bluuebunny/crossref_metadata_2025_split huggingface dataset:
On the Role of the Coulomb Interaction of Charge Carriers in the Electronic Raman Scattering on Donor Levels in Direct Band Gap Semiconductors
Authors: An Nguyen Ba , Van Hieu Nguyen , Thang Nguyen Toan , Viet Nguyen Ai 
Published: July 2007

AbstractThe electronic Raman scattering of light on the donor levels in the semiconductors with direct band gap is revised, taking into account approximately the Coulomb interaction between the charge carriers (conduction electron and hole). Except for the scattering in the resonance energy domain, where the polariton effect is essential, the influence of the Coulomb interaction of the charge carriers on the scattering cross section is not significant.
Towards a Molecular Theory of the Solid–Liquid Phase Boundary
Authors: Klupsch Th. 
Published: July 2007

AbstractA rigorous statistical description of the interface formed by the coexisting liquid and f.c.c. crystal‐line phase of an one‐component Lennard‐Jones system at thermal equilibrium is presented taking into account the aspect of structural change. Based on correlation functions resulting from the coupled Ornstein‐Zernike and Percus‐Yevick equations for inhomogeneous systems, the one particle distribution function is found from minimization a free energy functional. For temperatures kT/ε = 0.752 slight above the triple point, the calculated mean free interface energy (continuum approximation) is ΔJ σ2ε−1 = 0.96 and the interface width l = 3.6σ which is comparable with computer simulation results, but not with lattice models.
Non‐Condon Approximations and the Static Approach in the Theory of Non‐Radiative Multiphonon Transitions
Authors: Gutsche E. 
Published: July 2007

AbstractThe off‐diagonal matrix element of the non‐adiabaticity operator, on which usually the theory of non‐radiative multiphonon transitions is based, is recast into a form much more convenient for the calculation of the transition probability W in non‐Condon approximation. This is demonstrated first for a two‐level system coupled to a single vibrational mode and then extended to the more general case of a complete set of non‐degenerate electronic states coupled linearly to N normal modes. The strong anharmonicity of the adiabatic potentials due to the mixture of states caused by the electron–phonon interaction operator is stressed, which limits the applicability of the theory to situations where only transitions well below “level crossing” are important, and, consequently, imposes serious restrictions on the parameters of the system and the temperature. Keeping to these restraints and to two electronic levels, the transformed matrix element of the non‐adiabaticity operator is identical with that of the perturbation operator used in the static coupling scheme of Haug and Pässler, which turns out in this way to be equivalent to a closed‐form of non‐Condon approximation based on a well defined set of adiabatic wave functions. Explicit expressions for W are also given, and some aspects of the theory in general are discussed.
The Influence of Compositional Disorder on Electrical and Optical Properties of ZnSxSe1−x Single Crystals
Authors: Mach R. , Flögel P. , Suslina L. G. , Areshkin A. G. , Maege J. , Voigt G. 
Published: July 2007

AbstractThe influence of compositional disorder in mixed crystals on the electrical and luminescence properties of ZnSxSe1−x single crystals grown by iodine transport are investigated by measuring the spectral distribution of photoluminescence, the excitonic reflection spectra, and the temperature dependence of free‐carrier concentration and mobility. Obviously there are effects describable in a virtual crystal approximation (VCA) as the dependence upon composition x of donor (iodine) depth and a net shift of the self‐activated (SA) luminescence. Beyond VCA the fluctuations of composition result in a broadening of excitonic spectra as expected for extended wave functions or resolvable spectral shifts (subbands) of the SA luminescence as expected for highly localized states, corresponding to the well‐defined varieties of nearest‐neighbour compositional configurations. There are indications that the abundances of the latter are not statistical.
Effect of Heavy Doping on the Electronic Heat Capacity in Semiconductors
Authors: Chakravarti A. N. , Ghatak K. P. , Ghosh S. , Chowdhury A. K. 
Published: July 2007

AbstractAn attempt is made to derive an expression for the electronic heat capacity in heavily‐doped semiconductors having Gaussian band‐tails. With the help of this expression, the electronic heat capacity is studied as a function of the electron concentration corresponding to different temperatures, taking heavily‐doped n‐GaAs having Gaussian band‐tails as an example. It is concluded that the nature of the dependence is determined exclusively by the movement of the Fermi level with changing electron concentration through the allowed energy states.
Electrical Properties of InSb Irradiated with Fast Neutrons
Authors: Baramidze N. V. , Bonch‐Bruevich V. L. , Giorgadze M. P. , Kurdiani N. I. 
Published: July 2007

AbstractVariations are studied of the electrical properties of n‐ and p‐InSb induced by fast neutron irradiation (fluences from 1 × 1017 to 8 × 1019 n/m2). Temperature dependences of the concentration and mobility of the charge carriers is studied by the Hall effect method in the temperature range from 77 to 300 K — both before and after irradiation. Parameters of a random field produced by disordered regions are calculated. Charge carrier scattering by a smooth random field created by disordered regions seems to be the dominant scattering mechanism after irradiation.
Fermi Surfaces in NbcMo1−c Random Alloys
Authors: Donato E. , Ginatempo B. , Giuliano E. S. , Ruggeri E. , Stancanelli A. 
Published: July 2007

AbstractWithin the KKR‐CPA framework the Bloch spectral function of some NbcMo1−c alloys are computed. By looking at the results for E = EF the topology of the Fermi surface is studied as function of concentration. The results are in agreement with experimental indications given by the measurements on elastic constants in such alloys. The calculations confirm that a rigid band model for these systems can explain the observed properties at the Fermi level.
Luminescence Spectra of Anthracene Crystals at 0.4 K
Authors: Aaviksoo J. , Liidja G. , Saari P. 
Published: July 2007

AbstractFor the first time the luminescence of a molecular crystal is studied at sub‐Kelvin temperatures. Despite the fact that at ultralow temperatures the number of phonons in the crystal is negligible the bandshapes in spectra do not exhibit any pronounced “bottle‐neck” features that follow from the polariton picture. In order to explain the experimental results strong coupling of excitons with intramolecular vibrations in anthracene is taken into account.
Force Constant Change in Sn–Impurity Systems: 107Pd:119 Sn, 197Au:119Sn, and 63.5Cu:119Sn
Authors: Paul P. , Puri S. P. , Raj D. , Puri R. K. 
Published: July 2007

AbstractThe recoilless fraction f and the SOD data for the Sn as impurity in 107Pd, 197Au, and 63.5Cu are analysed for any force constant change in the framework of Mannheim's model, using the experimentally determined phonon frequency distribution function for the hosts. Furthermore, correction for anharmonicity is applied, wherever necessary. On the basis of f‐values, the force constant ratio λ′/λ turns out to be 0.46 ± 0.02, 0.86 ± 0.04, and 0.58 ± 0.03, respectively, for the systems 107Pd:119Sn, 197Au:119Sn, and 63.5Cu:119Sn. All these cases are of weak binding. This conclusion is at variance with an earlier report of strong binding for the system 107Pd:119Sn. Expectedly no localized modes are found to exist for either of the systems.
Excitons Perturbed by a Sodium Ion in CsI:Na Crystal
Authors: Kayal A.‐H. , Mori Y. , Rossel J. 
Published: July 2007

AbstractThe emissions around 420 and 370 nm of CsI:Na excited by the UV absorption associated with the Na+ ion are studied by measuring the temperature dependence of decay times, the magnetic circular polarization, and ESR by optical detection. The results suggest that the 420 nm band is due to a localized exciton adjacent to a substitutional Na+ ion. The basic properties of the electronic structure and kinetics of the exciton are obtained. These results are discussed in relation with the self‐trapped excitons in CsI.
Local Density Approximation Applied to Bound Excitons in Polar Semiconductors
Authors: Haufe A. , Henneberger K. , Röseler J. , Wünsche H.‐J. 
Published: July 2007

AbstractBinding energies of excitons at donors in polar semiconductors are calculated in the frame of the Fröhlich model for the interaction of the particles with LO phonons. Beside the exchange‐correlation parts of the direct particle‐particle interactions, the dynamical effects of the particle‐phonon interactions are also treated within the LDA. For this purpose, a single parametrized formula for the dependence of the corresponding energies of a homogeneous e‐h plasma on the particle densities is used. The numerical results for both, the bound polaron D° and the bound exciton D°X agree with the best available theoretical data as well as with experimental values. From these facts it is concluded that LDA is an appropriate method for treating not only electron–electron interactions but also the electron–phonon interaction in inhomogeneous e‐h systems.
EPR and ENDOR Investigations of an Oxygen Centre in CaF2
Authors: Fuchs H. J. , Karthe W. , Böttcher R. 
Published: July 2007

AbstractA paramagnetic centre is produced in CaF2 by oxygen diffusion and subsequent X‐irradiation. From EPR and ENDOR results it is possible to ascribe C1 symmetry to this centre. The experimental data at measuring temperatures T ≦ 77 K can be fitted well to an oxygen‐fluorine‐vacancy complex. The anisotropy is averaged due to inner motions at room temperature and therefore in the spectra C2v symmetry results.
Energy Bands of Krypton and Xenon with the GOPW Method
Authors: Baroni S. , Grosso G. , Parravicini G. Pastori 
Published: July 2007

AbstractThe Hartree‐Fock band structures of krypton and xenon are calculated from first principles, using the Gaussian orthogonalized plane wave method. This method, which exploits the Gaussian representation of occupied orbitals, allows to include the exchange potential in its nonlocal from. As a side‐product, it is shown that some drawbacks, erroneously attributed to the OPW method, disappear if appropriate care is done in describing core states and the consequent orthogonalization effects.
Electronic Structure of Fe—45Al Films
Authors: Nemoshkalenko V. V. , Lesnik A. G. , Kudryavtsev Yu. V. , Lezhnenko I. V. , Nikolaev L. I. , Voskrekasenko L. S. 
Published: July 2007

AbstractFe−45 Al films of the ordered (OS) and disordered (DS) states are examined with a RSM‐500 spectrometer. Fe Lα1,2, Fe M2,3, and Al L2,3 spectra are obtained. The Al L2,3 spectrum structure is less pronounced in DS than in OS, which may be accounted for by a different degree of symmetry in aluminium atom neighbourhood in DS. The slopes of high‐energy edges for Al L2,3 spectra differ, which indicates higher density of s‐states at Fermi level in OS, as compared to DS. While comparing the Fe Lα1,2 spectra in DS and OS, an integral intensity increase is observed, narrowing and shift towards low energies. This confirms the previously proposed hypothesis for the electron transition from Al to the iron 3d subband. The X‐ray spectral data correlate with previously obtained data on high‐frequency conductivity.
Cohesive Energies and Bulk Modulus for Alkali Halide Mixed Crystals
Authors: Shanker J. , Jain G. D. 
Published: July 2007

AbstractAn interionic potential model is developed for evaluating the cohesive energies and bulk modulus of alkali halides mixed crystals. The short range overlap repulsive interactions up to second neighbours and the van der Waals interactions are taken into account. The model is applied to study the mixed crystals NaCl‐NaBr, KCl‐KBr, and KBr‐KI for the entire range of composition. The results are discussed and compared with available experimental data.
Induced Magnetism in a System Consisting of van Vleck Ions Coupled to an Electron Gas in the Narrow Band Limit
Authors: Palermo L. , da Silva X. A. 
Published: July 2007

AbstractThe magnetic properties of a model consisting of an electron gas interacting by exchange with van Vleck ions, is studied under the action of a crystal field in the narrow band limit. Iso‐Tc curves (in the plane of the interaction parameters), ionic and electronic magnetizations and susceptibilities versus temperature, as well as the magnetic specific heat, are obtained for several values of exchange and crystal field parameters.
Static Atomic Polarizabilities from Norm‐Conserving Pseudopotentials
Authors: Bachelet G. B. , Tanner C. , Schluter M. 
Published: July 2007

AbstractThe transferability of norm‐conserving pseudopotentials, recently developed by Hamann, Chiang and Schluter is examined by calculating static atomic polarizabilities using Sternheimers procedure. Excellent agreement between full‐core atoms and pseudo‐atoms confirm the high quality of norm‐conserving pseudopotentials.
Theory of Donor–Bound Exciton Complexes in Semiconductors
Authors: Clark T. D. , Bajaj K. K. , Theis W. M. , Phelps D. E. 
Published: July 2007

AbstractThe ground‐state energy of a system consisting of an exciton in the presence of a neutral effective mass donor in semiconductors is calculated for an arbitrary value of the electron to the hole mass ratio using a variational approach. Both, the conduction band and the valence band are assumed to be simple and parabolic. The variational wave function used is a product of a generalized Hylleras‐Ore type wave function for the two electrons and an envelope function which depends on the hole—positive ion distance only. It is shown that the exciton—neutral donor complex is bound for all values of the electron to the hole mass ratio.
Spectra of Rare‐Earth Ions in the Crystal Fields of Double Tungstates and Molybdates
Authors: Malkin B. Z. , Kaminskii A. A. , Agamalyan N. R. , Bumagina L. A. , Butaeva T. I. 
Published: July 2007

AbstractThe Hamiltonian of neodymium and erbium ions in low‐symmetric crystal fields of KLn(MeO4)2 (Me = Mo, W and Ln = Y, Gd, Er, and Lu) crystals is constructed with fifteen crystal field parameters calculated within the framework of the exchange charge model. The theory using only one empirical scaling factor gives a satisfactorial description of Nd3+ and Er3+ ion spectra Stark structure and of its changing in the homologous series of tungstates investigated by absorption and luminescence.
The Luminescence of Broad‐Band Emitters in LiLaP4O12
Authors: Blasse G. , Dirksen G. J. 
Published: July 2007

AbstractThe luminescence of LiLa1−xMxP4O12 (M = Ce3+, Eu3+, Tb3+, Bi3+) is measured. Only for the Ce3+ ion pronounced concentration quenching is observed. The spectra of pairs of activators differ slightly from those of isolated activators. The Bi3+ emission is strongly Stokes shifted and is ascribed to AX emission. The Sb3+ ion shows a very efficient luminescence in this host lattice with an unusually small Stokes shift.
Lattice Mode Anharmonicity in Sodium Nitrite
Authors: Brehat F. , Wyncke B. , El Sherif M. 
Published: July 2007

AbstractThe anharmonicity of the infrared active lattice modes of sodium nitrite is studied from measurements of the infrared reflectivity from 60 to 400 cm−1, in the temperature range 80 to 460 K. The infrared reflectivity spectra are analysed with the four‐parameter dispersion model based on the factorized form of the dielectric function. The comparison between the results of the quantum theory and the dependence observed of damping shows that cubic anharmonicity drives the lattice dynamics of sodium nitrite when the crystal structure is ordered, and that disorder occurs below the phase transition temperature. The results confirm the breakdown of the selection rules in the paraelectric phase and suggest the existence of dielectric dispersion in the low frequency region.
The Temperature Dependence of the Spin Resonance in Boron Doped a‐Si:H
Authors: Overhof H. 
Published: July 2007

AbstractThe temperature dependence of the g = 2.01 ESR line in boron doped a‐Si has recently been studied by the Marburg group. For this line the g‐value, linewidth, and lineshape factor depend both on temperature and doping level. The temperature shift of the g‐value is explained by a model in which the g‐factor depends explicitely on energy and the temperature dependence is a result of the temperature shift of the mean energy of the spins. This model is combined with a density of states distribution recently reported to interpret the de transport data. From this the energy dependence of the g‐factor is obtained and the linewidth ΔH due to g‐value broadening as a function of temperature and doping level is calculated. At elevated temperatures an additional contribution to the linewidth, δHpp(T), is observed and is interpreted by the Marburg group as due to spin relaxation via exchange interaction between the localized spins and rapidly relaxing carriers in extended states. It is shown that long‐ranged potential fluctuations combined with this relaxation mechanism can easily explain both the relation between the dc conductivity σ and δHpp(T) and the rapid rise of the lineshape factor l as δHpp(T) begins to dominate the total linewidth.
Phase Transition of Fröhlich Polarons, in the Feynman Approximation, Subjected to a Magnetic Field
Authors: Peeters F. M. , Devreese J. T. 
Published: July 2007

AbstractIt is shown that the Fröhlich polaron in a magnetic field (calculated in the Feynman approximation) exhibits a first‐order phase transition if the electron‐phonon coupling constant α is larger than 4.2. For α = 4.2 the transition is of second order. The phase transition manifests itself as a discontinuity in the magnetization, the susceptibility, and the polaron mass for a critical value of the magnetic field. It is found that at the transition point the phonon cloud surrounding the polaron cannot follow the electron in its motion in the magnetic field.
Interactions in Non‐Simple F.C.C. Metals
Authors: Agrawal R. M. , Rathore R. P. S. 
Published: July 2007

AbstractFive schemes characterised by the nature of the interactions are developed on the lines of a recent model due to Fielek, which includes the interaction among all the constituents of a non‐simple metal. Equilibrium conditions are derived for each of the schemes. Volume interactions are described on the lines of a simple scheme which explains realistically phonon dispersion in non‐simple metals like palladium and nickel. These schemes are employed to explain cohesion, the Cauchy deviation, anisotropy, and phonon dispersion in the said metals. Overall standard errors of the mean percentage deviation are calculated to draw conclusions regarding the nature of the relevant interactions.
EPR Line Critical Broadening Asymmetry and Shape Peculiarities Due to Dipole‐Dipole Electric Interaction in Ferroelectrics
Authors: Vikhnin V. S. , Borkovskaya Yu. B. 
Published: July 2007

AbstractThe effect of the electric dipole‐dipole interaction by the soft optical phonon field on the EPR line shape in ferroelectrics is studied by means of the line shape statistical theory. The critical dependence of the EPR line broadening and asymmetry is examined. The EPR line shape critical broadening and asymmetry are shown to depend on the soft optical phonon damping. Two mechanisms of the EPR line broadening are considered: i) the dipole electric fields and ii) the spin‐spin cross‐relaxation caused by the electric dipole‐dipole interaction in “soft” matrices. New critical dependences are discovered.
Correction of the Knight Shift for Demagnetizing Effects
Authors: Bakonyi I. , Panissod P. , Tompa K. 
Published: July 2007

AbstractThe NMR line shift contributions originating from demagnetizing fields due to classical macroscopic magnetic effects are discussed for ellipsoidal samples. It is shown that by measuring the line shifts along two main axes of the ellipsoid, the measured difference is sufficient to correct for demagnetizing effects in materials with homogeneous magnetization. It is also found that for special sample geometries even the demagnetizing factors are unnecessary for calculating the demagnetization correction term. Based on line shift and magnetization measurements, the measured and calculated differences of the NMR line positions are compared for sandwich‐type samples. Alloys with inhomogeneous magnetization are also briefly discussed.
Tunneling into Proximity Electrodes with Magnetic Impurities
Authors: Meyer H.‐G. , Seidel P. 
Published: July 2007

AbstractStarting from a model of classical spins a proximity electrode with magnetic impurities in the barrier‐near layer is investigated theoretically. The rising differences to the common McMillan tunneling model (MTM), especially, the impurity band in the former gap region of the density of states provide significant changes in the tunneling properties of such a electrode, for example, in all current amplitudes of the Werthamer theory. Detailed investigations of the current‐voltage characteristic for tunnel junctions with proximity electrodes containing magnetic impurities show enhanced excess currents below the sum jump which are qualitative similar to experimental results on tunnel structures with electrodes of Nb or V.
Resonance Spectrum of Elliptically Polarized Spin Waves in Thin Magnetic Films
Authors: Duda A. 
Published: July 2007

AbstractThe resonance consequences of elliptic spin‐wave polarization are analysed in the general case where both, internal and surface anisotropy contribute independently to the ellipticity. The surface source of ellipticity is found to modify essentially the quantization rule of wave numbers, leading to new effects in the frequency and surface anisotropy dependence of the resonance modes.
The Coherence Description of the Dynamical X‐Ray Diffraction from Randomly Disordered Crystals I. General Formalism
Authors: Holý V. 
Published: July 2007

AbstractThe problem of the incoherent diffraction of X‐ray from randomly disordered crystals is solved by means of the mutual coherence formalism. On the basis of rigorous solving of the Takagi equations by the Green method a formula is found which determines the mutual coherence functions of waves emitted from disordered crystals. The coherence formalism enables to compute easily diffracted intensities and the angular distribution of intensities. The connection is shown between the theory presented and other theories of incoherent diffraction.
Electronic Energy Bands of Nearly Free Electron Metallic Glasses An Application to Mg0.7Zn0.3 Amorphous Alloy
Authors: Sen M. , Chatterjee S. 
Published: July 2007

AbstractA theory of electronic energy bands of nearly free electron like metallic glasses is presented by extending the l‐dependent pseudopotential method of Ziman. First an averaged Green's function is obtained for the substitutional alloy assuming average T‐matrix approximation (ATA). Then this Green's function is again averaged for the topological disorder by a Gaussian distribution of the lattice points in a manner similar to Kramer. The secular determinant obtained from the singularity condition of this doubly averaged Green's function is now complex and hence the energy‐eigenvalues obtained from this secular determinant are also complex. This theory is applied to the nearly free electron like metallic glass Mg0.7Zn0.3. From the complex energy bands the density of states and joint density of states for the optical absorption spectra are obtained as a function of the disorder parameter α. The results show that the Fermi energy falls at the minimum of the density of states for α = 0.05 confirming the observation of Nagel and Tauc. From this density of states the Pauli spin paramagnetic susceptibility is also calculated and the results show a temperature independence of this quantity completely in agreement with the experiment.