bluuebunny/crossref_metadata_2025 huggingface dataset:
Scattering probabilities for holes. II. Polar optical scattering mechanism
Authors: Costato M. , Reggiani L.
Published: July 2007

The integrated scattering probabilities per unit time for the hole‐polar optical scattering mechanism have been evaluated for a typical two‐band (Ev1 and Ev2) valence band structure (spherical and parabolic). The wave functions of the two bands are mostly p‐like, the first (P3/2, M±1/2), the second (P3/2, M±3/2). The symmetry properties of the valence band wave functions are shown to introduce important effects in the coupling and decoupling of the two bands by mixing of Bloch states. The apparent paradoxon of an infinity in the transition probability, for emission and absorption processes in a vertical transition between Ev1 and Ev2 if Ev1 ‐ Ev2 = hω0 the optical phonon energy, is removed by the symmetry of the valence band wave functions.
Optical absorption and Faraday rotation in yttrium iron garnet
Authors: Wettling W. , Andlauer B. , Koidl P. , Schneider J. , Tolksdorf W.
Published: July 2007

Optical absorption and Faraday rotation of yttrium iron garnet have been investigated in the spectral range of 1 to 0.35 μm, at 300, 20, and 6 K. At wavelengths shorter than 0.7 μm the spectra were taken on thin films epitaxially grown on gadolinium‐gallium garnet substrate.
Intervalence band transitions in tellurium. II. Polarization E ⟂ c
Authors: Bangert E. , Fischer D. , Grosse P.
Published: July 2007

For the polarization E ⟂ c a weak absorption band dependent on hole concentration was found in tellurium in the spectral range 50 to 200 meV. This absorption is found at low temperatures and for hole concentrations > 1017 cm−3 It can be explained by intervalence band transitions H6‐H4 on the basis of the k·p perturbation treatment of part I. Further‐more the coupling between the valence bands H6, H4 and their energetic distance are determined. Other possible interpretations for the absorption band – the quadrupole and the forbidden transitions between the H5, H4 bands – are discussed.
The migration of vacancies in aluminium
Authors: Harrison E. A. , Wilkes P.
Published: July 2007

A migrating vacancy has been simulated using the pair potential for aluminium derived from the pseudopotential of Heine and Animalu. In view of the continued use elsewhere of a kinetic criterion for truncating the structural relaxation, the method of relaxation is discussed and the case for the correct procedure clarified. It is pointed out that calculations of the barrier height which perform relaxation after placing the defect at the mid‐point of its path can be seriously in error. To avoid this it is essential to carry out a quasi‐dynamic relaxation, progressively moving the defect from the initial site to the energy saddle.
Study of NH4 motion in some antiferroelectric crystals by inelastic scattering of cold neutrons
Authors: Dimic V. , Osredkar M. , Slak J. , Kandušsar A.
Published: July 2007

The spectra of the inelastic scattering of cold neutrons by antiferroelectric NH4H2PO4, NH4H2AsO4, and (NH4)2H3IO6 have been measured above and below their transition point, using a rotating crystal spectrometer together with a cold source. The low temperature neutron measurements show very little change as compared with the room temperature results. The torsional bands are narrow in both phases. The broadening of the bands is inversely related to the hindrance, and therefore the measurements suggest that the rotation of the NH+4 ion is strongly hindered, which is supported by the angular distribution of elastic scattering. The deuteron magnetic resonance of ND4D2AsO4 indicates that in addition to rotational motion of the ND4 group this group might oscillate in the paraelectric phase. The oscillational mode condenses at Tc. In order to check the assignments obtained from the inelastic neutron scattering studies the ir absorption spectra of NH4H2PO4, NH4H2AsO4, and (NH4)2H3IO6 and their deuterated analogues were measured at room temperature.
Binding of an exciton to a donor‐acceptor pair in a semiconductor. I. Critical binding in the case of a Coulomb interaction
Authors: Munschy G. , Stébé B.
Published: July 2007

It is shown that a stable binding of an electron and a hole in the finite dipole field of both an ionized donor and an ionized acceptor cannot occur, if the donor‐acceptor pair distance is smaller than a certain critical value depending on the dielectric constant ϵ and on the electron and hole effective masses m and m. Accurate upper and lower bounds of the critical distance are derived in the model defined by these physical constants, and compared to the experimental data available from the observed luminescence spectra in doped ZnSe and AlSb.
Contribution of configuration interaction to the intensity of crystal field transitions in tetrahedral Fe2+ion
Authors: Basu C. , Ghosh U. S.
Published: July 2007

The effect of configuration interaction via crystal field on the intensity of crystal field transitions in tetrahedral Fe2+ions has been discussed. The mixing of the excited configurations 3d54p and 3d54f to the ground 3d6configuration of the tetrahedral Fe2+ion via crystal field results in a parity allowed electric dipole transition between crystal field levels of E and T2symmetry. The contribution of such configuration interaction to the oscillator strength of crystal field transition of the tetrahedral Fe2+ion in ZnS has been estimated within the framework of crystal field theory using Racah formalism and Richardson functions for the radial integrals. This contribution to the oscillator strength is found to be quite significant and approximately equal to 0.28x10−4.
Orientation‐dependent resonant raman scattering in InSb and GaSb at the E1–E1+Δ1 region
Authors: Dreybrodt W. , Richter W. , Cerdeira F. , Cardona M.
Published: July 2007

The resonance of the first order Raman scattering by LO and TO phonons near the E1 and E1 + Δ1 electronic gaps of InSb and GaSb is presented. Whereas for forbidden LO scattering the spectra are independent of the orientation of the crystal surface, for allowed TO and LO scattering the resonance spectra depend strongly on the surface orientation. This orientation dependence is discussed in terms of both allowed and first order vector induced (q‐dependence, electric field, etc.) scattering processes.
Crystal potentials and one‐electron states near the fermi surface of calcium
Authors: Perrot F.
Published: July 2007

Using the APW method an investigation is made of the band structure of f.c.c. calcium in two directions which are not explored in recently published APW calculations on solid Ca. The first of these is related to a detailed description of the crystal potential including the correct Hartree‐Fock core‐valence exchange (exact under the restriction of the frozen core approximation), a local valence‐valence exchange and correlation potential and a crude core polarization contribution. The corresponding self‐consistent band structure is very similar to the classical one obtained with a free‐electron Kohn‐Sham exchange. The modification of the band structure appearing when the core polarization is deleted is in qualitative concordance with the pseudo‐potential results of Vasvari et al., but a quantitative agreement is excluded. The second part of the work is interested in the effect of the non spherical potential on the band structure. It is not strong enough to modify the ordering of the levels near the Fermi surface found in the Kohn‐Sham approximation and does not confirm the results of the OPW calculation of Chatterjee and Chakraborti.
Underdamped soft tunnelling modes in hydrogen‐bonded ferroelectrics below T
Authors: Blinc R. , Lavkenčič B. , Levstek I. , Smolej V. , Žekš B.
Published: July 2007

Underdamped soft tunnelling modes, which disappear on deuteration, are observed in KHZP04 type crystals below Tc in addition to a central mode which exists both above and below Tc. These results can be understood in terms of a Bloch type description of pseudo‐spin motion.
A further synthesis of sextic and integral theories for dislocations and line forces in anisotropic media
Authors: Asaro R. J. , Hirth J. P. , Babnett D. M. , Lothe J.
Published: July 2007

A further synthesis of the sextic and the integral theories for the elastic fields of line forces and dislocations in anisotropio media is made. The expressions derived for the distortions and displacements are believed to be the most convenient ones for purposes of numerical computation. In addition expressions are given for the derivatives of the field quantities for use in Lothe‐Brown‐Indenbom‐Orlov theorems which allow for the construction of three dimensional fields from two dimensional data. Some numerical examples for cubic media are included.
A decoupling procedure for green functions: Test at the ising model and application to an extended hubbard model
Authors: Ihle D. , Lorenz B.
Published: July 2007

A decoupling procedure for the double‐time three‐particle Green functions is presented. The formalism is tested at the spin ½ nearest‐neighbour interaction Ising model yielding more accurate results than Bethe's first approximation. The decoupling procedure is applied to the problem of electron‐charge ordering on the basis of an extended Hubbard model investigated by Bari, the corresponding phase diagram being calculated.
Photoemission and density of valence states of the H‐YI compounds II. ZnSe, CdS, and HgS
Authors: Shevchik N. J. , Tejeda J. , Langer D. W. , Cardona M.
Published: July 2007

The density of valence states of the II‐VI compounds ZnSe, CdS, and HgS has been determined with far uv (h v = 21.1 and 40.8 eV) photoemission. Discrepancies in the widths of the top portions of the valence bands between theory and experiment, similar to those reported for other II‐VI compounds in part I, are also found here. The results for ZnSe are compared to those obtained by others using synchrotron radiation and monochromatized X‐rays.
Screening of a static charge in the electron liquid
Authors: Jain Madhu , Jain S. C.
Published: July 2007

Numerical results are presented for the screening charge density around a static foreign charge in an electron liquid in the metallic density regime using a recently proposed expression for the local field correction term G(q) on the basis of the theories of Singwi et al. and using additional information of g(0) from the partial‐wave phase‐shift analysis. Present values are found to lie in‐between the values of Singwi et al. (Theory I) and of Vashishta and Singwi (Theory V).
Isoelectronic Impurity States in Tellurium
Authors: Takita K. , Suzuki K. , Tanaka S.
Published: July 2007

The galvanomagnetic properties of Se‐doped tellurium measured in the temperature range from 1.2 to 77 K were compared with those of undoped tellurium. The hole concentrations were not changed by the Se‐doping (from several p.p.m. t o 1500 p.p.m. (0.15%)). The temperature dependence of the weak field Hall coefficient was greatly changed by doping and showed two peaks at 4 to 6 and 20 to 25 K in sufficiently Se‐doped samples. The temperature dependence of the resistivity was also changed and showed a broad peak around 15 K. These results were interpreted on the base of a two‐carrier model in which the impurity band‐like states are degenerate with the valence band as was proposed previously and the number of the states increases with the Se‐concentration. This means that the impurity band‐like states of undoped tellurium may also consist of isoelectronic impurity states due to the residual Se‐impurity. The nature of the short range potential of the Se‐impurity in tellurium is discussed.
On Interaction Potential, Correlation Factor, Vacancy Mobility, and Activation Energy of Impurity Diffusion in Diamond Lattice
Authors: Hu S. M.
Published: July 2007

An intuitive concept was proposed earlier by the author that for the activation energy of impurity diffusion in the diamond lattice to be smaller than that of self diffusion, there must exist a long‐range vacancy‐impurity interaction potential. The present work explores more quantitatively certain required characteristics of the potential. The relationship between the activation energies of impurity diffusion and of self diffusion, QA and QB, respectively, is approximately given by QA ≈ QB − u(r3), where u(r3) is the potential when the vacancy is at the third coordination site of the impurity atom. Most of known physical models of interaction do not satisfy the required characteristics of u(r), leaving that of the extended vacancy as a probable one. Irrespective of the interaction potential, the relationship between the migration energies of the simple vacancy and the vacancy‐impurity complex, H and H, respectively, is simply given by H = H + QB − QA − Eb, where Eb is the binding energy. Utilizing this relationship and published experimental data of impurity diffusion, the migration energy of simple vacancy in silicon is found to be N (0.5 ± 0.1) eV. It is also shown that the impurity‐vacancy saddle point potential will not affect QA, contrary to common concept.
Exciton Spectra with Spatial Dispersion in Case of Non‐Normal Incidence
Authors: Skettrup T.
Published: July 2007

The general case of non‐normal incidence of light on a crystal exhibiting spatial dispersion is treated. The light wave will in general excite two transverse and one longitudinal polariton in the crystal. Additional boundary conditions are obtained for the three‐dimensional case by means of the Lagrange formalism. The Fresnel formulae for reflection and refraction are derived, and exciton spectra for CdS are computed. Additional structure in the reflection spectrum near the longitudinal resonance energy is obtained for non‐normal incidence when the electric field of the light wave is parallel to the plane of incidence.
Valence and Conduction Band Structure and Infrared Optical Properties of Tellurium in the Presence of Pressure
Authors: Enderlein R. , Hache A.
Published: July 2007

The influence of pressure on the valence and conduction band structure and on the infrared optical properties of tellurium is investigated by means of group and perturbation theory. The first peak of the 11 μm‐band which corresponds to a direct intervalence band transition at the BZ corner H is shifted linearly by stress of any symmetry. At a certain critical value of hydrostatic pressure or uniaxial pressure parallel to the c‐axis it changes over into a second peak of the 11 μm‐band which is due to a transition on the symmetry line P. For hydrostatic pressure and uniaxial pressure parallel to the c‐axis the alteration of the fundamental edge results from a strain dependence of the energy gap being approximately linear. The deformation potential constants of the gap and of the first peak of the 11 μm‐band are determined by means of experimental data.
GaAs Luminescence Transitions to Acceptors in Magnetic Fields
Authors: Willmann F. , Dreybrodt W. , Bettini M. , Bauser E. , Bimberg D.
Published: July 2007

Low temperature luminescence spectra of pure and Sn‐doped epitaxial GaAs are reported. Distant donor‐acceptor pair transitions and conduction band to acceptor transitions are investigated in magnetic fields up to 12 T. The shifts of donor‐acceptor emission lines in unintentionally doped samples are in quantitative agreement with the calculated variation of the donor binding energy and of the Coulomb term. A considerable change in the magnetic behaviour at donor concentrations n > 5 × 1015 cm−3 is qualitatively discussed in terms of screening effects by free carriers on the impurity potential and impurity band formation. The shift of conduction band to acceptor transitions is linear up to the highest field.
The Anderson Model for Random Lattices with Statistically Distributed Overlap Potentials
Authors: Herscovici C.
Published: July 2007

Anderson's model for random lattices, considering not only the lattice‐site energies, but also the overlap potentials statistically distributed, is investigated. Assuming for both of them Lorentzian distributions, a calculation is performed for the mobility edges in second order of perturbation theory, and it is found that the statistical character of the overlap potentials has an effect of delocalization. This conclusion is enforced by the results obtained for the upper bounds of the mobility edges.
Réflectivité infrarouge du cinabre synthétique (α‐HgS)
Authors: Marqueton Y. , Ayrault B. , Decamps E. A. , Toudic Y.
Published: July 2007

Nous avons mesuré à T = 300 et 80 K les spectres de réflectivité infrarouge du cinabre (α‐HgS) en lumiére polarisée. Pour la première fois, tous les modes de vibrations prévus par la théorie des groupes ont été observés et analysés en termes d'oscillateurs. Ces expériences ont été effectuées sur un cristal synthétique de bonne qualité. Elles complètent les résultats antérieurs et conduisent à un modèle satisfaisant pour la dispersion de la constante diélectrique.
Symmetry of Lattice Vibrations in Selenium and Tellurium
Authors: Teuchert W. D. , Geick R.
Published: July 2007

A group theoretical analysis of the lattice vibrations in trigonal selenium and tellurium was performed for all symmetry lines and points in the Brillouin zone. For this analysis, the formalism of irreducible multiplier representations has been used.
Spinabhängige und optimal lokalisierte Funktionen geringer Energieunschärfe in Metallen
Authors: Krüger E.
Published: July 2007

Die Theorie der verallgemeinerten Wannierfunktionen wird durch die Berücksichtigung des Elektronenspins erweitert. Auf diese Weise ist es möglich, “spinabhängige lokalisierte Funktionen” zu definieren, die eine weitere Verallgemeinerung der verallgemeinerten Wannierfunktionen darstellen. Sie werden zur Beschreibung der Elektroneneigenschaften insbesondere der Metalle geeigneter als die letzteren sein, da ihre Energieunschärfe kleiner ist. Darüberhinaus wird dargelegt, wie man lokalisierte Funktionen bilden kann, die eine vorgegebene Spinstruktur im Festkörper beschreiben. Dabei zeigt es sich, daß nicht jede Spinstruktur auftreten kann, die auf Grund der Kristallsymmetrie möglich wäre, sondern nur solche, die auch mit den Symmetrieeigenschaften der Blochfunktionen verträglich sind.
Dynamics of Single Flux Lines in Superconducting Films by Vortex Microscopy Experiments
Authors: Boersch H. , Lischke B. , Söllig H.
Published: July 2007

To study single magnetic flux lines in superconductors a Vortex‐Microscope is developed and the motion is investigated of a single vortex through a superconducting thin film. Extremely small jumps between pinning centers are observed, which are compatible with the Anderson model of flux creep. The motion of a single vortex is thermally activated in agreement with the flux‐creep model. Henceforth the interactions of single flux lines and well defined pinning centers can be studied by vortex‐microscopical observations.
Further Aspects of the Electrical Conduction in the Highly Anisotropic Organic Semiconductor TEA (TCNQ)2
Authors: Brau A. , Farges J.‐P.
Published: July 2007

A complete report of experimental results on the dc electrical conductivity of TEA (TCNQ)2 is presented. In order to reconcile these results with the known structural and magnetic properties, it is suggested that the electron interactions play a fundamental role in the low lying magnetic excitations but have only a small influence on the much more energetic excitations to the conducting states. Conduction thus appears to resemble that of a band gap semiconductor modified by band tailing as a result of the cation disorder.
Luminescence Spectra Due to High‐Density Excitons in CuBrxCl1−x Mixed Crystals
Authors: Suga S. , Koda T.
Published: July 2007

Luminescence spectra due to high‐density excitons are investigated on CuBrxCl1−x mixed crystals under the N2 laser lightexcitation. Fine structures observed in the excitonic molecule luminescence in CuCl and CuBr are interpreted in terms of a predicted model for the excitonic molecule transition taking acount of the spin exchange and polariton effects. Binding energies of the excitonic molecule are estimated to be about 32 and 21 meV for CuCl and CuBr, respectively. A possible effect of the random potential in the mixed crystals on the high‐density excitons is also discussed in order to interpret an unusual behaviour of the luminescence spectra in the intermediate concentration region.
X‐Ray K‐Spectra of Chromium in Cr3X‐Compounds
Authors: Kurmaev E. Z. , Belash V. P. , Nemnonov S. A. , Shulakov A. S.
Published: July 2007

The results of investigation of CrKβ5‐emission bands from pure metal and from Cr3X‐compounds are considered. A conclusion about the structure of the energy bands in Cr3X‐compounds is made after discussion of these data together with X‐ray spectra of the second component, theoretical calculation of the electron structure, and experimental results obtained by photoemission. A detailed comparison of the X‐ray spectra of V3X‐ and Cr3X‐compounds is made.
A Model for the Deposition of Amorphous Ge
Authors: Shevchik N. J.
Published: July 2007

It is proposed that the continuous random network structure of amorphous Ge depends upon the types of configurations of atoms which are stable at the surface of the film during the time it takes to form a monolayer. As the temperature is raised and/or the deposition rate decreased, the average bond angle distortion decreases and the number of higher membered rings increases at the expense of lowered membered rings. It is argued that these changes may, in part, account for the observed variations in the electronic properties of amorphous Ge.
Approximate Analytical Description of the E(k)‐Dependence of the Bands of Heavy and Light Holes in Si and Ge
Authors: Von Bozeszkowski J.
Published: July 2007

Explicit analytical expressions of the E(k)‐dependence of the valence band of Ge and Si are derived. These expressions describe approximately the nonparabolicity of the bands of heavy and light holes which is caused by the interaction of these bands with the split‐off band. The approximate band structure is compared with the E(k)‐dependence of Kane's three‐band‐model of the valence band following from the (K. p.)‐perturbation theory.
Low‐Energy Phonons in Magnetite
Authors: Samuelsen E. J. , Steinsvoll O.
Published: July 2007

Acoustic and some optic phonon branches have been observed by means of inelastic neutron scattering in magnetite at room temperature and near the Verwey transition at Tv = 119 K. No appreciable effect on the phonon spectrum was found in passing Tv. Sound velocities determined at room temperature were found to agree only moderately with ultrasonic data, and they show marked deviation from cubic symmetry, which possibly could be interpreted in terms of anharmonic effects.
Grüneisen Constant of Alkali Metal: Calculation of Its Wave Number Vector Dependence and Its Volume Dependence
Authors: Shimada K.
Published: July 2007

In the case of alkali metal, the wave number vector dependence of the Grüneisen constant and its derivative with respect to the volume are calculated on the basis of the lattice dynamical theory. From the results calculated using second order perturbation theory, the following statements are obtained: 1) the T1 mode, in which wave number vector and polarization vector are parallel to (110) and (110), respectively, gives largest change to the Grüneisen constant. 2) As temperature raises, the volume dependence of the Grüneisen constant corresponding to this T1 mode reaches to the formula obtained assuming that the adiabatic compressibility depends only on the volume.
A Model Pseudopotential in Metallic Properties
Authors: Srivastava S. K.
Published: July 2007

A new pseudopotential model (distinct from the Ashcroft model) having only one parameter rc (core radii) of the metal has been proposed. The present model as well as Ashcroft's model have been used in evaluation of several properties like electrical resistivity and thermoelectric power of liquid metals, electrical resistivity of solid metals, temperature dependence of Knight shift at constant volume and constant pressure, and Fermi energy and density of states of simple metals. A new correction term for thermoelectric power has been given, which gives a better result for lithium and cesium. The results obtained have been compared with possible experimental and theoretical data. Good agreement has been achieved.
The Model Potential Method for an Extra Electron in Ionic Crystal
Authors: Abarenkov I. V.
Published: July 2007

The pseudo‐potential and mode. potential equations for an extra electron in ionic crystals are derived. The overlapping of the core orbitals is taken into account in the approximation linear in the overlap integrals. By means of this method the position of the bottom of the conduction band in KCl and NaCl is calculated.
Model for Long ‐ Wavelength Optical‐Phonon Modes of Mixed Crystals
Authors: Genzel L. , Martin T. P. , Perry C. H.
Published: July 2007

A model is presented which describes the optical modes of a mixed crystal. The model emphasizes a realistic use of the local electric field and is completely defined by the macroscopic parameters of the pure end members. The concentration dependence of the optical frequencies can be categorized into four distinct classes in contrast to the usual two classes, “one‐mode” and “two‐mode”. We suggest that experimental evidence already exists which supports this new classification scheme.
Investigation of Hyperfine Interaction and Structure in FeSiF6·6HO2 by Mössbauer Measurements
Authors: Spiering H. , Zimmermann R. , Ritter G.
Published: July 2007

Mössbauer, proton resonance, and susceptibility measurements (T ≦ 4.2 K) on FeSiF6. · 6H2O can be understood with the hypothesis that there are three equivalent Fe(II) sites related by C3 operation and the effective symmetry of the ligand field at each Fe(II) ion site is c2h (or lower). The nonaxial susceptibility tensor χ is related to the measured axial tensor χm by the equation χm = ⅓(χ + C3χC3−1 + CχC). A new interpretation of proton resonance measurements on single crystals yields χxx/χyy = 1,54 being in good agreement with the value deduced from Mössbauer powder spectra. The hyperfine constants are reconsidered. The quadrupole moment Q of the 14.4 keV 57Fe state is determined to be Q =0.20 b.
Vibronic Spectra and the Dynamic Jahn‐Teller Effect of Cubic ZnS:Cu2+
Authors: Maier H. , Scherz U.
Published: July 2007

Near infrared absorption and emission spectra due to the transitions 2T2 ↔ 2E of the Cu2+ ion in cubic ZnS have been measured at 4K. The distinct vibronic sidebands of the absorption spectrum exactly correspond to various critical point energies of TA, TO, and LO lattice modes, whereas the structure of the luminescence spectrum cannot be interpreted in terms of lattice phonon satellites. A dynamic Jahn‐Teller interaction in the 2T2 ground state being in the same order of magnitude as static lattice spin‐orbit splitting and phonon energy is shown to produce this deviation from the mirror symmetry. Weak and strong coupling approximations in the cluster limit have been extended to include vibronic states with up to six E‐modes.
Nonlocal Xα‐Exchange for s‐ and d‐Electrons in Transition Metals
Authors: Karsch P. , Rennert P.
Published: July 2007

Starting from Hartree‐Fock expressions a nonlocal exchange potential of the Xα‐type for transition metal valence electrons is calculated, respresented by different values αs and αd. No fitting parameter was introduced. Whereas αs remains nearly constant within one period αd increases nearly linearly with the number of d‐electrons. The dependence on the chosen atomic configuration and the influence of pressure were investigated. For Cu the energy bands mere calculated. They agree well with fitted local calculations.
Spin–Lattice Relaxation (SLR) of Paramagnetic Centres in the Vicinity of Off‐Central Ions
Authors: Vikhnin V. S. , Deigen M. F. , Shanina B. D.
Published: July 2007

The SLR mechanism of paramagnetic centres in the vicinity of off‐central ions due to the modulation of spin‐Hamiltonian constants by transitions between ground‐state multiplet (GSM) and excited‐state multiplet (ESM) is observed. These transitions are induced by interaction with phonons. The situation is investigated when the internal fields in crystal influence essentially the GSM. Agreement with experimental results for FA(Li)‐centres in KCI is obtained.
Galvanomagnetic Properties of HgTe in Strong Magnetic Fields
Authors: Dziuba E. Z.
Published: July 2007

Results of measurements are presented of the Hall coefficient and conductivity in undoped samples of HgTe in the temperature range 4.2 to 300 K and magnetic fields up to 30 kG. The results are explained using a three‐carrier model of conductivity in conduction band states, valence band states, and impurity states. The temperature dependence of the electron concentration and the contribution to the electrical conductivity of “heavy” carriers are determined.
The sd Bond and the Localized Magnetic Moment in the Solid Solutions of Transition Metals
Authors: Galperin F. M. , Kizheav F. G. , Shvedkov V. I.
Published: July 2007

The role of the sd bond is considered in the formation of the magnetic moment of the 3d‐transition elements dissolved in 4d‐metals. It is shown that in consequence of the sd bond the Coulomb interaction of the 3d‐electrons on an impurity atom is reduced by about 15 to 20% in comparison with a free atom.
Wavelength‐Modulated Absorption Spectra of Pseudodirect Bandgap A2B4C Compounds
Authors: Babonas G. , Ambrazevičius G. , Grigoreva V. S. , Neviera V. , Šileika A.
Published: July 2007

The wavelength‐modulated absorption spectra of ZnGeP2, ZnSiAs2, ZnSiP2, and CdSiP2 chalcopyrite crystals have been investigated with polarized light in the region of the absorption edge at 77 and 300 °K. Structures due to the pseudodirect optical transitions derived from indirect ones in sphalerite have been observed. The valence band structure and the relative location of the energy levels in the conduction band of the pseudodirect‐band gap A2B4C compounds have been determined.
Investigation of the Infrared‐Active Lattice Vibration in SrCl2
Authors: Droste R. , Geick R.
Published: July 2007

SrCl2, single crystals were grown by the Czochralsky method. Their reflectivity at 300 K and transmission at 4.2 K were measured for frequencies from 10 to 930 cm−1 and 10 to 150 cm−1, respectively. The reststrahl band found in the reflection spectrum has been analyzed by means of a classical oscillator model. In addition, a Kramers‐Kronig analysis was performed since a satisfactory fit could not be achieved with the classical model. The frequencies of the TO‐mode and the LO‐mode were determined to be 138 and 233 cm−1, respectively. A pronounced shoulder on the reststrahl band was observed as is also the case for CaF2, BaF2 etc. Its origin is discussed in terms of multi‐phonon processes. The results of the transmission measurements show that SrCl2, is transparent in the far infrared up to 110 cm−1 where the lattice absorption starts at 4.2 K.
A Simple Tight‐Binding Model Applicable to Calculations of the Band Structure of Amorphous Germanium
Authors: Henderson D.
Published: July 2007

A simple semi‐empirical tight‐binding model applicable to germanium is presented which takes into account the effects of rotation of the dihedral angle and of bond distortions. The effects of rotation of the dihedral angle are taken into account by including all interactions between nearest‐neighbors, the effects of distortions in bond angles by means of a two‐center approximation together with the properties of spherical harmonics, and the effects of distortions in bond‐length by fitting the matrix elements to the sophisticated band calculations of Herman et al. not only for crystalline Ge at the observed density but also for uniformly compressed and dilated crystalline Ge. Comparison of the results of this model with sophisticated calculations for various polymorphs of Ge shows that this model is, at very least, qualitatively satisfactory and should be useful in band structure calculations for amorphous Ge.
Temperature Dependence of the Cyclotron Resonance Absorption of Electrons in AgBr
Authors: Baxter J. E. , Ascarelli G.
Published: July 2007

The temperature dependence of the cyclotron mass and mobility of electrons in zone‐refined AgBr has been measured from 5 to 22 °K. The electron mobility, measured at 55 GHz, approaches 6 × 105cm2/Vs at 5 °K (ωc τ ≈︁ 30). The measurements indicate that there are two types of zone‐refined AgBr the difference arising from the relative electron and hole trap densities. The bulk of our experiments were performed on material where the electron traps are dominant. In this material the mass change with temperature is exponential with an activation energy (95 °K) nearly equal to the binding energy of the n = 2 bound state of the electron traps. The same 95 °K activation energy is also observed in the temperature dependence of the mobility. The exponential temperature dependence of both the mass and the mobility can be explained as arising from a resonant scattering of the electron by the traps with the aid of a virtual phonon. The AgBr where the hole traps dominate, on the other hand, shows a linear temperature dependence of the effective mass that is in agreement with what is expected of an electron moving in a polarizable continuum.
Interaction between a Vacancy and Impurity Atoms
Authors: Masuda K.
Published: July 2007

The vacancy‐impurity interaction energy is calculated on the Wolff‐Clogston model using the Hartree‐Fock approximation. It is suggested that if a bound state exists below the band bottom and if most of the excess electrons are localized at the impurity sites, the interaction energy tends to become negative. There is a qualitative agreement between the theory and the experimental results in Fe base alloys with 3d‐transition metal impurities. The interaction due to the magnetic origin inherent in the host metal structure is also taken into account using the simple Stoner model.
LCAO MO Treatment for Electronic Structure of Deep Levels in Semiconductors — S+Donor in Silicon
Authors: Shimizu T. , Minami K.
Published: July 2007

The energy and wave function of the ground state of the S+donor in silicon are calculated by empirical LCAO MO method. The donor state is simulated by a cluster of a S+ion and 274 silicon atoms surrounding it. The interaction and overlap integrals determined by Al‐strup and Johansen are used which fit the bands of silicon calculated by LCAO method to those of OPW calculation. The ground state is known to be totally symmetric, so that only the totally symmetric energy states are calculated. The fact enables to take the large cluster. The calculated MO coefficients agree rather well with those estimated from ENDOR data. Extended Hückel theory is found to be unsuccessful in describing the donor state in this case.
Polarized Optical Reflection Spectra of the Highly Anisotropic Organic Semiconductor TEA(TCNQ)2
Authors: Brau A. , Brüesch P. , Farges J. P. , Hinz W. , Kuse D.
Published: July 2007

From polarized reflection spectra of TEA(TCNQ)2 single crystals at room temperature, quantitative values of the complex dielectric function ε(ω) and the optical conductivity σ(ω) in the range from the far infrared to the ultraviolet have been derived. The polarization of the vibrational bands almost exclusively parallel to the highly conducting direction suggests strong interaction of conduction electrons with intramolecular TCNQ vibrations.
Electron–Phonon Interaction in the Photoluminescence of CdTe
Authors: Gippius A. A. , Panossian J. R.
Published: July 2007

The intensity of electron‐phonon coupling in the optical transition (characterized by the value of parameter N in the formula of relative intensity of phonon replicas, In = IoNn/n!; n = 0, 1, 2, …) was studied as a function of the ionization energy E1 of the luminescence centres in CdTe. It was found that N = 76 (eV−2) E. This dependence is in agreement with the results of the theory assuming bound carrier coupling with LO‐phonons for deformation potential coupling.
A Theory of Two‐Exciton Light Absorption in Antiferromagnetic Dielectrics
Authors: Gaididei Yu. B. , Loktev V. M.
Published: July 2007

The light absorption in antiferromagnetic dielectrics by the creation of two Frenkel excitons in the crystal is considered. It is shown that the absorption lines accompanied by the formation of bound states split into three perpendicularly polarized components. The form of the absorption spectrum both in the presence and absence of bound states for different polarizations of incident light, as well as the ratio of the intensities of the components are found. The object of the investigation is a crystal with a body‐centered orthorhombic lattice.
The Dislocation Loop in an Anisotropic Medium and Its Interaction with an Interstitial Atom
Authors: Meissner N. , Savino E. J. , Willis J. R. , Bullough R.
Published: July 2007

Several explicit expressions for the distortion field of an elliptical dislocation loop in a general anisotropic medium are presented. These are used to evaluate the interaction energy between an interstitial dislocation loop in copper and a nearby interstitial atom. The interstitial atom is represented by either a simple spherical inclusion or by realistic Kanzaki forces for its dumb‐bell configuration. The effects of both the microscopic anisotropy of the point defect and of the elastic anisotropy of the body on the form and magnitude of the interaction energy is thus exposed.
The H2O− Centre in KCl: An F‐Like Paramagnetic and Paraelectric Defect
Authors: Rusch W. , Seidel H.
Published: July 2007

ESR, ENDOR, optical, and electrooptical investigations of the H2O− centre and its deuterated versions in KCl are reported. The centre is produced by photochemical reactions in a KCl: OH− crystal. It can be considered as an F centre perturbed by an embedded water molecule: optical absorption bands at 2.40 and 2.09 eV are similar to the F band in energy and width; the hyperfine interaction constants of the surrounding nuclei are only changed up to 20%. The C2v, axis of the water molecule lies in one of the eight {lll) directions. Reorientation occurs below 7 K as a one‐phonon process, above 15 K by thermal activation with δE = 0.025 eV. Above 30 K motional averaging results in an ENDOR spectrum of cubic symmetry. An electric field induces strong dichroism in the optical absorption bands due to partial alignment of the H2O molecules. The effective electric dipole moment is 0.31 eÅ. The hyperfine interaction constants of the protons and of nearest neighbours can be calculated with fair agreement by a model wavefunction formed by orthogonalization of the F‐centre wavefunction to the H2O molecular orbitals.
Improved Perturbation Treatment of Bound‐State Problems with Special Applications to the Exciton
Authors: Pollmann J.
Published: July 2007

The Hamiltonian H0 + Hp for a perturbed bound state problem is separated in a self‐consistent way into a new exactly solvable part H0v and a new perturbation Hvp. Perturbation theory on H Hpv leads in many cases to a better converging result compared to Hp Especially the calculations of the phonon‐ and anisotropy‐influence on the bound exciton states compare satisfactory with experimental data and with results of involved variational methods. This good agreement is achieved by a partial summation of important parts of all higher order perturbation terms of Hp, without using any free parameters.
Sur le facteur de structure du gallium liquide Par
Authors: Badiali J. P. , Regnaut C.
Published: July 2007

Le facteur de structure du gallium liquide diffère, dans la zone du pic principal, de celui que l'on peut construire à l'aide du modèle des sphères dures. A cette différence peut‐ětre associée une fonction indépendante de la structure et de la température. En identifiant cette fonction à une variation de potentiel interionique, on montre à l'aide d'un modèle approché, que le pseudopotentiel peut jouer un rǒle déterminant dans la structure du gallium liquide, comme l'ont suggéré Heine et Weaire.
Magnetic Structure of CsCoCl3 at 4.2 °K
Authors: Melamud M. , Pinto H. , Makovsky J. , Shaked H.
Published: July 2007

The compound CsCoCl3 is paramagnetic at room temperature and belongs to the space group D−P63/mmc with two formula units per unit cell (CsNiCl3 type structure). The neutron diffraction of CsCoCl3 powder and single crystal samples were studied as a function of sample temperature. A transition to antiferromagnetism was found at TN = 21.5 °K. The magnetic structure determined from the diffraction pattern at 4.2 °K is collinear and consists of ferrimagnetic ab planes stacked antiferromagnetically along the c‐axis with spins parallel to the c‐axis. The magnetic moment consistent with the diffraction at 4.2 °K is (3.0 ± 0.3) and (2.3 ± 0.3) Bohr magnetons per Co2+ ion according to the powder and single crystal data, respectively. The magnetic unit cell is the hexagonal H‐cell (a = √3a0, c = c0) with six formula units per unit cell. This structure belongs to the magnetic space group P63′/m′cm′ (III‐ P63′/m′cm′). The powder and single crystal data show that the magnetic structure near TN is different from the magnetic structure at 4.2 °K.
Thermally Activated Unpinning of Dislocations from Point Obstacles in Terms of a Non‐Equilibrium Transition‐State Theory
Authors: Frank W. , Frydman R.
Published: July 2007

The wide‐spread treatment of thermally activated unpinning of dislocations from point obstacles in terms of the absolute rate theory is criticized. In particular, doubts are raised about the validity of the assumption that a thermodynamic equilibrium distribution is established between the equilibrium state of a pinned dislocation and its saddle‐point configuration. In analogy to Rice's dynamical theory of diffusion an alternative approach to dislocation unpinning is suggested, which does not make use of this assumption and which furthermore accounts for unpinning transitions by‐passing the saddle‐point configuration.
Infrared Absorption in Microcrystals of MgO
Authors: Lagarde P. , Nerenberg M. A.
Published: July 2007

The absorption coefficient of small crystals of the NaCl structure is calculated following a microscopic approach: a perturbed Green's function formalism with a change of the force constants of the ions at the surface of the microcrystals. Theoretical and experimental results are compared for the case of MgO samples.
Inverse Raman Effect by Polaritons in LiIO3 Single Crystals
Authors: Kneipp K. , Werncke W. , Ponath H. E. , Klein J. , Lau A. , Thuys Chu Dinh
Published: July 2007

First experimental observation of inverse Raman scattering (IRS) from polaritons are reported. The IRS frequency shifts measured in LiIO3 crystals using different scattering geometries are discussed and compared with SRS experiments. Using extraordinary continua and ordinary laser fields, the polaritons associated with the 769 cm−1 El‐phonon shift to 595 cm−1. In addition in this scattering geometry an absorption at 860 cm‐I was detected, due to a polariton in the upper dispersion branch. It is shown that the polariton absorption frequencies in IRS can be determined as in SRS from “undamped” quasi ‐momentum conservation laws. The IRS absorption coefficient for polaritons has a Lorentzian form. In some scattering geometries in anisotropic crystals, IRS and SRS can result in different polariton frequencies for the same fixed laser polarization; especially large polariton shifts in SRS are accompanied by small shifts in IRS and vice versa.
The Flow Stress of the Flux Line Lattice and the Magnetization Curve of Low‐x Type II Superconductors
Authors: Essmann U. , Schmucker R.
Published: July 2007

In low‐x type II superconductors there exists a long range attractive interaction between flux lines. This leads to a step B0 in the magnetization curve at Hc1. Experimental results frequently deviate from the ideal behaviour. The deviations are caused by the necessity to perform a plastic deformation of the intruding flux line lattice in order to accommodate the specimen geometry, and by flux line pinning. It is shown that both mechanisms lead to a finite slope of the magnetization curve near Hc1. The flow stress of the FLL and the volume pinning force may be obtained from magnetization measurements.
Optical Mode Gammas, Pressure Derivatives of Elastic and Dielectric Constants, and Stability of Rutile‐Structure Fluorides in the Rigid Ion Approximation
Authors: Striefler M. E. , Barsch G. R.
Published: July 2007

The microscopic Grueneisen parameters of all optical modes at zero wave vector, and the pressure derivatives of the elastic and dielectric constants of the difluorides XF, (X = Mg, Mn, Fe, Co, Ni, Zn) have been calculated from a rigid ion model with an effective ionic charge and with first and second nearest neighbor Born‐Mayer‐type central force short range interaction. The parameters of the model were previously determined from zero pressure values of the optical frequencies and elastic constants. The calculated values agree quite well with the few available experimental data. Several optical mode frequencies and elastic constant eigenvalues have negative pressure coefficients, which reflects and is related to the presence of several high pressure phases.
Crystal Field Calculations of Nd3+ Ions in Scheelites with D2d Symmetry
Authors: Kumar V. , Dass N. , Chandra K.
Published: July 2007

Crystal field calculations of the temperature dependent principal and mean magnetic susceptibilities, μeff, and the Schottky specific heat have been considered over the temperature range 10 to 400 °K in Nd3+: PbMoO4 and Nd3+: CaWO4 systems with D2d point symmetry at the crystal ion site. The spectroscopic splitting factors, Curie constants, and the extra entropy associated with Schottky anomaly are compared with available experimental data.
Theory of Lattice Thermal Conductivity of Anharmonic Crystals with Impurities. (II). Interference Effects
Authors: Altukhov V. I. , Zavt G. S.
Published: July 2007

The interference of the anharmonic and impurity scattering of phonons is investigated. In particular, a general formula is obtained for the resonant scattering of phonons by impurities taking into account the inelastic channel which is responsible for the temperature dependence of the total cross‐section of impurity scattering. It is found that the anharmonic scattering is decreased by interference effects. The latter is connected with the finite life‐time of the phonons scattered by impurities. The case of resonant scattering of phonons by isotopic defects is considered in detail.
A Theory Accounting for Electron–Phonon Interaction in a Compositionally Disordered System
Authors: Böttger H.
Published: July 2007

An incorporation of the electron–phonon interaction into the current theoretical concept of electronic states in disordered solids is investigated on the basis of a simple model of a compositionally disordered solid. In particular a single‐site approximation including contributions of the electron–phonon interaction is discussed.
A Theoretical Analysis of Cation Diffusion in Potassium Azide
Authors: Danemar A. G. , Royce B. S. H. , Welch D. O.
Published: July 2007

A theoretical analysis has been made of the temperature dependence and anisotropy of the self‐diffusion of tracer potassium ions in KN3. A vacancy mechanism is assumed, and the effects of correlation on diffusion are examined. An approximate analytic expression is obtained for the correlation factor, and its validity is determined by comparison with more accurate numerical calculations. The temperature dependence of the elements of the diffusion tensor including correlation is evaluated, making use of theoretical values of the migration energy of cation vacancies, and the role of correlation in determining the crystallographic anisotropy of cation diffusion is discussed. Comparison is made to available experimental data.