bluuebunny/crossref_metadata_2025 huggingface dataset:
Vibrational Spectrum of InSe
Authors: Belenkii G. L. , Alieva L. N. , Nani R. Kh. , Salaev E. Yu.
Published: July 2007

Reflection and absorption of light by InSe single crystals are investigated in the range of wave numbers 500 to 100 cm‐1. The measurements are carried out at room temperature in E ⟂ C orientation of the electric vector. The linear chain model is used for calculating the phonon frequencies at k = 0. The phonon energies at the edge of the Brillouin zone (M point) are calculated by means of the force constants model including the atoms of a single layer.
A classical analysis of the resonance modes in a randomly disordered chain
Authors: Chen G. L. , Wu Shi‐Yu , Schwartz M.
Published: July 2007

A classical analysis of the resonance modes in a linear configuration composed of two light impurity atoms in the sea of heavy atoms is carried out for the purpose of understanding the underlying reason for the existence of the resonance peaks in the main band of a randomly disordered chain. The study leads to the conclusion that the peaky resonance modes in the main band of a randomly disordered chain are pseudolocalized modes and that the condition for the existence of the resonance peaks is closely related to the condition for total transmission.
Optical absorption in non‐crystalline semiconductors
Authors: Tripathi R. S. , Moseley L. L. , Lukes T.
Published: July 2007

The density of states is calculated near the band edges for amorphous semiconductors and insulators assuming that these can be described by the model Anderson Hamiltonian in single band approximation. It is shown that the transition matrix element which appears in the interband optical absorption, cannot be treated independent of photon frequency. These are used to calculate the absorption coefficient above the exponential tail in an amorphous material. Also the role of extended to extended transitions is considered, and found that this is smaller than the contribution coming from the extended‐localised absorption. The theory is compared with the experimental data of Greaves et al. on a‐As and good agreement is found between theory and experiment.
A layer summation for electrostatic surface problems. Application to the classical cleavage energy
Authors: Paasch G. , Hietschold M.
Published: July 2007

A rather general method is given for calculating the electrostatic potential due to a half‐infinite 2D‐lattice periodic charge distribution. Such kind of potentials arises in the Coulomb integrals of the classical cleavage energy (a contribution to the surface energy) or in calculating ionic lattice relaxation near metal surfaces. For the former quantity numerical results are presented here. It is found that the contribution due to bulk electron density oscillations must be taken into account even for simple metals to get results for the total surface energy comparable with experimental ones (rather than with experimental surface tensions). Taking into account these density oscillations the anisotropy ratios are markedly improved, too. The calculation is made for all simple metals in terms of pseudopotential theory.
Electric field dependence of the electron mobility in tellurium at 77 K
Authors: Behrendt H. , Hoeestel W.
Published: July 2007

The field dependence of the electron mobility is measured in Te at 77 K using an electron drift technique. In the range up to 80 V/cm the electron mobility is nearly field‐independent. In the range from 100 to 400 V/cm the mobility lowers with E−0.6. At fields above 600 V/cm only a weak field strength dependence is observed. The zero field mobility ratio of electrons and holes at 77 K is about (3.55 ± 0.25) independently of the hole mobility of the samples.
On a variational procedure for obtaining the thermodynamic properties of statistical models
Authors: Ferreira L. G. , Salinas S. R. , Oliveira M. J.
Published: July 2007

A procedure is developed for obtaining approximate thermodynamic properties of statistical models, based on a well known variational principle for the free energy. The procedure involves the choice of a suitable parametrized trial Hamiltonian which contains some elementary interactions. The free trial Hamiltonian leads to the usual mean‐field approximation. When the trial Hamiltonian includes a certain number of pair interactions only, the results are regained of the constant‐coupling approximation for the Ising model if the number of interacting pairs is conveniently chosen by a comparison with the first few terms of the exact high‐temperature expansion. This procedure is simpler than existing approximations and can be easily generalized. Besides treating the Ising model, some applications are presented to the spin‐1/2 antiferromagnetic Heisenberg model, and to the spin‐1 Heisenberg model with uniaxial anisotropy.
Electron energy loss studies of direct nonvertical interband transitions in silicon
Authors: Chen C. H.
Published: July 2007

Direct nonvertical interband transitions in single‐crystal silicon of {001} orientation are detected in the electron energy‐loss spectra for the momentum‐transfer q in the directions of 〈100〉 and 〈110〉. The dependence of the transition energies as a function of q is measured and possible correlations with the energy band structure are discussed.
Off‐stoichiometry effects in the antiferromagnetic ferh alloy
Authors: Khwaja Y. , Nauciel‐Bloch M.
Published: July 2007

A model is developed for the band structure of the Fe0.5Rh0.5 antiferromagnetic ordered alloy, and the local effects are studied of a substitutional impurity on the electronic and magnetic properties of the host. It is found that an Fe impurity substituted for Rh creates a perturbation extending at least to the nearest neighbours of the impurity, and a total ferromagnetic moment close to 3.5μB A Rh impurity substituted for Fe has a localized and less important effect. The influence of the magnetic state of the host and the case of other impurities substituted for Rh are also investigated.
Energy band calculations on helical systems
Authors: Blumen A. , Merkel C.
Published: July 2007

The electronic band structure of systems with screw symmetry is developed using the smallest screw displacement as elementary operation. For atomic and molecular helical systems the resulting Hartree‐Fock SCF‐LCAO formulae are presented. Results for ferroelectric HC1 and HP are reported, obtained with the MUNICH‐CHAIN programme, in which the new formalism is implemented. The connection to the translational symmetry and the numerical results are discussed.
Recombination in Pb0.83Sn0.17Te at high levels of optical excitation
Authors: Hoai T. X. , Herrmann K. H.
Published: July 2007

The photoconductivity and the photomagnetoelectric current in low‐concentration, high‐lifetime Pb0.83Sn0.17Te samples are measured at strong optical excitation using a Q‐switched ruby laser. At quantum flux Q > 2 × 1021 cm−2s−1 nonlinear recombination is observed. From the characteristics measured the coefficient of Auger recombination C = (4.5 ± 1) × 10−27 cm6s−1 is obtained. The results are confirmed by lifetime data obtained at low excitation levels.
Many‐body effects on the second‐order elastic constants of solids with ZnS structure
Authors: Goyal S. C. , Peakash R.
Published: July 2007

The method of homogeneous deformation is used to derive the expressions for the elastic constants of solids crystallising in ZnS structure using the Lundqvist potential for the ionic cohesion. The derived expressions are utilised to explain several physical properties of the large number of semiconductor solids.
Phase transformations in hydrides of rare‐earth metals under pressure
Authors: Bashkin I. O. , Ponyatovskii E. G. , Kost M. E.
Published: July 2007

An analysis of the specific volume dependences on atomic number is carried out for rare earth dihydrides and trihydrides. It is shown that under high pressures the following phase transformations are possible in these compounds: a) structural phase transitions h.c.p.→f.c.c., the ion valency being unchanged, b) phase transitions accompanied by a change of metal ion valency. The dependences of volume versus pressure to 24 kbar and resistivity versus pressure to 20 kbar are measured for NdH2.82 at 20 °C. A reversible resistivity anomaly and an abrupt change of the volume by 1.6% are detected under high pressures. These anomalies are explained to be due to the phase transformation h.c.p.⇄f.c.c.
Modes of cross‐relaxation in nuclear double‐resonance
Authors: Whitaker M. A. B.
Published: July 2007

The modes of cross‐relaxation of a double‐resonance system are discussed, and calculated for a number of simple cases. The action of the dipolar reservoirs in inhibiting the equilibration of the Zeeman reservoirs is described. The behaviour of the system may be interpreted in terms of maximisation of entropy. Numerical results are obtained for the case of double‐resonance in sodium fluoride with the Zeeman field in the (111) direction.
Phonon frequency, electrical resistivity, and inter‐ionic pair potential of Li
Authors: Singh R. N. , Srivastava P. L. , Mitra N. R.
Published: July 2007

The effect of the form of model potential and different forms of exchange and correlation on the phonon frequency, liquid electrical resistivity, and inter‐ionic pair potential is investigated. The metallic properties are found to be sensibly affected with the choice of the form of the model potential. It is concluded that an r‐dependent form of the model potential in the inner region of the ion may be important for a good reproduction of the metallic properties.
The electronic spectra and electromagnetic properties of charge‐ordered systems
Authors: Manakova L. A. , Makarov E. F. , Ionov S. P.
Published: July 2007

The spectrum of collective excitations is found for charge‐ordered systems with a one‐electron gap far less than the band width. The contribution of these excitations to electromagnetic wave absorption is considered. The complex impedance of the charge‐ordered state is calculated.
Three‐phonon scattering relaxation rate and phonon conductivity. Application to Mg2Ge
Authors: Dubey K. S. , Misho R. H.
Published: July 2007

The new expression τ = g(ω) (BN + BUe−θ/αT) Tm is proposed for the three‐phonon scattering relaxation rate taking into consideration normal and umklapp processes. Incorporating the above expression, the phonon conductivity of Mg2Ge is calculated in the entire temperature range 4 to 1000 K and good agreement is found between calculated and experimental values of phonon conductivity of the sample in the entire temperature range of investigation. Analytical expressions are reported to calculate an approximate value of lattice thermal conductivity. The role of four‐phonon processes is also included in the present study. Using the expression for τ proposed by Joshi and Verma and Sharma et al. the phonon conductivity of InSB and Mg2Ge is calculated to compare the results obtained using the proposed expression for the three‐phonon scattering relaxation rate.
Generalization of the heisenberg hamiltonian for the case of an atomic system with a variable atomic spin value
Authors: Popov V. A. , Loginov A. A.
Published: July 2007

The representation invariant relative to spin rotations of the Hamiltonian of electrostatic electron interactions is derived for a dielectric. The temperature dependence of the exciton spectrum and that of the value of the site spin moment, 〈S〉, due to exciton‐magnon interactions are considered.
Spectroscopic investigation of orientational disorder in an acenaphthylene molecular crystal
Authors: Korets A. Ya. , Fedorov V. P. , Korshunov A. V. , Naumov V. A.
Published: July 2007

The electronic absorption spectra of an acenaphthylene single crystal are obtained in polarized light at 4.2 to 300 K. The temperature dependence of band width, maximum and integral intensity of the lowest singlet‐singlet transition at v = 21762 cm−1 are discussed. Both the band broadening of the exciton doublet with va = 21260 cm−1 and vb = 21280 cm−1 and its intensity decrease are shown to be due to a change of orientational disorder, when approaching the orientational phase transition at T = 130 K. The constancy of Davydov splitting Δ = 20 cm−1 with temperature is associated with inter‐ordering of two sets of translationally non‐equivalent acenaphthylene molecules, which does not influence the value of resonance interaction between the pair molecules.
Calculation of a resonant model potential for copper, silver, and gold
Authors: Dagens L.
Published: July 2007

The ionic resonant model potential (RMP) v0(E) = w0(E) + vres(E) for d‐band metals considered previously is slightly generalized in order to take into account the energy dependence and nonlocality of the s and p scattering which were previously neglected. The RMP v0 is written as w0(E) + + vres(E) where w0 is a general Heine‐Abarenkov‐like potential and vres is a finite‐rank operator which acts on d states and is strongly energy‐dependent. The RMP parameters appropriate for the metallic state are calculated from first principles by requiring that the screened metal RMP \documentclass{article}\pagestyle{empty}\begin{document}$ \mathop \sum \limits_{ions} {\rm}v_0 (E){\rm +}V_e $\end{document} is equivalent to the true HFS self‐consistent potential. The calculation is done using a Wigner‐Seitz spherical approximation, consistently for the true potential and the model potential. The method is applied to the three noble metals. The results are: (i) the enrgy dependence of the s and p potentials is significant; (ii) the s–p non‐locality is large; (iii) the d potential vres has indeed the resonant form U/(E − ℰ(E)) with ℰ(E) only slightly energy‐dependent. A simpler model potential is then derived (ℰ(E) is replaced by its Fermi level value; the energy dependence of w0(E) is only approximately taken into account through an effective mass approximation) and applied to the calculation of a few illustrative physical quantities. The results are satisfactory, at least for copper and silver, but some physical quantities (such as the elastic constants calculated up to second order according to the long‐wave method) are found to be sensitive to the value of the somewhat arbitrary model radius Rm (the best results are obtained for the largest Rm satisfying the non‐overlap condition).
Absorption and luminescence of V (d3) in II–VI compound semiconductors
Authors: Hoang Le Manh , Baranowski J. M.
Published: July 2007

The absorption and luminescence spectra of the V (d3) in ZnS, ZnSe, CdSe, and CdTe are presented. Values of the crystal‐field parameters Δ, B, and C are derived from the spectra and discussed. The infrared luminescence at about 5000 cm−1, characteristic for the V (d3) impurity in II–VI and III–V compound semiconductors, is shown to be due to the 4A2(F)‐4T2(F) transition.
Spin–orbit‐allowed tunneling splitting in the T × εg Jahn‐Teller problem splitting of the zero‐phonon line
Authors: Ranfagni A. , Viliani G.
Published: July 2007

An orbital triplet state T in a lattice of cubic symmetry (Oh), which by the Jahn‐Teller effect is coupled to tetragonal vibrational modes (εg), is considered. The tunneling splitting in this T × εg, Jahn‐Teller problem with spin‐orbit interaction is computed in Ham's framework and by the WKB approximation in several cases. The results are compared to zero‐phonon line splitting of V2+ impurities in MgO and KMgF3.
Raman spectrum and dielectric relaxation in K4Fe(CN)6 · 3 H2O
Authors: Savatinova I. , Anachkova E.
Published: July 2007

The temperature dependence of the two Raman active modes at 62 and 126 cm−1 corresponding to the symmetry Bg/A″ (z) is investigated. In the vicinity of the phase transition point (TC = 249 K) the mode bandwidths undergo a sharp increase which is assigned to the reduction of the barrier height characterizing the water Brownian motion. A semi‐empirical expression for the temperature dependence of the barrier height is given. Mason's relaxation theory is used to correlate the temperature behaviour of the barrier with the dielectric constant of KFCT as function of temperature and frequency.
Spin–lattice relaxation in Fe3+‐doped andalusite crystals II. The effect of lattice oscillator heating
Authors: Korolev V. D. , Peskovatskii S. A. , Shulga V. M.
Published: July 2007

The phonon bottleneck effect of Fe3+ ions in andalusite crystals is investigated at temperatures T < 0.3 K. In concentrated crystals (c = 0.56%) heating of the phonons within a frequency range exceeding the ESR line width is revealed. An analysis of the influence of the lattice oscillator heating on the spin–lattice relaxation rate is made.
The mean field phase diagrams of YbIG
Authors: Loos J.
Published: July 2007

The existence of the symmetry allowed magnetic phases in ferrimagnetic YbIG is discussed. The continuous and quasi‐continous transformations of these phases are treated using the thermodynamic potential expansions whose coefficients are determined from the well known effective spin Hamiltonian of Yb ions. The special cases with the magnetic field H along the <100>, <111> and <110> symmetry directions are dealt with. The existence of a low symmetry phase connected with the occurrence of a tetracritical point is stated for H ∥ <110>. The collinear‐canted phase transition is of the first order for H ∥ <111> but at high fields quasi‐continuous with a very narrow metastability region. An isolated critical point, in which three first‐order and two second‐order transition lines meet, is found on this first‐order phase boundary. The connection with the Potts model is outlined. The calculated phase diagrams are compared with experimental results.
A Raman and far‐infrared investigation of phonons in the rhombohedral V2–VI3 compounds Bi2Te3, Bi2Se3, Sb2Te3 and Bi2(Te1−xSex)3 (0 < x < 1), (Bi1−ySby)2Te3 (0 < y < 1)
Authors: Richter W. , Becker C. R.
Published: July 2007

The Raman‐active lattice vibrations of Bi2Se3, Bi2Te3, Sb2Te3, and their solid slutions, whose symmetries correspond to the R3m space group, are investigated by Raman scattering. Three of the four expected Raman modes, Eg and A1g, could be determined. The FIR optical properties of Bi2Te3 crystal surfaces of improved quality (E ∥ c and E ⟂ c) and Bi2Se3 (E ⟂ c) are re‐examined near helium and room temperature with a Fourier spectrometer, allowing a determination of the infrared‐active mode frequencies with higher accuracy. The results for Bi2Te3 are compared to the predicted frequencies from the lattice dynamical model, given by Jenkins et al. The frequncy shifts of the Raman‐active modes in the mixed crystals show single‐mode and two‐mode behaviour, which is in agreement with simple models for the substitution of antimony and selenium atoms for bismuth and tellurium, respectively, in Bi2Te3.
Drag effects in a heated electron–phonon system. N‐germanium and n‐silicon
Authors: Kocevar P.
Published: July 2007

A linearized version of a recently developed theory of phonon amplification by hot electrons in high‐mobility semiconductors is used to estimate mutual electron–phonon drag and heating effects in materials of lower mobility with dominant acoustic deformation potential and ionized impurity scattering. Accordingly a weakly drifting heated Maxwell distribution is assumed for carriers with quadratic and isotropic energy dispersion. Simple closed expressions are found for the steady‐state mobility, showing explicitly how mutual drag effects (increasing the mobility) dominate at lower electric fields, whereas the effects of phonon heating (lowering the mobility) dominate at fields for which the electron temperature is more than twice the lattice temperature. The results are applied to n‐germanium.
Vibration modes of split screw dislocations in b.c.c. metals
Authors: Kroupa F.
Published: July 2007

Internal vibrations of the core of a crew dislocation in a b.c.c. lattice are studied using a simplified model of dislocation splitting on three planes into four partials. While the eigenfrequency of the optical mode is very high, of the order of 1012 s−1, the eigenfrequency of the acoustic mode strongly decreases with decreasing Burgers vector of the central partial. It is proposed that the acoustic mode can be detected from internal friction measurements or from the influence of ultrasound on the yield point of b.c.c. metals at low temperatures.
On the heat capacity of Fe(HCOO)2·2 H2O
Authors: Gochev I. G. , Grozdev K. I.
Published: July 2007

The anomalous long high temperature tail of the magnetic part of the heat capacity of ferrous formate dihydrate is considered. A theoretical model for the explanation of such heat capacity behaviour is proposed. Quantitative consistence with experimental data is obtained.
Concentration of “impurity” ion clusters in a two‐dimensional host lattice
Authors: Trutia A. , Iova F. , Vodâ M.
Published: July 2007

The concentrations of magnetically active ions in clusters occurring in a diamagnetic two‐dimensional host lattice are statistically calculated. This is done for an initial, total active ion concentration ranging from 1 to 100 mol% and for all geometrically possible cluster types from singlets to septets, 449 in all. The model taken into consideration is a real Z(M)X2‐type crystal, where it is presumed that a direct exchange intra‐layer is the only important interaction (no superexchange). These calculations are made in order to provide a basis for understanding the nature of the concentration‐sensitive optical absorption bands and magnetic behaviour of some crystals containing transition metal ions.
Electron energy spectrum of a finite crystals in a uniform electric field
Authors: Berezhkovskii A. M. , Ovchinnikov A. A.
Published: July 2007

An explicit expression for the shift of levels of Wannier‐Stark ladders, which appears due to finite crystal dimensions, is derived. The surface states are analyzed. It is concluded that Wannier‐Stark ladders do exist if crystal dimensions are sufficiently large.
Density of states and itinerant ferromagnetism in amorphous systems with dense random packed hard sphere structure
Authors: Richter J. , Kobe S.
Published: July 2007

Itinerant ferromagnetism in amorphous systems is investigated. Both, the lattice model and the model of dense random packing of hard spheres (DRPHS) are used to simulate the amorphous structure, for the last one the conncective topology is discussed. The density of states of electrons is calculated using a continued fraction method. The influence of off‐diagonal disorder on density of states and stability of ferromagnetism is considered, where qualitatively similar tendencies are obtained for lattice model and DRPHS model.
Angular dependence of the reflection spectra and directional dispersion of the anisotropic exciton polaritons in ZnO
Authors: Hümmer K. , Gebhardt P.
Published: July 2007

The reflection spectra of the ordinary and extraordinary polaritons near the A1‐, B1‐exciton resonances of ZnO are presented for two geometries: normal reflection of planes inclined to the c‐axis at varying degrees, and oblique reflection of as‐grown (10I10) faces. The experimental and theoretical spectra are compared. The calculations are based on a) the dispersion relations derived from Fresnel's equation taking account of spatial dispersion, b) the Pekar additional boundary conditions combined with an exciton free surface layer. There are indications of the correlation between the thickness of this layer and decreasing oscillator strength of the polaritons.
Lattice vibrations of Bi2Te3
Authors: Wagner V. , Dolling G. , Powell B. M. , Landweher G.
Published: July 2007

The dispersion curves for phonons propagating along the trigonal axis of the layer‐structure emiconductor Bi2Te3 at 77 K have been determined by coherent inelastic neutron scattering techniques. Analysis of these results in terms of a simple interplanar force model shows a) that the forces between adjacent planes of Te atoms are comparable to those between nearest neighbour planes of Bi and Te and b) that foreces between next‐nearest‐neighbour planes have to be considered. In addition, a limited number of phonons were measured at 300 K and some low‐frequency modes propagating along the bisectrix within the planes were determind. The results are compared, where possible, with previous Raman scattering, infrared reflection, and elastic constant measurements.
Photoelectron measurements of α‐phase alloys CuZn, CuGa, and CuGe
Authors: Norris C. , Williams G. P.
Published: July 2007

Photoelectron measurements using 21.2 and 40.8 eV photon energies with α‐phase Cu0.83Ga0.17 and Cu0.87Ge0.13 alloys and several α‐phase CuZn alloys are reported. No clear evidence of a virtual bound or split‐off impurity level at the bottom of the matrix band is found. Comparison is made between the results of published calculations and the measured valence spectrum of CuZn. Core level shifts as determined with AlKα (1486.6 eV) radiation indicate a transfer of charge to the Cu sites takes place as multivalent impurity atoms are added.
Scattering and decay of hot excitons interacting with longitudinal optical phonons
Authors: Aristova K. A. , Giner C. Trallero , Lang I. G. , Pavlov S. T.
Published: July 2007

Scattering and decay probabilities are obtained for a „hot”︁ Wannier‐Mott exciton of arbitrary kinetic energy which interacts with the longitudinal polarizational lattice vibrations (LO‐phonons). All computations are performed for three different values of the ratio m2/m1, where m1(m2) is the electron (hole) effective mass. It is shown for the case of quite different electron and hole effective masses that the scattering and decay probabilities are essentially comparable. These results show a theoretical evidence in favour of the existence of hot excitons.
Multiple phase transitions in disordering systems
Authors: Kharkats Yu. I.
Published: July 2007

The possibility of realization of multiple first‐order phase transitions in disordering systems is studied. It is shown that for a rather loosely defined law of attraction interaction, pairs of genetically related transitions, or bitransitions, should occur in both symmetrical and asymmetrical disordering systems. Critical conditions for bi‐transition origination and possible schemes of multiple phase transition occurrence are studied. The widely used law of short‐range pair interaction, f(x) = x2/2 (where x represents a long‐range parameter), is shown to feature a specific degeneration owing to which there are no multiple phase transitions in symmetrical systems with this law.
Raman scattering in some III‐VI layer single crystals
Authors: Faradev F. E. , Gasanly N. M. , Mavrin B. N. , Melnik N. N.
Published: July 2007

Polarized Raman spectra of InSe and InS crystals are obtained, the assignment of frequencies is given, and atomic displacements are found at all normal vibrations. In the InSe crystal, force constants of interaction of In‐Se and In‐In atomic planes are evaluated. It is shown that the Raman spectrum of InS has a doublet nature typical for layer crystals. The frequencies of rigid‐layer modes forbidden in the Raman spectrum are calculated in the InS crystal. It is found that interlayer force constants in the InS crystal are only 5 to 10 times smaller than the intralayer covalentbond force constants.
Temperature shift of the maximum of neutron critical scattering in the second born approximation
Authors: Mrygoń B. , Urbaniak A.
Published: July 2007

Two approximate forms of the cross‐section obtained in the second Born approximation are discussed with respect to the temperature shift of the main maximum of critically scattered neutrons in ferromagnets. The disscusion is given for the correlation of the Ornstein‐Zernike type and the correlation function reflecting the lattice symmetry of a simple cubic crystal. It is shown that the temperature shift depends on the momentum transfer vector q, the diffusion coefficient D, and the initial wave vector k0.
On the electronic absorption and amplification of sound in semiconductors at “intermediate” frequencies
Authors: Gurlyaev Yu. V. , Ivanov S. N. , Kozorezov A. G.
Published: July 2007

On the basis of the general theory developed earlier of electronic absorption (EAb) and amplification (EAm) of sound (acoustic waves), which is valid, in particular, at the so‐called „intermediate”︁ frequencies ql ≈︁ 1 (q wave number, l mean free path of electrons), explicit expressions are obtained for the coefficients of EAb and EAm of sound for various mechanisms of electron momentum scattering and for arbitrary degree of degeneracy of the electron gas. With the help of these expressions the large number of published experimental data are analysed concerning the measurements of EAb and EAm of sound in the wide frequency range including intermediate frequencies. In all cases quite satisfactory agreement between theory and experiment is reached without using any „matching”︁ parameters.
On the dynamics of electrons in the strong‐coupling Hubbard chain
Authors: Jelitto R. J. , Heise M.
Published: July 2007

The dynamics of electrons is investigated in a Hubbard chain in the strong‐coupling limit. This problem may be figured as the motion of a double‐occupancy (consisting of one spin‐up and one spin‐down electron fixed at the same lattice site) on a linear chain, all other sites of which are occupied by single electrons of arbitrary spin orientation. The spectrum of this problem is derived exactly and from it the partition function is calculated. It agrees with the result derived by Beni and coworkers formerly with the aid of thermodynamic perturbation theory.
Theory of electron spin resonance in graded mixed semiconductors
Authors: Leibler L.
Published: July 2007

In semiconductor alloys with non‐uniform composition the spin—orbit coupling leads to specific spin‐dependent effects in free‐carrier dynamics. As a result, conduction electron states in the uniform magnetic field substantially differ from those in homogeneous alloys. It is shown that the electron spin resonance (ESR) is strongly affected by the composition gradient. The polarization dependence of ESR absorption permits to separate easily the effect of crystal non‐homogeneity. The measurement of ESR in graded mixed semiconductors may furnish parameters crucial for determination of the band structure of semiconductor alloys.
On the nature of the top of the valence band in layered Mo and W dichalcogenides
Authors: Fonville R. M. M. , Geertsma W. , Haas C.
Published: July 2007

The magnetic susceptibilities of single crystals of MoS2, MoSe2, α‐MoTe2, and WSe2 are measured between 2 and 300 K. Above 60 K the susceptibilities are temperature independent and strongly anisotropic. The observed anisotropy is attributed to Van Vleck temperature‐independent paramagnetism of the d electrons. The electrical resistivity and the Hall effect of As‐doped p‐type single crystals of MoS2, MoSe2, α‐MoTe2, WS2, and WSe2 are measured between 2 and 300 K. Electron paramagnetic reasonance of p‐type crystals of MoS2, MoSe2, α‐MoTe2, WS2, and WSe2 shows strongly anisotropic g‐values. An explanation of these g‐values is not possible in terms of only metal d‐orbitals or only chalcogen p‐orbitals, but requires a strong mixing of d‐ and porbitals in the top of the valence band.
Effects of bond dilution on dynamics of anisotropic paramagnets at high temperatures
Authors: Kawasaki K. , Tahir‐Kheli R. A.
Published: July 2007

Wave‐vector dependent frequency moments, for longitudinal and transverse spin correlations, in a cylindrically symmetric, anisotopic paramagnet at T = ∞ with exchange bond dilution are evaluated. Using the phenomenological, two parameter Gaussian construct for the diffusivity, the correlation functions are computed. Two types of dilution are considered: first, when the existence of transverse and longitudinal exchange bonds depends only on a single random variable, and secondly, when these bonds are functions of two independent random variables. It is found that the independent fluctuation of transverse and longitudinal exchange bonds has far reaching consequences. In particular, for a given concentration of connected bonds, the effects of dilution are considerably enhanced when these bonds are fluctuating independently. The relevance of such a model to amorphous paramagnets is noted.
Theory of the X‐ray and optical properties of polysulphur nitride
Authors: Friesen W. I. , Litvin D. B. , Bergersen B.
Published: July 2007

The extended Hückel method is used to calculate various band structure dependent properties of polysulphur nitride (SN)x. X‐ray emission spectra are computed and are presented as a means of differentiating between conflicting reported band structures. The interband contribution to the imaginary part of the dielectric function is also calculated and is discussed in relation to experimental results quoted in the literature.
Thermal expansion and Grüneisen parameters in alkali metals
Authors: Vaks V. G. , Zarochentsev E. V. , Kravchuk S. P. , Safronov V. P. , Trefilov A. V. , Kravchuk S. P.
Published: July 2007

Thermal expansion and Grüneisen microscopic and macroscopic parameters γvk and γ(T) in the alkali metals are calculated in the pseudopotential model described earlier. γvk is proved to be sensitive to the form of the dielectric function ε(q) and of the pseupotential V(q) so that measurements of γvk may give an information on the ε(q) and V(q). γ(T) has a pronounced variation at small T. Comparison with experiment reveals a high accuracy of the description of the thermal expansion in Na and Cs with the models from [1] and in K and Rb with the models from [2]. Results for Li disagree noticeably with experiment. The sensitivity of all the results to the form of ε(q) and V(q) is discussed.
Phonon scattering on small‐radius colloids in KCl crystals
Authors: Altukhov V. I. , Kvachadze V. G.
Published: July 2007

The heat conduction of KCl is considered taking into account phonon scattering on colloids of different sizes, Estimations for average sizes and concentrations of colloids in KCl are obtained. Peculiarities of formation of small colloids (10 to 30 Å) are discussed. It is shown that with the increase of low‐temperature reactor irradiation dose (or degree of doping) of crystals four characteristic stages of defect formation can be differentiated: (a) point defects, (b) large size colloids and point defects, (c) small colloids (partially due to the decrease of number of large colloids), (d) small and large colloids which are formed in succession. Annealing (in case of doping) leads to a significant enlargement of colloids (partially due to the decrease in number of point defects).
The electronic band structure and interatomic bond in nickel and titanium hydrides
Authors: Kulikov N. I. , Borzunov V. N. , Zvonkov A. D.
Published: July 2007

Using an approximation for solving the Korringa‐Kohn‐Rostoker equation the band structure of titanium and nickel dihydrides and nickel hydride are calculated. The results are compared with experimental data. The applicability of the anionic and protonic models of hydrides are discussed. From the tendency of the palladium hydride band structure one can conclude that nickel dihydride has a superconducting transition at nonzero temperature. The results of band structure calculations of titanium dihydride allow to explain the f.c.c.‐f.c.t. phase transition for this compound.
On the influence of background radiation on Landau emission spectra
Authors: Müller W. , Overhamm M. , Bauer G. , Gornik E. , Grosse P. , Pötzl H. W. , Rautenberg M.
Published: July 2007

Landau emission in n‐InSb has been investigated by photoconductive techniques and Fourier transform spectroscopy (FTS). It is found that effects of 300 K background radiation can strongly influence the observed spectra through the electric field induced variation of the optical constants. Only under 4.2 K background conditions or by using special experimental arrangements the influence of the background radiation can be avoided and pure emission spectra are obtained. Real emission spectra consist of two main lines due to Landau level transitions with different spin orientation and a weak impurity line. No emission is observed above the reststrahlen band.
Local Heine‐abarenkov model potential for covalent crystals
Authors: Soma T.
Published: July 2007

A local Heine‐Abarenkov model potential is proposed for diamond type crystals. Two parameters are determined by satisfying the zero pressure condition and the first zero of the empirical pseudopotential interpolated from band calculations. Calculated values of bulk modulus for Si, Ge, and α‐Sn are in good agreement with the experimental data.
Some observable consequences of kinetic many‐body treatment of large energy fluctuations and of rate constants in solids
Authors: Khait Y. L.
Published: July 2007

Semiphenomenological classical non‐equilibrium collective treatment of short‐lived large energy fluctuations (SLEFs) of heavy particles (atoms, etc.) in bulk and on surfaces of solids up to ε ≧ E ≫ kT are considered. The SLEF probability and rate constants are calculated. In the Arrhenius approximation the calculated pre‐exponential factors are exponential functions of E, effective coordination numbers χeff, Debye temperatures θ, etc. The new interpretation of diffusion and desorption experimental data narrowing the discrepancies between the latter and theoretical predictions is suggested.
Non‐linear fluorescence quenching in molecular crystals I. Recombination of localized excitons
Authors: Benderskii V. A. , Kh. Brikenshtein V. , Lavrushko A. G. , Filippov P. G.
Published: July 2007

From the measurements of quantum yield and fluorescence decay time of anthracene and naphthalene crystals for different pumping levels at 300 K the rate constants of bimolecular recombination of excitons are found to γ = (1 ± 0.3) × 10−8 and (3 ± 1.5) × 10−11 cm3 S−1, respectively. The relationship between the recombination constants and the interaction radius R0 is calculated for the dipole‐dipole mechanism of recombination. Based on this assumption the values of R0, (40 ± 5) Å in anthracene and (25 ± 5) Å in naphthalene, agree with the values calculated from the overlap of fluorescence and lower excited singlet state absorption spectra.
Exchange splitting of ionic S‐State in MnFe2O4 studied by neutron spectroscopy
Authors: Ligenza S.
Published: July 2007

Inelastic neutron scattering is used to investigate spin interactions in polycrystalline MnFe2O4. Neutron spectra connected with local spin interaction (not perturbated by cooperative phenomena) are observed and interpreted basing on the 6S5/2‐term splitting of ions situated in octahedral B‐sites and tetrahedral A‐sites. In the analysis of 6S5/2‐term splitting the phenomenological spin‐Hamiltonian is used, assuming a magneto‐electric interaction of spins. The transition energy peaks connected with different magnetic coordinations at B‐sites and A‐sites are observed. Defining the interaction between pairs of spins as — 2JABSA · SB it is found that JAB/k = (– 20.0 ± 0.7) K, in agreement with the result obtained from magnon dispersion measurements.
Electromigration in liquid metal alloys
Authors: Sorbello R. S.
Published: July 2007

Starting from an earlier pseudopotential result of Sorbello an expression is obtained for the driving force for electromigration in liquid metal alloys. The resulting force expression is equivalent to the Faber formula. This formula is extended to include electron‐ion potentials which are described by t‐matrices in a phase‐shift representation. Calculations are made for Na–K and Na–Rb alloys using a modified substitutional model for partial ionic structure factors and using the phase shifts computed by Meyer, Nestor, and Young. The theoretical calculations predict reversals in the direction of alloy separation near the experimentally observed values.
Phonon scattering and effect of dislocations on the low‐temperature phonon conductivity in Ge
Authors: Singh M.
Published: July 2007

It is shown that the theory, which is based on the scattering of phonons by bound dangling electrons associated with the dislocation core, gives excellent agreement between the theoretical and experimental results of phonon conductivity for deformed germanium. No adjustable physical parameter is used in the calculation except the difference of energy splitting. From a comparison of theory and experiment is found that the density of dangling electrons is directly proportional to the dislocation density.
Organic metals: Chain stabilisation in bipyridinium‐TCNQ salts
Authors: Ashwell G. J.
Published: July 2007

A method of conductivity enhancement applied to bipyridinium‐TCNQ salts is reported. By altering the cation geometry, with careful consideration to the effect on the stacking characteristics of the counter ion, chain stabilisation and conductivity enhancement are achieved. The crystal structures and properties of several bipyridinium‐TCNQ salts are reported. Their conductivities are in the range 10−5 to 103 Ω−1 cm−1 at 300 K. The effect of clathrated solvent molecules on the properties is also discussed.
Quadrupolar–Paramagnetic Critical Temperature of a Spin‐One Isotropic Heisenberg Film with Biquadratic Interactions
Authors: Corciovei A. , Mazilu D. , Mihalache D.
Published: July 2007

Using the Green function method, the transition temperature from the quadrupolar to the paramagnetic phase of an isotropic Heisenberg film with free surfaces in the presence of biquadratic exchange is obtained as the unique solution of a non‐linear system of equations. The other unknowns entering the system are related to the distribution of the quadrupolar order parameters at the critical temperature. The index λ of the relative shift of the critical temperature satisfies the relation λ = 1/ν = 2, ν being the bulk correlation length exponent.
On Integeral Characteristics of the Electron Structure of Crystalline Surfaces
Authors: Bartoš I. , Hietschold M. , Paasch G.
Published: July 2007

Formulas giving new applications of the surface Green function formalism to the integral characteristics of surfaces — deviations of the total density and integrated density of electron states, surface energy — are given and applied to a step potential two‐band model of a crystal surface. The role of surface electron states on the behaviour of integrated characteristics is described. The formalism is applicable to any interface problem.
Electron Paramagnetic Resonance of Divalent V, Mn, and Co in Single Crystals of CdI2 and PbI2
Authors: van der Valk H. J. L. , Meertens P. , Haas C.
Published: July 2007

EPR spectra are reported of V2+, Mn2+, and Co2+ in CdI2 and PbI2 single crystals. The g‐values of V2+ are strongly affected by covalent mixing of metal 3d with iodine 5p orbitals. The ligand hyperfine interaction is different for Mn substituted in CdI2 and PbI2, respectively. The change is attributed to a different covalent bonding in the two lattices due to the local distortion of the MnI6 octahedra. The temperature dependence of the zero‐field splitting of Mn2+ is explained in terms of the anisotropy of the nuclear vibrations.
Negative Magnetoresistance in Indium Arsenide in the Extreme Quantum Limit
Authors: Mansfield R. , Azhdarov G.
Published: July 2007

The results of magnetoresistance measurements of n‐InAs with carrier concentration ≈ 1016 cm−3 are given in a longitudinal magnetic field up to 40 kG and the temperature range from 20 to 110 K. In a large magnetic field a negative magnetoresistance is observed over the whole investigated temperature range. Under the extreme quantum limit conditions and when impurity scattering predominates, a comparison between the experiment and Argyres and Adams' theory with allowance of Dubinskaya for forward scattering is made and is discussed.
Model Calculations for the Anisotropy Formation by Resputtering Processes during the Growth of Amorphous GdCo Films
Authors: Müller H.‐R. , Perthel R.
Published: July 2007

In order to understand the formation of a magnetic anisotropy during the preparation of amorphous GdCo films by bias sputtering, model calculations are carried out for simple cubic or hexagonal close packed lattices. A structural anisotropy is always obtained, if differences in the binding energies of CoCo, GdCo, and GdGd pairs are assumed. The anisotropy can be described as a difference of the pair numbers parallel and perpendicular to the film plane. Sign and magnitude of the anisotropy depend strongly on the surface configurations involved in the resputtering process (adatoms or inner atoms) and on the binding energies assumed for the different pairs.
Phase Transformations in Hydrides of Rare‐Earth Metals under Pressure. II. The Sc‐H and Yb‐H Systems under High Hydrogen Pressure
Authors: Bashkin I. O. , Ponyatovskii E. G. , Kost M. E.
Published: July 2007

The ScH and YbH systems are investigated at hydrogen pressures up to 13 kbar. A new scandium hydride of the composition ScH2.80 and an ytterbium hydride of the composition YbH2.72 is obtained. The hydrides obtained liberate hydrogen at atmospheric pressure to compositions YbH2.70 and ScH≈2.65. According to the results of X‐ray studies, YbH2.70 remains cubic (a0 = 5.178 Å), while the metastable ScH2.65 consists of the following two phases: f.c.c. (a0 = 4.784 Å) and h.c.p. (a0 = 3.380 Å; c0 = 6.135 Å; c/a = 1.815).
Higher Anharmonicities in the Improved Unsymmetrized Self‐Consistent Field Approximation for a Crystal. I. General Consideration
Authors: Zubov V. I.
Published: July 2007

Strongly anharmonic crystals are described by the unsymmetrized self‐consistent field method. When the lowest‐orders anharmonicities are taken into account, the basic nonlinear integral equation is reduced to a set of transcendental equations which can be solved numerically. Such an approach is used as a zeroth‐order approximation. The statistical perturbation theory enables one to take into account the effect of higher‐order anharmonicities on the Helmholtz free energy and on the thermodynamic properties of strongly anharmonic crystals. First‐ and second‐order perturbation theory is considered. The various contributions to the properties of solid Ar are calculated versus temperature and volume.
Stepped Ordering in Binary Solid Solutions
Authors: Ratishvili I. G.
Published: July 2007

The free‐energy functions of ordered solid solutions described by the two‐parameter distribution functions are investigated. It is shown, that in the systems under consideration, as a rule, intraphase transitions are formed which provide a stepped character of ordering.
Localized Bipolarons in Ionic Crystals
Authors: Vinetskii V. L. , Kudykina T. A.
Published: July 2007

The localized bipolaron state in ionic crystals is investigated taking account of the exchange interaction. The state is shown to be thermally stable under all values of the parameter ϵ/n2 (ϵ is the dielectric constant, n is the index of refraction). At large enough values of ϵ/n2 (> 26) the existence of two electron centres and positive vacancies is energetically profitable, and the one‐electron (neutral) centres are absent. Such a situation is apparently realized in chalcogenide glasses where the local lattice distortions near the centres are large and hence the local polarization is large as well.
Propagation of High‐Frequency Electromagnetic Waves in the Voigt Configuration through Samples of Bi at 45, 70, and 300 GHz
Authors: Braune W. , Lebech J. , Saermark K.
Published: July 2007

Experimental results on the propagation of very high frequency electromagnetic waves through Bi are presented. The experiments at the frequencies 45 and 300 GHz are performed at 4.2 K on a sample of thickness d = 0.89 mm, and the experiments at 70 GHz are performed at 1.4 K on a sample of thickness d = 1.3 mm. The waves observed propagating through the samples are of the cyclotron wave type. It is pointed out that a satisfactory theoretical understanding of the wave phenomena can only be hoped for if realistic numerical calculations, including all ellipsoids of the Bi Fermi surface and a finite ωτ value, are carried out.