bluuebunny/crossref_metadata_2025_split huggingface dataset:
Splitting of the valence band of copper by X‐ray K‐emission spectroscopy
Authors: Badzian A. R. , Kłokocki A. 
Published: July 2007

AbstractThe valence band of copper is studied by X‐ray emission spectroscopy. The profile of the Kβ2,5 line is measured by an one‐crystal spectrometer taking advantage of a fine focused electron beam and a high‐angle Bragg reflection of silicon crystal. The half‐width of the CuKβ2,5 line is 4.5 eV and there is a splitting of the line. The separation between the two maxima is 2.7 eV. The shortwave slope of the curve is very sharp. It is similar to the emission band of simple metals where the threshold singularities are observed according to Mahan's theory. The comparison with the theoretical density of states and ultraviolet photoelectron spectrum measured by Lindau and Hagström suggests that in the CuKβ2,5 emission band two transition mechanisms occur. In the low‐energy part of the band the quadrupole transitions (1s → 3d) are dominant. The 3d states are partially localized. The dipole transitions (1s → 4p) occur in the high‐energy part, where s‐, p‐, and d‐bands are hybridized.
Energy loss of relativistic particles in solids
Authors: Komarov F. F. 
Published: July 2007

AbstractThe theory of bremsstrahlung from relativistic particles as function of impact parameter is developed on the basis of the virtual photon method using the Moliere atomic potential. The contribution to the particle energy loss by collisions is calculated by means of the quantum dielectric formalism. The channeled‐to‐random energy loss ratio is calculated for both, light and heavy particles. For the hyperchanneled, ultrarelativistic positrons it is a value of the order of 10−2. For heavy particles the ratio is of the order of 0.5 to 0.2. On the contrary for channeled electrons there is an enhancement of the average energy loss as compared with the random case. The contributions of transition bremsstrahlung and Kumakhov radiation are discussed, too.
Lattice dynamics of (NH4)2CuCl4 · 2 H2O
Authors: Chaplot S. L. , Sahni V. C. 
Published: July 2007

AbstractRaman scattering measurements of the external vibrations in (NH4)2CuCl4 · 2 H2O are analysed on the basis of a rigid molecular–ion model involving a crystal potential that allows for pairwise interaction between atoms. Lattice stability is used as an important criterion in obtaining the parameters of the potential.
Hot‐carrier infrared absorption in n‐type germanium
Authors: Seeger K. , Vana H. 
Published: July 2007

AbstractA modulation of the 10.6 μm CO2 laser transmission through n‐type germanium by carrier heating in a pulsed de electric field applied to the sample is observed for various crystallographic directions of the polarization and the field direction. The field intensity is varied up to 1200 V/cm the sample temperature is either 150 or 300 K. Although the maximum light modulation observed is less than 0.2% the directional dependencies are clearly visible. The modulation effect is interpreted in terms of carrier heating by the applied field. Calculations of the absorption coefficient assuming a hot‐carrier distribution function taking into account the many‐valley band structure qualitatively explain the field dependence as well as the anisotropy of the observed modulation.
The kinetics of electron transitions for donors with excited states
Authors: Pickin W. 
Published: July 2007

AbstractA new theory is presented which treats non‐equilibrium phenomena, such as photoconductivity and impact ionization, involving donors with excited states, essentially by means of a recasting of Lax's theory of cascade capture. Its point of departure is the set of rate equations describing the system of donors and conduction band. These are solved rigorously in the steady‐state, the solution being expressed as a balance between a net recombination rate and a net ionization rate. The former clearly describes a cascade capture, the sticking probabilities involved being generalizations of those of Lax; the ionization rate contains terms representing an inverse cascade, not considered by Lax, and these terms are usually the dominant ones. Applications are given to the calculation of the electron concentration‐field characteristic n(E) during impact ionization of shallow donors in germanium, and to photoconductive experiments in the presence of an ionizing field.
Parametric decay of a helicon in n‐InSb
Authors: Guha S. , Namjoshi P. 
Published: July 2007

AbstractThe parametric decay of a high power helicon into another helicon and an acoustic mode in a piezoelectric semiconductor is analysed using coupled mode theory. The acoustic mode is assumed to propagate across the applied magnetic field. The threshold electric field of the pump and the growth rates of the unstable modes well above threshold are obtained analytically. The analysis is applied to n‐InSb at 77 K. The threshold electric field is found to be of the order of 1.75 × 102 V m−1 and the growth rate at an electric field 1.75 × 103 Vm−1 is found to be of the order of 7.56 × 108 S−1. This order of wave amplitude is feasible presently.
Contribution of interband transitions to the conductivity of p‐Si at submillimeter wavelengths
Authors: Vindevoghel J. , Vindevoghel M. 
Published: July 2007

AbstractA complete calculation of free carriers absorption and of connected conductivity in p‐type silicon is performed including both acoustic and optical phonon and ionized impurity scattering, and direct transitions between the valence bands. The interband transition probability is determined for any direction of the wave vector taking the warped character of the valence bands into account. The theoretical results are compared to conductivity measurements in millimeter and far infrared ranges. A good agreement is observed if the spin–orbit splitting energy Δ is assumed to be 0.035 eV and if the band parameters L, M, N (expressed in h2/2m units) are chosen close to the values L = −6.69, M = −4.56, N = −8.50.
Long‐wavelength optical phonons in ZrSe3
Authors: Zwick A. , Renucci M. A. 
Published: July 2007

AbstractZone‐center optical phonons in ZrSe3, the prototype of the IVB‐trichalcogenides family, are investigated by Raman scattering for several incident and scattered light polarizations, and by infrared reflectance measurements. These layered compounds are characterized by isolated chains along the b‐monoclinic axis formed by the linear stacking of distorted trigonal prisms with Se atoms at the corners and Zr atoms in the center. Nine modes are found among the twenty‐ones theoretically predicted. Phonons assignment is made by a group theoretical analysis of the crystal structure, using the correlation method which relates single chain modes to crystal modes as the interchain coupling is truned on.
Polarized luminescence and EPR study of Sn3+ centres in KCl:SnCl2 crystals
Authors: Egemberdiev Zh. , Realo K. , Zazubovich S. , Haldre Ü. , Lehto T. , Reifman S. , Seeman V. 
Published: July 2007

AbstractSn3+ centres in KCl:SnCl2 crystals X‐irradiated at 77 K and subsequently warmed up to certain temperatures are investigated by absorption, EPR, and polarized luminescence methods in the temperature interval of 4.2 to 400 K. Three types of Sn3+ centres with different thermal, optical and EPR characteristics are observed. The number of Sn3+(I) centres, having isotropic g = 2.011 and A119 = 0.641 cm−1 and the 2.09 eV emission polarized along the C4 crystal axis, reaches its maximum after warming an irradiated crystal up to 230 K. The EPR spectrum of Sn3+(I) centres is characterized by a well‐resolved superhyperfine (shf) structure of absorption lines, indicating that the Sn3+ ion has an approximately octahedral surrounding and weak perturbation along the [111] axis. The Sn3+(I) centres are supposed to be Sn3+ ions in an off‐centre position. The number of Sn3+(II) centres with g = 1.997, A119 = 0.754 cm−1, ACl∥ = 2.65 × 10−3 T, ACl∥ = 1.3 × 10y3 T and the 1.71 eV emission polarized along the C2‐axis of the crystal reaches its maximum after warming the irradiated crystal up to 280 K. The resolution of SHF lines decreases considerably as compared with that in the case of Sn3+(I) centres. It is assumed that Sn3+(II) centres may be associates of Sn3+ ions with two cation vacancies. Immediately after an X‐irradiation at 77 K a small number of Sn3+(III) centres is observable. It is quite probable that Sn3+(III) centres are the associates of Sn3+ with one cation vacancy, whose structure is similar to that of Sn2+v−c centres in non‐irradiated crystals.
Level Anticrossing and Pseudonuclear Zeeman Effect in the Triplet State of KCl:PO
Authors: Suisalu A. , Avarmaa R. 
Published: July 2007

AbstractOptically detected microwave resonance spectra of a KCl:PO single crystal are measured in magnetic fields from 0 to 2 kG. The Ty—Tz triplet state resonance frequency at 2.93 GHz decreases at the field direction B ‖ [110] and undergoes a level anticrossing at B0 ≈ 1.5 kG. Anomalously large splittings of the ODMR lines in low magnetic fields (up to 500 G) are explained as a result of pseudonuclear Zeeman effect: the hyperfine splitting due to the spin I = 1/2 of the 31P nuclei occurring in the second‐order perturbation is linear in B0 at low field strengths and greatly exceeds the genuine nuclear Zeeman splitting.
EPR Investigation of Mo5+ in CaMoO4
Authors: Friedrich M. , Karthe W. 
Published: July 2007

AbstractIn single crystals of CaMoO4 a Mo5+ centre is investigated. The g‐tensor values are gx = 1.973, gy = 1.946, and gz = 1.845. Using the g‐values and results of optical measurements the ground state is derived and a centre model is suggested. The temperature‐dependent line broadening is caused by spin—lattice relaxation which is determined by a pseudolocal mode.
Lifetime of Charge Carriers in Intrinsic Indium Antimonide
Authors: Bruhns H. , Kruse H. 
Published: July 2007

AbstractThe lifetime of additional photoinjected electron—hole pairs in intrinsic InSb at 291 K is investigated by measuring the photoconductive (PC) decay. Apart from studying the usual PC‐decay an arrangement is used with superimposed magnetic field transverse to the electric field. Depending on the direction of the magnetic field the photoinjected plasma is either driven into the sample's bulk or travels parallel to the illuminated surface. The Auger‐lifetime is evaluated from the measurements by a numerical magnetohydrodynamical simulation taking into account surface recombination as well as the Suhl profile of the intrinsic plasma. A lifetime of τ = (57 ± 3) ns is found which is independent of the magnetic field up to 2.3 T.
Luminescence Accompanying the Recombination of VF and F Centres in KCl and KBr Crystals
Authors: Egemberdiev Zh. , Elango A. , Zazubovich S. 
Published: July 2007

AbstractThe spectra of thermally stimulated luminescence caused by the recombination of mobile VK centres, VF centres, and X centre decay products with F centres are studied at temperatures from 80 to 500 K for KCl, KCl:Sr, KBr, and KBr:Sr crystals X‐irradiated at 80 or 295 K. The recombination processes occurring near a cation vacancy are established to be accompanied by a new characteristic emission band located in a higher‐energy region as compared with the emission caused by the recombination of VK and F centres. The processes responsible for the emission are discussed.
Spin Wave Analysis of the Two‐Dimensional Heisenberg Antiferromagnets Rb2MnCl4 and (CH3NH3)2MnCl4
Authors: Schröder B. , Wagner V. , Lehner N. , Kesharwani K. M. , Geick R. 
Published: July 2007

AbstractThe frequencies are measured of the magnetic excitations (magnons) of Rb2MnCl4 and (CH3NH3)2MnCl4 by means of inelastic neutron scattering for [ξ, 0, 0] at 8 K and by magnetic resonance techniques for k = 0 at various temperatures. From the temperature dependence of the intensity of a magnetic Bragg peak, experimental values are obtained for the sublattice magnetization of those two 2D Heisenberg antiferromagnets. The experimental data are analyzed theoretically within the framework of Oguchi's renormalized spin wave theory. The spin wave parameters (exchange field and anisotropy field) are extracted from the measured magnon frequencies in a self‐consistent way. They are utilized to calculate not only magnon dispersion curves but also other magnetic properties as the sublattice magnetization and the magnetic susceptibility. Except for the susceptibility, the calculated values compare well with experimental data in the temperature range 0 ≦ T ≦ 0.7 TN.
Influence of a magnetic field on the characteristics of a ferroelectric semiconductor
Authors: Konsin P. , Örd T. 
Published: July 2007

AbstractThe influence of a magnetic field on the properties of a ferroelectric semiconductor is considered in the frames of the vibronic theory. The Zeeman and Landau splittings of valence and conduction bands are taken into account. The dependences of the Curie point, soft‐mode frequencies, and other characteristics on the magnetic field are calculated. The direction of the magnetic shift of the Curie point depends on the particular relations between the quantities of the spin and cyclotron splittings. In certain cases the magnetic field can change the potential ferroelectric phase transition into a real one.
Problems of the OPW Method. II. Calculation of the Band Structure of ZnS and CdS
Authors: Farberovich O. V. , Kurganskii S. I. , Domashevskaya E. P. 
Published: July 2007

AbstractFor the first time the MOPW method is applied for calculating the band structure of ZnS and CdS of sphalerite modification. Computations are made from first principles in a non‐(m‐t) approximation. Good agreement is obtained with the experimental data of the valence band and conduction band structures. It is shown that d‐states of Zn (Cd) form a narrow subzone in the lower part of the valence band. The compound CdS is used to investigate the effect of d‐states of Cd upon the energy spectrum. The d‐symmetry states are shown to have a rather significant effect not only on the states in the valence band, but also on the states of the conduction band.
Simple Two‐Band s–d Model for Ferromagnetic Semiconductors with Hybridization
Authors: Szőcs V. 
Published: July 2007

AbstractA simple two‐band model with hybridization between conducting s‐electrons and localized d‐(or f‐) electrons for ferromagnetic semiconductors in their low electron density regime is suggested and analyzed. Čápek's decoupling scheme is used for the time‐dependent Zubarev Green functions. A closed form is obtained for the spin‐dependent self‐energy. For a special case, the density of states is evaluated numerically.
Asperomagnetism and Short‐Range Magnetic Order in a Heisenberg Magnet with Random Exchange Bonds of Different Signs
Authors: Medvedev M. V. , Goryainova S. M. 
Published: July 2007

AbstractThe magnetic phase diagram of a Heisenberg model with nearest‐neighbour random exchange bonds of different signs is investigated in the molecular field approximation. It is shown that there is an asperomagnetic (random noncollinear ferromagnetic) state in the phase diagram of such a magnet. The temperature transition from a random collinear ferromagnetic state into the asperomagnetic one is considered. Characters of configurational short‐range magnetic orders in different types of magnetically ordered states are investigated as well.
Spin‐Wave Relaxation in Ferromagnetic Alloys
Authors: Kogan E. M. , Turov E. A. , Voloshinskii A. N. 
Published: July 2007

AbstractThe relaxation width of ferromagnetic and spin‐wave resonance lines in disordered alloys is investigated. Long‐wave spin waves are obtained in this system using simplest approximations (based on averaging over a physically small volume). The relaxation of these spin waves is due to the absorption of magnons by conduction electrons. The presence of disorder in the system leads to the non‐conservation of the total quasi‐momentum in these processes, thus making them effective, in contrast to ordered metals and alloys. The linewidth obtained, ΔB, is proportional to the resonance frequency and residual resistivity, and inversely proportional to the saturation magnetization. Both the linewidth and its dependence on the parameters are in good agreement with experiment.
Effects of Uniaxial Stress on the Absorption of the F‐Centre in CsBr
Authors: Dochy F. , Jacobs G. 
Published: July 2007

AbstractThe stress induced linear dichroism in the absorption spectrum of the F‐centre is measured on CsBr at 77 K. A moment analysis is applied to interpret the results. In order to show agreement with previous theoretical calculations of the electron–lattice coupling constants it is suggested that the coupling to the vibrations of the second‐nearest neighbours must be important.
Debye‐Waller Factor for a Vacancy‐Trapped Mössbauer Impurity in Metallic Solid Solutions
Authors: Tewari A. K. , Roy S. K. , Bhattacharya D. L. 
Published: July 2007

AbstractThe effect of vacancy trapping of 57Fe atoms present as a dilute impurity in solid solution of aluminium, on the Debye‐Waller factor is evaluated theoretically in the harmonic approximation in the high temperature limit with the help of the double‐time Green function technique. The change in the recoil‐free fraction for the impurity atoms in the presence of nearby vacancies is estimated by using the force constants obtained from the usual Debye relation. A significant change in the Debye‐Waller factor is found with the rise in temperature indicating the effect of temperature on the amount of trapping of point defects by the impurity atoms. The contributions due to the substitutional impurity alone and that in presence of a vacancy adjacent to it are evaluated for a simple cubic crystal with nearest‐neighbour central‐force interactions and are discussed for the zero phonon process.
The Roles of Soft Modes and the Central Peak in Phonon Relaxation for the Ising Model with Transverse Field
Authors: Kashcheev V. N. 
Published: July 2007

AbstractThe damping and frequency shifts of the longitudinal and transverse phonons are derived in the right neighbourhood of the Curie point using the microscopic theory for ferroelectrics described by the pseudospin Ising model with transverse field. The scattering of phonons both on the soft modes and on the central peak gives the same contributions to the critical anomalies. The long‐range contributions to the effective “exchange integral” are also taken into account. The results coincide with predictions of the phenomenological theory.
Quantum‐Chemical Calculations of Electronic and Hole Centres and Surface of NaCl Crystals (II)
Authors: Kotomin E. , Shluger A. , Dzelme Yu. 
Published: July 2007

AbstractParameters of the CNDO method in a molecular cluster model derived in the first part of the paper are used for calculating the electronic structure of a number of defects in the ionic NaCl crystal. Hole (VK, H) centres, the surface as a defect, the F centre on the surface and in the first layer below it are considered. The positions of one‐electron defect levels within the gap of the perfect crystal are discussed. The models of the VK, H centres as Cl2− and Cl43− molecular ions in a crystal are confirmed. The results of the calculations based on the crystal field estimates (given in the first part of the paper) and the standard CNDO calculation scheme indicate that a more correct estimate of the electron interaction energy is necessary.
Phase Transitions in [M(NH3)6] (XY4)2 Compounds
Authors: Parlinski K. 
Published: July 2007

AbstractThe group‐theoretical analysis of the phase transitions in the ionic crystals [Ni(NH3)6] (ClO4)2, [Mg(NH3)6](ClO4)2, and [Ni(NH3)8](BF4)2, accompanied by the lowering of the space groups from Fm3m to P21/b is carried out. It is shown that the symmetry reduction is associated with the two‐dimensional irreducible representation τ10 of the star {k10}, which corresponds to the point X of the f.c.c. Brillouin zone. The analysis of the lattice normal modes in Fm3m phase allowed one to specify the structural changes created at the phase transition point. The monoclinic crystal structure with the space group P21/b may arise as a result of translational displacements of all ions in the plane parallel to the unique symmetry plane. The relative orientations of anions become also fixed.
On the Electronic Structure of Transition Metal Carbonitrides, Carboxides, and Oxinitrides. III. Calculation of the “41” Signals in the X‐Ray Valence Photoelectron Spectrum of HfCxN1−x
Authors: Weinberger P. 
Published: July 2007

AbstractIn Part III the relativistic KKR‐ATA method is used to calculate the “4f” binding energies in HfCxN1–x. It is found that the applied method and the applied model can reproduce the experimental data very well. In particular the calculated Fermi energies can explain the breaks of the “4f”‐binding energies as a function of the molar fraction.
Electron–Phonon Interaction in the Vicinity of the van Hove Critical Point
Authors: Drozhov Yu. P. 
Published: July 2007

AbstractThe electron–phonon interaction in the vicinity of the van Hove critical point M1 is considered without making use of the perturbation theory. The characteristics of the charge carriers located near such a point (dispersion law, density of states) are shown to vary considerably even if the coupling constant is small. The contribution of the electrons in the vicinity of the point M1 to the transport properties is discussed.
Transient Spectrum, Intensity, and Intensity Correlation of the Resonance Fluorescence from an Impurity Atom in a Solid
Authors: Sü K.‐E. , Vogel W. , Welsch D.‐G. 
Published: July 2007

AbstractThe influence of the linear electron‐phonon coupling on the resonance fluorescence light of an impurity atom in solids is studied in the limits of low temperature and resonant excitation of the zero‐phonon transition. It is shown that with respect to the total intensity the electron‐phonon coupling gives rise only to a Debye‐Waller factor. The transient spectrum is studied taking into account the effect of the spectral apparatus. Further, it is shown that the intensity correlation can be modified substantially provided that the electron is coupled to a pseudolocal phonon mode of very narrow bandwidth.
ENDOR Study of the Superhyperfine Interaction of Ti2+ in CdS
Authors: Böttcher R. , Dziesiaty J. , Heinhold D. 
Published: July 2007

AbstractThe coupling constants of the ligand hyperfine structure of CdS: Ti2+ are redetermined at 4.2 K using ENDOR. The results confirm the model obtained by previous EPR measurements and give correct data for the anisotropic parts of the ligand interaction.
Conductivity of a Many‐Valley Semiconductor in a Heating Electromagnetic Wave
Authors: Drozhov Yu. P. 
Published: July 2007

AbstractThe high‐frequency conductivity of a many‐valley semiconductor traversed by a strong electromagnetic wave is calculated using the conventional Boltzman equation. The function o(E) is shown to decrease on raising the electric field strength in a certain region of the latter. The influence of the phonon nonequilibrium effects is discussed.
On Photon Production by Channeled Electrons (Positrons)
Authors: Baryshevskii V. G. , Dubovskaya I. Ya. , Ghubich A. O. 
Published: July 2007

AbstractLaue diffraction of radiation from channeled particles in crystals is considered. The explicit expression for the radiation spectrum taking into account the real photon beam collimation is derived. The classical limit of the theory is considered.