bluuebunny/crossref_metadata_2025 huggingface dataset:
Raman scattering in red mercury iodide. New improved polarization spectra
Authors: Prevot B. , Biellmann J.
Published: July 2007

The room temperature Raman spectra of α‐HgI2 are re‐examined using the backscattering configuration on natural crystallographic faces. It is shown that the assignments of the symmetry species involved in the three Raman peaks is strongly dependent on the experimental procedure and that a great care is recommanded in choosing the scattering surface as well as in selecting the scattered radiations. By this method, the 18 cm−1 peak is attributed to a pure Eg‐type symmetry, the 29 cm−1 peak to both Eg and B1g‐type symmetries and the 114 cm−1 structure to mainly A1g and B1g species. These attributions are based on intensity measurements of the lines.
To what extent are the observed lifetimes of F‐centers intrinsic?
Authors: Bosi L. , Nimis M.
Published: July 2007

New measurements, performed at near 65 K, of the F‐center radiative lifetime τR in KBr samples containing α‐ and F'‐centers show a τR‐increase which is related to low and, in some cases, scarcely detectable, critical α‐center concentrations. Analysis of experiments known in literature reveals that a far from negligible quantity of α‐centers is always present in real crystals. These facts lead us to the stimulating hypothesis that the τR‐values might be incorrect because of the perturbation due to the interaction between F‐ and α‐centers.
Optical absorption of the layer antiferromagnet Rb2MnCl4
Authors: Popov E. A. , Kotlyarskii M. M.
Published: July 2007

The optical absorption spectrum of the quasi‐two‐dimensional (2D) antiferromagnet Rb2MnCl4 is investigated in the region of the 6A1g → 4T2g(4D) transition (D group bands). It is found that short‐range magnetic order strongly influences the absorption spectrum at temperatures T > TN. The spin‐flop phase transition is observed in a magnetic field of 56 kOe. Investigation of the Zeeman effect allows to conclude the spectrum in this region to consist of magnon and magnon–phonon sidebands of three different purely excitonic lines.
Random field parameters and pseudopotential
Authors: Bonch‐Bruevich V. L. , Karaivanov V. D. , Proykova Ya. G.
Published: July 2007

Binary correlation functions are considered of the random fields produced by various types of atomic disorder in amorphous, liquid, and glassy semiconductors, both homopolar and heteropolar. Conditions are established under which the field may be considered as smooth, Coulombic or short‐ranged, depending upon the nature of the material. Parameters characterizing random fields in question are expressed explicitly in terms of directly observable material quantities with some numerical estimates included.
Temperature dependence of atomic core levels in solids I. Separation of the temperature dependence of conduction‐band and core‐exciton energies
Authors: Hübner K. , Bechstedt F.
Published: July 2007

For the first time an explicit investigation is made of the T‐dependence of atomic core levels in non‐metallic solids and shown that this dependence can be of the same order as that one of electronic energy bands. The basis for these investigations are models for the chemical and the relaxation shift of core levels, which lead to absolute core‐level energies and their shifts, in agreement with corresponding photoemission data. In the present part of this work the T‐dependence of conduction‐band and core‐exciton energies of GaP, Si, and SiO2 is separated, which is involved in the total T‐dependence of the corresponding core‐level to conduction‐band transitions. In the second part of this work it is shown that multiphonon and hydrostatic processes lead to large and different T‐coefficients of the Si2p level in Si and SiO2, whereas the different contributions to the T‐dependence of the Ga3d level in GaP give an almost vanishing total effect. Furthermore, it is shown that the main contributions to the T‐dependence of atomic core levels in semiconductors and insulators come from the electrostatic interaction of the core electrons with their environment, whereas the T‐dependence of relaxation energies is very small. The results are in agreement with data which are deduced from corresponding experiments performed by Aspnes et al.
Band structure of Hg1−xMnxSe from anomalous shubnikov‐de haas effect
Authors: Takeyama S. , Galązka R. R.
Published: July 2007

A systematic temperature investigation of the Shubnikov‐de Haas effect in Hg1−xMnxSe is reported. Band parameters are determined including exchange parameters which are characteristic for semimagnetic semiconductors and responsible for the anomalous temperature dependence of spin split energy levels. The effective mass is determined from the ShdH amplitude in restricted higher temperature region. The exchange parameters are used as adjustable parameters to fit the observed ShdH peak positions at all measuring temperatures.
The lattice thermal conductivity of aluminium at low temperatures
Authors: Borchi E. , De Gennaro S. , Pelosi G. , Rettori A.
Published: July 2007

Starting from the general theory, the lattice thermal conductivity of Al is evaluated at low temperatures. The calculation is carried out without free parameters using the complete lattice dynamics and the Ashcroft pseudopotential for Al. The results of the calculation are discussed in comparison with available experimental data.
Excition reflection spectra under high‐intensity excitation in CdS and CdSe
Authors: Kuroiwa A. , Saito H. , Shionoya S.
Published: July 2007

Exciton reflection spectra under high‐intensity excitation by a nitrogen laser are studied in CdS and CdSe at 4.2 K. With increasing excitation density, the reflection peak intensity decreases, simultaneously the spectral width becoming broader, and finally the reflection structure becomes very obscure. Shapes of observed spectra are analyzed in terms of the classical oscillator model using a phenomenological damping term. From the comparison of the results of the analysis with luminescence spectra simultaneously measured, it is concluded that the obscurity of the reflection structure is caused by the shortening of the transverse relaxation time of excitons due to the inelastic collision of excitons.
Untersuchungen zum elektrischen widerstand von versetzungen in metallen I. Allgemeine theorie
Authors: Rauh H.
Published: July 2007

Im Rahmen der Einelektronennäherung und des Gültigkeitsbereichs der linearisierten Boltzmann‐Gleichung wird eine allgemeine Theorie für den elektrischen Restwiderstand geradliniger Versetzungen in Metallen gegeben. Sie ist der Translationsinvarianz der betrachteten Kristallfehler angepaßt und gilt sowohl für beliebige Fermi‐Flächen als auch für beliebige elastische Streumechanismen. Die verwendeten Formulierungen des Streu‐ und des Transportproblems führen auf Sätze linearer Gleichungen. Vereinfachungen, die sich aufgrund von Symmetriebeziehungen ergeben, werden diskutiert.
A Contribution to the theoretical study of the magnetic surface anisotropy of transition metals
Authors: Kolář M.
Published: July 2007

A model calculation of the magnetic surface anisotropy of transition metals based on recent investigations of the surface density of states is presented. The numerical computation refers to nickel. The importance of including the deviations from the bulk properties in all atomic layers of a semi‐infinite crystal is shown.
Mean field theory of a single fröhlich polaron possible existence of phase transitions
Authors: Lépine Y. , Matz† D.
Published: July 2007

New results for the free polaron ground state energy are presented, based on a non‐perturbative Fock approximation mean field theory. From variational calculations a new energy upper bound for all couplings is obtained, whose newness lies in its cylindrical symmetry, thu sbreaking the spherical symmetry of the Fröhlich Hamiltonian. For α (the electron–phonon coupling constant)≦3 a translational invariant state is found, for 3 ≦ α ⪅ 3.8 a two‐dimensional localized state while for α ⪆ 3.8, a three‐dimensional cylindrical localized state is obtained. By linking the variational approach to a dynamical approximation of the Fröhlich Hamiltonian, the possibility is suggested of second‐order phase transitions for the structure of the polaron, in the framework of the Fock approximation.
Information about Dislocation Potentials from Free Carrier Absorption
Authors: Gerlach E.
Published: July 2007

It is shown to which extent a dislocation potential can be constructed from a measured dynamical conductivity depending on frequency and spatial orientation.
Classical Theory of a Metamagnet with Temperature‐Dependent Anisotropy
Authors: Michalski K. J. , Reich W. , Cofta H.
Published: July 2007

The collinear, two‐sublattice metamagnet with thermal dependence of the magnetic anisotropy parameter but with constant parameter of the inter‐sublattice isotropic exchange coupling is investigated in classical approximation. Using Pál's form of the phenomenological free energy, the magnetization curves for both mT(h) and mh(T) processes are derived. The possibility of occurrence of the spontaneous metamagnetism is demonstrated and its criterion is derived. Moreover, the stable oblique phase is studied, exhibiting new interesting abrupt magnetic transitions on its phase boundaries. Some rules for the accompanying volume jumps are established.
Dielectric Function of a Charge‐Density‐Wave Distorted Quasi‐One‐Dimensional Solid
Authors: Gasser W. , Heiner E.
Published: July 2007

The macroscopic dielectric function is calculated for a quasi‐one‐dimensional charge‐density‐wave distorted solid described by a half‐filled one‐band tight‐binding model with weak electron‐electron interaction and a charge‐density‐wave potential due to electron—phonon interaction. The Green function formalism is used treating the electron correlation by a modified RPA whereas the charge‐density‐wave potential is taken into account exactly. The real and the imaginary part of the dielectric function are discussed in the limit of vanishing wave numbers.
Energy Bands of the Copper Halides
Authors: Overhof H.
Published: July 2007

The energy bands of CuCl, CuBr, and CuI in the zincblende modification are calculated using the relativistic KKR method. The resulting bands confirm qualitatively the empirical band model derived from photoemission and ESCA data. A tentative interpretation of the optical absorption spectra is made in terms of critical points of this band model.
Hot Electrons in Semiconductors in Longitudinal Quantizing Magnetic Fields
Authors: Pinchuk I. I.
Published: July 2007

A method for calculating the power transferred to the lattice by electrons in longitudinal quantizing magnetic fields is developed without restriction on the degree of quantization. Both, the inelasticity of scattering and the spreading of Landau levels are taken into account. The quantizing magnetic field appears to eliminate the heating of the electron gas. Electron temperature oscillations due to energy losses through optical phonon emission are studied.
Collective Excitations in Dipole Pseudo‐Spin Glasses
Authors: Akhmadullin I. Sh. , Saburova R. V.
Published: July 2007

Excitations are considered in a system of tunneling dipoles randomly distributed over the host with electric dipole—dipole interaction. It is shown that excitations with small damping can exist in both a paraelectric phase and a dipole pseudo‐spin glass one. The phase transition can be a first—order or second—order depending upon the dipole concentration.
Auger Recombination with Traps
Authors: Haug A.
Published: July 2007

Auger recombination in semiconductors involving traps is calculated taking into account the statistics of the traps. The results are valid for different traps and different cases of ionization and excitation. In particular, localized traps (δ‐potential model) and non‐localized traps (hydrogen model) are compared with the result that the depth of the traps is essential for Auger recombination, but not their localisation.
Micromagnetic Theory of Phase Transitions in Inhomogeneous Ferromagnets. I. Basic Equations
Authors: Kronmüller H. , Fähnle M.
Published: July 2007

Landau's theory of second‐order phase transitions is applied for an investigation of inhomogeneous ferromagnetic materials near the Curie temperature. Using micromagnetic concepts it is shown that fluctuations of the Landau parameters as well as magnetostrictive and dipolar interactions lead to deviations from the so‐called linear Arrott plots. In addition it is found that these latter interactions give rise to transversal components of the spontaneous magnetization.
Theory of AC and DC Conductivity in Disordered Hopping Systems
Authors: Movaghar B. , Pohlmann B. , Sauer G. W.
Published: July 2007

A self‐consistent theory is given of ac and dc transport in disordered hopping systems. The method is an extension of an effective medium approximation and a Cayley tree formalism. The calculated dc and ac conductivity are compared with the results of computer simulations of R‐hopping networks and data of amorphous germanium. The agreement is very satisfactory. The exponent s of the ωs component decreases with temperature in the way observed experimentally.
Interstitial Motion During Radiation Damage and Sputtering Processes
Authors: Agullo‐Lopez F. , Townsend P. D.
Published: July 2007

There are two major models for the mechanism of interstitial motion away from the F centre during photon or low energy electron excitation of alkali halides. Previously these models of a focussed replacement collision sequence of halogen ions or a thermally activated H centre diffusion are considered to be alternatives. Some new detailed data on halogen ejection from alkali halides during low energy irradiation are reported which are relevant to this problem. A model is presented which offers an explanation for the data on halogen ejection: the energy spectrum, temperature dependence, and presence of molecular emission. Experiments which would further clarify the model are proposed.
Influence of the Quasi‐Local Acceptor Levels on the Kinetic Properties of Hg1−xCdxTe Type Semimetallic Materials
Authors: Mekhtiev M. A. , Mustafaev N. B.
Published: July 2007

Calculations are made of all the kinetic coefficients for semimetallic materials of Hg1−xCdxTe type related with resonance electron scattering at the quasi‐local acceptor levels. The results are compared with experiments. It is shown that at low temperatures all the characteristic features of kinetic coefficients are explained satisfactorily on the basis of the considered mechanism. It is also shown that this scattering mechanism gives a change of sign of the thermo‐electromotive force versus pressure and temperature.
A New Approach to Auger Recombination. Application to Lead Chalcogenides
Authors: Ziep O. , Mocker M.
Published: July 2007

The Auger transition rate derived by means of Green's functions is formulated in terms of exchange of energy and wave vector of the corresponding transitions. Hereby the transition probabilities are modified by dynamical corrections. This treatment allows to calculate the Auger coefficient in lead chalcogenides with sufficient accuracy. As a consequence Auger recombination in PbSe has to be considered.
Anisotropie des seebeck‐koeffizienten, der lorenz‐zahl und des hall‐koeffizienten von halbleitern, verursacht durch anisotrop gemischte streuung
Authors: Stordeur M.
Published: July 2007

Der Seebeck‐Koeffizient, die Lorenz‐Zahl und der Hall‐Koeffizient werden in halbleitenden Kristallen selbst bei nichtkubischer Symmetrie und anisotroper Standard‐Bandstruktur nur unter speziellen Bedingungen anisotrope Größen. Wenn nur eine Trägersorte am Ladungs‐ und Wärme‐transport partizipiert, führt eine anisotrop gemischte Streuung zur Richtungsabhängigkeit dieser Transportkoeffizienten. Für diesen Fall werden die Koeffizienten in Abhängigkeit vom reduzierten Ferminiveau und den Mischungsparametern für Streuung an akustischen Phononen und ionisierten Störstellen bzw. an akustischen Phononen und optischen Phononen (T > TD) jeweils approximiert durch die entsprechenden Relaxationszeiten berechnet. Die numerischen Resultate zeigen, daß die Transportkoeffizienten im Unterschied zur reinen Streuung deutliche Anisotropien aufweisen.
Crystal Field Investigation on PrMg3
Authors: Andreeff A. , Goremychkin E. A. , Griessmann H. , Lippold B. , Matz W. , Chistyakov O. D. , Savitskii E. M.
Published: July 2007

The results are given of crystal field investigations on the cubic intermetallic compound PrMg3 by inelastic neutron scattering and specific heat measurement. From the neutron spectra measured at T = 8 and 80 K the following crystal field parameters are obtained: B = −34.7 × 10−4 meV and B = −89 × 10−6 meV. The crystal field ground state of Pr3+ is the non‐magnetic doublet Γ3.
Calculation of Jahn‐Teller Coupling Constants of 3d Transition Metal Ions in Crystals. II. RbMnF3
Authors: Nikiforov A. E. , Shashkin S. Yu. , Krotkii A. I.
Published: July 2007

In the LCAO‐MO scheme using semiempirical approximations the first‐ and second‐order Jahn‐Teller coupling constants for the interaction of 4T1, 4T2 terms of the Mn2+ ion in RbMnF3 crystal with a1, e, and t2 vibrations are calculated. The problems of covalency and configuration interaction influence upon the Jahn‐Teller constants are considered.
Quantum Effects in the Plasticity of Crystals
Authors: Feltham P.
Published: July 2007

Below about a quarter of the Debye temperature the rate processes controlling creep and plastic yielding in crystalline materials are found to be increasingly less temperature dependent as T → 0. These observations, and the occurrence of creep down to helium temperatures, are not encompassed by classical rate‐theory. The effects are shown to be explicable in terms of the contribution of the zero‐point energy to the vibrational spectrum of the lattice: below a certain temperature this necessitates replacing kT in the classical Arrhenius rate‐equation τ−1 = v exp (−u/kT) by k(T0 + AT2), where T0 and A are constants.
Internal Stark Effect on Impurity States in Germanium
Authors: Ohyama T.
Published: July 2007

Effects of the Coulomb field by ionized impurities on the acceptor as well as on the donor states in germanium are studied by low‐temperature magneto‐absorption measurements. The broadening of the representative acceptor transition is roughly proportional to the two‐third power of the ionized impurity concentration. It is attributed to the Stark effect by ionized impurities which removes the degeneracy of the excited states. The effect is smaller for the donor state in which the level splitting by magnetic field is larger.
Effect of Spin–Lattice Relaxation on the Dependence of the Triplet Exciton Annihilation Rate on the Strength of Magnetic Field
Authors: Lesin V. I. , Sakun V. P.
Published: July 2007

A formula for the triplet exciton annihilation rate in molecular crystals is obtained with taking into account spin–lattice relaxation of the excitons. Using this formula, some experimentally observed peculiarities in the dependence of the annihilation rate on the magnetic field may be explained at least qualitatively.
EPR Investigation of Stabilized ZrO2 Single Crystals Doped with Chromium and Manganese
Authors: Zhilinskaya E. A. , Lazukin V. N. , Chepeleva I. V. , Osiko V. V.
Published: July 2007

EPR of Mn2+ and Cr3+ impurity ions in cubic single crystals of (ZrO2)0.9(Y2O3)0.1 solid solutions is studied in X‐ and Q‐bands at 300 and 77 K. A set of Mn2+ centres differing by coordination, value, and symmetry of the crystalline field as well as trigonal Cr3+ centres with considerable zero‐field splitting are found. For the Cr3+ centres and some of Mn2+ centres charge compensation by anion vacancies (main lattice defect) exists. Considerable linewidths are an indication of pronounced lattice distortion about the impurity centres.
Energy Spectrum of Thin Film Heterostructure
Authors: Gasparyan V. M. , Kasamanyan Z. A.
Published: July 2007

Using the Green's function method the charge carrier energy spectrum in a thin film heterostructure is studied taking account of the surface states. The density of states in various parts of the heterostructure is calculated. It is shown that their ratio may vary within large limits. This may lead to the appearance of a negative conductivity in presence of a longitudinal electric field.
Energy Bands and Optical Properties of HgTe and CdTe Calculated on the Basis of the Tight‐Binding Model with Spin–Orbit Interaction
Authors: Czyżyk M. T. , Podgórny M.
Published: July 2007

It is shown that inclusion of spin–orbit interaction and omission of the usual two‐center approximation in the second neighbour Slater‐Koster tight‐binding method leads to an improved interpolation formula for the energy bands of II–VI semiconducting compounds such as CdTe. Due to the inclusion of spin–orbit interaction it is possible to obtain the inverted band structure of HgTe. Reflectivity spectra are computed in fairly good agreement with experiment, up to 5 eV. A detailed discussion of critical points contributed to E1, E1 + Δ1 and E2, maxima is carried out. Moreover, the local properties near the γ point (e.g. effective mass, g factor, Kane's matrix element P, nonparabolicity, warping) of the valence and conduction bands are found to be in excellent agreement with experimental data.
Giant Oscillations of Intensity and the Lineshape of Secondary Cyclotron Emission in Polar Semiconductors
Authors: Goltsev A. V. , Lang I. G. , Pavlov S. T.
Published: July 2007

Secondary emission at the cyclotron frequency of a polar semiconductor located in an external homogeneous constant magnetic field and stimulated by monochromatic light of frequency within the region of fundamental absorption is discussed. Analytical expressions of the cross‐section at the cyclotron frequency as a function of the excitation frequency ω1 are obtained, and the shape of the line of cyclotron radiation (LCR) is studied. Giant oscillations of the LCR intensity under changes of ω1 are predicted. This effect is determined by the complete filling of the energy states in the Landau zones by electrons. It is shown that the shape of the LCR is not the result of a overlapping of Lorentz lines, and that it is determined to a high degree by a new type of quantum interference processes in which LO phonons take part. The contribution of these interference processes to the cross‐section may be positive or negative and is responsible for the difference in the shape of the LCR and the Lorentz line.
Electronic Spectrum of Wannier Excitons in Quasi‐Two‐Dimensional Structures
Authors: Kolychev N. N. , Tarasov G. G. , Yaremko A. M. , Sheka V. I.
Published: July 2007

The discrete energy values of excitons in uniaxial crystals are calculated in adiabatic approximation. A model adiabatic potential is discussed for the case of the intermediate anisotropy. It is shown that for the ground state the adiabatic approximation yields the results not worser than the variational ones in the actual range of the anisotropy constant.
Density of States Model for the Lattice Transformation in A‐15 Compounds. Application to the Magnetic Susceptibility of V3Si
Authors: Pietrass B. , Handstein A. , Behr G.
Published: July 2007

The cubic‐tetragonal lattice transformation in A‐15 compounds is described by an empirical model in which the density of states function near the Fermi energy is characterized by a two‐parametric peak in addition to the constant part. Two types of peak splitting under tetragonal deformation are considered, leading to qualitatively different results about the phase transition. Results are given for the order parameter, the phase stability, the soft elastic modulus, and the paramagnetic spin susceptibility. Comparing with measurements of the magnetic susceptibility of V3Si single crystals near the phase transition a better agreement is obtained for a twofold degenerate density of states peak than for a threefold degenerate one.
Stress Dependence of Anomalous Hall Effect in n‐InSb
Authors: Biernat H. , Kriechbaum M.
Published: July 2007

Consistent inclusion of the vector potential and the nonparabolicity in the impurity scattering leads to anomalous contributions in the Hall effect of n‐InSb in the magnetic freeze‐out regime. Their dependence on uniaxial stress is calculated. A measurable effect is found for stress up to 5 kbar.
Statistical Model and Experiments on Low‐Dimensional Exciton Transport
Authors: Erdle E. , Möhwald H.
Published: July 2007

A statistical model is presented to calculate the concentration dependence of the ESR line width of triplet excitons in mixed CT crystals. A comparison between computation and experiments yields the anisotropy of energy diffusion. As experimental example data on the charge‐transfer crystal anthracenec–phenanthrene1–c–TCNB (0 ≦ c ≦ 1) are presented. It is shown that triplet excitons move by a factor of 15 to 60 faster along one distinct direction than perpendicular to it.
Thermal Phonon Scattering in n‐Ge. Effect of Uniaxial Stress
Authors: Kobayashi A. , Suzuki K.
Published: July 2007

The thermal phonon scattering, at low temperatures, due to isolated donor impurities in Ge under uniaxial stress is studied theoretically. The calculation shows that the piezo‐thermal conductivity depends on the chemical species of impurities and this dependence arises from the difference in the electronic structure of their ground states. A comparison with the experiment is also given.
An Analytical Solution to Fick's Equations in the Case of the Dissociative Diffusion Mechanism
Authors: Edelin G.
Published: July 2007

The Fick's equations are solved by the Laplace transformation method in the case of an impurity diffusing by the dissociative mechanism into a semi‐infinite solid at constant surface concentration. The only assumption made in the calculation is that the interstitial diffusivity is very high. The form of the substitutional and vacancy concentration profiles and the influence of dislocations on these profiles are discussed. It is pointed out that under certain circumstances the tails on diffusion profiles can be due to the dissociative mechanism.
Lattice Dynamics and Elastic Properties of GaSe
Authors: Altshul V. Ya. , Bashenov V. K. , Marvakov D. I. , Petukhov A. G.
Published: July 2007

Lattice dynamics of gallium selenide is studied by using both, the Born‐von Karman model with 22 interatomic force constants and the central two‐body‐force model with 10 constants ignoring completely any long‐range interaction. The second model including four equilibrium conditions leads to a good description of the elastic properties. The isolated layer dynamics is also considered. The striking feature of the acoustical modes appearing in an isolated layer is the quadratic dispersion of the out‐of‐plane acoustical mode in a small part of the Brillouin zone.
New Mechanism of Electric Field Influence on Defect Creation in Non‐Metallic Crystals
Authors: Chaika G. E. , Vinetskii V. L.
Published: July 2007

The mechanism of radiation defect creation in crystals below threshold is considered. Such defects may be due to impurity atoms capable of occurring at intersites, the latter being acceptors. The probability of lattice site–intersite transition for an impurity atom is calculated by statistical and quantum mechanical methods. This transition is accompanied by band electron (hole) capturing at the level of the created defect. When calculating by quantum mechanical methods the impurity atomic mass is supposed to be smaller than those of the host atoms. Such an assumption enables one to apply the adiabatic approximation twice: host atoms–impurity atom–electron. The upper value of the above transition probability corresponds to an electron energy level higher than the band minimum. Thus the heating by an electric field (or, perhaps, by the light of a discrete spectrum), causing the electron density to increase in the high energy tail region, may enhance appreciably the defect creation efficiency.
Reduction Symmetry Method in Crystal Field Theory (IV)
Authors: Kustov E. F.
Published: July 2007

The rotation groups of the type R[γ]γ and branch rules for the representations of the groups (unitary and point) are introduced. Relations between the SC and the 6U, 6r coefficients are developed by using the graph technique. The main formulas for the matrix elements of one‐particle operators between states of complex configurations and the eigenvalues of the Casimir operators are given.
Commensurate‐Incommensurate Transition in the Quasi‐One‐Dimensional Fröhlich Model with a Nearly Half‐Filled Band
Authors: Mertsching J. , Fischbeck H. J.
Published: July 2007

The mean‐field approximation of the commensurate‐incommensurate (C‐IC) phase transition in the one‐dimensional Fröhlich model with a nearly half‐filled band is studied near Leung's triple point, including up to 19 harmonics of the charge‐density wave. The C‐IC transition appears to be discontinuous, and the C and 1C phases coexist in a small region of the temperature‐density plane.
Theory of Core Excitons in Semiconductors
Authors: Bechstedt F. , Endeblein R. , Koch M.
Published: July 2007

Core exciton binding energies are calculated for the Ga 3d‐X6 conduction band transition inGa‐V compounds and the Si 2p‐Δ6 transition in Si. Various corrections to the Wannier‐Mott theory are considered. Realistic core hole charge distributions, q‐ and ω‐dependent dielectric screening and an‐isotropic electron effective masses are taken into account. In the case of Ga‐V compounds, binding energies from the calculation are considerably larger than the Wannier‐Mott values, and close to experimental data. Smaller changes result for Si. The large discrepancies between theory and experiment cannot be resolved in this case.
Variations in the Exciton Spectra of CdTe and ZnTe Thin Films with Pressure and Temperature
Authors: Brothers A. D. , Brungardt J. B.
Published: July 2007

Exciton peak positions in thin films (≈ 700 Å) of CdTe and ZnTe are measured as a function of temperature between 90 and 300 K and hydrostatic pressures to 3500 atm at 90 K. The value of (∂E/∂T)P in the CdTe films for the E1 and E1 + Δ1 peaks is –2.3 ×10−4 eV/K and –1.7 ×X 10−4eV/K, respectively. For the ZnTe films these values are determined to be –2.5 ×10−4 eV/K and –1.4 ×10−4 eV/K, respectively. In CdTe films the values of (∂E/∂T)T are 7.4 ×10−6 eV/atm and 8.9 ×10−6 eV/atm, respectively, and for ZnTe films both are 8.3 ×10−6 eV/atm. A comparison of these results with previous results, and comments on the nature of the band structures of these materials are made.
A Contributory Mechanism to the Ground State Splitting of Gd3+ in C3h Symmetry
Authors: Dixon J. M. , Chatterjee R.
Published: July 2007

A contribution to the zero‐field splittings of Gd3+ 4f7(8S7/2) in lanthanum ethylsulphate is calculated using a spin correlated crystal field. A particular mechanism is provided and estimated the sign and magnitude of the coupling coefficient. It is found, that the sign is positive and the contribution to the zero‐field splitting is of the correct sign.
Ag Centres in KCl:Ag Crystals. A Thermoluminescence Study
Authors: Sridaran P. , Bhuniya R. C. , Ratnam V. V.
Published: July 2007

The optical transformation and thermal stability of Ag centres in KCl:Ag crystals stabilized in different valence states after X‐irradiation are studied using thermoluminescence (TL) as the tool. The much higher sensitivity of TL over optical absorption enables to monitor the transformation processes with the help of the data obtained from TL spectra. It is shown that the 555 nm recombination luminescence emission predominant in the 90 °C glow peak is due to Ag0 atoms at cation sites while the 543 nm emission predominant in the 135 °C glow peak is due to Ag+k: F centre complex. The results further reveal that electrons trapped by Ag+ ions during X‐irradiation are mostly not destroyed during optical bleaching but undergo transformation and stabilize the Ag+ ions in different valence states both in cationic and anionic sites. Results also indicate that Ag0 atoms in anion sites are non‐thermoluminescent.
Higher Harmonics of Spontaneous Radiation of Ultrarelativistic Channeled Particles
Authors: Kumakhov M. A. , Trikalinos Ch. G.
Published: July 2007

The case of spontaneous radiation of channeled ultrarelativistic particles is considered when the dipolarity condition is not satisfied. The change of the particle longitudinal velocity affecting the maximum radiation frequency is included. The angular and frequency characteristics of the radiation for superhigh energies are studied for the first time. It is shown that there is an optimum energy at which the radiation density is maximum. The influence of the angle at which electrons enter a crystal and of the beam divergence on the radiation is investigated. The problem of quasi‐channeled particle radiation and also the radiation in axis‐plane transitions are considered.
Sublattice Displacement Effects in the Electromodulation Spectra of Zincblende‐Type Crystals
Authors: Suisky D. , Enderlein B. , Lange H.
Published: July 2007

Expressions are derived for the deformation potential constants for pure piezomodulation (PM) and piezoelectrically induced linear electromodulation (LER EM), taking into account the difference in sublattice displacements caused by strain and field calculated in a previous paper. It is shown that in case of star degeneracy the sublattice contributions to the deformation potential constants C and C differ in LER EM and PM. The theory is applied to the experimental PM and LER EM spectra at the E1 E1 + Δ1 transitions of GaAs reported in the literature. In agreement with the predictions of the theory, the deformation potential constant C extracted from the LER EM data is found to be much greater than that obtained from PM spectra.
Lattice Dynamics of Si and Ge under Pressure
Authors: Soma T.
Published: July 2007

The lattice dynamics of Si and Ge under pressure is investigated using the higher‐order perturbation and the local Heine‐Abarenkov model potential. Then, the dispersion curves at the metallic‐transition pressure are estimated using the Grüneisen parameters of the individual modes of phonons in the phenomenological theory where the experimentally observed temperature dependence of the thermal expansion coefficient, i.e. the Grüneisen constant is reproduced.
Photoemission Cross‐Sections of Oriented Orbitals
Authors: Bartosš I. , Máca F.
Published: July 2007

Expressions for photoemission cross‐sections of oriented orbitals are derived in the surface Green function formalism. Centres, described by short‐range spherically symmetric potentials, are treated and results for 2s and 2p levels of Al are given and discussed in context with the experimental data for solids.
Band Structure of Hexagonal Tantalum Nitride
Authors: Tsvyashchenko A. V. , Popova S. V. , Alekseev E. S.
Published: July 2007

The energy band structure for hexagonal TaN is calculated.
Fermi Energy, Density of States, and Electronic Properties of Alkali Metals Exchange and Correlation Effects
Authors: Thakur J.
Published: July 2007

Fermi energy density of states, electrical resistivity, and thermoelectric power of liquid alkali metals are computed using first principle pseudopotential. Effect of various forms of dielectric screening procedures are also investigated. Slater's value of electronic exchange parameter α in the Xα‐exchange with unmodified orthogonalization hole potential (Vopw) presents a good picture.
Untersuchungen zum elektrischen Widerstand von Versetzungen in Metallen II. Anwendung auf Stufenversetzungen in Kupfer
Authors: Rauh H.
Published: July 2007

Die in einer vorangehenden Arbeit entwickelte Theorie zur Berechnung des elektrischen Restwiderstands wird auf Stufenversetzungen in Kupfer angewandt. Das Störpotential der betrachteten Kristallfehler wird hierbei als lineare Superposition eines starken, auf das Gebiet des Versetzungskerns begrenzten und eines schwachen, ausgedehnten Anteils beschrieben. Der Einfluß dieser exakt bzw. störungstheoretisch behandelten Anteile sowie derjenige des gesamten Potentials auf den Widerstand werden im einzelnen untersucht. Dabei zeigt sich, daß beide Anteile Widerstandsbeiträge derselben Größenordnung liefern. Die experimentell bekannte Widerstandsanisotropie kann im Rahmen dieses Modells gedeutet werden, welches insbesondere die Bestimmung phänomenologischer Parameter gestattet. Die für den Widerstand selbst erhaltenen Werte erweisen sich jedoch als zu klein verglichen mit experimentellen Daten.
Surface Dipole Barrier of Metals
Authors: Taut M. , Eschrig H. , Schubert M.
Published: July 2007

The surface dipole barrier of simple and transition metals up to atomic number 50 is calculated by a simple scheme using only parameters of the bulk band structure. Good agreement with semiempirical values is reached and the trend over the 3d and 4d series is explained. The results prove that the charge density of surface atoms can be derived from bulk atoms, but not from free atoms.
Lattice Stability and 2kF Anomaly in a Quasi‐One‐Dimensional System
Authors: Kato K. , Iguchi K. , Itoh R.
Published: July 2007

The lattice stability and the phonon dispersion of a quasi‐one‐dimensional systems are studied using the tight‐binding approximation. The dependence of these properties on the electron—phonon coupling constant λ, the electron—electron interaction, and the temperature are elucidated. The dip in the phonon dispersion curve increases with increasing λ, the repulsive electron—electron interaction suppresses the Peierls instability as well as the Kohn anomaly, while the attractive electron—electron interaction raises them. For K(q; ω) > 1 (dielectric constant) the phase transition does not occur even in a one‐dimensional system. The temperature dependence of the curves are in good agreement with the experiments on TTF‐TCNQ.
Exciton Effects in Photoconductivity of GaAs
Authors: Kravchenko A. F. , Nazintsev V. V.
Published: July 2007

Photoconductivity (PC) and photoluminescence (PL) spectra are investigated on epitaxial GaAs at T = 2 to 50 K. According to the way excitons manifest themselves, two types of crystals, A and B, are discovered in the PC spectra. In crystals of A‐type, the photocurrent maximum corresponds to the exciton maximum in absorption spectra; in crystals of B‐type, vice versa, the photocurrent minimum corresponds to the exciton maximum in the absorption spectra. In crystals of A‐type the position of the earlier observed lines b (1.5154 eV) and d (1.5175 eV) is defined more precisely, and new lines a (1.5141 eV), c (1.5167 eV), and e (1.5185 eV) are registered. An identification of the observed lines is carried out. The influence of temperature and additional illumination on the PC spectra of crystals of both types is studied. The results of investigation show the decisive role of the recombination processes in the volume and on the surface of a crystal in the formation of excitons in PC spectra.
The Two‐Phonon Resonant Effect in Far‐Infrared Reflectivity of HgSe
Authors: Witowski A. M. , Grynberg M.
Published: July 2007

Reflectivity spectra of HgSe with various carrier concentrations are measured in the spectral region from 80 to 600 cm−;1 at 6, 80, and 300 K. Their features are well explained by the theoretical dynamic dielectric function including the dispersive interband part. This part is evaluated using Kane's model of band structure. The properties of an additional mode observed in zero gap semiconductors can be well explained by means of two‐phonon resonant process.
On the Phase Transition between the Commensurate and Incommensurate Charge‐Density Wave States of the Nearly Half‐Filled Fröhlich Model
Authors: Fischbeck H. J. , Mertsching J.
Published: July 2007

The commensurate—incommensurate phase transition of the nearly half‐filled one‐dimensional Fröhlich model is studied by numerical calculations of the grand potential in the mean‐field approximation. The phase diagram in the μ, T and the n, T plane is calculated using one and three order parameters of the incommensurate phase. The question whether or not the discontinuous phase transition becomes continuous at zero temperature with inclusion of an infinite number of order parameters remains open.
Semi‐Empirical Calculations of the Configuration and Electronic Structure of Lithium‐Related Defects in Silicon
Authors: Singh Vijay A. , Weigel C. , Corbett J. W.
Published: July 2007

A modified extended Hückel theory method is employed to perform calculations for the lithium defect in silicon model crystals with and without vacancies. The energetically stable positions for the lithium atom appear to be the tetrahedral interstitial in models without vacancies; in the case of vacancies the substitutional position is preferred. The migration energy is found to be in the same range as experimental predictions. In models with no vacancy defects the electronic defect level is established to be a shallow donor.
Shielding by an Electron Gas in a Semiconductor in a Magnetic Field
Authors: Krupski J.
Published: July 2007

The macroscopic static dielectric function is used to study the effect of anisotropy of the electron effective mass on the screened Coulomb potential of a point charge impurity in semiconductor in a uniform magnetic field. Formulae for both degenerate and classical statitsics are derived. It is also shown how the positions of Kohn anomalies change due to the orientation of the crystal with respect to the magnetic field.
A New Infrared Luminescence of Nickel‐Doped ZnS and Its Interpretation by Means of Absorption Spectroscopy with Ni2+ Ions
Authors: Roussos G. , Schulz H.‐J.
Published: July 2007

At low temperatures, a new emission band is detected with Ni‐doped ZnS crystals. Zero‐phonon transitions at 4379 and 4199 cm−;1 and phonon side bands are resolved. The luminescence is interpreted as a 3T2(F) → 3T1(F) transition of substitutional Ni2+(d8) ions in a tetrahedral crystal field. This assignment is verified by the coincidence of (i) the fine structure in the emission and (ii) its excitation spectrum with the known absorption spectrum of the Ni2+ ion. The crystals exhibit all of the known internal absorption transitions of ZnS:Ni2+ and some weaker additional finestructured details which are in accord with the proposed interpretation.
Luminescence of Cs2NaYCl6—Bi3+ (6s2)
Authors: Van Steen A. C. Der
Published: July 2007

The luminescence properties of Bi3+‐activated Cs2NaYCl6 crystals are presented. The Bi3+ ion (6s2) occupies an Y3+ site which has cubic symmetry. Excitation in the A absorption band yields 3T1u emission. Excitation in the C absorption band, however, yields 3T1u and 3A1u emission, because both levels are populated by nonradiative processes from the 1T1u excited state. The emission and excitation spectra show vibrational structure. The vibronic lines are assigned and discussed.
Molecular Model Parameters for the Saddle‐Point Configuration of F, FA, FB, and FH Centres in the Alkali Halides
Authors: Kung A. Y. S. , Lagowski J. , Vail J. M.
Published: July 2007

A molecular model for the saddle‐point configuration of F‐type centres, which previously led to the correct prediction of type II emission for FA centres in RbF:Li and RbF:Na, based on an empirical parameter Z, is extended to other impurity F centres in the alkali halides. CsF:Li and CsF:Na are predicted to have type II FA centres, and a number of triangular FB centres in the NaCl structure are also predicted to be type II, particularly in materials with small host anions combined with Li+ or Na+ impurities. Materials having small Z values, presumed to favour type II behaviour, are also identified, for FH centres with large host anions and H−; or F−; impurities, and for FA and triangular FB centres in the CsCl structure containing Li+ or Na+ impurities, where the FB centre which has impurities on adjacent corners of a unit‐cube face is strongly favoured.
Two‐Phonon Resonance Raman Scattering in Polar Semiconductors
Authors: Giner C. Trallero , Lang I. G. , Pavlov S. T.
Published: July 2007

Indirect creation and annihilation probabilities are obtained for a Wannier‐Mott excition with arbitrary kinetic energy which interacts with longitudinal lattice vibrations (LO‐phonons). An analysis is made of the discrete and continuous spectra of the exciton intermediate (virtual) state contribution to these probabilities. These results are applied to the calculation of the two‐phonon resonance Raman scattering (RRS) cross‐section, which is directly proportional to Fröhlich's exciton—phonon coupling constant αexc. It is shown that the greatest contribution of intermediate states to the indirect hot‐exciton creation and annihilation probabilities is that one due to the continuous spectrum.
Phonon Coupling and Ferroelectric Phase Transition in Mixed As0.1Sb0.9SI Crystals
Authors: Valakh M. Ya. , Veshka Y. A. , Lisitsa M. P. , Svechnikov G. S. , Pinzenik V. P.
Published: July 2007

The Raman spectra of AsxSb1‐xSI (x = 0.1 and 0.05) are studied experimentally. The resonance interaction between soft mode and low frequency phonon excitations is observed. The effect appears to be stronger in mixed crystals, than in pure SbSI. The soft mode temperature dependence indicates that the Curie temperature falls when the As concentration x is raised. This effect is due to the increase of the anharmonicity in the mixed crystal lattice.
Analysis of the Phonon Drag Thermoelectric Power of the Doped Semiconductor at Low Temperatures Application to p‐Doped Ge
Authors: Dubey K. S.
Published: July 2007

The phonon drag contribution to the thermoelectric power of five phosphorus doped Ge samples with carrier concentrations of 1.2×1023 to 1.1×1024 m−;3 are studied in the temperature range 1 to 5 K. The variation of the phonon drag thermoelectric power with the reduced Fermi energy η*, the density of the states effective mass m*, the carrier concentration n, and the deformation potential Ed are also studied to see the role of the electron—phonon scattering relaxation rate in the analysis of the phonon drag contribution of the thermoelectric power of the doped semiconductor. The variation of the thermoelectric power with the lattice thermal conductivity is also reported in the entire temperature range of study. An analytical expression is also formulated to calculate an approximate value of the phonon drag thermoelectric power of the doped sample at low temperatures.
On the Use of Monte Carlo Techniques for the Calculation of Transient Dynamic Response in Semiconductors
Authors: Ferry D. K. , Barker J. R.
Published: July 2007

The transient dynamic response in InAs and GaAs is calculated by both, a drifted Maxwellian approach and a Monte Carlo approach. While previous calculations by the latter method yield results that differ from those obtained using the Maxwellian approach, using an ensemble Monte Carlo technique, which is free from errors introduced by velocity estimators, it is found that the results are extremely sensitive to the value of Γ, the self‐scattering parameter. However, when Γ is selected so that <Δt> = 1/Γ « >τ>, comparable results are obtained for the two techniques.
Electrons in Surface Phonon Field
Authors: Ueba H.
Published: July 2007

The motion of electrons in the surface phonon field is studied by means of the variational method. The phase diagram of surface polaron states is calculated as functions of the electron—surface optical and acoustic phonon coupling constants. Effects of an image potential on surface polarons are also investigated and a possibility of extrinsic surface small polaron states is predicted.
The Hole Effective Mass in Pb1—xSnxTe near the Zero Band Gap
Authors: Kushev D. B. , Zheleva N. N. , Yordanov S. P.
Published: July 2007

Using reflection methods in the plasma frequency range, nonparabolic valence bands of solid solutions Pb1—xSnxTe with composition near the inversion point of the bands (x = 0.55, 0.6, 0.65) are investigated. The Hall concentration of the samples are in the interval 6 × 1018 to 2 × 1020 cm−;3. The concentration dependence on wavelength in the reflection minimum and the effective masses correspond well with Kane's model. For the composition x = 0.6 the parameters of this model are evaluated.