kotera M. , Murata K. , Nagami K.
Published: July 2007

An angular scattering effect of electrons in solids is taken into account in the previous Monte‐Carlo simulation model which has employed the modified Blunck and Leisegang (MBL) energy straggling distribution. The Mott cross‐section of elastic scattering is adopted for angular scattering. The electron trajectory consists of two kinds of steps; one is an elastic scattering mean free path as used in the conventional single scattering model, and the other is a step length defined using the MBL distribution in the previous paper. This simulation is applied to calculate several physical quantities such as backscattering and transmission coefficients, energy deposition etc. The calculated results are verified by comparing with the experimental data.
Electronic structure of neutral and charged point defects. A charge self‐consistent empirical tight‐binding study
Authors: Strehlow R. , Kühn W. , Hanke M.
Published: July 2007

A charge self‐consistent description of the electronic structure of neutral and charged point defects in the framework of ETBM is presented. As in the case of recently performed charge self‐consistent TB parametrizations of pure crystals the approach is based on the consideration of both, intra‐and inter‐atomic electron‐electron interaction resulting in a functional dependence of TB eigen‐energies on the orbital population. Using the Koster‐Slater scattering‐theoretical method the theory is explicitly worked out for a five‐atom cluster containing the point defect and its four nearest neighbours. As a first application antisite defects in III–V compound semiconductors are treated. Results are discussed for both, neutral and charged defects.
Semiphenomenological theory of the Gd3+ S‐state splitting in low‐symmetry crystals
Authors: Levin L. I.
Published: July 2007

A semiphenomenological theory for Gd3+ ground state splitting in low‐symmetry crystals is proposed. It allows to explain this splitting with an explicit indication of the Gd3+ excited states taken into account and to extract the characteristic parameters of the splitting which are independent of the angular and radial coordinates of the ligands.
EPE and spin‐flip Raman scattering in the n‐type magnetically mixed semiconductors
Authors: Ryabchenko S. M. , Semenov Yu. G.
Published: July 2007

Effects on the EPR and spin‐flip Raman scattering (SFRS) of large‐radius electron centers (donors) are considered for magnetically mixed semiconductors. The effects are caused by the mixing of the spin states of electrons and the localized spin momenta (LSM) of magnetic ions through the carrier‐ion exchange interaction. The shape of the SFRS and EPR spectra in the “Zeeman region” is calculated as well as the dependence of the relative component intensity on the matrix element ratio of SFRS (EPR) transitions for the donor electron and LSM. The effects of the “disappearance” of the donor EPR in the course of the magnetic doping of semiconductors and the effect of the manifestation of LSM EPR in the magnetic resonance optically detected from the donor‐acceptor luminescence are explained. A superscattering effect is predicted for the collective spin of the LSM ensemble effectively interacting with the donor electron.
Orbit‐lattice interaction and mössbauer quadrupole splitting of Fe(II) in (NMe4)2FeCl4
Authors: Srivastava K. K. P. , Choudhary S. N.
Published: July 2007

The observed quadrupole splitting of 57Fe2+ in (NMe4)2FeCl4 shows a linear decrease with temperature over 87 to 237.5 K, which cannot be explained on the basis of the electronic states of Fe2+ in a static crystal field. The effect of orbit–lattice interaction is considered which produces a temperature dependent mixing between the dz2 and dx2–y2 electronic states with the emission and absorption of phonons of varying energies. The various lattice dynamical parameters are estimated and then quadrupole splitting is explicitely calculated as a function of temperature. One obtains a reasonably good agreement with the experimental data which shows that the vibrating lattice model is quite realistic and important.
Mössbauer emission studies of 57Co‐doped ZnO, Cu2O, and TiCoO3
Authors: Roset J. , Fernández A. , Obradors X. , Tejada J.
Published: July 2007

57Co‐doped Mössbauer oxide sources are prepared at different temperatures and oxidation pressures. The appearance of the 57Fe3+ anomalous charge state is related with the p‐character of semiconductor oxide. Increasing the acceptor concentration increases the anomalous ferric line intensity in the Mössbauer spectra. The two location sites of 57Co in the ZnO matrix correspond to substitutional and grain boundary sites, respectively. The n‐character of ZnO oxide makes possible the appearance of the ferrous state in the corresponding Mössbauer spectra.
Asymmetry of the EPR absorption line in CdF2 with Y
Authors: Wilamowski Z. , Oczkiewicz B. , Kacman P. , Blinowski J.
Published: July 2007

An EPR absorption in CdF2:Y is investigated as a function of temperature. The shape of the observed derivative absorption line, which is symmetric at low T, becomes asymmetric at higher. The theoretical model of the line‐asymmetrydependence on the sample dimensions and conductivity shows a non‐monotonic behaviour of the line asymmetry ratio A/B in theregion where the skin depth is comparable to the sample thickness, in agreement with the experimental data.
Boundary conditions at multichannel specular reflection of the conduction electrons on the surface
Authors: Ustinov V. V. , Khusainov D. Z.
Published: July 2007

A rigorous derivation of the boundary conditions for the quasiclassical distribution functiondescribing the multichannel reflection of the conduction electrons from the perfect surface of the ideal crystal is made by considering the equation of motion of the one‐electron density matrix. A generalization of the results obtained is given for the case of incoherent scattering of the charge carriers by the nonideal surface.
Effect of non‐locality in the calculation on liquid metal resistivity of transition metals
Authors: Oli B. A. , Ononiwu J. S.
Published: July 2007

The influence of non‐locality of pseudopotentials on liquid metal resistivity of transition metals is investigated. A simple first order approximation is used to evaluate this influence of non‐locality and calculations are carried out for a few transition metals. The agreement obtained between theory and experiment is good showing that local approximations are not adequate for the calculation of liquid metal resistivity of non‐simple metals.
The electrical properties of rapidly quenched CuNi alloys
Authors: Rossiter P. L. , Mair R. H.
Published: July 2007

A series of CuNi alloys containing 10, 20, and 30 at% were rapidly quenched by melt spinning. This results in an unusual atomic and magnetic structure which is sensitive to the thermal and magnetic history of a specimen. An explanation of the changes in electrical resistance and magnetic susceptibility which result from a variety of heat and thermo‐magnetic treatments is given in terms of Ni clusters possibly associated with sub‐surface segregation effects and spin enhancement of the surrounding matrix.
Improvement of debye‐hückel evaluation of free carrier screening effects in semiconductors
Authors: Farvacque J. L.
Published: July 2007

Most of the applications of the “energy loss” method for free carrier mobility calculations are based on Debye‐Hückel approximation for the evaluation of the free carrier screening properties. However, it is well known that, indeed, this approximation is fully available in a relatively high temperature range. The aim of this paper is to estimate, from Lindhard's dielectric function and in the effective mass approach some corrective terms which allow us to improve this approximation and consequently to extend the range of applicability of mobility calculations by the “energy loss” method.
Temperature and thickness dependence of electrical and thermal transport coefficients of Bi1–xSbx films in an anisotropic, non‐degenerate two‐band model
Authors: Völklein F. , Kessler E.
Published: July 2007

The thickness and temperature dependences of electrical and thermal transport coefficients (e.g. electrical conductivity, thermoelectric power, thermal conductivity) of Bi1–xSbx films are described by a non‐degenerated two‐band model, considering the anisotropic elliptical band structure (many‐valley model) of bulk Bi1–xSbx. The transport coefficients are measured in the temperature range 80 to 400 K on films with thicknesses 20 to 400 nm and the results are interpreted and discussed using the deduced relations.
AC transport in short n+nn+ layers
Authors: Sinkkonen J. , Eränen S.
Published: July 2007

The admittance of n+nn+ semiconductor structures is studied by solving self‐consistently the Poisson equation, the continuity equation, and the linearized Boltzmann equation in the relaxation time approximation for a spatially inhomogeneous electron system. Exact numerical results and an approximate, analytical solution are presented. In addition to the normal bulk admittance and the geometric capacitance of the central n region, the equivalent circuit of the structure consists of contact contributions, the magnitude of which depends on the length of the n region L. At low frequencies the effect of the contacts is to induce a conductance Gc, and a capacitance Cc, in parallel with Gc, in the equivalent circuit. On the other hand, above the plasma frequency of the n region the contact admittance vanishes because of the shunting of the capacitive elements.
Experimental study of the influence of lattice vibrations on the suppression effect at room temperature
Authors: Smirnov G. V. , Shvydko Yu. V. , van Bürck U. , Mössbauer R. L.
Published: July 2007

The anomalous transmission of resonant γ‐radiation through a perfect single crystal of 57FeBO3 is studied in the nearly pure nuclear Bragg reflection (330) at room temperature. The direct calibrations of the residual resonance absorption by means of reference absorber and the comparison of the obtained Mössbauer reflection spectra with computer calculations yield the result, that the anomalous transmission of resonant γ‐radiation does not follow the temperature law valid for the anomalous transmission of X‐rays. Evidence is obtained, that lattice vibrations at room temperature do not affect the suppression effect or do this at least much less than they affect the related Borrmann effect.
On the grain boundary segregation of sp‐valence impurities in B.C.C. transition metal
Authors: Masuda‐Jindo K.
Published: July 2007

Grain boundary segregation of sp‐valence impurities in b.c.c. transition metals (α‐Fe) is investigated using a tight‐binding (TB) type electronic theory of s, p, and d‐basis orbitals: Particular attention is paid for Mg, Al, Si, P, S, and Cl impurities at a ∑ = 5 tilt grain boundary in α;‐Fe. Band parameters for host and impurity atoms are determined within Harrison's universal TB scheme and relative electronic energy levels are taken from atomic structure calculations by Herman and Skillman. It is shown that the segregation energy ΔEsegr for sp‐valence impurities is negative (attractive interaction) and exhibits parabolic trend as a function of the number of electrons Nimp (= Nimps+ +Nimpp) in the sp‐band.
Green function theory of a semi‐infinite ising ferromagnet in a transverse field
Authors: Shiwai B. A. , Cottam M. G.
Published: July 2007

A Green function equation‐of‐motion method is employed to calculate the dynamic properties of a semi‐infinite spin system (or pseudo‐spin system) described by the Ising model in a transverse field. The excitations of the system are shown to be the bulk and surface spin waves, and the Green functions are employed to evaluate their spectral intensities and integrated power factors at temperatures above the transition temperature Tc. Some numerical examples are also included.
Multiple scattering approach to the XANES theory of alkali halide crystals. III. Comparison with the experimental X‐ray spectra
Authors: Gegusin I. I. , Datsyuk V. N. , Novakovich A. A. , Bugaev L. A. , Vedrinskii R. V.
Published: July 2007

The XANES K‐spectra of six alkali halide crystals (LiF, NaF, KF, LiCl, NaCl, KCl) are calculated in the framework of multiple scattering (Green function) cluster approach. The core hole and other potential effects are studied. The 57‐atom cluster predictions that employ the suitable crystalline potential accounting for the core hole effects as it follows from the “atomic relaxation” model, provide satisfactory agreement with the experimental spectra. Generally the core hole influence reveals as the nondramatic redistribution of the oscillator strengths along the spectrum although the striking changes occur in the Li K‐spectra.
The analytical deconvolution technique for the green function recursion expansion
Authors: Gläser U. H. , Rennert P. , Mašek J. , Velický B.
Published: July 2007

The analytical properties of Green functions in the complex energy plane are utilized in an approximative continuation of the Green function from the line Im z = ε towards the real axis. This procedure acts as an effective but incomplete deconvolution for the spectral density. As a result, a well‐resolved but smooth spectrum is obtained even in case where it is exactly represented by a set of delta functions. This property is employed in solving the termination problem of the recursion method, and the applicability of the whole proposed calculational scheme is demonstrated on the LCAO calculation of the electronic density of states in the ordered intermetallic compound TiTc.
Parametrization of electric‐dipole intensities in fN systems due to electron‐correlation effects
Authors: Kaminskii A. A. , Kornienko A. A. , Chertanov M. I.
Published: July 2007

The consideration of transfer processes of an electron from ligand to the trivalent lanthanide ion allows to obtain theeffective dipole‐moment operator containing the terms having complicated tensor structure. Using the second quantization technique as well as the canonical‐transformation method permit to write the expression for the electric‐dipole (4f‐4f)‐transition probabilities in a form, which is convenient for the interpretation of the experimental data. The expression for the transition probabilities contains traditional Ω2, Ω4, and Ω6 parameters as well as four additional D2, D4, L2, and L4 ones being due to the complicated tensorial structure of the electric‐dipole moment operator. The microscopic analysis carried out for the Er3+ ion in LaF3, single crystal shows that one can neglect the terms with L2, and L4 parameters. Using the new parametrization scheme containing five parameters (Ω2, Ω4, Ω6, D2, and D4,) the intensity spectroscopic properties of Pr3+ ions in Bi4Ge3O12, single crystal are non‐contradictorily described, where the hypersensitive inter‐manifold 3II4 → 3F2 transition is taken into account. On the basis of this parametrization scheme the best description of the experimental data as a whole as well as of the hypersensitive inter‐manifold 4I15/12 → 2H11/2, 4G11/2 transitions of Er3+ ions in Y3Al5O12, Lu3AI5O12, and BaYb2F8 single crystals are also obtained.
Localization in a one‐dimensional random potential with spatial correlation
Authors: Kasner M. , Weller W.
Published: July 2007

The role of oscillating vertices usually neglected in the Berezinskii diagram technique is analyzed in connection with a random potential, whose spatial correlation is generated by a Markov chain. It appears that the consideration of some of the oscillating vertices is necessary so that the theory can remark the spatial correlation. Correlation mainly leads to an increase of the localization length in comparison with an uncorrelated potential. However, there is a region of the parameter, where the localization length decreases. The Berezinskii diagram technique is used in a modified form.
A discussion on the “magic number” in Hooge's formula
Authors: Mihg‐Kang Yu
Published: July 2007

An expression of the “magic number” is given in this paper. On the basis of the expression some important experimental phenomena about 1/f noise are reasonably explained.
Metal‐insulator transition and metastable state in high‐purity n‐InSb under high hydrostatic pressure
Authors: Kraak W. , Sschaller U. , Herrmann R.
Published: July 2007

The effect of hydrostatic compression (up to 1.2 × 103 MPa) on the galvanomagnetic properties of pure n‐InSb crystals is investigated. For samples with different excess donor concentrations n = ND – NA ⪅ 1014 cm−3 at T = 4.2 K a pressure‐induced metal–insulator transition is found at a critical pressure p = pc. Furthermore, besides the M‐I transition at high pressures (p > pc) and low temperatures pressure‐induced metastable properties are observed. The experimental data are explained using a model of a particular defect state which is resonant with the conduction band when not occupied (at low pressures p < pc), but which relaxes deep into the gap after capture of an electron (p > pc). From the analysis of the time dependences of the electrical properties the value of the potential barrier EB between the neutral and the ionized configuration of the impurity atom is determined. A rapid decrease of the potential barrier EB for pressures p > pc is found.
A reduced angular momentum expansion in the multiple‐scattering theory
Authors: Fritzsche V. , Rennert P.
Published: July 2007

In order to improve the calculations of ARPES, ARAES, and EXAFS a new approximation in the multiple‐scattering theory for the excited electrons is introduced, which is called reduced angular momentum expansion (RAME). In the RAME the incoming waves are approximated in the range of the scattering potential by a limited set of spherical waves with low angular momenta. This is a much better description than the plane wave approximation in the often used small scattering‐centre approximation. The RAME possesses a high accuracy for energies down to 40 eV and needs a substantially lower numerical effort than the full angular momentum expansion. For higher energies it can be further simplified and it modified small‐scattering‐centre approximation is obtained, which takes into account the curvature of the waves by means of effective scattering amplitudes.
Raman scattering from polaritons and plasmaritons in 6H‐SiC
Authors: Azhnyuk Yu. M. , Artamonov V. V. , Ya. Valakh M. , Litvinchuk A. P.
Published: July 2007

The results of Raman scattering studies of polariton and plasmon‐polariton (plasmariton) excitations in 6H‐SiC are presented. Polariton anisotropy and resonant coupling with one‐ and two‐phonon host lattice vibrations are discussed. The effect of free charge carriers upon the dispersion of polaritons in nitrogen‐doped 6H‐SiC crystals is studied. Good agreement of theoretical calculations with the experimental results is obtained.
Raman spectra of a LiN(HxD1‐x)4SO4 mixed crystal
Authors: Torgashev V. I. , Yuzyuk Yu. I. , Smutný F. , Polomska M.
Published: July 2007

Raman spectra of a deuterated lithium ammonium sulphate single crystal are studied at 77 to 493 K. The results show that the I‐II‐III phase transitions are bonded essentially with the dynamics of Li‐SO4 framework; the NH4‐spectra are of a diffusive character so that no clear‐cut conclusions can be drawn about the role of the NH4‐sublattice in these phase transitions. The spectra corroborate the necessity of using several order parameters in the phenomenological description of the phase transitions in this crystal.
Euler's formulae and sturm's sequence and the stimulating regions for stimulated raman effect in simple piezoelectric cubic crystals
Authors: Schulz V. , Merten L.
Published: July 2007

Stimulated Raman effect in simple piezoelectric cubic crystals only occurs in the so‐called “stimulating regions” of the dispersion curves. It is shown that, if the dispersion equation of the quasiparticle component is of fourth degree in the wave number, the number and position of the “stimulating regions” can be determined by Euler's form of the solutions and by the method of Sturm's sequence.
Pressure‐induced polymorphic phase transitions of potassium and rubidium halides
Authors: Puri U. , Kumar V.
Published: July 2007

Pressure induced phase transitions in potassium and rubidium halides are studied. The screened Coulomb type potential form is used alongwith improved values of van der Waals constants. Parameters of the potential are determined separately for both the structures. The results are in good agreement with experimental values in case of KCl and KBr and show improvement over other theoretical values.
Superionic phase transitions in hydrogen bonded crystals
Authors: Plakida N. M.
Published: July 2007

A microscopic theory of phase transition in the protonic superionic conductors is proposed. By taking into account short‐range proton correlations on hydrogen bonds a order‐disorder Slater‐type phase transition of first order is obtained. Due to the linear coupling between the order parameter and lattice deformation the phase transition is ferroelastic with a soft elastic coefficient C11 ‐ C12.
γ‐Ray induced coloration of KCl:Eu2+ crystals
Authors: Opyrchal H. , Nierzewski K. D. , Macalik B. , Mladenova M.
Published: July 2007

The formation of color centres at RT in γ‐irradiated KCl crystals doped with Eu2+ ions in a wide concentration range is studied by optical absorption, thermoluminescence, and the ITC method. In contrast to the ordinary F‐band behaviour a decrease of the V2‐type band with increasing dopant concentration is observed. The thermoluminescence spectra reveal the presence of two glow peaks positioned at 363 and 453 K independently of the europium concentration. On the basis of the ITC measuremtens it is found that the number of F‐centres formed does not correlate with the number of the europium dipoles destroyed by irradiation for all samples studied. Moreover, optical and thermal bleaching of color centres F‐ and V2‐type is not accompanied by the recovery of europium dipoles. The results obtained are consistent with the previous model ascribing the decay of europium dipoles to a radiation‐induced aggregation process. It is proposed that the disappearance of the V2‐like band with dopant concentration is caused by the strong interaction of the europium clusters formed during irradiation with the halogen interstitials, drastically lowering the pertinent oscillator strength.
Curie temperature of a doped ferromagnetic semiconductor
Authors: Matlak M. , Skrobiś K.
Published: July 2007

On the basis of the s—f model (S = 1/2) a formula for the Curie temperature as a function of band filling and model parameters is derived. Taking the s—f coupling seven times greater as in the real case (S = 7/2) the comparison with experiments on doped EuO and EuS samples gives relative good agreement.

Auf der Grundlage des s—f‐Modells (S = 1/2) wird eine Formel für die Curietemperatur als Funktion der Bandfüllung und Modellparameter entwickelt. Mit einer s—f‐Kopplung, die siebenmal größer als im Realfall ist (S = 7/2) gibt der Vergleich mit Experimenten an dotierten EuO‐ und EuS‐Proben relativ gute Übereinstimmung.
Secondary emission of excitons in CuCl polycrystals
Authors: Mashchenko V. E. , Kharsik V. F. , Brezhneva S. V.
Published: July 2007

Secondary emission (SE) spectra of CuCl platelets and quenched bulk polycrystals, grown from a solution at 4.5 to 200 K, are studied. The low‐temperature SE spectra are caused by the radiative decay of free and bound excitons of the Γ6—Γ8 series. The SE at T ∼ 77 K is due to the annihilation of free excitons of the Z3(Γ6—Γ8) series. The growth of excitation gives rise to considerable increasing the phonon replica intensity (Z3−2LO), which is dominating in a spectrum within the range of excitation rates from 1027 to 1030 cm−3 s−1, when the emission appears to be stimulated one. The translational mass of excitons and the reduced mass of a hole (3.4m0 and 2.9 to 3.0 m0, respectively) are calculated from the line approximation by a Maxwellian contour. The increase of the exciton—phonon coupling constant when introducing imperfections is found experimentally, and the new data obtained are discussed.
Computed X‐ray emission spectra for rhodium under high pressure
Authors: Petrů J.
Published: July 2007

“Ab initio” calculations of the shapes of the X‐ray emission L‐spectra for f.c.c. rhodium are described for ambient pressures up to 65 GPa. The calculations are based on a self‐consistent density‐functional single‐particle electronic structure recently determined by the quadratic‐augmented‐plane‐wave method.
Energy gap, effective mass, and critical phenomena in NaNO2 crystal
Authors: El‐Dib A. M. , Hassan H. F.
Published: July 2007

The effect of thermal expansion on the energy gap of NaNO2 is studied. An attempt is made to estimate the effect of thermal vibrations on the energy gap. The temperature dependence of the effective mass in the conduction and valence bands is also studied. The energy gap shows a non‐linearity near the phase transition region. A sudden change is also observed at about 3 K above Tc. Both the effective masses show some oscillations in a wide range of temperature (from ∼ 140 to ∼220 °C). The results of the energy gap and the effective mass give evidence that a new phase transition exists at about 3 K above Tc. They also give an interpretation for the deviation of the dielectric constant from the Curie‐Weiss law.
Self‐consistent calculation of the electronic structure of n‐inversion layers adjacent to the grain boundary in InSb bicrystals
Authors: Gobsch G. , Paasch G. , Übensee H.
Published: July 2007

Self‐consistent calculations on the quantized electron inversion layer adjacent to the grain boundary in p‐doped InSb bicrystals are performed for the first time. A simple model of the fixed positive charge in the grain boundary is applied. Within a self‐consistent approximation scheme, taking into account the band non‐parabolicity, the band bending and the carrier concentrations in vicinity of the grain boundary are calculated. In addition, the calculation of the complete two‐dimensional subband structure is performed. The results are discussed for a wide range of the total electron inversion density n□ = 1011 to 5 × 1012 cm−2. In case that n□ > 2 × 1011 cm−2 charge self‐consistency is obtained. The theoretical values are compared with experimental ones taken from literature. The quality of the model and of the approximation scheme is demonstrated.
Electronic Structure of a‐SiHx with Arbitrary Hydrogen Concentration
Authors: Wilke S. , Mašek J. , Velický B.
Published: July 2007

The Bethe‐lattice approach is used to describe the electronic structure of a‐SiHx with arbitrary concentration of hydrogen. This is treated as a ternary alloy containing Si atoms, SiH and SiH2 units interconnected randomly, or clustered. The tight‐binding density of states is calculated for representative examples. Beside widening of the band gap, the local effects due to different hydrogen incorporation are obtained and discussed in terms of different degree of localization of H‐Si bonds.
Coherent four‐photon spectroscopy of two‐photon eesonances of trivalent rare‐earth ions
Authors: Yuguryan L. A. , Makhanek A. G.
Published: July 2007

Using wave functions which are transformed in irreducible representations of corresponding point groups of symmetry, an analysis is carried out of the tensor structure of resonance cubic susceptibility. Polarization characteristics are found of a four‐photon parametric process in the conditions of two‐photon resonance between the components of fine structure of trivalent rare‐earth ions in crystals. The number of independent and nonzero tensor components of resonance cubic susceptibility is determined and their number is shown to be much smaller than it follows from the general features of the crystal symmetry. The signs of resonance cubic susceptibility are calculated for concrete two‐photon transitions.
Diffusion of non‐interacting quantum particles in a disordered system the structure of the density matrix and an effective wave number
Authors: Lenk R.
Published: July 2007

Within the muffin‐tin concept arguments are given to determine the local structure of the incident field density matrix including higher angular momentum channels. The anisotropy of the incident field in a current‐carrying state is formulated. The result is employed to calculate the mean current density within a scatterer and to define an effective wave number, especially for an over dense model. In this way the double role of the scatterers as obstacles and conducting entities is taken into account.
Chemical short‐range order in the computer simulated transition metal‐metalloid alloys
Authors: Jezierski A.
Published: July 2007

Different computer simulated models of the structure of transition metal‐metalloid alloys are presented. For each model a local analysis is made and the chemical short range order parameter is calculated. In the models obtained by different algorithms a similar type of chemical ordering is observed.
Generalised morse potential for B.C.C. complex metals
Authors: Singh G. , Rathore R. P. S.
Published: July 2007

A generalised Morse potential with exponential repulsive and attractive components is analysed to derive numerically (i) the second and third order elastic constants, (ii) the pressure derivatives of the second order elastic constants, and (iii) the neighbour‐wise contributions towards (a) the cohesive energy, (b) the interatomic forces, and (c) the second order elastic constants, in body centered metals like zirconium (Zr), tantalum (Ta), and thallium (Tl). The potential is assumed to extend out to the eight neighbour in these metals and thus involve couplings among 112 atoms.
Hellmann‐Feynman forces on and between jellia
Authors: Lehmann D. , Ziesche P.
Published: July 2007

Force and torque on a finite jellium in an external field or near another jellium — defined via changes of the total energy – are according to the Pauli‐Hellmann‐Feynman theorem expressed by the mean electrostatic potential. Force and torque sum rules following from the Ehrenfest theorem and electrostatics are included into the discussion. For cavities similar relations are valid. An example for the interaction of two jellia is the cleavage of a jellium. Special cases are considered. The cleavage force is simply related to the pressure.
Application of molecular models to electronic structure calculations of defects in oxide crystals
Authors: Geisser Christa , Shluger A.
Published: July 2007

Ab initio and INDO methods are applied to investigate the interaction between several SiO2 molecules and for electronic structure calculations of idealized β‐cristobalite within the framework of the cluster model. Stoichiometric fragments are chosen for simulating perfect and imperfect crystal structures of SiO2 by means of combinations of interacting structural units OSiO. The boundary conditions for such clusters are imposed in the form of the electrostatic fields in the rest of the crystal. The results of the electronic structure calculations are only slightly dependent on size and shape of the chosen clusters and agree quite well with experimental data.
Induced magnetic form factors for 3d transition metals and 3d–3d alloys
Authors: Röll H. , Pabst J.
Published: July 2007

It is proved that band structure calculations are required for the theoretical discussion of neutron scattering on magnetic moments induced in crystalline solids. Band structure calculations are done using a linearized APW version. Potentials for transition‐metal alloys in CsCl structure are determined from atomic HFS densities of 3dn/482 configuration with the exchange potential according to Slater. Band structure calculations are done for ScCo, TiFe, VMn, FeCo, and MnNi.
Exciton absorption spectrum (II)
Authors: Sherman A. V.
Published: July 2007

In a previous paper the method of the exact calculation of the Green's function and the absorption spectrum of an exciton interacting with phonons a t zero temperature has been developed. For the basis served an expansion of the Green's function into a continued fraction. The calculation of a large number of the continued fraction elements confronts one with some computational difficulties. Here an approximate method of calculating these elements is suggested, which is applicable for arbitrary parameters of the Hamiltonian and allows one to verify the obtained results in the framework of a unified approach. By making use of this method the absorption spectra of a Frenkel exciton interacting with nonpolar optical phonons are calculated for different parameter sets. The spectra reveal the features of both, the limiting cases of nearly free, vibronic, and self‐trapped excitons and the intermediate situations. Direct and indirect band edge cases are considered.
Thermally stimulated depolarization measurements in AsO‐doped potassium halides at different heating rates
Authors: Prakash J.
Published: July 2007

Thermally stimulated depolarization measurements are carried out in AsO‐doped KCl, KBr, and KI lattices at different linear heating rates. It is observed that with the increase in the heating rate, the position of the maximum depolarization current shifts towards higher temperature side alongwith an increase in its peak value. These changes are utilized to evaluate the dielectric relaxtktion parameters. Evaluated parameters are found to be in good agreement with the reported values.
Carrier density in layer structures of microelectronics. A modified local density approximation for semiconductor layers
Authors: Kelber J. , Schnittler Ch.
Published: July 2007

Recently the local density approximation (LDA) was modified for taking into account the influence of one interface barrier in the potential. In this paper a more general modification of the LDA is presented including the influence of two potential steps at plane parallel interfaces. It is shown to be a relatively simple and nevertheless accurate method for calculating the carrier density and other electronic properties of semiconductor layers and heterostructures. The validity of the modified LDA is tested for a simple model potential which can be treated exactly by solving Schrödinger's equation. Very good results are obtained for the electron density down to a layer thickness of about 10 nm. First self‐consistent calculations are presented for an n‐AlGaAs‐GaAs superlattice.
Optical absorption in binary semiconductors containing substitutional impurities
Authors: Chetouane K. , Hugel J. , Parlebas J. C.
Published: July 2007

The optical absorption spectrum of binary semiconductors with substitutional impurities is studied in terms of a one‐electron theory. A previous tight‐binding calculation of the imaginary part ε2(ω) of the dielectric constant in a two‐independent‐band insulator is extended to a general hybridized multiband binary semiconductor as well as to interatomic optical excitations. As in the previous simplified model it is shown that it is still possible to explore the critical points of the host band structure through wave‐vector non‐conserving transitions due to the presence of the impurity. In order to visualize that, a numerical calculation is performed in the case of a binary linear chain of atoms containing one substitutional impurity.