bluuebunny/crossref_metadata_2025 huggingface dataset:
Spontaneous hall effect and magnetization of Fe–(B, Zr) and Co– Mo amorphous films
Authors: Stobiecki T. , Pbzybylski M.
Published: July 2007

Amorphous Fe1–x(B, Zr)x and Co1‐x(B, M.o)x films are prepared by the rf sputtering technique over a wide range of concentration where the alloys show ferromagnetism. From the magnetization and mean hyperfine field values at low temperatures the magnetic moment of Fe(μFe) is determined. Using a rigid‐band model the charge transfer per ß and Zr atom to the Fe d‐band is calculated. The best fits are obtained for a charge transfer of 1.48 electrons per ß atom and of 1.8 electrons per Zr atom, yielding the observed critical concentrations at which ferromagnetism disappears: xc = 0.6 and Xc = 0.5 for FeB and FeZr films, respectively. From spontaneous Hall effect and resistivity (ϱ) measurements it is obtained thatRs ∼ ϱn in a wide range of concentrations with an exponent n = 1.97. The side jump parameter (Δy) calculated from the free‐electron Berger formula decreases with increasing concentration of non‐magnetic elements of the alloy. This tendency is similar as in the case of magnetic moment. The observed correlation between Δy and μFe shows that both parameters are of the same origin.
Charge ordering in intermediate‐band crystals
Authors: Ionova G. V. , Kosteubov Yu. N. , Nikolaev A. V.
Published: July 2007

The charge ordering phenomena in intermediate band crystals are considered using the extended Hubbard Hamiltonian as a model. The average 〈a+iaj〉 is taken into account for describing the delocalized electron density. The new criterion of the charge‐ordered state existence, including the boundary condition for the bandwidth, is formulated.
The temperature dependence (4.2 to 293 K) of the resonance energies of excitonic transitions in II–VI compounds
Authors: Dmitrenko K. A. , Shevel S. G. , Taranenko L. V. , Marintchenko A. V.
Published: July 2007

Excitonic reflectivity spectra R(hw) are measured by a digital technique for a number of II–VI compounds within a wide temperature range from 4.2 up to 293 K. The exact position of exciton resonance energy within the experimental R(hw) profiles is determined by comparison with reflectivity curves calculated in the model of bulk excitonic oscillator with classical dispersion and exciton‐free surface layer. The temperature dependences of exciton resonance energies thus obtained are found to satisfy the known Varshni formula which includes two empirical parameters. These are determined for each compound under study, so that reference data become available for the position of exciton resonance at any temperature ranging from 4.2 up to 293 K.
Optical properties of α‐ and β‐CuZn brasses in the region of quantum absorption
Authors: Sasovskaya I. I. , Korabel V. P.
Published: July 2007

The optical constants n and k of CuZn brasses with Zn content of 39, 40, 41, 47, 50 at% (β‐phase) and 35 at% (α‐phase) are measured at 293 K, and with Zn content of 35, 39, and 50 at% at 78 K also, in the 1 to 0.25 μm spectral range by the polarimetric method. From n and k reflectance R(λ), high‐frequency conductivity σ(ω) (where ω is the light wave cyclic frequency), the real and imaginary parts ε1(ω) and ε2(ω) of the complex dielectric constant, and the electron characteristic loss function ε/ε + ε are derived. Their concentration and temperature dependences are analyzed. The different characters of the concentration and temperature dependences of the absorption edge of α‐ and β‐brasses confirm that its origin in these alloys is not the same: in α‐brasses the edge is formed by interband transitions from EF to vacant states of the conduction band, while in β‐brasses by d‐band to EF transitions. No substantial change in the optical interband absorption is observed in both, the concentration and temperature (martensitie) b.c.c. to f.c.c. transitions.
Phonon wind generation in Ge by C02 laser induced heating of electron‐hole drops
Authors: Manenkov A. A. , Mikhailova G. N. , Sokolov S. Yu. , Tikhodeev S. G.
Published: July 2007

The processes occurring at high power CO2 laser pulse irradiation (λ = 10.6 (μm, t = 100 ns) of electron‐hole drops (EHD) in Ge are analyzed. It is shown that the features of the recombination radiation and microwave conductivity kinetics of the sample after CO2 laser pulse at intensities up to 105 to 106 W/cm2 are associated with recondensation of the evaporated EHD and with a phonon wind produced driving of nonequilibrium carriers. A theoretical model of phonon wind is suggested taking into account the delay between emission and absorption of the phonons. In comparing the theory with experiments a portion of the IR radiation quanta energy involved in the phonon wind generation is determined. The thermalisation channels of hot carriers are analysed.
Effects of a thin curved transition layer on surface polaritons. Local states
Authors: Wendler L. , Pechstedt E.
Published: July 2007

When a thin curved transition layer is placed on a semi‐infinite dipole‐active substrate, local states exist in the spectrum of surface polaritons. The dispersion relation and the electromagnetic fields are derived analytically in an explicit form for the case of resonance of the transition layer excitations with the surface polaritons. The spatial dependence of the electric field of the local states is presented in graphical form. It is shown that the field is localized sharply and enhanced within the characteristic distance of the valley in the surface profile of the transition layer.
The magnetic contribution to electrical resistivity in thin gadolinium films
Authors: Urbaniak‐Kucharczyk A.
Published: July 2007

The magnetic contribution to the electrical resistivity in thin magnetic films for the special case of h.c.p. structure is derived. Special attention is given to anomalies due to the magnetic phase transition. The numerical results obtained for the case of polycrystalline gadolinium films show the resistivity dependence on the film thickness and the surface properties.
The temperature dependence of the AC hopping conductivity of lightly compensated semiconductors
Authors: Klimkovich B. V. , Poklonski N. A. , Stelmakh V. F.
Published: July 2007

The temperature dependence of the ac hopping conductivity of lightly compensated semiconductors is explained by taking into account the transitions of a hole within three donor clusters. The effect of the defect wave function anisotropy is discussed. The anisotropy does not change the temperature and frequency dependence of the conductivity. The results are compared with experimental data on Si:P and Ge:P.
The absolute “lattice parameter” of crystals with defects measured with X‐ray methods
Authors: Habtwig J. , Hoiý V.
Published: July 2007

The physical meaning and the physical contents of a “lattice parameter” of a finite crystal with statistically distributed small defects is given. After a short discussion of the problem of defect models and of the elastic state of a finite crystal with defects, appropriate dynamical theories to treat the given problem are discussed. On the basis of a dynamical theory of X‐ray diffraction for crystals with statistically distributed defects in the coherent approximation an expression for the basis vectors of the unit cell of this kind of deformed crystals is derived.
Magneto‐optical measurements in Zn1‐xMnxTe with high manganese concentration
Authors: Desjardins‐Deruelle M. C. , Lascaray J. P. , Coquillat D. , Triboulet R.
Published: July 2007

Measurements of magnetoreflectivity and magnetization are performed on ZnMnTe alloys with Mn concentration x = 0.25 and .x = 0.45 for magnetic fields up to 5.5 T. The exchange constants α and ß are evaluated and compared to previous data. Magnetic circular dichroism measurements are performed in the temperature range 4.2 to 200 K for 0.25 < x < 0.71, to determine the variation of the energy gap as a function of the temperature and the Mn concentration.
Effect of carrier degeneracy on the screening length in degenerate tetragonal semiconductors
Authors: Mondal M. , Gnatak K. P.
Published: July 2007

An attempt is made to study the effect of carrier degeneracy on the Debye screening length of the carriers in tetragonal semiconductors taking degenerate n‐Cd3As2 as an example. It is found on the basis of the Karavaev and Borisenko model, which includes all types of anisotropies in the energy spectrum and has recently been demonstrated in the literature to be the most valid model for Cd3As2, that the screening length decreases with increasing carrier concentration as expected for degenerate semiconductors. Moreover, the tetragonal crystal field effectively reduces the same length with increasing amount of reduction with decreasing electron concentration. The corresponding results for isotropic parabolic energy bands are also obtained from the expressions derived.
Optical spectra and energy band structure of layer‐type AIVBVI compounds
Authors: Valiukonis G. , Guseinova D. A. , Keivaitb G. , Sileika A.
Published: July 2007

The electroreflectance and absorption spectra as well as the hydrostatic pressure dependence of the fundamental absorption edge of GeS, GeSe, SnS, and SnSe crystals are investigated in polarized light. The lowest direct energy gaps are found to be 1V1— 1V1 (E | | a) and 1Λ4— 1Λ4 (E || b) for Ge and Sn monochalcogenides, respectively. The pressure coefficient of the energy gap 1Λ4— 1Λ4 dE/AP = = — (1.3 ± 0.1) × 10−4 eV/MPa of SnSe and SnS is almost twice larger than that of the gap 1V1— 1V1 in GeSe, GeS, and SnSe. On the basis of these investigations, different absorption mechanisms responsible for the fundamental absorption edge are discussed.
Excitation und deexcitation of Tm3+ centres in ZnS involving “External” Excited States
Authors: Zimmermann H. , Boyn R.
Published: July 2007

The excitation and thermal quenching behaviour of two Tm3+ centres in ZnS crystals are studied by measuring broad‐band excitation spectra and the temperature dependence of the decay time, (τ), of the blue 1G4, → 3H6, emission of samples with different codopants. It is shown that these centers possess “external” excited states which manifest themselves by excitation peaks and τ(T) dependences characteristic of the centre investigated. Values are given of the transfer rates from the external to the 4f states, which lie between 1010 and 1012s−l. It is believed that the occurrence of external states is a general property of RE3+ centers in 11‐VI compounds and that these states, in many cases, have a crucial effect on luminescence yield.
Piezoelectric and deformation potential acoustic scattering mobility of a two‐dimensional electron gas in quantum wells
Authors: Chattopadhyay D.
Published: July 2007

The piezoelectric‐scattering mobility in a semiconductor quantum well is evaluated incorporating the effect of the finite width of the structure. The mobility is found to be enhanced in wider channels, but the effect is smaller than that in the case of deformation‐potential acoustic scattering. The combined screened mobility due to deformation potential acoustic and piezoelectric scattering using the Fcrmi‐Dirac statistics is seen to vary inversely with the temperature over the range of about 20 to 60 K. The slope of this variation is greater for smaller electron concentration and wider channels.
A pseudopotential approach to the disorder effects in III‐V ternary semiconductor alloys
Authors: Ito T.
Published: July 2007

Disorder effects for bond lengths, lattice parameters, and mixing enthalpies in III‐V ternary semiconductor alloys are investigated using a pseudopotential perturbation treatment. The calculated results are improved by taking into account both, chemical and structural disorder effects. A bimodal distribution of anion‐cation bond lengths, lattice parameter congruence with Vegard's law, and a mixing enthalpy in reasonable agreement with experimental results are obtained.
Heisenberg‐type and double exchange in mixed‐valence clusters
Authors: Belinskii M. I. , Ya. Gamurar V. , Tsukerblat B. S.
Published: July 2007

A theory of the vibronic reduction of the energy levels of transition metal mixed valence clusters is developed. The 2T2(t2) ‐ 3T1(t)‐type system is considered in detail. The vibronic model takes into account the interaction with the totally symmetric (A1) mode as well as the interaction with the Jahn‐Teller tetragonal (E) displacement of each d‐ion ligand. The dispersion of crystal vibrations is considered. The correlation interionic interactions via the phonon field are found and discussed in detail. It is indicated that the Heisenberg‐type exchange interaction is partially reduced by the Jahn‐Teller interaction, and the expressions for the reduction factors are calculated. The double exchange parameter is reduced completely by Jahn‐Teller and totally symmetric vibrations. It is shown that the reduction of the double exchange leads to the antiferromagnetic ground state in mixed valence systems with ferromagnetic sround state arising from the double exchange.
Localization of excitons in space‐charge layers
Authors: Kiselev V. A. , Novikov B. V. , Batyrev A. S. , Ubushiev E. A. , Cherednichenko A. E.
Published: July 2007

Exciton localization in near‐surface regions of semiconductors is discussed. Various mechanisms are listed responsible for the effect based on the binding of the excitons by nearsurface imperfections in crystals. One of the most important mechanisms of the localization is the Stark‐effect on excitons in space‐large layers of semiconductors. It is accounted for in the numerical computation of the exciton reflectance. Essential is a nonuniform character of the electric field. The localization is accompanied by a large enhancement of the exciton reflectance and the appearance of a low‐energy spike in the reflection lineshape. The computed lineshapes are typical of the A n = 1 exciton in a number of CdS and CdSe samples. It is shown that the increase of the bulk damping from 1 to 5 em−1 diminishes the influence of localization and transforms the enhanced lineshapes to the ideal form. The latter is typical of the B‐type excitons in the same crystals. This finding resolves the paradox of different sensitivity of the A‐ and B‐excitons to various (nondestructive) treatments of the surfaces. It explains also the anomalous behaviour of the minimal reflectance with temperature in CdS reported recently in the literature.
Excitonic spectra in 1, 2, 3 dimensions a numerical approach
Authors: Zimmermann R.
Published: July 2007

The Green's function of the Schrödinger equation is used to develop an efficient method for calculating excitonic spectra in d dimensions. The complex dielectric function (including broadening) near the band gap is found by a numerical integration of the exciton equation in real space. Model calculations are presented for the dynamically screened exciton in d = 3, the exciton in an MQW layer (d = 2), and the diamagnetic exciton (d = 1).
Energy transfer processes between Ten centres in ZnS:Te and CdS:Te
Authors: Heimbrodt W. , Goede O.
Published: July 2007

ZnS:Te, CdS:Te, and (Zn, Cd)S:Te crystals are studied by photoluminescence emission and excitation spectroscopy and by thermal and optical quenching measurements. In ZnS:Te besides the well‐known uv and blue emission bands caused by Te1 and Te2 centres, respectively, a new lower‐energy emission band is found at higher Te concentrations which has to be ascribed to the radiative annihilation of excitons bound to Te3 clusters consisting of three Te impurities on nearestneighbour anion sites. The exciton binding energies and Franck‐Condon relaxation energies of the various Ten centres are discussed. The energy transfer between the Ten centres in ZnS:Te and CdS:Te is studied and quantitatively analyzed in the framework of a kinetic model. In the lowtemperature region a radiationless resonant energy transfer dominates whereas at higher temperatures a thermal release of the bound excitons followed by an exciton‐recapturing by other Ten centres occurs. The observed optically induced energy transfer from Te2 to Te1 centres in ZnS is discussed on the basis of a configuration‐coordinate model.
Effect of alloy composition on the thermoelectric power in inversion layers on ternary semiconductors in the presence of a classically large magnetic field
Authors: Ghatak K. P. , Mondal M.
Published: July 2007

An attempt is made to derive in the presence of a classically large magnetic field expressions for the thermoelectric power of the carriers in n‐channel inversion layers on ternary semiconductors under both, weak and strong electric field, limits. It is found, taking n‐channel inversion layers on Hg1−xCdx, Te as examples, that the same power, for both the limits, increases with increasing alloy composition. The corresponding results for parabolic semiconductors are also obtained from the expressions derived.
Influence of charge transfer on ab initio calculated impurity resistivities in noble metals
Authors: Lodder A. , Mertig I. , Zeller R. , Mrosan E. , Dederichs P. H.
Published: July 2007

A method is proposed to obtain values for the impurity resistivity, given an alloy potential. Correct single‐site values which account for the bandstructure of the host and which are calculated by solving the Boltzmann transport equation form the starting‐point. Effects due to charge transfer and lattice distortion can be estimated reliably using an approximate finite‐cluster model method. The selfconsistent potentials for impurities in copper and silver represent correctly the differences between the sp impurities and the 3d and 4d impurities in a host and also the difference between the two hosts for a given impurity. The agreement of the absolute values with experiment is not yet satisfactory.
Energies and Structures of (111) Coincidence Twist Boundaries in 3C‐SiC, Diamond, and Silicon
Authors: Kohyama M. , Yamamoto R. , Doyama M.
Published: July 2007

The energies and structures of (111) coincidence twist boundaries in covalent crystals, 3C‐SiC, diamond, and silicon are calculated for the first time using the tight‐binding type electronic theory (bond orbital model). The repulsive interactions between atoms at short distances are expressed by Born‐Mayer potentials. After lattice relaxation, the energies of the twist boundaries do not scale with the Σ‐values in each material.
Charged Elementary Excitations in Anthracene Polymers. A Systematical Electrical and EPR Study as a Function of Doping
Authors: Grigoryan L. S. , Kharutyunyan I. L. , Matnishyan A. A. , Nikogosyan R. S. , Sharoyan E. G.
Published: July 2007

A systematical study of electrical conductivity and EPR of iodine‐doped anthracene polymers (C14H6Ix)n is carried out within a wide range of iodine concentrations (0.07 ≦ x ≦ 0.85). The room temperature electrical conductivity has a broad maximum near x = 0.5. No metallic‐type conduction is observed. The intensity of EPR signal for all of the investigated samples depends on temperature according to the Curie law and has a minimum near x = 0.19. A clear decoupling of paramagnetism with iodine concentration and electrical conductivity is detected. An idealized model of the structure of (C14H6Ix)n including polarons and bipolarons is proposed. On the base of the model a mechanism of generation and compensation of spin and charge during the doping process is discussed and an interpretation of experimental data is given.
Electron Mobility in Heavily Doped Strongly Compensated ZnSe Crystals
Authors: Kasiyan V. A. , Nedeoglo D. D. , Simashkevich A. V. , Timchenko I. N.
Published: July 2007

In the temperature range 1.65 to 300 K the temperature dependence of the electron mobility is studied in n‐ZnSe crystals with a concentration of electrically active impurities ranging from 7 × 1015 to 5 × 1018 cm−3 and a compensation degree of 0.16 to 0.98. The anomalously low values of the electron mobility and its sharp change with temperature by a power law with an exponent 2 to 4 in heavily doped strongly compensated crystals are accounted for by the specific character of conductivity and Hall effect in samples with a random large scale impurity potential rather than by the peculiarities of the electron scattering. The dependence of the electron mobility on the concentration and the degree of impurity compensation is studied.
The Effect of Temperature and Coupling Strength on the Thermoelectric Power in the Small‐Polaron Hopping Regime
Authors: Triberis G. P.
Published: July 2007

The effect of temperature and coupling strength on the thermoelectric power of the small‐polaron hopping disordered regime is investigated. The thermoelectric power is evaluated for the high‐and low‐temperature case assuming the electron‐lattice interaction to be weak. Results are also given for the low‐temperature and strong‐coupling case. The “macroscopic” thermoelectric power of the material is evaluated for the low‐temperature regime.
Phonon Shifts in GaP Due to Temperature and Pressure Rise Induced by a Laser Beam
Authors: Irmer G. , Monecke J. , Bairamov B. Kh. , Toporov V. V.
Published: July 2007

Raman spectroscopic measurements of the TO‐ and LO‐phonon shifts of GaP in the temperature field induced by a laser beam are performed and compared with measurements in a uniformly heated sample. The temperature and the stress distribution in the sample volume irradiated by the laser beam are calculated and their influence onto the phonon frequencies is discussed with the result that thermoelastic effects besides the temperature rise due to the laser beam cannot be neglected, in general.
Evaluation of Electronic Dielectric Constant and Fractional Ionic Character of Mixed Alkali Halide Crystals
Authors: Shanker J. , Sharma S. C.
Published: July 2007

The electronic dielectric constant and fractional ionic character of the chemical bond are calculated for the mixed crystals NaClNaBr, KClKBr, KBrKI, CsClCsBr, CsClRbCl, and CsClKCl for the entire range of composition. The first four solid solutions are with common cations whereas the last two are formed of substances with common anions. For the electronic dielectric constant a comparison is given of the values calculated from the Clausius‐Mossotti relation and the Pantelides formulation. For evaluating the fractional ionic character application is made of Phillips' and Pauling's theories. The calculated values are found to depend sensitiviely on the composition parameter of mixed crystals.
Rotational Excitations of Methyl Groups in 2,3‐Dimethylnaphthalene
Authors: Kalus J. , Schleifer J. , Hbmpelmann R. , Richtee W.
Published: July 2007

2,3‐dimethylnaphthalene (2,3‐DMN) crystallizes similar to naphthalene but with dipolar structural disorder of the acentric molecules. Quasielastic neutron scattering of the methyl groups between 12 and 270 K is studied for scattering vectors up to 17.7 nm−1. The experimental results are fitted to a rotational jump model. From a fixed window experiment a broad band of activation energies around 1350 K is deduced.
Influence of a Surface on Lifetime Spectra of Positrons
Authors: Belbnkii V. M. , Begzanov R. B. , Bolotov V. N. , Kuznichenko A. V.
Published: July 2007

Positrons implanted into the solid are thermalized and can diffuse to the surface. The probability of trapping positrons by the solid surface and by the surface of defects is calculated. Obvious analytic expressions for W(t), F, and Iv(t) in terms of special functions are obtained, as well as an obvious criterion for the case of many defects. The obtained results show that the dynamics of a thermalized positron interaction with a surface affects the positron lifetime spectra.
Density Functional Approach to the Surface Tension of Liquid Metals
Authors: Lai S. K.
Published: July 2007

The local density functional formalism of Evans and Hasegawa, previously developed for the study of surface properties, is re‐examined by including nonlocality of pseudopotential in the theory. It is found that (i) when the pseudopotential is nonlocal, the fourth order density gradient correction of Ma and Sahni must be included in order that the density profiles obtained are physically meaningful and (ii) the first order perturbation is inadequate for understanding the surface tension of simple liquid metalsin accordance with conclusions made by other investigators.
The Spectral Behaviour of a General Damped Anharmonic Oscillator
Authors: Bose S. K. , Dubey U. B. , Tewari V. N.
Published: July 2007

The spectral behaviour is investigated of the radiation emitted by a charged particle executing the motion of a general anharmonic oscillator under the influence of damping forces. The presence of many maxima is noticed which are in general not symmetric, in the intensity distribution as a function of frequency due to the presence of anharmonic terms.
27Al Hyperfine and Quadrupole Interactions for the [A104]0 Center in Quartz
Authors: Bossoli R. B. , Halliburton L. E.
Published: July 2007

An electron‐nuclear double resonance (ENDOR) study at 20 K of the [AlO4]0 trapped‐hole center in α‐quartz gives the principal axes and principal values of the 27Al hyperfine and quadrupole matrices. These are in substantial agreement with previous ESR results obtained by Nuttall and Weil. A model involving both dipole‐dipole interactions and the admixing of unpaired spin into aluminum 3p‐type orbitals is used to explain the small anisotropic 27Al hyperfine matrix components. The “best fit” with this model results in 3.7% of an unpaired spin in aluminum 3p‐type orbitals and a 0.188 nm distance from the aluminum ion to the oxygen ion containing the trapped hole.
Electron Energy Levels in GaAs/Ga1−xAlxAs Heterojunctions
Authors: Tomak M. , Godwin V. K.
Published: July 2007

A theoretical study of the subband structure and impurity related levels in GaAs/Ga1−xAlxAs heterojunction is given.
Quantum Oscillations of Thermogalvanomagnetic Coefficients in Two‐Dimensional Electron Systems
Authors: Havlová H. , Smrčka L.
Published: July 2007

Based on the one‐electron version of the Kubo formula and assuming only the elastic scattering of carriers on static impurities the quantum oscillations of the transport coefficients are evaluated of two‐dimensional electron systems in weak/intermediate magnetic fields. The changes in the oscillating pattern due to the variation of the magnetic field, the carrier density, and the temperature are investigated. Numerical examples give results in qualitative agreement with recent experimental data.
A Model for the Variations in the Field‐Dependent Behaviour of the Poole‐Frenkel Effect
Authors: Choi W. K. , Delima J. J. , Owen A. E.
Published: July 2007

The Poole‐Frenkel effect is often observed in the field‐dependent properties of amorphous materials. Experimentally, it is frequently found that the slopes of log σ versus E1/2 plots differ from that predicted by the Poole‐Frenkel equation and several theorems have been postulated to explain this discrepancy. Recently, Török used the concept of multiple ionisation to account for such discrepancies. In this paper some of the arguments presented by Török and others is examined in more detail, and the Poole‐Frenkel effect is discussed for two limiting cases. The situation when the free carrier density (n) in the case of an n‐type material containing both donor (Nd) and acceptor (Na) impurities, is of the same order of magnitude as Na where the two approximations are invalid, is more closely examined. It is shown that by assuming a field dependent value of n, a transition region situated between the two approximations is evident. It is also shown that by considering basic parameters such as temperature, and acceptor densities, a Poole‐Frenkel plot is obtained which is very sensitive to variations in temperature and acceptor density.
X‐Ray Electron Charge Density Distribution in Silicon
Authors: Pietsch U. , Tsirelson V. G. , Ozerov R. P.
Published: July 2007

During the last two years new highly accurate X‐ray structure amplitudes for silicon are published. Also the scattering phases of some „forbidden”︁ reflections are determined using the X‐ray threebeam case. This allows the construction of most precise valence and difference electron density plots and the comparision with those calculated on the basis of the Aldret‐Hart X‐ray pendellösung data and by theory. The density plots are discussed in details of both, the bond and the atomic site. The contributions of various Fourier components and the influence of different temperature factors on the difference density are studied.
Fluctuation Unpinning of Dislocations
Authors: Zilberman L. A.
Published: July 2007

The dynamics of thermally activated unpinning of dislocations from point defects under the action of an applied stress is studied. It is shown that the Fokker‐Planck infinite‐dimensional equation describing the diffusion of a particle in the configurational space is reduced to a one‐dimensional one in the concentrated‐force approximation. Moreover it is shown that over a wide range of parameters dislocation unpinning from the point defect occurs in two stages: at the first stage the dependence of the unpinning probability on the initial configuration of a dislocation disappears and at the second stage the system, passes from one stationary state to another. Characteristic times of the problem are found, and their dependence on temperature and dislocation length are studied.
Bound Domain Wall Pairs in Wolffram's Red Salt
Authors: Ichinose S.
Published: July 2007

The relative ordering of the dimerized patterns of neighboring Wolffram's red salt chains is studied with a model where the coupling is due to the interchain Coulomb interaction. It is shown that this mechanism favors antiferromagnetic order between neighboring chains. It also leads to bound domain wall pairs on the same chain. The energy associated with a pair of domain walls increases asymptotically linear with its length.
The Perturbative Influence of Donors and Acceptors on the Value of the Kinetic Coefficient of Electron Transfer along a One‐Dimensional Molecular Chain Achieved by Davydov Solitons
Authors: Ivić (a) Z. , Satarić M. , Žakula R.
Published: July 2007

A perturbation theory is developed for the kinetic coefficient of the electron transfer from donor molecules (Dm) to acceptor molecules (Al) along a one‐dimensional molecular chain to which Dm and Al are statistically joined. The influence of donors and acceptors to the soliton states is reflexed to the value of corresponding kinetic coefficient.
Absorption Edge of SnSe
Authors: Lukeš F. , Schmidt E. , Humlíček J. , Dub P. , Kosek F.
Published: July 2007

The absorption of SnSe single crystal is studied near the absorption edge at 95 and 295 K in polarized light for ϵ |a and ϵ | b, where a and b are crystallographic axes within the cleavage plane. Two indirect transitions (0.907 and 1.01 eV at 295 K) are identified for both orientations and a first direct transition for ϵ | b with E0d = 1.051 eV and for ϵ | a with E1d = 1.236 eV as well, all at 295 K. The temperature coefficients of all transitions are determined also within the range of 95 to 295 K. Also is suggested the interpretation of these results considering the band structure of SnSe given in the literature.
Metallic Systems Containing Crystal‐Field‐Split Impurities. Thermodynamic Properties in the Presence of Magnetic Field
Authors: Kumar S. , Ahluwalia P. K. , Sharma K. C.
Published: July 2007

In the presence of magnetic field H, an investigation is made in second order of the possiblity of an anomalous behaviour in various thermodynamic properties viz. heat capacity, susceptibility etc. existing in dilute magnetic alloy systems. Basically, the anomaly is attributed to the CEF splitting of the impurity level; the H dependence in the heat capacity is linear. Electronic susceptibility also exhibits an anomaly of the type 1n T. These results are found to be consistent with earlier work.
Co Contribution to Anisotropy of R–Co Type Pseudobinaries
Authors: Kąkol Z. , Figiel H.
Published: July 2007

The magnetocrystalline anisotropy of the Y2Co17 compound is caused by Co atoms. The anisotropy is calculated within the point charge model in the crystal field approach. The shielding effects of band electrons are taken into account. The calculations are extended to Y2(Co1−xMnx)17 and Gd2(Co1−xMnx)17 with 0 ≦ x ≦ 0.3. The results of the calculations fit the experimental anisotropy data, describe well the changes of the anisotropy versus temperature and Mn concentration, and are consistent with conclusions concerning the local Co anisotropy drawn from NMR data.
Luminescence Properties of Rb2ZnCl4 and K2ZnCl4 Single Crystals
Authors: Martin A. , López F. J. , Diéguez E. , Agulló‐López F. , Arend H.
Published: July 2007

First data the on X‐ray‐induced luminescence (RL) and thermoluminescence (TL) spectra in the range 10 to 300 K of K2ZnCl4 and Rb2ZnCl4 are reported. For both the materials, two main emission bands peaking at 280 and 545 nm are observed in the RL spectra. They are proposed to be associated to intrinsic electron–hole recombination processes. The TL spectra show the most intense glow peaks near 205 K for both, K2ZnCl4 and Rb2ZnCl4. The wavelength spectrum of the TL peaks essentially consists of the same bands appearing in the RL spectrum measured at the same temperature. Therefore, the glow peaks should also have their origin in the same electron–hole recombinations.
IR Transmission Investigations of (Bi1−xSbx)2Te3Single Crystals
Authors: Stölzer M. , Stordeur M. , Sobotta H. , Riede V.
Published: July 2007

IR transmission spectra are measured at (Bi1−xSbx)2Te3single crystals withx= 0.5, 0.7, 0.9 near the absorption edge at 84 and 300 K. For the determination of the optical constants also the reflectivity of polarized infrared light is recorded in the plasma range at 300 K. The dependence of the free carrier part of the dielectric function on the wave number ϵ(v̄) indicates that acoustic phonon scattering is the dominant mechanism. The interband contribution ϵ(v̄) is interpreted by indirect allowed band transitions. The energy gap and the phonon energies are calculated andlie in a physically reasonable range.
Temperature Dependences of 6A1g → 4A1g, 4Eg(4G) and 6A1g → 4Eg(4D) Absorption Bands in RbMnF3 in Paramagnetic State
Authors: Malakhovskii A. V. , Vasilev G. G. , Morozova T. P.
Published: July 2007

The temperature behaviour of RbMnF3 absorption spectra at T > TN in the region of the transitions 6A1g → 4A1g, 4Eg(4G), and 6A1g → 4Eg(4D) is investigated. Pair–vibronic absorption bands are identified and it is shown that 1. the structure of the spectra in the region of both transitions is caused by the transitions to the 4Eg states, 2. the replicas of the basic lines are caused by excitation of an even number of quanta of odd vibrations, and 3. the theoretical temperature dependence of the intensity of the pair–vibronic absorption describes the experimental results sufficiently well.
An Electron Spin Resonance Study of Cubic Fe3+ in Alkali Chloride Crystals
Authors: Nistor S. V. , Velter‐Stefănescu M.
Published: July 2007

Cubic Fe3+ is formed by X‐irradiating LiCl:Fe crystals grown in a reactive atmosphere. The spin Hamiltonian parameters are consistent with the Fecub3+ center, earlier observed in AgCl and NaCl, consisting of an interstitial Fe3+ forming a tetrahedral (FeCl4)− complex, the four nearest‐neighbour cation sites being vacant. The superhyperfine structure analysis in samples containing 57Fe enriched iron gives the hyperfine splitting 57A = (9.4 ± 0.5) × 10−4 cm−1. No such center is found in KCl:Fe and RbCl:Fe crystals.
Electrical Resistivity and Thermoelectric Power of Intercalation Compounds MxTiS2 (M = Mn, Fe, Co, and Ni)
Authors: Koyano M. , Negishi H. , Ueda Y. , Sasaki M. , Inoue M.
Published: July 2007

The temperature dependence of electrical resistivity and thermoelectric power of the intercalation compounds of MxTiS2 (M = Mn, Fe, Co, and Ni; 0 ≦ x ≦ 1/3) with layered structures are measured over the temperature range 1.5 to 300 K. These experimental results can be explained by a simple model, which takes into account a temperature‐independent residual term and intra‐ and intervalley scattering by acoustic phonons. It is also shown that a phonon drag effect is effective for the thermopower. The effect of intercalation of 3d metals into TiS2 layers on the electronic properties is discussed.
Cohesion of Solids under Very High Electronic Excitation Conditions
Authors: Wautelet M.
Published: July 2007

When a solid is subject to an intense electronic excitation, it is expected that its cohesive properties differ from the non‐excited state. The variation of crystal instability temperature, Tc, with the concentration of excited electron–hole pairs is examined theoretically. Using a phenomenological model of electron–phonon–defect interactions, it is shown that Tc decreases quasi‐linearly with increasing electron–hole pair density. The consequences of this on diffraction broadening, threshold energy for transformation, premelting, and optical properties are discussed.
Spin‐Wave Damping in Uniaxial Ferromagnets at the Orientational Phase Transition
Authors: Bulgakov E. N. , Sadreev A. F.
Published: July 2007

A damping of spin waves is considered near the orientational phase transition (OPT) in the easy plane ferromagnet in an external magnetic field using the diagram technique for the Hubbard operators. It is shown that in the normal phase where uniaxial symmetry is not broken the damping takes place for nonzero temperature and increases with approaching the OPT point. In the broken symmetry phase the damping of spin waves takes place even at T = 0 and increases with going away from the OPT point.
Electronic Structure of the Ce Systems. II. Results
Authors: López‐Aguilar F. , Costa‐Quintana J.
Published: July 2007

Several electronic structures are determined of some Ce systems, the effects of the Coulomb correlation analyzed together with the spd/f hybridization by means of the pseudopotential model described in the paper I of this series. Firstly, the electronic structure is determined of the γ‐α‐transition of CeAl2. The features of this isostructural transition are: an increase of the 4f coupling with other bandstates; a widening of the 4f band and a light decrease of the 4f population. All these features are quantitatively determined and it is concluded that the pressure effect is the cause of the loss of the magnetic order and this leads to the increase of the spd/f hybridization, the 4f band broadening, and the decrease of the f‐count. In addition, the electronic structure of CeOs2 is determined whose band structure presents certain similarity with that of the α‐phase of CeAl2 and moreover this compound presents a clear heavy fermion behaviour, including a superconducting transition.
A Quantum Field Theoretical View on the Surface Plasmon
Authors: Kleinert P.
Published: July 2007

From a quantum‐field theoretical point of view the surface plasmon on a plane is treated as an extended object with an oscillating surface singularity created by the boson condensation of supplementary fields. Due to topological singularities the macroscopic equations describing free electromagnetic fields become inhomogeneous. The surface plasmon dispersion relation results from the steadiness of the surface impedance.
Pressure Effects of Superfluidity in Liquid 3He
Authors: Singh R. A. , Kachhava C. M.
Published: July 2007

A sophisticated formulation for the pressure dependence of superfluidity in liquid 3He is established on the basis of the generalized BCS‐theory due to Leggett. The pairinteraction for individual partial waves is obtained by Ostgaard's t‐matrix theory in which derived parameters of Fermi momentum, energy density of states, and effective mass are used. The variable parameter, the cut‐off energy ϵc, is computed by coupling it to reproduce the experimental Tc at zero, melting, and intermediate pressures. The agreement between theoretical and experimental Tc is, in general, quite satisfactory, but depends on the choice of ϵc.
Electron Paramagnetic Resonance (EPR) and Related Magneto‐Microwave Birefringence (MMB) Powder Spectra of Copper Nitrate Cu(NO3)2 · 2.5 H2O
Authors: Gharbage S. , Bissey J.‐C. , Servant Y.
Published: July 2007

EPR and related MMB powder spectra of Cu(NO3)2 · 2.5 H2O are recorded at X‐band and room temperature. A good agreement is found with computer simulated spectra. An automatic fitting procedure gives accurate principal values of the g‐factors and linewidths.
Derivation of the Ginzburg‐Landau Equation in the Triplet Local‐Electron‐Pair System
Authors: Li Yan‐Min , Zhang Li‐Yuam
Published: July 2007

The Ginzburg‐Landau equation is derived in the triplet local‐electron‐pair system with the broken‐symmetry mean‐field approximation. Ginzburg‐Landau parameters αGL and βGL are obtained, which have similar forms with those derived by Gorkov in the framework of the BCS theory. It is found that the coherence length ξ(0) is of the order of the pair‐site distance and the penetration depth λ(0) is quite large. The upper critical field Hc2 is also discussed.
Stationary and Resonance States at the Core of a Screw Dislocation and Their Contributions to Electrical Resistivity
Authors: Föckel H.‐J.
Published: July 2007

Within the framework of the pseudo‐potential concept and the field of validity of the Ziman‐formula the contribution to the residual electrical resistivity of a 1/2<111>‐screw dislocation is calculated in a b.c.c. metal (potassium). The perturbation potential is specified for a dislocation model, in which the core is described discretely, on the contrary the surrounding matrix as a non‐linearly elastic continuum. The potential of the dislocation core contains resonance states below the Fermi energy. The contributions to the resistivity caused by these states prove to be in the same order of magnitude as experimental data.
Lattice Dynamics of Tin Tetrabromide
Authors: Zeng W. Y. , Higgs J. F. , Anderson A.
Published: July 2007

A simple force constant model is developed and applied to the vibrations of solid tin tetrabromide. Three intra‐ and four intermolecular force constants are adjusted to obtain the best fit to the crystal field splittings and lattice mode frequencies observed by Raman and infrared spectroscopy. Isotopic and molecular distortion effects are also investigated. The dependence of the BrBr interaction on separation is found to be similar for SnBr4 and Br2.
Surface Phonons in Molecular Crystals
Authors: Podoprigora V. G. , Remizov I. A. , Shabanov V. F. , Botvich A. N.
Published: July 2007

The lattice dynamics of the surface layers of anthracene and β‐paradichlorobenzene crystals as well as of the adsorbed monolayer of paradibromobenzene on β‐paradichlorobenzene is investigated using the method of atom—atom potentials in slab dynamical calculations. The dynamic, structural, and electro‐optical parameters of the surface crystal layers are compared with those for the bulk.
The Impurity States in Bismuth
Authors: Bodiul P. P. , Garabazhiu V. F. , Gitsu D. V.
Published: July 2007

The influence of a lattice deformation and the degree of valency states filling of the impurity atom on the impurity subsystem behaviour is investigated. The states are found in which the electron is localized in the region of the impurity centre and their energies are evaluated. The size of this region is of an order of 1 to 2 cell size. A mechanism of mixing these states, forbidden in a free atom, and which allows to treat these states as nonstationary, is discovered.
Pressure Dependence of Electrical Resistivity in Intercalation Compounds MxTiS2 (M = 3d Transition Metal)
Authors: Inoue M. , Koyano M. , Fukushima K. , Negishi H. , Sasaki M.
Published: July 2007

Electrical resistivities of intercalation compounds of MxTiS2 (M = Mn, Fe, Co, and Ni; x = 0.05) with the 1T‐CdI2‐type layered structure are measured under hydrostatic pressure up to 15 × 108 Pa over the temperature range 1.7 to 300 K. The resistivity change with pressure at room temperature and the temperature dependence at constant pressure are strongly dependent on the guest 3d metals. These experimental results can be explained by taking account of the pressure dependences of the residual resistivity, as well as the temperature‐dependent intra‐ and intervalley scatterings by acoustic phonons.
Ohmic Mobility of Quasi‐One‐Dimensional Semiconducting Structures. Acoustic and Piezoelectric Phonon Scattering
Authors: Comas F. , Giner C. Trallero , Tutor J.
Published: July 2007

Momentum relaxation times and ohmic mobilities are calculated for a quasi‐one‐dimensional (QID) semiconducting system assuming that carriers are scattered by acoustic and piezoelectric phonons. A detailed discussion of inter‐sub‐band transitions is done with special emphasis on the conditions where size‐quantum‐limit (SQL) is accomplished. A comparison of the acoustic and piezoelectric mechanisms is done for GaAs and CdS with detailed analysis of which mechanism dominates transport under given conditions. The temperature dependence of the mobilities is also discussed and asymptotic analytical expressions are obtained for the low temperature regime.
Donor‐Type Tm Centres in ZnS Crystals
Authors: Zimmermann H. , Boyn R.
Published: July 2007

4f—4f excitation and emission spectra involving various intermanifold transitions are determined for two Tm3+ centres in ZnS crystals by dye‐laser site‐selective measurements at helium temperatures. A crystal‐field analysis together with polarization data indicates that in both cases Tm is located on lattice sites, probably Zn sites. One of the sites (D3) is thought to be in „unperturbed”︁ environment, whereas in the second case (D2) the four nearest‐neighbour atoms are probably replaced by impurity atoms. The excitation and deexcitation mechanisms of the blue 1G4 → 3H6 emission of these centres are studied by site‐selective broad‐band excitation spectra and kinetical measurements. These studies demonstrate that donor‐acceptor pairs involving the two Tm centres as the donors play an important role in the excitation process. Estimates are given of the relevant pair to 4f state transfer rates.
Magnetoresistivity of ZnSe in the Region of Hopping Conduction over Localized States in the Coulomb Gap
Authors: Kasiyan V. A. , Nedeoglo D. D. , Simashkevich A. V. , Timchenko I. N.
Published: July 2007

In the temperature range from 1.65 to 4.2 K and in magnetic fields with a strength up to 4.6 T conductance and magnetoresistivity of heavily doped (ND + NA ≈︁ 1×1018 cm−3) compensated (HDC) (0.84 ≦ K ≦ 0.98) n‐ZnSe crystals are investigated. In the temperature range investigated a conductivity with a smoothly changing activation energy is observed. It is established that the positive magnetoresistivity (PMR) is conditioned by a compression of electron wave functions at impurities. From an analysis of PMR within the framework of the recently derived theory of the magnetoresistivity for the variable range hopping conduction and σ(T), parameters as the localization radius of the electron wave function a and the dielectric constant χ are determined. The character of their behaviour while approaching the metal—insulator transition in HDC n‐ZnSe crystals is studied. The ratio of critical indices is found to be ξ/v = 2.5 ± 0.5.
Partial structures of compound‐forming liquid gold–caesium alloy. A model potential approach
Authors: Rao R. V. Gopala , Bhattacharyya M.
Published: July 2007

The compound‐forming AuCs alloy is studied with a square‐well potential as a perturbation over a hard‐sphere mixture. The partial structure factors S11(k), S12(k), S22(k) and also SNN(k), SCC(k), and SNC(k) are computed at various concentrations and temperatures. Here 1 refers to gold and 2 refers Cs. The total structure factors obtained by the present method agree very well with the measured values. The most important aspect of the computations is the accurate evaluation of the number density of each of the species. Density measurements indicate strong contraction at 50% concentration and it is found to give a subsidiary peak in S11(k) and a high principal peak for SNC(k) at this concentration. The present calculations show that if the correct density measurements and hence the number densities are available, the evaluation of partial structure factors with sufficient accuracy is possible. Also the present calculations show many similarities with the CuPb alloy which also forms a compound.