bluuebunny/crossref_metadata_2025 huggingface dataset:
NQR Study of Phase Transitions in Proustite at High Pressure
Authors: Baisa D. , Bondar A. , Gordon A. , Maltsev S.
Published: July 2007

The 75As nuclear quadrupole resonance frequency and spin‐lattice relaxation (SLR) time are measured in proustite (Ag3AsS3) in the temperature range 4. 2 K < T < 77 K at the high hydrostatic pressure. The pressure shifts of the first‐ and second‐order phase transition (PT) temperatures are detected. The tricritical point is reached at T 55. 5 K and p = 3. 2 kbar. A theory explaining the behaviour of SLR times at the first‐order PT and in the environment of the tricritical point is developed.
Zero‐point effect in ferrimagnetic and antiquadrupolar biquadratic systems (S = 3/2)
Authors: Westwański B.
Published: July 2007

Two negative branches of the spectrum in the antiquadrupolar phase and a negative one in the ferrimagnetic phase for Heisenberg‐biquadratic interactions with S = 3/2 lead to the zero‐point motion in energy and order parameters in the (1/z)1 approximation.
Electron‐hole drops in uniaxially stressed silicon
Authors: Wagner J. , Sauer R.
Published: July 2007

The photoluminescence of electron‐hole drops (EHD) in silicon is studied under uniaxial stress P ≦ 5 × 103 kp/cm2. The infinite stress limit is virtually reached, and characteristic EHD parameters are derived from lineshape fits including lifetime broadening effects. For P ∥ [100] and [110] “hot” EHD luminescence is observed due to electrons in the up‐shifted conduction bands. Thermalization with the “cold” electrons in the down‐shifted conduction bands only occurs for large band splittings above ≈︁ 20 meV and is suggested to be initiated by TA‐phonon assisted intervalley scattering. An extra line ≈︁ 1.3 meV below the cold free exciton emission for P ∥ [100] is attributed to the radiative decay of biexcitons.
Electronic polarization (relaxation) effects in the core level spectra of semiconductors. I. General theory of electronic polarization (relaxation) in semiconductors
Authors: Bechstedt F. , Enderlein R.
Published: July 2007

The core electron binding energies of semiconductors cannot correctly be described without taking into account of polarization (relaxation) energies due to the core hole. A formula is developed which relates the polarization energy to the dielectric function ϵ(q, ω) of the semiconductor. Band structure effects and the dynamics of polarization are considered. An approximate expression for ϵ(q, ω) is derived which can be shown to give a reasonable description for the relevant q‐ and ω‐regions. The theory represents the basis for the calculation of polarization energies in terms of only a few experimental parameters. The numerical results are given in the forthcoming paper (II).
Positron annihilation studies of the electronic structure of B.C.C. Fe
Authors: Szuszkiewicz S. , Rozenfeld B. , Szuszkiewicz M.
Published: July 2007

Angular distributions of annihilation quanta are measured for monocrystalline b.c.c. Fe samples oriented along the following five crystallographic directions: [100], [110], [111] [210], and [211]. Based on experimental data, the distributions of momentum density of annihilation quanta are calculated for the principal directions. The results obtained are analyzed on the basis of electronic band structure and following from this the shape of the Fermi surface.
On the theory of a natural (orientational) superlattice in a two‐dimensional electron gas
Authors: Volkov V. A. , Sandomirskii V. B.
Published: July 2007

The energy spectrum of electrons in the inversion layer on a high‐indexed surface of Si is considered The natural superlattice due to such surface orientation mixes the states with wave vectors differing by a reciprocal surface lattice vector. The classification of minigaps obtained is given for the various combinations of quantum numbers (the valley and subband numbers) of the states in question. The position of all types of minigaps in the k‐space is found.
Volume dependent lattice dynamics of solid argon A pseudo‐harmonic approach
Authors: Massa N. E. , Mitra S. S. , Vetelino J. F.
Published: July 2007

The volume dependent lattice dynamics of solid argon is calculated using a pseudo‐harmonic approach. The volume dependence of the elastic constants, from which the lattice dynamical model parameters are deduced, is obtained by relating the elastic constants to a m‐n pair potential of the Mie‐Lennard‐Jones type. The volume dependence of the phonon states is used to obtain the first and second Grüneisen parameters and constants. The thermal expansion coefficient is then calculated from the Grüneisen parameters in the quasi‐harmonic approximation. Finally, the Mie‐Grüneisen equation of state and the Lindemann melting criterion are combined to predict the melting curve of argon. Reasonable agreement is obtained between the calculated and experimental results.
Structure and kinetics of Fe3+‐doped PbMoO4
Authors: Friedrich M. , Karthe W.
Published: July 2007

In single crystals of PbMoO4 three Fe3+centres are measured by means of EPR. The zero‐field constants are determined. The kinetics of centre concentration and the magnetic relaxation are interpreted. Models of the centres are discussed.
Plasmons in three‐component systems
Authors: Salustri C.
Published: July 2007

Properties of plasma oscillations in a metal, taken as a three‐component liquid, are investigated. The role of the position of the Fermi level in determining the excitation energies for the band transitions is also studied in the three representative cases of Cr, Ni, and Pd.
On the nature of dielectric permittivity of PbTiO3 single crystals
Authors: Turik A. V. , Shevchenko N. B. , Gavrilyachenko V. G. , Fesenko E. G.
Published: July 2007

An investigation of the frequency dependence of dielectric permittivities ϵ11 and ϵ33 in single‐domain tetragonal PbTiO3 crystals enables one to determine all the permittivity tensor components and shows the presence of only the piezoelectric dispersion. Comparing the dielectric measurements with the Raman data, it may be concluded that, in contrast to many other oxygen‐octahedra ferroelectrics, ψ and ϵ of PbTiO3 are entirely determined by the resonance mechanisms of electronic and ionic polarizations.
Photoelectron spectra of core electrons from palladium—silver alloys
Authors: Berndt K. , Marx U. , Brümmer O.
Published: July 2007

For a number of PdAg alloys the photoelectron spectra of the core electrons are studied in a systematical way. The role of the so‐called extrinsic and intrinsic losses, satellite structures, and line‐shapes is to be discussed for 3p and 3d lines. Existing theories are discussed for the given cases. A multi‐electron mechanism for explaining satellite structures is proposed. Asymmetry of the Pd 3d lines is studied and a strong dependence on the density of states at the Fermi energy is found.
Weak‐field galvanomagnetic coefficients for structures with orthorhombic symmetry
Authors: Kyriakos D. S. , Economou N. A.
Published: July 2007

A formulation for obtaining the galvanomagnetic coefficients for the D2h group is presented based on Wasscher's method for the electrical measurements. The method is suitable to yield all possible transport coefficients.
Luminescence du centre dimère des ions Sn2+ dans le phosphore CaSe
Authors: Asano S. , Yamashita N.
Published: July 2007

Emission and excitation spectra of the dimer center of Sn2+ ions in the CaSe phosphor are measured at 6 K. The temperature quenching of the luminescence of the dimer and monomer centers is also measured. Eight excitation bands originating from the dimer center are found. The values of the spectroscopic parameters appearing in the energy matrices of the dimer center are determined so that the electronic levels obtained experimentally and theoretically may coincide with each other.
The effective screening function in Si, Ge, and GaAs and the effects of exchange
Authors: Duggan G. , Morgan G. J. , Lettington A.
Published: July 2007

Calculations are reported of the effective dielectric function for screening a pseudopotential in Si, Ge, and GaAs. The effects of exchange are also investigated by numerical calculations and an interpolation formula is given which fits the computed values. Screening the exchange interaction results in very small corrections to the effective dielectric function.
Nonradiative multiphonon carrier capture by deep neutral traps
Authors: Bhattacharya D. P. , Kachlishvili Z. S.
Published: July 2007

The galvanomagnetic effects and the Faraday rotation are investigated in the general case for any mechanism of the energy and momentum scattering of hot electrons in the strong and weak magnetic field limits and under the condition when the free carriers are captured in a nonradiative way by deep neutral traps described by a δ‐like attractive potential. For some definte scattering mechanisms the investigations are carried out in the presence of any finite magnetic field. The possibility of using the results for the estimation of some semiconductor parameters and for the determination of the dominant scattering mechanism is discussed. The calculations are carried out assuming spherical constant energy surfaces in the κ space.
Electronic states for the Al overlayer on the Si (111) surface
Authors: Nishida M.
Published: July 2007

Calculations are iteratively carried out for the overlayer of Al chemisorbed on the Si (111) surface using extended Hückel theory. The total, local, and orbital densities of states are presented for threefold‐coordinated substitutional and interstitial site chemisorption geometries. It is found that the electronic structure for Al on the Si(111) surface depends strongly on the chemisorption geometries and that the interstitial site geometry presents better agreements with existing spectroscopic experiments.
Anharmonic effects in ferroelectric Pb5Ge3O11
Authors: Suski T. , Müller‐Lierheim W.
Published: July 2007

Raman spectroscopic studies of Pb5Ge3O11 at various temperatures (300 to 400 K) and pressures (up to 6 kbar) are performed to obtain the variation of the frequency, width, and intensity of the ferroelectric and other low frequency symmetric modes. The results of the measurements allow separation of the measured temperature dependent frequency shift into the pure volume and the pure temperature parts. It shows that the higher order anharmonicities determine the temperature evolution of the modes Raman active only in the ferroelectric phase. Additional examination of the temperature and pressure dependency of the intensities and the self‐energy contribution of the lowest frequency modes leads to the conclusion that modes observed in the Raman experiment behave as uncoupled oscillators. The measured specific heat as well as the calculated Debye temperature (θ ≈︁ 230 K) are almost temperature independent and exhibit only weak anomaly in the phase transition region. To correlate the ferroelectric mode behavior with variation of the thermodynamic properties the calculation of the thermodynamic mode and Debye Grüneisen functions are performed.
Electron paramagnetic resonance of Er localized electron magnetic states in thorium hydrides
Authors: Drulis H. , Suleimanov N. M.
Published: July 2007

EPR of Er3+ ions in polycrystalline ThH2 and Th4H15 is studied and the possibility of the Kondo effect in ThH2 is discussed. In Th4H15 electron bottleneck is observed. The lineshape calculation is made for a metallic system in the case of an axial crystalline field. It is shown that in the point charge approximation a proton model is realized in Th4H15.
Raman scattering and phase transformations of TlGaSe2 and TlGaS2 under pressure
Authors: Vinogradov E. A. , Zhizhin G. N. , Melnik N. N. , Subbotin S. I. , Panfilov V. V. , Allakhverdiev K. R. , Salaev E. Yu. , Nani R. Kh.
Published: July 2007

Raman spectra of single crystals TlGaS2 and TlGaSe2 are investigated in equilibrium conditions at room temperature under various hydrostatic pressures up to 7.25 and 9.27 kbar, respectively. Phase transitions at about 5 kbar are shown to occur in both the single crystals. Mode parameters γi = (1/vi) (dvi/dP) are determined for most of the Raman bands observed. The different values of these parameters are used to find out which frequencies have to be assigned to interlayer vibrations. It is shown that Raman spectra can be explained best when the unit cell of TlGaS2 and TlGaSe2 is supposed to contain two layers and the structure of the layer is supposed to be similar to that of TlSe.
On the spin‐disorder resistivity of amorphous ferromagnets
Authors: Richter R. , Wolf M. , Goedsche F.
Published: July 2007

The spin‐disorder resistivity of amorphous ferromagnets is investigated in the temperature regimes 0 ≦ T ≫ TC and T ≫ TC. The resistivity is calculated within the force–force correlation function method up to the second order in the sd‐exchange constant. A simple structural model for a structurally disordered Heisenberg ferromagnet is presented. At lowest temperatures the spin‐disorder resistivity varies as T3/2 for a sufficient high degree of disorder. It is concluded that the experimentally observed T2‐dependence at these temperatures is of non magnetic origin. This dependence can be qualitatively understood if the thermal smearing of the structure factor is taken into account.
Optical studies of alkali trihalogeno‐plumbate mixed crystals
Authors: Heidrich K. , Trendel G.
Published: July 2007

Optical measurements on pseudoternary alloys of the alkalitrihalogeno‐plumbates (AHPs), CsPbCl3 and CsPbBr3 are reported for the whole range of mixing. With these results it is demonstrated that an empirical LCAO band scheme is suitable for a description of optical and electronic properties of plumbates. The mixed crystal behaviour of the AHPs is compared to that of thallous halides, their binary III–VII analogs.
A comparative study of phonons in polycrystalline and single‐crystalline LiF films by electron spectroscopy
Authors: Jakobs R.‐H. , Geiger J.
Published: July 2007

The electron energy loss spectra of thin polycrystalline and single‐crystalline LiF films are measured by means of a high‐resolution electron spectrometer (resolution 5 to 8 meV for 30 keV electrons) in the range from 30 to 100 meV. Theoretical spectra are calculated by using the dielectric theory of inelastic electron scattering and expressing the relevant frequency‐dependent dielectric constant analytically by a dispersion formula. The over‐all agreement between experiment and theory is good. Noticeable differences are found between the spectra of polycrystalline films and of thin single crystals: an excess of energy loss intensity is observed for polycrystalline films between 60 and 80 meV. The interpretation is, that the interfaces between the microcrystals give rise to the development of additional surface modes near 72 meV, which may be related to certain normal modes of isolated cubes.
Reflectance spectra of CdSiP2 and ZnSiP2
Authors: Ambrazevičius G. , Babonas G. , Šileika A.
Published: July 2007

Reflectance spectra of CdSiP2 and ZnSiP2 are measured at 300 K in the range 1 to 12 eV. These ternary compounds are electronic analogs of AlP and have the shortest bond SiP among the AIIBIVC2V semiconductors. The peculiarity of the investigated optical spectra is a close proximity and possible overlap of peaks which correspond to the structures E1 and E2 in AIIIBV compounds. The mean energies of the characteristic peak groups in the AIISiC2V compounds are shown to scale linearly with the average energy gap calculated by the dielectric theory.
A Pseudopotential study of the electronic properties of simple metals
Authors: Khanna K. N. , Sharma P. K.
Published: July 2007

A one‐parameter model potential is applied to the problem of energy–wavenumber characteristic and monovacancy resistivity of simple solid metals, and resistivity and thermoelectric power of liquid metals. The results agree well with available experimental values and better than several theoretical values.
Effective medium theory for the hopping conductivity in high electrical fields
Authors: Böttger H. , Bryksin V. V.
Published: July 2007

Starting from the rate equation in presence of an electrical field with arbitrary strength the hopping conductivity in a system with nearest neighbour hopping is investigated by using an effective medium approximation. At not too high fields the differential conductivity is shown to decrease with increasing field. This behaviour is qualitatively in agreement with experimental results on doped semiconductors.
Generation of dichroic h centres in KCl by polarized optical bleaching of interstitial atomic hydrogen
Authors: Reuter G. , Lohse F. , Spaeth J. M.
Published: July 2007

Upon optical bleaching of interstitial atomic hydrogen (H or U2 centres) with polarized light U and H centres (H and Cl) are produced, the latter in an unbalanced distribution which is measured by optical absorption and ESR. Similar results are obtained for bleaching of U2 centres in a mixed configuration with one Br− as nearest neighbour (H(Br)). In the H centre formation Clo is ejected to form a Cl−2 crowdion only into those [110] directions which appear perpendicular to the [111] optical transition moment of the U2 charge transfer transition. It is concluded that H centres are formed in an excited π‐state.
Exciton states in semi‐infinite molecular crystals with a point defect near the surface
Authors: Sugakov V. I. , Tovstenko V. I.
Published: July 2007

The energy spectrum of a semi‐infinite molecular crystal with a point defect on the surface is studied. It is shown that the criterion of uncoupling and the position of the impurity level depend on the distance of the impurity to a crystal boundary. In the case when a level of a surface exciton exists in the system, the uncoupling of the impurity term from the surface exciton band occurs at any slightest distortion of the molecule term. The data obtained can be used to investigate a number of phenomena such as the phonon spectrum and the electron spectrum in the approximation of tight coupling and in some other cases.
Readily computable expressions for LCAO two‐centre integrals over slater‐type orbitals with arbitrarily high quantum numbers
Authors: Eschrig H.
Published: July 2007

Readily programmable formulas for the LCAO two‐centre integrals over Slater‐type orbitals are derived which have numerically proved to give correct results in any practical case even for very high quantum numbers and which due to very simple recursion formulas require a minimum numerical effort. Also formulas for the LCAO electron–phonon matrix elements are given, and the way to use the given formulas to calculate the electron–electron interaction two‐centre integrals is described.
The influence of spatial dispersion and of the angle of incidence on thermomodulation spectra of the An=1‐exciton in CdS
Authors: Stössel W. , Wagner H. J.
Published: July 2007

Relflectance (R) and thermomodulated reflectance spectra (ΔR/R) of CdS in the region of the An=1‐exciton are measured at 8 K for angles of incidence between 5° and 85°. Because of the higher resolution obtained with the thermomodulation technique, a different behaviour of the “spike”, i.e. the additional reflection structure due to spatial dispersion, is detected than that previously derived from reflectance measurements alone. Measurements of its temperature dependence show that the spike is not very sensitive to thermal broadening. Fitting calculations, made with Pekar's additional boundary condition and allowing for an exciton‐free surface layer, show that the underlying models describe very well the experimental data, namely the behaviour of the transverse and the longitudinal exciton modes as well as that of the longitudinal‐transverse mixed mode.
Calculation of the electronic energy spectrum of a thin disordered solid film
Authors: Leipold W. C. , Feuchtwang T. E.
Published: July 2007

The effects of positional disorder on the electronic energy spectrum of a model finite insulating barrier are considered. The spectrum is studied for two different sets of boundary conditions imposed at the film surfaces: 1) traveling wave boundary conditions, leading to transmission resonances, and 2) periodic boundary conditions. Ledermann's theorem relates the transmission resonances to the corresponding discrete spectrum obtained using periodic boundary conditions. Halpern's reduced Green function technique for the calculation of approximate spectra of infinite systems is extended from a single to a multiband formulation and applied to the thin film problem. A quantitative estimate of the effect of the loss of short range order on the integrated density of states in a thin film is presented. The spectrum is discussed and related to the elastic tunneling transmission coefficient of a metal–insulator–metal heterojunction in which the insulating film is the tunneling barrier.
Balance equation for non‐equilibrium electrons in the mobility gap of a disordered semiconductor in the presence of light
Authors: Sulimov V. B.
Published: July 2007

Using non‐equilibrium Green's functions a balance equation is obtained describing the light induced stationary non‐equilibrium distribution of electrons over the localized states in a disordered semiconductor. The light is assumed to be monochromatic and in the final results only the terms linear in and independent of the light intensity are retained. Electron–phonon interaction is accounted for by perturbation theory.
Splitting of the valence band of copper by X‐ray K‐emission spectroscopy
Authors: Badzian A. R. , Kłokocki A.
Published: July 2007

The 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

The 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

Raman 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

A 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

A 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

The 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

A 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

Zone‐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

Sn3+ 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

Optically 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

In 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

The 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.
Cyclotron Frequencies near a Magnetic Subband
Authors: Claro F.
Published: July 2007

The energy spectrum of an electron in the presence both of a periodic potential and a magnetic field is extremely rich in fine structure. In particular, recent findings suggest that any subband of the spectrum contains a fine structure of Landau levels in its vicinity. An expression is derived for the energy spacing of these levels near an arbitrary subband.
Luminescence Accompanying the Recombination of VF and F Centres in KCl and KBr Crystals
Authors: Egemberdiev Zh. , Elango A. , Zazubovich S.
Published: July 2007

The 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

The 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

The 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

For 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

A 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

The 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

The 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

The 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

The 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

The 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

Parameters 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

The 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

In 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

The 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

The 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

The 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

The 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

Laue 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.
Raman Scattering in ε‐GaSe and ZnIn2S4 Single Crystals under Pressure
Authors: Vinogradov E. A. , Zhizhin G. N. , Melnik N. N. , Subbotin S. I. , Panfilov V. V. , Allakhverdiev K. R. , Baeaev S. S. , Zhitar V. F.
Published: July 2007

The influence of hydrostatic pressure on the Raman scattering spectra in ε‐GaSe (up to 8.5 kbar) and ZnIn2S4 (up to 10.9 kbar) is investigated at 295 K. Parameters γi – (1/vi) (dvi/dp) are obtained for both the single crystals; for e‐GaSe values of the mode‐Gruneisen parameters are also obtained. The set of the parameters γi(Γi) shows that these two crystals are layered ones with ionic‐covalent bonds inside the layers; the degree of ionicity in ZnIn2S4 is higher than in ε‐GaSe. “Rigid‐layer” (interlayer) vibrations determined for ZnIn2S4 and ε‐GaSe using γi‐parameters show that ZnIn2S4 is not a one‐packet polytype.
The Density of States at the Band Tail of a Disordered System with Correlations
Authors: Dúc Nguyẽn Manh
Published: July 2007

Edwards' formulation of the electronic states in a disordered system is extended for a generalized probability distribution in which the correlations between the positions of scatterers of different kinds are included. Using Feynman's path integral it is shown that the density of states may be defined in amorphous materials where the short‐range order may play an important role. The evaluation is considered for pure and binary liquid semiconductors and for a heavily doped and compensated semiconductor to give the asymptotic form of the density of states for ε < 0.
Perturbation Expansion for the Asymmetric Anderson Hamiltonian
Authors: Hobvtić B. , Zlatić V.
Published: July 2007

Asymmetric single orbital Anderson model is studied by the rapidly convergent perturbation method of Yosida and Yamada. The change in the density of states, specific heat, and transport coefficients due to the second order self energy corrections is evaluated for a dilute alloy with nearly half‐filled virtual bound state.
The Effect of Hydrostatic Pressure and Temperature on the EPB Spectrum of the Eu2+ Ion in CdF2b40 as a Function of the Nearest‐Neighbour Distances
Authors: Rewaj T. , Krupski M.
Published: July 2007

The effect of temperature and hydrostatic stress on the b spin‐Hamiltonian parameter for Eu2+ in CdP2 single crystal is investigated. The measurements are carried out in X‐band in the temperature range from 77 to 447 K and the pressure range up to 5000 at. The following results are obtained: (∂b/∂T)P = 1 at = −220 × 10−8cm−1K−1 and (∂b/∂p)T = 300K = +1.66 × l0−8 cm−1 at−1. It is deduced, on the basis of these results, that about 70% of the temperature changes in b(T) can be related to the thermal expansion of the crystal i.e. to the changes in metal‐ligand distance.
Reflectance and Thermoreflectance of GeTe
Authors: Baleva M.
Published: July 2007

The reflectance spectra of p‐type GeTe crystals are measured in the energy range 0.4 to 3.0 eV at liquid nitrogen and room temperature. The principal optical constants are obtained by inverting the spectra using the Kramers‐Kronig technique. The thermoreflectance spectra at room and liquid nitrogen temperature are measured over the energy range from 0.8 to 3.0 eV. The results are quantitatively interpreted. The relatively large and sharp changes in the thermoreflectance spectra near 1 eV are explained with the thermal width of the Fermi function, and with δ‐type transitions at 1.36 eV.