bluuebunny/crossref_metadata_2025 huggingface dataset:
The magnetic moment of Cr0.6Mn0.4
Authors: Williams D. E. G. , Spraget H. W. G. , Perrin R.
Published: July 2007

The results of a neutron diffraction experiment on a b.c.c. single crystal of Cr0.6Mn0.4 are analysed in terms of a spherical atom form factor to give a mean magnetic moment per atom of (0.82 ± 0.04) β. The deviations from spherical shape of the spatial distribution of the magnetic moment are explained in terms of a predominantly t2 symmetry.
Absorption, excitation, and fluorescence spectra of thallium‐activated ammonium bromide
Authors: Sharan V. B. , Srivastwa D. N. S. , Sen S. C.
Published: July 2007

The optical spectra of Tl+ ion in a CsCl‐like environment is found to differ considerably from those of a Tl+ ion in NaCl‐like environment. Absorption, fluorescence, and excitation spectra of ammonium bromide which has a CsCl‐like structure at room temperature, activated by various amounts of thallium are investigated at room temperature in order to ascertain the nature of the electronic states involved in the luminescence centres in a CsCl‐like host lattice. The A and B absorption bands are obtained at 259 and 224 nm even at low thallium content. With increasing thallium concentration additional absorption bands are obtained at 234, 242, 265, 275, and 285 nm. The emission bands are obtained at 390, 428, 490, and 570 nm. The absorption and fluorescence bands are assigned to the electronic transitions with Tl+ in cubic symmetry and in dimer centres having D4h site symmetry. The pattern of luminescence spectrum is compared to that of NH4Cl:Tl reported earlier.
Infrared absorption of silicon irradiated by protons
Authors: Gerasimenko N. N. , Rollé M. , Cheng Li‐Jen , Lee Y. H. , Corelli J. C. , Corbett J. W.
Published: July 2007

Hydrogen implantations into silicon samples at room temperature and at 190°C are carried out. Infrared studies are performed on these samples before and following annealing. Previously observed divacancy and hydrogen vibrational bands are found as well as higher‐order‐bands not previously found in proton irradiation. In addition new hydrogen vibrational bands and other bands are observed and discussed.
Channeling and a semistatistical model for the interatomic potential
Authors: Pathak A. P. , Srivastava M. P.
Published: July 2007

A semistatistical model is used for neutral and ionized atoms to calculate channeling parameters like critical angles. The variation of interatomic potential with interatomic distance based on this model, is compared with that obtained with other approximations of the Thomas‐Fermi model. It is found that the interatomic potential itself and the channeling parameters obtained compare well with predictions of TF model and with experiment.
Spin diffusion and spin–lattice relaxation in paramagnetic crystals
Authors: Vugmeister B. E.
Published: July 2007

The spin diffusion effect on the paramagnetic relaxation due to fast relaxing paramagnetic centres is investigated theoretically. The derived expressions for the relaxation rate take into account peculiarities of the Zeeman energy migration in a disordered spin systems and are valid for an arbitrary relation of the paramagnetic particle interaction between themselves and with the fast relaxing centres. The homogeneously and inhomogeneously broadened EPR spectra are considered and compared with the experiment.
Superconductivity originating from quasi‐orbital electrons. III. Quasi‐orbital conduction electrons in non‐adiabatic systems
Authors: Krüger E.
Published: July 2007

Quasi‐orbital conduction electrons as defined in Part I are considered in non‐adiabatic systems. It is shown that for any interaction in such systems the “crystal spin” of the electrons and phonons is a conserved quantity, with phonons possessing the crystal spin quantum number one. Furthermore, it is shown that a spin–phonon exchange interaction may occur in the non‐adiabatic system. According to Part II, this spin–phonon interaction yields a coupling of the electrons to Cooper pairs.
Localization of additional screening charge around 3d‐transition metal impurities in Al
Authors: Lautenschläger G. , Mrosan E.
Published: July 2007

The additional screening charge around 3d‐transition metal impurities in Al which is localized inside the muffin‐tin sphere around the impurity is calculated. From the results it is concluded that the greatest part of the charge perturbation due to the impurity is screened within a spherical region of radius rMT. This result is in agreement with the assumption of strongly localized impurities usually applied in the theory of substitutional impurities in metals.
Interaction between a metal surface and an external molecular complex
Authors: Alfred L. C. R.
Published: July 2007

The long and intermediate range interaction between a metal surface and an external molecular complex is investigated. The calculation is based on a simplified model where the complex is represented by an ensemble of point multipole fields and the metal by a semi‐infinite jellium of smeared out ionic cores and free electrons. The response of the metal electrons to the external field is obtained in closed form by a linearized Thomas‐Fermi treatment. The energy of the complex in the metal surface response field is determined from perturbation theory. Applications to the effective multipole moments of the complex and to the changes in its internal couplings are discussed.
Effect of three‐body interactions on the electronic polarizabilities and photoelastic behaviour of alkali halides
Authors: Shanker J. , Lashkari A. K. G. , Gupta V. P.
Published: July 2007

The effect of three‐body interactions which are responsible for the Cauchy breakdown in ionic solids, is investigated on the electronic polarizabilities and photoeleastic behaviour of alkali halides. A new set of electronic polarizabilities of alkali and halogen ions is produced. The strain derivatives of electronic polarizabilities are evaluated by considering the influence of the crystalline potential on the polarizabilities of ions. The photoelastic behaviour is studied by determining the strain derivatives of electronic dielectric constant. Results obtained agree closely with experimental data.
Hopping conductivity in heavily doped strongly compensated GaAs
Authors: Arnaudov B. G. , Domanevskii D. S. , Yanchev I. Y.
Published: July 2007

The hopping conductivity in heavily doped and closely compensated LPE gallium arsenide is investigated in the temperature range 4.2 to 250 K. It is found that the resistivity in n‐type samples increases with lowering the temperature as In Q ∼ (T★/T)α where α takes successively the values 1, 1/2, and 1/4. The values of T★ in the corresponding temperature ranges are in a good agreement with theoretically calculated ones provided one takes into account the correlation in the impurity distribution. The resistivity in analogous p‐type closely compensated samples depends on temperature as In Q ∼ T−1/2 as a rule.
The electrical conductivity of bismuth chalcogenides in the liquid state
Authors: Satow T. , Uemura O. , Sanzyo M.
Published: July 2007

The electrical conductivities of liquid BiTe and BiSe systems are measured as a function of temperature. Plots of the electrical conductivity and its temperature derivative versus composition for liquid BiTe system give a relatively smooth curve near the stoichiometric composition of Bi2Te3. The electrical conductivity of the liquid BiSe system is considerably small compared with liquid BiTe system. The temperature dependence of the electrical conductivity indicates that the liquid BiSe system becomes metallic rapidly with increasing Bi content beyond the composition of Bi2Se3. The impurity doping (Bi, Ga, and In) effects are investigated on Bi2Se3 melt using both the electrical conductivity and the magnetic susceptibility. The results of Bi‐doped melts suggest that a complete ionization occurs of the excess Bi atoms, whereas an appreciable non‐localization of valence electrons is seen in alloys containing excess Ga and In atoms.
121Sb mössbauer spectroscopy in some mixed‐valence antimony hexachlorides
Authors: de Jesus Filho M. F. , Sanchez J. P. , Friedt J. M.
Published: July 2007

The 121Sb Mössbauer spectra of (NH4)2Sn1−xSbxCl6 (x = 0.13, 0.21, 0.28, and 0.33) and Cs2SbCl6 are reported in the temperature range from 4.2 to 140 K. The spectra consist in the whole temperature range of two lines with isomer shifts characteristic for SbIII and SbV ions. Not observed is the thermal activation of a fast electron transfer between the SbIII and SbV ions suggested previously.
Ionization of low donor levels and recombination of hot electrons in n‐Si at low temperatures
Authors: Asche M. , Kostial H. , Sarbey O. G.
Published: July 2007

The concentration of electrons and the decay time of carriers additionally excited from the donor states are measured in dependence on the electric field strength in n‐Si in the temperature region of partial freezing out. From these data the parameters characterizing the processes of phonon assisted and impact ionization and recombination are determined. It is shown that at not too low temperatures the Auger recombination and the impact ionization at weak electric field strength are noticeable and are determined by the contribution of the highly excited states of the donors. The phonon assisted recombination is described by the improved model of the cascade process including intervalley scattering of the electrons.
Calculation of the transition temperature Tc of superconductors
Authors: Nowotny H. , Hittmair O.
Published: July 2007

An iterative solution of the Eliashberg equations for isotropic superconductors is approximated by an analytical expression and gives as a result an equation for the superconducting transition temperature Tc. For small Tc (Tc ≪ mean phonon energy) a formula is derived, which agrees within a few per cent with the well‐known McMillan formula, if in this formula the mean logarithmic phonon energy ωlog is taken as pre‐factor, a correction which was already proposed earlier. For large Tc the (λ < ω2)1/2 behaviour of Allen and Dynes is found. Numerical results are presented for 0.5 < λ < 8, where the α2F(ω)‐shapes are taken corresponding to Hg, Pb, In, and Nb.
Excitons in WS2 films pressure and temperature effects
Authors: Brothers A. D. , Brungardt J. B.
Published: July 2007

A technique for producing thin film samples WS2 is reported. Exciton peak positions are measured as a function of hydrostatic pressure to 3500 atm at 90 K and temperatures in the range 90 to 300 K. Values for (∂E/∂P)T for the A‐ and B‐peaks are 5.9 × 10−6 and 7.2 × 10−6 eV/atm, respectively. Peak C shifts 0.3 × 10−6 eV/atm, while values of (∂E/∂T)P are −1.8 × 10−4, −2.8 × 10−4, and −0.3 × 10−4 eV/K for peaks A, B, and C, respectively. The value of (∂E/∂T)V is estimated at 1 × 10−4 eV/K. A comparison of these results with those for MoS2 is made, and comments are made concerning the nature of the band structure of WS2.
Calculation of the dielectric function of the one‐dimensional Hubbard model
Authors: Gasser W. , Höfling R.
Published: July 2007

The dielectric function of the one‐dimensional Hubbard model is evaluated in the strong correlation limit for small wave numbers and arbitrary electron concentrations in the paramagnetic phase. Expressions are given for the plasma frequencies, the plasmon stiffness, the critical wave number and for the real and imaginary part of the dielectric function in the whole frequency region. The results are compared with recent experimental studies of K‐TCNQ (potassium‐tetracyanoquino‐dimethane) performed by Tanner et al.
Calculation of first‐order and second‐order Jahn‐Teller coupling constants in MgO:V2+ and KMgF3:V2+
Authors: Bacci M.
Published: July 2007

The Jahn‐Teller coupling constants for the systems MgO:V2+ are computed up to the second order, following a new parametrization method, which is based on the angular overlap model. The results are then discussed in respect of the interpretation of the zero‐phonon line splitting (4A2g → 4T2g) in MgO: V2+, previously given.
Atomic configuration of a ½ 〈111〉 screw dislocation in pure Mo and in Mo containing He interstitials
Authors: van Heugten W. F. W. M. , Caspers L. M. , de Hosson J. Th. M.
Published: July 2007

The atomic configuration around a screw dislocation with ½ 〈111〉 Burgers vector is calculated using two different sets of interatomic potentials for Mo. The boundary conditions are given by anisotropic elasticity theory. A narrow dislocation without a distinct stacking fault region results. Two different molybdenum‐helium potentials are used to calculate the positions with maximum energy gain for helium atoms near the ½ 〈111〉 screw dislocation in Mo. The strongest binding energy of the helium atom of ≈︁ 1.6 eV is found for the dilatational sink close to the dislocation line. The present calculations confirm earlier results on the interaction between a helium atom and a ½ 〈111〉 {110} edge dislocation that elasticity theory gives a reasonable description far away from the dislocation core but fails in the neighbourhood of the core region.
Dynamic properties of [X] centres in cesium halides
Authors: Pilloud J.‐J. , Jaccard C.
Published: July 2007

In thallium doped cesium halides, the evolution of the number of self‐trapped holes with different orientations is monitored by measuring EPR spectra intensities. With a linearly polarized excitation in a suitable geometry, the relative absorption dichroism of the individual centre is determined, i.e. the absorption cross‐section ratio with polarization parallel/perpendicular to the centre axis. It amounts to 8 ± 2 at 436 nm and 10 ± 2 at 604 nm in CsI, and to 16 ± 2 at 406 nm in CsBr. Measurements with increasing temperature indicate that the first thermoluminescent peak is due to recombination following the movement of the centres along their axis only, whereas the second peak results of 90° jumps. The critical temperatures are 58 and 86 K in CsI, 106 and 130 K in CsBr, and 146 and 167 K in CsCI.
First and second order Raman scattering by pair modes in silicon
Authors: Jouanne M. , Morhange J. F. , Balkanski M.
Published: July 2007

Ion implanted silicon with two types of impurities is studied using Raman scattering. The splitting of the localized modes into two pair modes is observed. In the case of 10B31P pairs the two modes are ω ∥ = 650 cm−1, ω ⊥ = 620 cm−1, and for 11B31P pairs, ω ∥ = 628 cm−1, ω ⊥ = 605 cm−1. Results for BAs pairs in silicon are also reported. It is believed that for the first time the second order Raman scattering by pair modes is observed. The second order spectrum gives information about the density of states of these modes.
Off‐center Cu+ in mixed crystals
Authors: Li M. Siu , de Souza M.
Published: July 2007

Perturbed off‐centre Cu+ ions by Cl− ions in KI and by I− ions in KCl are studied using uniaxial stress induced dichroism on the Cu+ uv absorption band and ionic thermocurrent (ITC) technique. Barrier height for the Cu+ reorientation is found to have a small decrease as compared with pure KI crystal. The symmetry of the multiwell potential minima changes from 〈111〉 orientation in KI to 〈110〉 in mixed KI + KCl crystals. When I− ions are added to KCl the off‐centre behaviour of the Cu+ is found to degenerate in a single deep potential well.
Optical and vibronic spectra of MnO in cesium bromide
Authors: Radhakrishna S. , Hariharan K.
Published: July 2007

Optical absorption spectrum of cesium bromide doped with MnO ion shows five bands. All these above bands are interpreted in terms of transitions within molecular orbital levels using the Ballhausen‐Liehr scheme. It is observed that, superposed on the electronic transition associated with the band at 6000 Å, there is a vibrational fine structure which arises due to the coupling between the electronic transition and the totally symmetric stretching vibration of the ion. The IR absorption spectrum of specpure CsBr:MnO shows four lines which are interpeted on the basis of different local symmetries of MnO ion in the lattice.
Anomalous magnetoresistance and band crossing in uniaxially compressed HgTe
Authors: Takita K. , Onabe K. , Tanaka S.
Published: July 2007

Resistivity at helium temperatures of uniaxially compressed slightly p‐type HgTe decreases greatly by application of a magnetic field along the stress direction. It increases again above a certain magnetic field HM showing a large resistance minimum. The minimum position HM increases proportionally to the applied compression. These properties are investigated using a magnetic field up to 55 kOe under a uniaxial compression up to about 7 × 108 dyn/cm2. By comparison with the magnetic sub‐band scheme calculated by the effective mass theory, it is concluded that the resistance minimum is due to a band‐crossing HM between the lowest Landau levels of the conduction and the valence bands. A second band‐crossing point is also observed by using a magnetic field modulation technique. A shear deformation potential constant of the Γ8‐band b is deduced; b = (−1.5 ± 0.2) eV. Further, an acceptor impurity band in the stress‐induced band gap is found by the analysis of the temperature dependence of weak field Hall coefficient.
Effect of crystal field on the inelastic neutron scattering cross‐section (II)
Authors: Sugawara K.
Published: July 2007

The linewidth of magnetic inelastic neutron scattering in metals is studied theoretically. In particular the linewidth due to the sf interaction is investigated on the basis of the Hirst theory for magnetic ions with substantial crystal‐field splitting. The theory is applied to the quasi‐elastic and the inelastic neutron scattering cross‐sections due to Ce3+. The experiments of Loewenhaupt and Steglich on the (CexLa1−x)Al2, considered to be the first to demonstrate the non‐vanishing values of the linewidths associated with excited states near zero temperature, can be qualitatively explained by the present theory.
Polarized luminescence and EPR study of Sn+ centres in KCl:SnCl2 crystals
Authors: Egemberdiev Zh. , Seeman V. , Zazubovich S. , Jaanson N.
Published: July 2007

Three types of Sn+ centres, recently found by Delbecq et al. in KCl:SnCl2 crystals irradiated at 77 K and warmed up to certain temperatures, are investigated by absorption, EPR, and polarized luminescence methods at 25 to 450 K. The intra‐centre luminescence peaks at 2.03, 2.06, and 2.02 eV are observed for all types of Sn+ centres under excitation in the most intensive absorption bands of Sn+ in the region from 6.4 to 5.6 eV and also in weak absorption bands at 5.1 to 3.1 eV. The connection of the observed absorption and emission bands with the Sn+ centres of a certain structure is established by comparing the thermal stabilities of the Sn+ centres obtained by the EPR and optical methods. The emission of all three types of Sn+ centres is polarized along the C4 crystal axis, which is probably caused by the orientation of the SnCl molecular ion in the crystal. The spectral bands of Sn+ centres are connected with the electronic transitions between the fully occupied ground state and two groups of excited states of the SnCl molecular ion whose energies depend on the location of v with respect to SnCl. The connection of the geometrical structure of Sn+v centres with that of Sn2+vc centres in KCl:SnCl2 crystals is discussed.
Superconductivity and phonon softening in instable systems
Authors: Postnikov V. S. , Postnikov V. V. , Fedorov V. M.
Published: July 2007

The effect of softening of phonon modes on the coupling parameter λ for superconductors with strong electron—phonon interaction is considered by taking into account electron effects. New formulae are derived which relates the increase in coupling parameter with optical phonons λopt for the PdH system and the increase in the parameter λ for A3B‐superconductors with A15‐structure to changes in the density of states at the Fermi level. Using these formulae the role of electron factor N(0) G2 in the increasing of superconductive transition temperature Tc is discussed for the most high temperature superconductors.
The electronic structure of MgO I. Calculation method
Authors: Abarenkov I. V. , Antonova I. M.
Published: July 2007

A method for calculating the electronic structure of an ionic crystal is developed which is an approximated self‐consistent field method. In this method the concept of an ion in crystal is used and a variational principle for the energy is employed. The method proposed is useful especially when applied to a crystal such as MgO where the corresponding free negative ion is unstable.
Study of initial stages of F‐centre aggregation in NaCl by Raman scattering
Authors: Ghomi M. , Rzepka E. , Taurel L.
Published: July 2007

Raman spectra of F‐centres in NaCl are very dependent on colouration method. First‐order spectra of “isolated” F‐centres are very well interpreted when a 70 and 10% softening in the interionic force constant between the F‐centre and its 1 nn's and between its 1 nn's and 4 nn's, respectively, is considered and if the electron‐phonen interaction is extended up to the 5th ion shell. At the very initial stage of colloidal aggregate formation, the change of the Γ Raman spectrum may be interpreted assuming F‐centre clusters whose sizesare likely much smaller than the laser wavelength.
The influence of the valley splitting and lineshape in the density of states on the quantum oscillations of n‐type (100) inverted silicon MOSFET surfaces
Authors: Köhler H. , Roos M.
Published: July 2007

Quantum oscillations in the channel resistance of n‐type inverted silicon (100) surfaces are investigated in quantizing magnetic fields up to 10 T as a function of the electron concentration ns. The data obtained at various tilt angles of the samples in the magnetic field are simulated numerically for ns ≧ 1 × 1012 cm−2, leaving out of consideration the range below this electron concentration, where the influence of many‐body effects is regarded to be important. The results are in good agreement with previous findings for the magnitude of the spin and valley splittings, and confirm the theoretical predictions about the lineshapes in the density of states as a function of the energy.
Temperature dependence of the electrical resistivity of disordered alloys
Authors: Richter J. , Schiller W.
Published: July 2007

The temperature dependence of the electrical resistivity of disordered alloys is investigated using a modified version of the model of Chen, Weisz, and Sher. Within this model the mechanism of negative temperature coefficients is discussed. For the relation between the temperature coefficient of the resistivity and the resistivity itself a qualitative agreement of the theoretical results and Mooij's experimentally observed universal rule is found.
Isomer shift of Eu2+ in fluorites
Authors: Schroeer D. , Kuo Ch. S. , Lambe R. L.
Published: July 2007

Mössbauer studies are carried out for divalent europium as dopant in the fluorites CaF2, SrF2, and BaF2. The 151Eu Mössbauer isomer shift in these materials increases, increases and decreases, respectively, as the Eu2+ concentration decreases below a few mole percent. Previous explanations of these effects as due to lattice pressure or host covalency are found to be wrong. Instead these trends are interpreted as primarily due to variations in the admixture of the prevalent defect structure of Eu2+OF (i = 1, 2, 3, or 4) which stabilizes the Eu2+ in these crystals.
Reaction field approximation for the ordered phase of heisenberg systems
Authors: Gusmão M. A. , Scherer C.
Published: July 2007

The approximation method to obtain the static properties of a system of interacting localized magnetic moments, called “reaction field approximation” (RFA), which is previously used for the paramagnetic phase, is extended to cover the ordered phase of a spin system with Heisenberg interaction. The presence of a small anisotropy is also considered and an application to MnF2 is made.
TO Phonon–Helicon Coupling in Polar Semiconductors
Authors: Sato K. , Kobayashi M. , Iwabuchi S. , Yokota I.
Published: July 2007

TO‐phonons coupled with helicons in a polar semiconductor are studied in detail in the Faraday configuration by the method of Green's functions technique, and are numerically analyzed for n‐InSb in two cases when the crossing would occur in‐ and out‐of‐Doppler shifted cyclotron resonance region, respectively.
On Singlet–Triplet Ferromagnet Dynamics
Authors: Szczepaniak E.
Published: July 2007

The spectral density method (SDM) is applied to the singlet–triplet model in the ferromagnetic region. The energy spectrum of the system and one‐site averages are obtained. A detailed analysis of these quantities at T = 0 is performed. The energy spectrum has two branches and at T = 0 two cases can be distinguished: the one when the two branches are positive, corresponding to the ferromagnetic and fully magnetized ground state, and the other when the two branches have opposite signs corresponding to the ferromagnetic but not fully magnetized ground state. Comparison between SDM and RPA results shows that RPA neglects transversal correlations in contradiction to SDM.
Anomalies in Thermal Expansion and Heat Capacity of Ferromagnets
Authors: Gurevich M. E. , Mitsek A. I. , Zhuravlev A. F.
Published: July 2007

Polymorphic transformations (PT) f.c.c. → h.c.p. in Co are investigated on the basis of Born's thermodynamic theory. The spontaneous deformation u23 is the PT parameter; the volume exchange ω is the additional variable. The PT problem is reduced to Landau's theory with the variable u23. The elastic moduli in this case are: (C11 – C12) → 0 and C44(T) = −C44(T) in the point T = T00 (T00 is the point of the instability). The maxima of the thermal expansion coefficient (TEC) and the elastic moduli as functions of T are calculated in the case of the first‐order PT. TEC anomalies are calculated by the method of near the orientational phase transition (OPT) point in Co and Ni. TEC is measured by the method of the continual T‐excchange. Anomalies of the TEC are found in the region of the PT in Co and near OPT in Co and Ni (near 500 K). The TEC quantities are in accord with the theoretical estimations. The TEC peak in the PT region permits to find the parameters of anharmonicity.
Diffusion of the Laue Spots in Electron Diffraction
Authors: Tamura E. , Ohtsuki Y. H.
Published: July 2007

Diffusion of Laue spots in electron diffraction is studied with changing the crystal thickness and temperature. Multiple inelastic scattering with diffraction is taken into account by coupled diffusion equations including diffusion coefficients, which are calculated humerically by the same method developed in dechanneling theory. The asymmetrical diffusion observed experimentally between the diffraction direction and its transversal direction is in agreement with the theoretical results.
Phonon‐Assisted Two‐Photon Absorption of the Excitonic Molecule in CuCl I. Bare‐Exciton Approach
Authors: Ekardt W. , Brocksch H.‐J.
Published: July 2007

Phonon‐assisted two‐photon absorption of biexcitonic levels in CuCl is considered including damping of the nearly resonant excitonic intermediate state. A pronounced structure of the line shape due to resonance effects, threshold effects, and structure in the Fourier transform of the envelope of the excitonic molecule is predicted. A detailed discussion of both temperature and damping effects is given. Large cross sections are predicted. The most favourable energetic range to observe the effects derived here is the low energy tail of the line, on the left of the Γ⅕ exeiton.
Activation Energies for Migration of K+ and N0 in KN3
Authors: Chang Chaik , Neuberger J. , Fischer R.
Published: July 2007

Activation energies for the migration of K+ and N0 interstitials in KN3 crystals are calculated. The total cohesive energy is obtained from a modified Born model. Both double‐spherical and triple‐spherical potentials are used as the repulsive interaction. Polarization effects according to the Hatcher‐Dienes scheme are employed. N0 interstitial migration is found to require very little energy and thus becomes a good candidate for explaining the explosive instability of the azides.
On the Symmetry Groups of Non‐Rigid Impurity Centres in Crystals
Authors: Kiselev A. A. , Lüders K.
Published: July 2007

The conception of the permutation‐inversion symmetry group developed by Hougen and Longuet‐Higgins in the theory of non‐rigid molecules is applied to non‐rigid impurity centres in crystals, i.e. to impurity centres showing large‐amplitude motions of the nuclei. Examples of derivation of the symmetry groups for some molecular impurity centres are given and the transformations of the molecular coordinates induced by permutation‐inversion operations are discussed.
The Electronic Structure of MgO II. Results of Calculations
Authors: Abarenkov I. V. , Antonova I. M.
Published: July 2007

The method proposed in a previous paper is applied to the calculation of electronic structure of MgO. The first and the second nighbours are taken into account and well localized crystal orbitals of O2− are obtained. The results for the lattice constant, cohesive energy, and compressibility are in good agreement with the experiment.
Frequency Dependence of Some Functions Associated with Surface Polaritons
Authors: Nkoma J. S. , Rwaboona S. K.
Published: July 2007

The frequency dependence of the ratios of the magnitudes of the Poynting vectors and energy densities associated with surface polaritons for a semi‐infinite specimen are derived using electromagnetic theory. Strength functions characterising the quantitative composition of the surface polariton are calculated. The ratio of the tangential and normal components of the mean square electric fields is found to be a decreasing functions in the surface polariton frequency range. Graphs to illustrate the derived expressions are plotted taking parameters applicable to GaP.
The Reabsorption Mechanism of the Donor–Acceptor Energy Transfer
Authors: Serikov A. A. , Khomenko Yu. M.
Published: July 2007

The reabsorption mechanism of electronic excitation energy transfer between two impurities at sufficiently great distances in a crystal is investigated. The kinetics of energy transfer between the molecules of interest is considered taking into account the longitudinal relaxation of the excited terms. The spectral density of the radiation field and the quantum yield of luminescence depending on the system parameters and the temperature of a crystal‐dissolvent are discussed.
Spectra of Directionally Deformed Naphthalene Crystals and Exciton–Phonon Interaction Constants
Authors: Ostapenko N. I. , Sugakov V. I. , Chernomorets M. P. , Shpak M. T.
Published: July 2007

The absorption spectra of directionally deformed naphthalene crystals on anisotropic substrates of indole, deuteronaphthalene, and paradibrombenzene are investigated experimentally and theoretically. Directional deformations are created by changing the angle between the crystal and the substrate axes. A technique for determination of the thermal expansion coefficients of the crystals and substrates is worked out by which the deformation tensor for the naphthalene crystal is obtained. Using the data of the bands position in the absorption spectra and values of the deformation tensor components, the deformation potential constants Dxx = 4.2 × 103 cm−1, Dxy = Dyx = 1.9 × 103 cm−1, Dyy = 3.5 × 103 cm−1, Mxx = −2.7 × 102 cm−1, and Myy = −2.2 × 102 cm−1 are found, where Dij and Mij are the coefficients in the expansion of, respectively, the static and resonance interaction energy with respect to the deformation tensor.
Absorption Band Shape of Free Excitons in Indirect Band Gap Semiconductors at High Excitation Density
Authors: Lelyakov A. V.
Published: July 2007

The shape of the excitonic absorption band is studied theoretically for free Wannier‐Mott excitons in a semiconductor with an indirect band gap at high excitation density at T < Tc. The band shape is very different from the band of indirect excitons in semiconductors at small excitation density.
Localized Phonons Due to Substitutional Impurities in Dilute Copper Alloys
Authors: Kesharwani K. M.
Published: July 2007

A detailed theoretical study of the effects of force constant changes as well as defect concentration on localized vibrational mode frequencies observed in dilute copper alloys is made after employing a localized perturbation model which includes the change in mass at the impurity site as well as the change in nearest neighbour central force constant. The force constant change, when calculated after considering exactly the effects of impurity concentration c in single site approximation, is found to be appreciably different from that calculated in very low concentration approximation (c → 0). An effective force constant, described in the framework of a nearest neighbour rigid‐ion model of lattice dynamics, is calculated in a self consistent manner and utilized to study its frequency dependence. The force constant changes introduced explicitly by volume effects due to impurity atoms are evaluated in a way which does not involve any arbitrary parameter. The experimentally measured inband‐phonon shifts in a Cu‐4.1% Al alloy are described well by the calculated force constant change.
Solitary Bound State of Magnons and Lattice Deformation in an Anharmonic One‐Dimensional Ferromagnet
Authors: Pushkarov Kh. I. , Pushkarov D. I.
Published: July 2007

The presence of excited spins in ferromagnetic systems can change the potential energy of interaction between atoms. In a ferromagnetic anharmonic linear chain the deformation formed and the spin excitations can create a bound state which can move along the chain with constant velocity without changing its shape. The quantum‐mechanical treatment of the problem leads to a nonlinear Schrödinger‐like equation with nonlinearity of third and fifth powers which has soliton solutions.
Certain features of semiconductor behaviour in strong parallel magnetic and electric fields. IV. Zener tunnelling
Authors: Berezhkovskii A. M.
Published: July 2007

An expression is derived for the tunnelling current density in a semiconductor subjected to a strong magnetic field parallel to an electric field, in regard to the Wannier‐Stark levels generated in an electric field. Tunnelling in InSb under magnetic field is investigated.
Anisotropy of the electron—phonon interaction in copper. II. Scattering and transport properties
Authors: Schmidt H. , Mann E.
Published: July 2007

By use of the electron‐phonon matrix elements for Cu derived in a preceding paper (in the form with plane‐wave parts only) the anisotropic functions of the scattering rate and the mass enhancement, as well as the electrical resistivity and the Hall coefficient for several orientations of the magnetic field are calculated as functions of the temperature. The agreement with the experimental data is satisfactory, though the local maximum of the Hall coefficient, characteristic for the scattering anisotropy, appears at lower temperatures than measured. This and other deficiencies, however, may be uniquely related to the simplified form of the matrix elements and should be overcome when the d‐parts of the pseudo wave functions are retained. The present considerations are thought to explain also some discrepancies reported for Al.
The volume change in internal stress fields
Authors: Schoeck G.
Published: July 2007

In linear elasticity theory the total volume change of a body subject to internal stress fields vanishes. Nonlinear theory gives a volume change (generally an increase). The magnitude of this effect is calculated by thermodynamic arguments from linear theory by perturbation methods.
Bound magnetic polaron in magnetic semiconductors
Authors: Kuivalainen P. , Sinkkonen J. , Kaski K. , Stubb T.
Published: July 2007

The bound magnetic polaron (BMP) model is studied for a ferromagnetic non‐degenerate semiconductor. Using Zubarev's Green's function technique a set of coupled equations for the nonuniform spin polarization around an impurity is obtained and the binding energy of a shallow impurity state. A variational solution of these equations indicates that near the magnetic transition temperature the binding energy increases and the orbit of the bound electron shrinks. The application of a magnetic field decreases the binding energy and increases the electron orbit. The calculated temperature and magnetic field dependences of the resistivity are compared with the measured values for a EuSe sample.
Excitation spectroscopy of the I2 bound exciton and the excitonic molecule in CdS. I. Excited states of the I2 bound exciton
Authors: Puls J. , Voigt J.
Published: July 2007

Using a narrow band dye laser three excited states of the I2 bound exciton in CdS can be detected in the excitation spectrum of luminescence. Their behaviour at different excitation intensities is investigated giving essential conclusions to distinguish EM‐ and I2‐emission. From the corresponding lines in the transmission spectrum the oscillator strengths are estimated. The properties of the excited states refer to a deuteron‐like model of exciton weakly bound to the donor.
Theoretical description of elastic atom—atom scatteringd
Authors: Gärtner K. , Hehl K.
Published: July 2007

Recent measurements of Lindhar's scattering function are used as starting point for some theoretical investigations of the elastic atom‐atom scattering within the quasistatic model. Good agreement is found for scattering of light ions on heavy atoms. For heavy collision partners the theoretical results agree in average with the experiments but don't provide the oscillations in full magnitude. This deviation is caused by neglecting the deformation of electron distributions.
Conduction electron spin resonance and inhomogeneous broadening due to local moments
Authors: Witters J. , Stesmans A. , van Meijel J.
Published: July 2007

A simple theory is developed for the interaction of conduction electron spins with local moments in the bulk or at the surface of the metal, with emphasis on the conduction electron system, which is considered most important. When considering a local moment system with a distribution in g‐values and introducing an interaction strength in the electron system, this can give rise to extra linewidth terms, depending on the coupling strengths between the d‐s, d‐d, and s‐s subsystems, as compared to the width of the g‐distribution in the d‐system.
Calculations on the properties of helium in silicon
Authors: Kaplan D. R. , Weigel C. , Corbett J. W.
Published: July 2007

The electronic properties, lattice location, and diffusion coefficient of helium are investigated in silicon by extended Hückel theory calculations. The electrical properties are unchanged, the helium sits in the tetrahedral interstitial position, and the calculated diffusion coefficient is (1.28 ± 0.11) × 10−3 cm2s−1 exp (− 1.8 eV/kT).
Mixing of frenkel excitons and ionic excited states in a linear crystal of donor‐acceptor complex
Authors: Petelenz P.
Published: July 2007

The Merrifield model of the coupling between neutral and ionic excited states of a linear molecular crystal is applied to a crystal of a weak donor‐acceptor complex. The interaction of the ionic excited states with Frenkel excitations of donor (acceptor) molecules is taken into account. The results are discussed in relation to recent experimental data. Some other possible experimental consequences are pointed out.
Oxidation of clean cleaved Ge (111) surfaces
Authors: von Wienskowski J. , Froitzheim H.
Published: July 2007

The oxidation process of clean Ge (111) surfaces is followed up with low‐energy electron loss spectroscopy (ELS). Quasimolecular binding with a characteristic loss at 9.2 eV is recognized first. As oxide is formed at the surface an intense loss at 7.2 eV governs the spectra up to complete oxidation. In comparison with recent results on cleaved Si (111) surfaces the oxide is determined to be non‐stoichiometric.
The Clebsch‐Gordan coefficients of the crystallographic space groups
Authors: van den Broek P. M.
Published: July 2007

A recent method for the determination of Clebsch‐Gordan coefficients is applied to the crystallographic space groups.
Critical temperature of a compressible ising magnet
Authors: Chakrabarti B. K. , Barua B. P. , Sinha S. K.
Published: July 2007

The shift in critical temperature due to spin‐phonon interaction in a two‐dimensional compressible Ising magnet under zero pressure is obtained using a self‐consistent field approach. Fluctuations near the shifted critical temperature are also discussed. The observed shift in critical temperature is compared with that of Matsudaira.
Optical identification of substitutional acceptors in refined ZnTe
Authors: Magnea N. , Bensahel D. , Pautrat J. L. , Pfister J. C.
Published: July 2007

A systematic study of acceptors incorporated by diffusion is carried out on refined melt‐grown ZnTe. The properties of five substitutional acceptors are investigated by low‐temperature photoluminescence. Since the binding energy of excitons on neutral acceptors is almost unaffected by the central cell potential, the neutral acceptors are identified by the two‐hole transitions which give accurate values of acceptor ionization energies. The two dominant acceptors “b” at 61 meV and “a” at 149 meV are identified as LiZn and CuZn, respectively, while the hole binding energies on NaZn, AgZn, and AuZn are established as 62.8, 123, and 272 meV, respectively. These experiments show that all the relatively shallow acceptors involve impurities and not stoichiometric defects.
An extended deformable shell model for ionic crystals including quadrupolar deformation of the charge cloud
Authors: Ghosh S. , Basu A. N. , Sengpta S.
Published: July 2007

It is well known that the dipolar and scalar deformation of the charge cloud around an ion in ionic crystals are quite significant in describing the different lattice mechanical properties. Even after the inclusion of the above deformations systematic discrepancies between theory and experiment persist. An attempt is made to incorporate the effect of the quadrupolar distortion of the charge cloud in the framework of the deformable shell model. All the relevant equations and lattice sums are evaluated for the CsCl structure and a preliminary application of the complete model which takes into account simultaneously the scalar, the dipolar and the quadrupolar deformation considered for a CsCl structure crystal. So far there is no estimate of the effect of the quadrupolar distortion on the different properties of a crystal belonging to CsCl structure. The calculation indicates that the effect is quite considerable for certain properties and its inclusion improves the overall agreement with experiment.
Angle‐resolved UPS of GaS, GaSe, and GaS0.6Se0.4
Authors: McGilp J. F. , Parke A. W.
Published: July 2007

Angle‐resolved photoemission spectra are recorded from cleaved single crystals of GaS, GaSe and the alloy GaS0.6Se0.4. While energy band dispersion curves obtained for the three crystals are very similar, the azimuthal dependences of the emission from the top of the valence bands show considerable differences.
Quantum‐limit cyclotron resonance linewidth in semiconductors
Authors: Arora V. K. , Spector H. N.
Published: July 2007

A quantum theory developed earlier is used to study the cyclotron‐resonance linewidth for the electron scattering via the acoustic phonon, the ionized‐impurity, and the piezoelectric scattering mechanisms. For the electron‐acoustic‐phonon scattering, the linewidth is found to increase linearly with the magnetic field, while the peak‐value decreases with the increasing magnetic field. For the electron‐ionized impurity scattering, the line width decreases with magnetic field, while the peak‐value increases. The linewidth and the peak‐value are independent of the magnetic field in the case of piezoelectric scattering. Under the combined effect of all three scattering mechanisms, a minimum of the linewidth as a function of the magnetic field is predicted. The critical magnetic field for which the linewidth is minimum and the minimum value of the linewidth are found to vary as the square‐root of the impurity concentration. Wherever possible, comparison is made with the existing experimental data.
Static magnetic properties of doped magnetic semiconductors mean field approach
Authors: Spałek J. , Tarnawski Z.
Published: July 2007

The magnetic field and temperature dependences of static magnetic characteristics: magnetization, susceptibility, and paramagnetic Curie temperature of doped ferro‐, antiferro‐, and ferri‐magnetic semiconductors, are investigated within the mean field approximation. The case of deep impurities is considered, i.e. kBTC,N≪ ϵa. The general behaviour of the results is in agreement with the experimental data for some chalcogenides with spinel structure and those of rare earths. On this basis general conclusions are drawn, concerning the distinction between space homogeneous and inhomogeneous magnetic ground states.
A study of the collective properties of the degenerate electronic gas in metals using the (e, 2e), (e, 3e), and (γ, 2e) processes at high energies 103 to 104 eV
Authors: Neudachin V. G. , Yudin N. P. , Zhivopistsev F. A.
Published: July 2007

The process of quasielastic knock‐out of an electron by the projectile electron (e, 2e) allows one to study the κ‐ and also ε‐dependence of the single‐particle spectral density A(κ, ε). The plasmaronhole excitations of the metal conduction band and the modification of Mahan‐Nozières singularities in the production of a deep hole in a metal are considered as examples. Depending upon the experimental procedure the (e, 3e) and (γ, 2e) processes of knocking out the electron pair provide direct information either about the two‐hole spectral density B(κ1, κ2, ε) or about the Fourier image fk1κ2 (q) of the electron‐electron correlator f(r2).
Non‐linear fluorescence quenching in molecular crystals II. Recombination of free excitons
Authors: Benderskii V. A. , Brikenshtein V. Kh. , Burshtein A. G. , Lavrushko A. G. , Prikhozhenko A. G. , Filippov P. G.
Published: July 2007

The decrease of quantum yield and the fluorescence decay time of naphthalene and anthracene crystals with increasing exciton concentration (non‐linear quenching) in the range from 10 to 80 K is measured. Rate constants of bimolecular recombination, γ, found from these data with regard to diffusional escape of excitons from the light absorption layer, are increased by the factor of 1.5 to 2.0 with the increase in temperature from 10 to 30 K. In the same temperature interval the diffusion coefficient of excitons is decreased. Free‐pass model explaining an increase of γ with temperature (by the increase in the mean thermal velocity of free excitons) is suggested. From the measurements of non‐linear quenching for different light absorption coefficients of pumping the diffusion coefficients of excitons along the c′‐axis at 10 K are found to be equal to (1.3 ± 0.5) and (3 ± 1.5) × 10−3 cm2s−1 in anthracene and naphthalene crystals, respectively.
Superconductivity in spin‐glasses
Authors: Sadovskii M. V. , Skryabin Yu. N.
Published: July 2007

It is shown that spin glass ordering does not affect the superconductivity as a result of total compensation of the paramagnetic effect and the effect of spin‐flip scattering freezing out in a spin‐glass phase.
Tunneling investigations on V3Si
Authors: Schumann J. , Elefant D.
Published: July 2007

On bulk single phase V3Si single crystals (residual resistivity ratio ϱ(293 K)/ϱ(17.5 K) = 15 to 30) tunnel junctions are prepared by different preparation methods. The tunnel characteristics obtained by means of modulation technique yield energy gap values in the range of δo = (1.93 to 2.66) meV on a lot of different tunnel junctions. The relation 2δo/kTc > 3.52 found on some junctions indicates strong electron‐phonon interaction. Above the energy gap phonon induced structures are found in some tunneling characteristics.