bluuebunny/crossref_metadata_2025 huggingface dataset:
The Exponential Tail of Light Absorption in Disordered Solids
Authors: Szczyrbowski J.
Published: July 2007

The exponential shape of the optical absorption edge tail in disordered solids is discussed. An approximated calculation is made which gives an explicit relation for the steepness parameter in such materials. The model discussed predicts quantitatively the values of the steepness parameter for several amorphous and fine grained polycrystalline solids.
The Electronic Structure of a Hydrogen Impurity in Aluminium I. The Jellium Model
Authors: Craig B. I. , Smith P. V.
Published: July 2007

All attempts to calculate the electronic structure of a proton in a metal have involved the approximation of spherical symmetry. One possible way of including the effects of the crystal field into such calculations is to extend the Grees function method of Gunnarsson and Hjelmberg to treat the non spherical nature of the induced charge density. The aim of the present paper is therefore to establish that this basic approach can yield reliable results for the proton—jellium system and hence provide a means of studying the real metal impurity problem. The actual application of this Grees function technique to a proton interstitial impurity in aluminium is then presented in a forthcoming paper.
Heavy Doping Effects on the Energy Band Structure of n‐Type Crystals
Authors: van Cong H. , Charar S. , Brunet S. , Averous M. , Birman J. L.
Published: July 2007

The density of states, ϱ(E), the penetration of the Fermi level into parabolic conduction bands, En, relative respectively to optical and electrical conduction band edges Ec and E′c, the band‐gap narrowing for the optical energy gap, ΔEg, opt., the physical band‐gap narrowing (ΔEg, elec.), and the effective band‐gap narrowing (ΔEg, eff.) for the electrical energy gap, the “apparent” band‐gap narrowing due to the Fermi‐Dirac statistics effect, ΔEg, F.D., the band‐gap narrowing due to the changes in ϱ(E), Γ + Γ, are investigated for n‐type heavily doped crystals at an arbitrary temperature T, basing on a second‐order Thomas‐Fermi model and on a polaron model. It is suggested, in the n‐type heavily doped silicon at 300 K, that (i) while En is larger than the penetration of Fermi level into the unperturbed conduction band, E, for 5 × 1025 m−3 ≦ n0 ≦ 1026 m−3, En is found to be smaller than E, for n0 ≧ 2 × 1026 m−3, (ii) ΔEg, elec, is significantly larger than ΔEg, opt. because of important band edge shifts caused by the polaron effect, (iii) ΔEg, FD < 0 is much more important than (Γ + Γ), and (iv) ΔEg, eff. is thus smaller than ΔEg, elec., The results of band‐gap narrowings are in good accordance with some existing experimental results, and also compared with those obtained by other theories.
Thermodynamic properties of the s–f model (spin 7/2, atomic limit)
Authors: Matlak M. , Ramakanth A. , Skrobis K.
Published: July 2007

The exact solution of the atomic limit of the s–f model and S = 7/2 is given. The thermodynamic averages 〈n↑〉, 〈Szn↓〉, 〈Szn↑〉, 〈Sz(n↑– n↓)〉, 〈S+a↓+a↑〉 are calculated as functions of temperature and for different values of the average electron occupation numbers N. The validity of the factorization of some correlation functions is investigated. It is found that the factorization is acceptable only for low temperature and small values of N.
Temperature dependence of the thermoelectric power of disordered alloys
Authors: Schiller W. , Richter J.
Published: July 2007

The temperature dependence of the thermoelectric power of strongly disordered alloys is studied describing phonons in alloys by a modified Chen‐Weisz‐Sher model. Within this model the thermopower can be calculated by means of Mott's formula. For the treatment of the disorder problem the coherent potential approximation is used. Numerical results are discussed for different values of alloy concentration, number of electrons, and degree of chemical disorder with respect to experimental observations. The mixing of chemical and thermal disorder can cause strong deviations from the linear temperature variation of the thermopower.
The influence of exchange spin splitting on exciton in Cd1—xMnxTe mixed crystals
Authors: Twardowski A. , Ginter J.
Published: July 2007

The magnetoabsorption of Cd1—xMnx Te is measured for 0.00 ≦ x ≦ 0.10 at temperatures 1.6 to 50 K. A complicated exciton spectra consisting of split ground and excited states are observed. As a result of phenomenological analysis a continuous transition between the spectra of pure CdTe and CdMnTe is found.
Plasmon approach to the band gap of alkali halides
Authors: Kumar Srivastava V.
Published: July 2007

Quantitative order of the band gap of Li, Na, K, and Rb halides is calculated using the plasma oscillation theory of solids. The present method is not limited to binary or ternary compounds but can be used for all the semiconducting and insulating compounds. The calculated values are in excellent agreement with the observed and calculated values of different workers.
On the theory of long‐range electron hopping in polar media
Authors: Kuznetsov A. M. , Ulstrup J.
Published: July 2007

Expressions for the probability of a nonadiabatic electron transfer between a donor‐trap and an acceptor‐trap in a polar medium are obtained. The transition probability is expressed in terms of the zeroth‐order electron densities near the traps. The interaction of the electron with the phonon field is analyzed. A way of definition and calculation of the zeroth‐order electron states with due account for their modulation by the phonon field is suggested. The effects of deviation from the Condon approximation due to the modulation of the electron densities and of the interaction with the phonon field causing the transition are estimated. The effects of this modulation on the kinetic parameters of the transition in the Condon approximation and in the improved Condon approximation are analyzed. It is shown that these effects are rather large for the processes involving solvated, trapped, or weakly bound electrons. The deviations from the Condon approximation should be taken into account for long‐range electron transfer.
Nonhomogeneous kinetics of quasiparticles in steady‐state packet representation
Authors: Ya. Glushko E.
Published: July 2007

The steady‐state packet representation of exciton wave functions (WF) as a basis for nonhomogeneous kinetics description is proposed. The steadiness of the packet system of WF is reached by integration on the small region near the isoenergetic surfaces of excitons, when the packet basis is maked up. The Pauli‐master‐equation for the exciton—phonon system in steady‐state packet representation is considered. The problem of evolution of the nonhomogeneous exciton density matrix to small interactions with phonons is solved.
The cluster investigation of the q‐state potts model
Authors: Zinenko V. I.
Published: July 2007

The thermodynamics of the q‐state Potts model is calculated by the cluster approximation. With two, three, and four particles as the basic cluster the free energy is obtained for any q. It is found that the transition is of the first order for all two‐dimensional and three‐dimensional Potts models. In the case of planar lattices for q = 3 and q = 4 it is found that the critical point approaches the Curie‐Weiss temperature but the discontinuity of the order parameter remains almost equal to that obtained by the mean‐field approximation.
Susceptibility and specific heat of spin glasses in a magnetic field
Authors: Dubey O. N. , Tripathi R. S.
Published: July 2007

The susceptibility and specific heat of spin glasses for an Ising model in the presence of a magnetic field are calculated. Gaussian probability distribution is taken for exchange interaction with positive mean J0. It is shown that the presence of J0 enhances the reduction of susceptibility and specific heat around the freezing temperature.
Interaction of high power CO2 laser radiation with a nonequilibrium carrier system in Ge at low temperatures
Authors: Manenkov A. A. , Mikhailova G. N. , Prokhorov A. M. , Sidorin A. V. , Sokolov S. Yu. , Tikhodeev S. G.
Published: July 2007

CO2‐laser produced damping of electron‐hole drop (EHD) luminescence in Ge at laser intensities of 104 to 5 × 106 W/cm2 is reported. The observed effect is explained to be due to heating of the EHD by 10.6 μm radiation and driving of e‐h plasma by phonon wind generated during absorption and relaxation of hot nonequilibrium carriers.
Autolocalized collective excitations in molecular chains with cubic anharmonicity
Authors: Davydov A. S. , Zolotariuk A. V.
Published: July 2007

The cubic anharmonicity effect on the soliton motion in molecular chains with electron(exciton)—phonon interaction is investigated. This anharmonicity is shown to remove the infinite increase of the soliton energy as the soliton velocity is reaching the longitudinal sound velocity.
Estimation of second‐order Auger recombination in lead chalcogenides
Authors: Ziep O.
Published: July 2007

Three‐electron recombination, LO‐phonon‐assisted Auger recombination; and recombination by two‐plasmon emission are qualitatively discussed by means of q‐ and ω‐dependent inverse dielectric functions in an unitary manner. In case of PbSe‐like semiconductors the effectivity of three‐electron and two‐plasmon recombination is estimated. Whereas two‐plasmon recombination is mostly less effective than Auger recombination it is predicted that three‐electron recombination neglected till now in analysis of recombination dominates at carrier concentrations 1018 to 1019cm−3 as compared to Auger recombination and should be provable experimentally.
Electric field dependent conductivity in amorphous semiconductors
Authors: Kahnt H. , Schirrmeister F.
Published: July 2007

The field dependence of the conductivity is related to the basic properties of the electronic structure in amorphous semiconductors, i.e. charged intrinsic defects with negative effective correlation energy and localized states in the tails at the band edges. The general formalism of the model considers the Poole‐Frenkel effect which causes an increased carrier density and the field dependence of the mobility of carriers moving by hopping among the localized states in the tails at the band edges. Special cases are discussed leading to the various types of field dependence, that have been observed experimentally.
Two‐beam interferometry in the exciton spectroscopy of CdS
Authors: Lisitsa M. P. , Terekhova S. P. , Onishchenko N. A.
Published: July 2007

The independence of the oscillator strength on the thickness of the sample is determined for the exciton transitions in CdS by Rozhdestwenskii method of hooks. Many‐beam interference patterns are obtained. The values of the refractive indexes and of the light group velocity are calculated. The possibility to determine picosecond times of the light flight by this method is established.
Galvanomagnetic effects in semiconductors of p‐Ge type
Authors: Ivashchenko V. M. , Mitin V. V. , Zakhleniuk N. A.
Published: July 2007

It is shown that the rate equations for the light and heavy hole distribution functions in p‐Ge can be solved analytically using the real anisotropic dispersion law since for acoustic lattice scattering the collision terms can be described by the isotropic relaxation time depending only on the energy of holes, which is proved by numerical computations. The even Hall effect, the transverse and longitudinal magnetoresistance (MR) as a function of the current and the magnetic field orientation with respect to the crystallographic axes in non heating electric fields E as well as the transverse γ⊥ and longitudinal γ∥ anisotropy of conductivity arising in the heating fields, and the MR linear in the magnetic field are calculated. The linear MR is determined largely by light holes (without these or with their isotropic spectrum the MR would have the reverse sign for the same direction of the magnetic field). The relative contributions of heavy holes to γ⊥ and γ∥ are nearly half of that in the earlier approximate calculations. The even Hall effect, the longitudial MR, and the anisotropy of the transverse MR are almost entirely due to the anisotropy of the heavy hole dispersion law.
On the problem of electron phase stability
Authors: Maslov V. A. , Naumov I. I. , Panin V. E.
Published: July 2007

In terms of the pseudopotential method the Hume‐Rothery electron phase stability is studied. Unlike the previous studies here the effects related to the nonsphericity of the Fermi surface are taken into account. The numerical calculations are carried out for the CuZn system. It is shown that the theory results in a phase alternation which is observed at rather high temperatures. The conclusion is made that the account of real Fermi surface is in principle necessary in analyzing the electron phase stability.
Recombination luminescence and energy transfer in ionic crystals at XUV excitation by synchrotron radiation
Authors: Elango M. , Pruulmann J. , Zhurakovski A. P.
Published: July 2007

The relative quantum yield spectra of recombination luminescence for MgO, α‐Al2O3, SiO3, and several alkali halide crystals are measured by synchrotron radiation in the photon energy interval 50 to 250 eV. The main feature of the spectra of oxides is a suppression of the volume luminescence due to surface losses of electrons and holes. For alkali halides surface as well as volume recombination luminescence take place. The more intensive the surface luminescence is the larger the absorption coefficient for exciting photons. The quantum yield spectra may be interpreted quantitatively on the basis of the hot carrier diffusion theory, the diffusion lengths being 2200 Å for MgO, 1500 Å for α‐Al2O3, and 300 Å for SiO2.
Phonon dispersion in the perovskite‐type layer material K2ZnF4
Authors: Rauh H. , Geick R. , Lehner N. , Bouillot J. , Eckold G.
Published: July 2007

The perovskite‐type layered crystal K2ZnF4 is built up from the same structural units as the perovskite KZnF3, namely ZnF6 octahedra which have almost the same dimensions in both the materials. While the lattice dynamics has been studied in detail for the perovskites, in this investigation the first measurement of the phonon dispersion curves of K2ZnF4 is presented as an example for a perovskite‐type layer material with the K2NiF4 structure. By comparing corresponding phonon modes in the perovskite and the layer structure it is found that the interatomic forces within the octahedra do not change with the crystalline environment.
Current density near the semiconductor‐insulator interface
Authors: Paasch G.
Published: July 2007

A modified local density approximation which takes into account that the wave functions are zero at the semiconductor‐insulator interface is used to investigate the influence of this behaviour of the wave function on the mobility. The result follows from a generalization of the classical transport description. It is shown that the decrease of the mobility due to surface scattering is reduced by the influence of the wave functions. In addition a modification of the expression for the diffusion current connected with the influence of the wave functions is given.
γ‐magnetic resonance in the presence of electronic spin relaxation
Authors: Mitin A. V. , Polyakov N. V.
Published: July 2007

The theory of γ‐magnetic resonance (GMR) in paramagnetic crystals in the presence of electronic spin relaxation is discussed. A general expression for the GMR lineshapes applicable to the spectrum with or without quadrupole interactions is derived. The theory is applied to the calculation of the GMR lineshapes for an 57Fe nucleus for different values of the electronic relaxation rate. The results obtained can be used to investigate the dynamics of the electronic‐nuclear system.
Solitons and proton motion in ice‐like structures
Authors: Antonchenko V. Ya. , Davydov A. S. , Zolotariuk A. V.
Published: July 2007

The proton motion in hydrogen bonded quasi‐one‐dimensional molecular chains is investigated It is shown that elementary processes in one‐dimensional ice lattice are nonlinear autolocalized collective exitations which can spread over macroscopic distances retaining the energy, momentum, and charge. The results obtained can be used to explain some phenomena in biological systems.
Relation of recombination radiation spectra to the concentration of structure defects in CdS single crystals
Authors: Brodin M. S. , Davydova N. A. , Shablii I. Yu.
Published: July 2007

It is shown that the interaction of the ruby laser radiation with a CdS single crystal leads to the formation of structure defects (largely of donor type) in a thin subsurface layer, essentially influencing the optical properties of the crystal. In particular, at low concentrations of the donors formed the radiative recombination spectra at 4.2 K exhibit a redistribution of the emission intensity in the group of lines of bound excitons whereas at higher concentrations new emission bands, 4875 and 4880 Å, appear. From the data obtained the former line is interpreted in terms of an optical transition involving donor centres and the valence band, and the latter is attributed to band‐to‐band recombination.
Raman scattering in K2SO4 at high temperatures
Authors: Ishigame M. , Yamashita S.
Published: July 2007

Temperature dependence of Raman spectra of K2SO4 is measured in the temperature region from 300 to 1173 K. A remarkable change of the Raman frequencies is not observed through the phase transition temperature Tc. Most of the Raman spectra measured above Tc can be explained by the vibrational modes of the K2SO4 crystal with space group D. From the spectra of internal modes, however, it is suggested that a correlation between directions of two SO ions in unit cell will exist locally in K2SO4 crystal above Tc.
Investigation of Oguchi's procedure applied to the ising model
Authors: Ferreira J. R. Faleiro , Silva N. P.
Published: July 2007

Approximate critical temperature of the anisotropic ferromagnetic Ising model is calculated using the procedure proposed by Oguchi, with better results than those obtained by the use of Bogolyubov's principle. The calculation is made with linear and double chain trial Hamiltonians.
Theory of intrinsic recombination at zero temperature in small gap semiconductors
Authors: Mocker M. , Beiler Marion
Published: July 2007

A theory of intrinsic recombination at zero temperature is developed. Numerical results in a wide range of excitation and doping concentrations are given for a model adapted to PbS0.1Se0.9. In order that first‐order Auger recombination is possible a minimum value of majority carrier concentration has to be reached. Consequently, a finite small signal lifetime only exists if doping concentration ND > N D min, where for PbS0.1Se0.9 N D min ≈ 4.5 × 1018 cm−3 in case of parabolic model and N Dmin ≈ 9 × 1019 cm−3 in case of Kane model of band structure. Radiative recombination rate only depends on minority carrier concentration p. At strong excitation the radiative lifetime behaves like p−213 in parabolic and like p−113 in Kane band approximation. Quantum efficiency η of radiative processes in dependence on ND decreases steplike near N D ≈ N D min.
Effect of three‐body forces on thermophysical and anharmonic properties of rare gas solid mixtures
Authors: Singh R. K. , Neb D. K. , Sanyal S. P.
Published: July 2007

The effects of three‐body forces on the thermophysical and anharmonic properties of rare gas solid (RGS) mixtures are investigated using the virtual crystal approximation and an interatomic potential consisting of the long‐range van der Waals dipole–dipole interaction and three‐body forces, the short‐range Born‐Mayer type overlap repulsion, and the zero‐point energy. The agreement between experimental and our theoretical results of various properties of the host RGS is, generally, better than obtained by most earlier workers. The results on RGS mixtures follow systematic trends identical to those of diatomic solid mixtures but reliance in them will be deferred until the report of the corresponding measured data.
Phonon transmission theory of heat transfer through solid–gas interfaces
Authors: Dharmadurai G.
Published: July 2007

The heat flow is investigated from a hot solid into a gaseous medium using the phonon transmission theory. This basic approach correctly predicts the essential features of the temperature jump occurring at solid–gas interfaces during heat flow across the boundary and the predictions agree well with recent measurements of heat transfer between microspheres of UO2 in helium and nitrogen atmospheres. The results suggest that the medium–medium acoustic mismatch dominates the heat transfer through these interfaces.
Perturbation‐theoretical model calculation of the lattice mechanics of low polarisability ionic crystals
Authors: Bose D. , Ghosh A. , Basu A. N.
Published: July 2007

Starting from the Hartree‐Fock wave functions of free ions different lattice mechanical properties of a low‐polarisability ionic solid, namely, the RbF crystal are calculated within the framework of the perturbation‐theoretical‐model approach of ionic solids developed by Basu and Sengupta. In a recent investigation it is shown that the dipolar polarisation in an ionic solid may be additively decomposed into three parts, two short range polarisation effects and a long range one apart from the displacement polarisation. From an analysis of the Szigeti relations it is found that both the short range polarisation effects in the low polarisability ionic crystals are small compared to those in high polarisability crystals. This fact leads to a major simplification in calculation for this group of solids. The overall agreement obtained broadly justifies the approximations. Since no crystal property is used to obtain the parameters the discrepancies clearly indicate the regions where the omitted interactions are important. Finally a critical analysis of the results is presented and the difficulties of the existing phenomenological models for these solids are also discussed.
Influence of the orientation of anisotropic impurity–vacancy complexes upon dislocation charging in NaCl crystals
Authors: Andronikashvili E. L. , Galustashvili M. V.
Published: July 2007

Electrical effects are investigated observed during charged dislocation motion in NaCl crystals containing impurity–vacancy dipoles oriented in an electric field (E = 12 kV/cm). It is shown that the efficiency of dislocation charging, i.e. vacancy absorption from the dipole by the dislocation, depends on the mutual orientation of the dipole and the moving dislocation. The data obtained can be explained within a model taking into account both the elastic dislocation–dipole interaction and the electrostatic interaction of the dipole components of opposite charges.
Optical phonons and structure of TlGaS2, TlGaSe2, and TlInS2 layer single crystals
Authors: Gasanly N. M. , Goncharov A. F. , Melnik N. N. , Ragimov A. S. , Tagirov V. I.
Published: July 2007

The polarization properties of bands in Raman scattering and IR reflection spectra are studied experimentally in TlGaS2, TlGaSe2, and TlInS2 layer single crystals and in solid solutions based on them. Additionally the angular dependence of IR‐active modes on the angle between the phonon wave vector and the direction of the optical axis c of single crystals is investigated. It is shown that the observed phonon spectra can be interpreted on the basis of a primitive cell which contains two tetragonal‐symmetry layers bonded to each other by an inversion operation. Bands corresponding to cells with a mixed composition are observed in the Raman spectra of the solid solutions.
Parametric generation of submillimeter radiation in semiconductors in the field of a bichromatic pulse
Authors: Avetissian S. K. , Kazarian E. M. , Melikian A. O. , Minasian H. R.
Published: July 2007

The self‐consistent problem of the interaction of three collinear laser pulses with frequencies ω1, ω2, ω3, propagating in a semiconductor, is discussed. The quasi‐energy spectrum of the semiconductor is determined for the excitation frequencies ω1, ω2 ⪆ Eg/ħ, where Eg is the forbidden band width, and ω3 = ω2 – ω1 ≪ Eg/ħ. The problem of resonance parametric generation of the difference frequency ω3 is considered on the basis of an exact expression for the semiconductor polarization. The possibility of submillimeter radiation generation in semiconductors with Eg ≈ ≈ 0.1 eV is shown. The efficiency of a conversion of the corresponding process is determined.
Quadrupole splitting of hydrogen‐like atom levels in crystals
Authors: Baryshevskii V. G. , Kuten S. A. , Rapoport V. I.
Published: July 2007

The theory of the behaviour of a hydrogen‐like impurity atom with quadrupole moment in a crystal is presented. It is shown that available EPR data on atomic hydrogen trapped in crystalline SiO2 testify to the fact that it has an electric quadrupole moment. Another proof is presented of atomic hydrogen and muonium (a light isotope of hydrogen) trapped at the same sites in the α‐quartz lattice.
Phonon lifetime and thermal conductivity in amorphous solids
Authors: Handrich K.
Published: July 2007

After a short discussion of the static structure factor S(κ) in the small angle region and the low‐temperature thermal conductivity χ(T) of amorphous solids, a perturbation theory is developed, which yields the phonon lifetime τκ and the thermal conductivity χ of a weakly and randomly inhomogeneous solid. It is shown that the strong increase of S(κ) for κ ⪅ 10−2 Å−1 leads to τκ ∽ κ and χ ∽ T2 for T ⪅ 1 K. From S(κ) ≈ const. for κ ⪆ 10−2 Å−1 it follows τκ ∽ κ4 (Rayleigh scattering). Thus phonons with wave vectors κ ⪆ 10−2 Å−1 will be strongly scattered and will not contribute to the thermal conductivity. This is the reason for the plateau of χ for T ⪆ 1 K.
Spectrum of magnetization oscillations in a uniaxial ferromagnetic plate
Authors: Bespyatykh Yu. I. , Dikshtein I. E. , Meriakri S. V. , Tarasenko V. V.
Published: July 2007

A theoretical investigation is made for the ground statè of a ferromagnetic plate in the vicinity of the Curie temperature in a normal magnetic field. It is shown that there can exist either a uniform magnetic state, a strip domain structure, or a hexagonal domain lattice depending on the temperature and the magnetic field. The spectrum of magnetization oscillations in each of the possible states is calculated and the stability regions of different phases are determined. The results are generalized for orientational phase transitions in the uniaxial ferromagnetic plate in a oblique magnetic field.
The influence of parameter nonuniformity on the two‐dimensional einstein relation in periodic and non‐periodic semiconductor structures
Authors: Tjapkin D. , Milanović V.
Published: July 2007

Taking into account the fact that the effective mass of carriers is spatial dependent, the expression for the Einstein relation (the diffusion coefficient to mobility ratio) are derived for the two‐dimensional electron gas. The derived expressions are general and do not assume exclusively the parabolic dependence of the carrier energy on the wave vector, as well as the case of the quantum limit. The numerical results are given for GaAs‐AlxGa1−xAs superlattice structure assuming that the dependence of the potential energy is rectangular. The maximum and the minimum are found for D/μ versus Ns which could be explained as a consequence of the spatial dependence of effective mass.
Ionic conductivity of BaFCl
Authors: Somaiah K. , Hari Babu V.
Published: July 2007

The ionic conductivity of undoped and doped BaFCl single crystals is measured. In BaFCl, the measurements are performed parallel and perpendicular to the crystallographic c‐axis. Incorporation of monovalent impurities (Tl, Na) enhances the conductivity while it decreases by doping with trivalent impurities (Gd). The results indicate that BaFCl has anionic conduction via halide ion vacancies and that the thermally generated lattice defects are of Schottky type. The probable mechanism for the conduction process in these crystals is discussed on the basis of structural considerations of the unit cell.
De‐correlation technique for separation of drude parameters from wavelength modulation spectroscopy data
Authors: Burd M. , Stearns R. , Braunstein R.
Published: July 2007

Separation of bound‐ and free‐electron contributionsto the dielectric function is necessary for an accurate analysis of interband transitions. A technique for doing this separation which does not require low energy data is presented. The technique makes use of the fact that the functions which describe the contributions of each part are sufficiently uncorrelated, allowing the construction of a correlation function which uses the Drude effective mass and Drude relaxation time as adjustable parameters. The technique is shown to properly separate a test function and to yield reasonable results from experimental data.
Optical properties of polaritons in thin crystal films
Authors: Myasnikov V. N. , Marisova S. V. , Lipovchenko A. N.
Published: July 2007

The dispersion relation for polaritons in a crystal slab of an arbitrary thickness is derived by the quantum Green function method. The equation is reduced to the classical electrodynamics form with an effective dielectric function depending on the crystal thickness. The energy and the radiation damping of polariton modes in thin anthracene crystals are calculated and compared with the experimental values based on the studies of low‐temperature luminescence and refractive index dispersion.
Inverse dielectric function for a semi‐infinite solid
Authors: Bechstedt F. , Enderlein R. , Reichardt D.
Published: July 2007

An old problem is addressed being the description of the dielectric response of electrons near the surface of an infinite half space to perturbing potentials and external charges. Taking into account spatial dispersion, expressions are derived for the screened potential and the inverse dielectric function within the approximation of specular electron reflection. The expressions generalize former results in a way that spatial symmetries of the problem are properly reflected. The boundary conditions are shown to follow from the definition of the screened potential. The inverse dielectric function obtained in the treatment fulfils the orthogonality relation to the dielectric function and the f‐sum rule.
EPR transitions for ions with S = 3/2 in the presence of small distortions of the cubic crystal field
Authors: Harris E. A. , Tucker J. W.
Published: July 2007

The effect of small distortions from cubic symmetry on the EPR line positions for S = 3/2 is calculated using a perturbative approach for the case where there is a well resolved hyperfine splitting. It is found that for the Ms = −1/2 to Ms = +1/2 transitions, where the line shifts due to these distortions are small compared to the linewidths, the centre of gravity of each line show a pseudo‐cubic angular dependence −9/5 (udβH + Udm) [1 – 5(α21α22 + α22α23 + α23α21)] with ud/Ud = −3g/(11A), and αi the direction cosines of the magnetic field with respect to the cubic axes.
Electronic properties of dilute copper alloys I. theory
Authors: Mertig I. , Mrosan E. , Zeller R. , Dederichs P. H. , Ziesche P.
Published: July 2007

The electronic properties of 4d transition metal impurities and sp impurities of the third, fourth, and fifth rows of the periodic table in a Cu host are calculated self‐consistently. The impurity is embedded in the perfect crystal environment and described by a single perturbed muffin‐tin potential in the KKR‐Green function scheme. The influence of the impurities on the de Haasvan Alphen effect (Dingle temperatures and changes in areas of the Fermi surface) and the residual resistivity are discussed. For the residual resistivity the linearized Boltzmann equation is solved taking into account the full anisotropic band structure of the host.
Quantum tunneling between inequivalent locations small polaron motion
Authors: Riseborough P. S.
Published: July 2007

The rate at which an electron transfers between bound states with differing energies as well as different spatial locations is examined. The coupling to a phonon bath not only serves to provide or dissipate the excess electronic energies involved in the transition, but also dephases the quantum coherence thereby dramatically increasing the time or Poincare reccurence of the system. At high temperatures, the description of a particle at a site is reasonable, and the inter‐site transition rate is calculated. At lower temperatures, when thermally activated phonons are scarce, the description in terms of bonding and antibonding states is more appropriate. For this regime, the rate for transfer between the bonding and antibonding states is calculated.
Impurity band conduction in single crystals of p‐type GaSb
Authors: Chaudhuri K. D. , Malik Anita , Kukreti Sunita , Mathur P. C.
Published: July 2007

Measurements of the Hall coefficient, dc conductivity at low and moderate electric fields, and magnetoresistance are made on heavily doped and compensated GaSb single crystals from liquid helium to room temperature range. The electrical transport in the low temperature region up to about 50 K is found to be mainly due to impurity band conduction by thermally activated hopping. The population of carriers in the impurity band and valence band is calculated from the Hall effect and low field conductivity data. The values of the average hopping distance in the impurity band at various temperatures are calculated from the observed data on high field dc conductivity. The magnetoresistance in the cryogenic temperature range is found to be negative while for temperatures between 40 and 150 K the magnetoresistance though positive shows significant deviation from the square law behaviour. For temperatures above 150 K, ΔQ/Q is found to vary with magnetic field B in accordance with the square law (ΔQ/Q ∼ B2) which is the normal behaviour of free charge carriers.
On the Magnetic Structure of the Intermetallic Compounds Gd2Al And Gd2Au
Authors: Brédimas V. , Papatriantafyllou K. , Gamari‐Seale H.
Published: July 2007

Using the molecular field model to non Bravais lattices the following results are obtained: The sub‐lattices of Gd for the compound Gd2Au in the first ordered state below the paramagnetic state order ferromagnetically while in the Gd2Al compound they possess a helicoidal spin structure. In the ground state, Gd2Au is ferromagnetic and Gd2Al is antiferromagnetic when a quite large number of neighbours is included in the calculation and for a propagation vector k = 0 (ferromagnetic sublattices).
The Microscopic Theory of the Gyration and Electrogyration in Dielectric Crystals
Authors: Stasyuk I. V. , Kotsur S. S.
Published: July 2007

In the framework of a microscopic model general expressions for the components of the gyration and electrogyration tensors for dielectric crystals are obtained. The lattice contributions to the effects and contributions from single ions (or ionic complexes) are separated. The temperature and frequency dependences of the components of the calculated tensors are analyzed.
Electronic Properties of Dilute Copper Alloys II. Residual Resistivity
Authors: Mertig I. , Mrosan E. , Zeller R. , Dederichs P. H.
Published: July 2007

The residual resistivity of 4d transition metal impurities and of sp impurities of the third, fourth, and fifth rows of the periodic system in a Cu host is calculated. The linearized Boltzmann equation is solved using the degenerate kernel technique taking into account the full anisotropic band structure of the host. The results are compared with experimental information and some other theoretical treatments.
Knight Shifts of Protons in Some Rare‐Earth Dihydrides
Authors: Żogal O. J.
Published: July 2007

Proton NMR Knight shifts are measured in the paramagnetic state of RH2 (where R = Pr, Nd, Sm, Gd, and Tb). The data are interpreted in terms of the effective hyperfine field at the proton site, being equal to −16.7 × 104 A/m for the Pr, Nd, Gd, and Tb dihydrides and −7.96 × 104 A/m for SmH2. The temperature dependence of the magnetic susceptibility in SmH2 is also measured. The anomaly observed at 9 K is attributed to antiferromagnetic ordering. Analysis of the susceptibility data indicates that SmH2 is the Sm3+ compound.
Resonant Brillouin Scattering in HgI2 Investigated by Acoustic Domain Injection Method
Authors: Itoh Y. , Hamaguchi C.
Published: July 2007

Resonant Brillouin scattering by the transverse acoustic phonons is investigated for the first time in red HgI2 single crystal at room temperature by using the acoustic domain injection method. The measured results in the spectral region 579 to 800 nm show a non‐dispersive feature at the longer wavelength region and a decrease in the region very close to the fundamental absorption edge. The analysis based on the resonant Brillouin scattering theory and piezobirefringence theory shows excellent agreement with the present observation and predicts a resonant cancellation of the scattering cross section at 574 nm.
Application of CPA to the Magnon Hamiltonian
Authors: Jezierski A.
Published: July 2007

The coherent potential approximation is applied to the effective magnon Hamiltonian. The magnon creation operator is defined in this method for the average medium. The average exchange spin wave stiffness constant is calculated and the expression is given for the magnon scattering contribution to the stiffness constant. The method of calculation of the magnon energy in disordered alloys presented in this paper gives the same result as the method based on the dynamical transverse susceptibility.
The Dynamical Electron–Phonon Mode Coupling in Jahn‐Teller Crystals with Antiferroelastic Ordering
Authors: Kaplan M. D.
Published: July 2007

The dispersion equation for the coupled electron‐phonon modes, active in the antiferrodistortion ferroelectric phase transition, is obtained by the Green function method. It is shown, that in this case the odd (at T > Tc) quasielectronic branch is the soft mode, which gives a principal contribution to the dielectric anomalies of the crystal. The acoustic property anomalies of the system are due to the interaction of the acoustic mode with the even electronic mode, which is also soft, but is non‐vanishing at T = Tc. The characteristics of the dynamical coupling of the odd electronic mode with the acoustic mode are discussed in the long wave approximation.
On the Electrical Conductivity of Disordered Alloys in the Muffin‐Tin Model
Authors: Schwartz L. , Paja A.
Published: July 2007

A formula for the electrical conductivity of a disordered substitutional binary alloy in the muffintin model is given. The non‐vanishing vertex correction gives rise to an additional term. A simple expression for the transport relaxation time is also obtained.
Model Potential Calculation of Phonon Dispersion in Tb and Ho
Authors: Upadhyaya J. C. , Sharma M. L.
Published: July 2007

The nonlocality of the rare earth metal model potential (REMMP) of Upadhyaya and Animalu is considered in the full modified scheme of Eschrig and Wonn to study the lattice dynamics of Tb and Ho. The computed phonon dispersion curves are raised by 10 to 15% when compared to those of the former authors. Next a parameter is suitably adjusted in order to have a reasonable fit with the experimental data. The scheme of Eschrig and Wonn considers only the first order E‐ and (k q)‐dependent terms in the Taylor expansion of the form factor. In the present work the expansion is truncated at the second order and an expression for the energy wave number characteristic, containing additional terms corresponding to E‐, (k q)‐ and mixed dependence, is deduced. When the phonon frequencies of Tb are calculated by including the second order terms, a substantial effect is found. The calculation of phonon frequencies, using nonlocal parameters evaluated from the basic data, is suggested.
The Internal Soft‐Mode Phase Transition in Solid Biphenyl
Authors: Plakida N. M. , Belushkin A. V. , Natkaniec I. , Wasiutyńki T.
Published: July 2007

The phonon dispersion curves in solid biphenyl are calculated. It is shown that the commensurate‐incommensurate phase transition is induced by mixing of anharmonic molecular torsion and acoustic phonons. The parameters of the anharmonic potential for torsion vibrations and temperature dependence of the soft mode are obtained.
Some Extensions of the Shell Model of Ionic Crystals
Authors: Regiński K.
Published: July 2007

A model of an ionic crystal is constructed ab initio in terms of moving charged particles interacting mutually with an electromagnetic field. On the basis of the model the equations of motion of the crystal are derived by means of the Lagrangian formalism. Special attention is given to a precise description of interactions between polarizable ions and the electromagnetic field. Retardation of electromagnetic interactions as well as the existence of an external electromagnetic field are taken into account. The system of equations obtained seems to be convenient for an analysis of electromagneto‐optical processes in ionic crystals.
A Method for the Evaluation of Dielectric Relaxation Parameters in Electronic Excited State
Authors: Prakash J. , Rahul
Published: July 2007

A method is suggested to evaluate the dielectric relaxation parameters of impurity‐vacancy dipoles in the electronic excited state (ees). The value of the maximum increase observed during the photo‐induced polarization measurements helps in evaluating the dielectric relaxation parameters in ees. Relevant expressions are developed and discussed. The activation energy and fundamental relaxation time in ees in KI:S− − are found to be smaller than their corresponding values in the electronic ground state (egs), whereas the activation energy in ees in KI:Se− − is found to be greater than that observed in egs. In both these cases the product of activation energy and fundamental relaxation time in ees is found to be less than its corresponding value in egs.
The Activation Energy of Phosphorus Donors in Silicon‐Rich Silicon–Germanium Alloys
Authors: Krüssmann R. , Vollmer H. , Labusch R.
Published: July 2007

The activation energy of phosphorus substituted into Si1−xGex alloys (0 ≦ x ≦ 0.27) is investigated by IR absorption. A weak shift of the activation energy with germanium content is found: E(A1) = (45.5 − 26x) meV. This can be explained by multivalley effective mass theory with a phenomenological central cell potential which does not depend on alloy composition within the investigated range. The experiments show that P atoms are distributed at random in the alloy and that their positions are uncorrelated to those of the Ge atoms.
Vibrational Behaviour of Mixed Diatomic Crystals AB1−c Cc within the Bethe Lattice
Authors: Kleinert P.
Published: July 2007

The lattice dynamics of a simple Bethe lattice is treated exactly for the single‐defect problem and within the framework of the coherent potential approximation (CPA). There is a critical mass ratio of an impurity for the emergence of localized modes, if the coordination number is greater than two. This simple approach successfully predicts the one‐ and two‐mode behaviour as well as the mixed‐mode behaviour of many III–V and II–VI mixed crystals. The CPA calculation reproduces essential results already obtained by more elaborated theories.
Theory of Electron–Hole Liquid in Doped Semiconductors. Application to GaP
Authors: Rösler M. , Thuselt F. , Zimmermann R.
Published: July 2007

Functional equations for the self‐energy of an electron‐hole plasma in doped semiconductors are derived and specialized to RPA expressions. Numerical calculations are performed for doped GaP. From thermodynamical considerations a theoretical phase diagram is deduced indicating a critical point and immediately below a coexistence region of two plasma phases with finite densities. The RPA results are compared with simple analytical formulas.
Phonon Spectrum of Boron Nitride with Wurtzite Structure
Authors: Sokolovskii T. D.
Published: July 2007

Using the quantum mechanics methods the interatomic force constants for the rigid‐ion model of boron nitride with wurtzite structure are calculated. An analysis of the symmetry of the fundamental vibrations of the lattice is performed by construction of the projection operators. The calculations of the phonon dispersion relations along seven directions of high symmetry of this lattice are carried out in the harmonic approximation. In terms of this model the phonon state density and the specific heat temperature dependence are determined for boron nitride with wurtzite structure, the results being in good agreement with the experimental data on the specific heat.
Radiation at Planar Channeling of Relativistic Electrons in Thick Crystals
Authors: Baier V. N. , Katkov V. M. , Strakhovenko V. M.
Published: July 2007

The distribution kinetics with respect to the transverse energy at electron channeling is discussed. The asymptotic expressions for the radiation intensity into a given collimator at electron channeling in thick crystals are derived. An optimal thickness at which the radiation output is maximal is found. The spectral distribution of the radiation intensity is analysed for the case of a single diamond crystal.
Valence Fluctuations and Magnetic‐Nonmagnetic Transitions in a Model for Intermediate‐Valence Systems
Authors: Sharma H. V. , Singh I.
Published: July 2007

The magnetic properties of the mixed‐valence systems are studied using the Anderson lattice model, including an intersite exchange interaction. It is found that (i) the ferromagnetic ordering is favoured in the nearly integral‐valent case and (ii) in the intermediate‐valence case the ratio of exchange to hybridisation dictates the absence or presence of magnetic ordering. The magnetic phase diagram and the variation of magnetic moment with exchange and temperature is investigated and also the static magnetic susceptibility and specific heat in the paramagnetic phase. Fairly good qualitative agreement with the experimental findings is obtained.
Magneto‐Resistance of a Semiconductor with the Dislocation Wall in the Quantum Limit
Authors: Kechechyan K. O. , Kirakosyan A. A.
Published: July 2007

By the use of the “energy loss” method the longitudinal and the transverse magneto‐resistances of a semiconductor at magnetic field orientations, normal to and along the wall of edge dislocations are calculated. The dependences of the magneto‐resistance on temperature, the charge carrier concentration, the magnetic field, and the interdislocation distance in the wall are obtained. In particular it is shown that there is a maximum in magneto‐resistance versus interdislocation distance dependence, the location of which depends on the values of the rest of parameters.
Cobalt Centres in Ammonium Chloride: Optical Absorption Studies
Authors: Rambabu B. , Ramasastry C. , Chowdari B. V. R.
Published: July 2007

The optical absorption data for Co2+ ions in NH4Cl single crystals grown under different conditions and measured in the temperature range of 300 to 10 K are presented. The observed absorption spectrum is interpreted by considering the absorption within the crystal field levels determined mainly by the ligands of octahedral coordination. The spectrum at low temperatures is considered to be due to two different centres in which Co2+ ion occupies an interstitial position, i.e. the centre of a square of four Cl− ions with either two NH3 ions or H2O ions on either side of the square. In addition to these, the stabilization of a centre in which a Co2+ ion occupies an edge centre position at room temperature is also suggested. The crystal field parameters for the cobalt centres stable at low temperature are evaluated.
On the Chemical Shifts of the K‐Absorption Discontinuity of Copper in Some of Its Systems
Authors: Rao B. Jagannatha , Chetal A. R.
Published: July 2007

The K‐absorption edge of copper in different copper systems is studied using a 40 cm Cauchoistype bent crystal spectrograph. It is observed that the K‐edge shifts towards the high‐energy side in all the copper systems under study (except in Cu2O). This indicates that the copper ion behaves as a cation (except in Cu2O). The shift is correlated with the partial charge on an absorbing ion in the system and the correlation is found to be linear. The partial charge on the copper ion in the systems chalcopyrite, copper perchlorate, and copper fluoborate is determined from the plot of the chemical shift versus the partial charge.