bluuebunny/crossref_metadata_2025 huggingface dataset:
Conduction electron spin resonance due to exchange and spin‐orbit scatterings by silute impurities in superconductors
Authors: Tsallis C.
Published: July 2007

A simple theory is developed to calculate the transverse relaxation time, T2, of the spin of the conduction electrons in a slightly dirty superconductor. Two scattering mechanisms are considered: exchange interaction between the conduction electron spin and the impurity spin (for magnetic impurities only), and spin‐orbit interaction of the conduction electron around the impurity (for all kinds of impurities). As in Maki's Green‐function theory, a sudden increase (decrease) of T with respect to its value in the normal state, for the exchange (spin‐orbit) mechanism is obtained immediately below the critical temperature T0 which separates the normal and superconducting states. For vanishing temperature, T vanishes in both the cases. The asymptotic behaviours for T → T0 and T→0 are calculated. In the spin‐orbit case, T goes to zero, for T→0, surprisingly slowly. In order to exhibit the great sensitivity of T2 on the density of electronic states, it is re‐calculated, for both mechanisms, using an heuristic density of states which is physically reasonable but different from the BCS one. The height and width of the density of states modify not only the proportionality coefficients of T vs. T, but even the exponents in the limit T→0.
The model hamiltonian and some properties of magnetic resonance of triplet excitons. II. Kubo‐tomita approximation
Authors: Berim G. O. , Kessel A. R.
Published: July 2007

The temperature effects of the electron paramagnetic resonance (EPR) spectrum of triplet excitons described earlier by the exchange Hamiltonian are considered on the basis of the Kubo‐Tomita theory of exchange narrowing of EPR lines. It is shown that the proposed model qualitatively explains both the temperature behaviour of the lineshift and the linewidth of the fine‐structure components of the EPR spectrum and the non‐existence of hyperfine structure over the whole temperature range.
On the electric field dependence of the conductivity of holes in Si at low temperatures. II. The influence of the variation of steady‐state hole density with electric field on the conductivity
Authors: von Borzeszkowsei J. , Scholz J.
Published: July 2007

Measurements of the electric field dependence of the hole conductivity of Si with various doping levels and orientations are performed at 20.3 and 27.1 K. A description of the essential characteristics of the experimental results is achieved within the frame of a theoretical model. In this model, the field dependence of the hole mobility (taking into account non‐parabolicity of the valence band and non‐equipartition of acoustic phonon energy in the distribution function as well as in the momentum relaxation time) and the field dependence of the hole concentration (based on Lax′ cascade theory) are combined. Comparison of experimental and numerical results gives the relation between the participation of optical phonons in the hole capture process on shallow acceptors and the transition from super‐ to sublinear current‐voltage characteristics in high‐purity p‐Si at low temperatures and at electric field strengths below the breakdown range.
Giant spin splitting induced by exchange interactions in Hg1−kMnkTe mixed crystals
Authors: Bastard G. , Rigaux C. , Mycielski A.
Published: July 2007

T6 → T8, magnetoabsorption spectra of semimetallic Hg1−kMnkTe alloys (k ≦ 2%) provide evidence of striking modifications in the “spin” states of the T8 Landau levels, in particular a drastic increase of the electronic Lande factor is observed. These anomalous spin effects are interpreted as the manifestation of the exchange interactions between the mobile electrons and the d electrons localized on the Mn atoms. The exchange integral for T8 levels is estimated.
Calibration of the isomer shift for 119Sn
Authors: Antončík E.
Published: July 2007

The isomer shift calibration constant for 119Sn is determined using the calculated electron contact densities for α‐tin and for an isolated tin atom in the solid rare‐gas matrix. The theoretical value of 8R/R = 0.92 × 104 thus estimated is compared with the experimental values.
On the binding energy of wannier excitons in strong anisotropic crystals
Authors: Gerlach B.
Published: July 2007

The strong anisotropic limit of the discrete energy‐values of excitons in uniaxial crystals is calculated. It is shown that all states of a given quantum number m of the z‐component of angular momentum approach the same limit – 4/(2 ∣m∣ + 1)2. First corrections to this value are discussed in terms of the anisotropy constant A  ε⟂μ⟂/ε∥︁μ∥︁ They come out to be at most of order A1/3 for m  0 and A1/2 for m ≠ 0.
Effect of hydrostatic pressure on the vibrational properties and the structure of SrWO4 and PbMoO4
Authors: Ganguly B. N. , Nicol M.
Published: July 2007

Raman spectra of SrW04 are measured up to 35 kbar at 300 K. At (21 ± 2) kbar the doubly‐degenerate Eg modes are observed to split which indicates a structural transformation to a lower symmetry. The high pressure Raman spectra are similar to spectra of the structure of ZnW04. Raman spectra of PbMoO4 are also measured up to 35 kbar at both 300 and 80 K, but no evidence of a structural change is observed. The pressure dependence of the phonon spectra suggests the presence of harmonic phonon‐phonon interaction in this system. The possible origins of the different high pressure form of the scheelites are discussed on the basis of lattice phonon‐phonon interaction.
Electrical and magnetic properties of two crystallographic forms of (DEPE)2+(TCNQ)
Authors: Ashwell G. J. , Eley D. D. , Willis M. R. , Woodward J.
Published: July 2007

1,2‐di(N‐ethyl‐4‐pyridinium)ethylene2+ (7,7,8,8‐tetracyanoquinodimethane) crystallises in two forms: a metallic form (DEPE)2+(TCNQ) I and a semiconducting form (DEPE)2t(TCNQ) II. On cooling from room temperature to 30 mK the electrical conductivity of I increases monotonic‐ally such that σ30mk/σRT=3.7. The thermoelectric power, in the temperature range studied, and the paramagnetic susceptibility of I, in the range of 60 to 300 K, are nearly independent of temperature, indicative of metallic behaviour. The magnetic susceptibility of II, however, exhibits singlet‐triplet behaviour with a singlet‐triplet separation of 0.029 eV. The electrical conductivity and thermoelectric power are similarly activated. The electrical and magnetic properties of both forms are discussed.
Conduction electron spin resonance in aluminium at 20.98 and 9.27 GHz
Authors: Sambles J. R. , Sharp‐Dent G. , Cousins J. E. , Stesmans A. , Witters J.
Published: July 2007

The linewidths of the conduction electron spin resonances from high purity aluminium foils and films are measured at frequencies of 9.27 and 20.98 GHz using reflection spectrometers. An attempt is made to fit a breakdown of motional narrowing model to the data. It is found that such a model cannot satisfactorily explain the dependence of the linewidths on frequency, temperature, and sample thickness. Likewise a model based on many‐body effects, although explaining some of the features of the results, does not fit all the data. It is possible that a contribution to the impurity induced linewidth which is frequency dependent would provide a better fit and it is concluded that to fully interpret the data a more complex theory is necessary.
LCAO approach to Mn2+ in ZnSe
Authors: Biernacki S. W. , Hamera M.
Published: July 2007

LCAO method is used to study the magnetic d‐electrons of Mn2+ in ZnSe. The splitting Δ of d‐orbitals and the parameters of SHFS tensor are calculated and compared with experimental data.
Dispersion of cyclotron waves in metals and observability of many‐body effects
Authors: Saermark K. , Lebech J.
Published: July 2007

Experimental results on the dispersion of cyclotron waves of the extraordinary and the ordinary type are analyzed in order to examine whether or not numerical estimates for some of the Landau An coefficients can be deduced. The analysis includes results on silver and potassium and the conclusion drawn is that no such estimate can be given. On the contrary, the experimental results are in good agreement with dispersion curves calculated on the basis of a finite value of Ωτ. The behaviour of the dispersion relations in the vicinity of thc Azbel‐Kaner rosonances is examined in the limit ωτ → CO.
The double resonance in two‐phonon Raman scattering
Authors: Abdumalikov A. A. , Klochikhin A. A.
Published: July 2007

The two‐LO‐phonon and one‐LO plus one‐TO‐phonon Raman scattering cross‐sections are calculated in a two‐band model. Double resonance is taken into account. It is shown that the cross‐section maxima are disposed at incident light frequencies of ω = ϵg + 2ΩLO and at ω = ϵg + ΩLO ΩTOfor the 2LO and LO + TO cross‐sections. The cross‐sections decrease with increasing |ϵg – ω| with different laws below and above the band gap ϵg. The cross‐sections above the band gap are strongly dependent functions of the damping constant of the electron system. The results of the numerical calculation are compared with experimental data.
Lo‐phonon‐assisted two‐photon absorption of the first excited state of the biexciton in CuCl
Authors: Ekardt W. , Sheboul M. I.
Published: July 2007

LO‐phonon‐assisted two‐photon absorption of the first excited level of the excitonic molecule in CuCl is considered on the basis of the previously derived symmetry properties of this state. A giant cross‐section for this process is predicted mainly due to the “resonant” intermediate state Γ 1/5 of the single exciton. The process under consideration overcomes the difficulties of pure two‐photon absorption (TPA) of p‐type envelope states of the excitonic molecule as stated by Hanamura.
Plasmon‐enhanced sound amplification in piezoelectric semiconductors under a strong magnetic field
Authors: Lima C. A. S. , Miranda L. C. M.
Published: July 2007

The effect is considered of a strong dc magnetic field upon the contribution to sound amplification in piezoelectric semiconductors arising from the energy conversion mechanism “plasmon + + carrier → phonon + carrier”. An explicit expression is derived for the amplification coefficient. It is shown that under suitable conditions such contribution largely differs from that in the absence of a magnetic field both in the strength of the effect and in the angular distribution of the emitted phonons. A physical interpretation of the results is presented.
Galvanomagnetic effects and alloy scattering in n‐type Pb1–xSnxTe at low temperatures
Authors: Takita K. , Thanh Truong Dinh , Tanaka S.
Published: July 2007

Galvanomagnetic effects are investigated in n‐type Pb1‐‐‐xSnxTe with comparatively low carrier concentration (1.4 × 1017 to 3.5 × 1018 cm―3) grown from the melt. From the analysis of the longitudinal and transverse magnetoresistances and Hall coefficient at low temperatures together with the Shubnikov‐de Haas data, it is found that the scattering is very much isotropic in spite of the large anisotropy of the effective mass. Further analysis of the scattering relaxation time, τ, indicates that the alloy scattering is dominant at low tmperatures. The matrix elements of the alloy scattering potential at the band edges are deduced; Uc(Pb‐Sn) = 8.2 × 10―35 erg cm3 and Uv(Pb‐Sn) ≈ 3Uc(Pb‐Sn). These values are close to those estimated from the pseudopotential theory of alloy scattering after Harrison.
The formation energies of a vacancy and a divacancy and the binding energy of a divacancy in simple metals
Authors: Takai O. , Yamamoto R. , Doyama M.
Published: July 2007

The formation energies of a vacancy and a divacancy and the binding energy of a divacancy in simple metals are formulated up to third‐order terms on the basis of the Lloyd‐Sholl theory. The calculations are performed using the Harrison approach under the condition of constant volume and lattice distortions are neglected.
Investigation of plasma effects in bismuth‐antimony alloys in the submillimeter wave range
Authors: Herrmann R. , Goy P.
Published: July 2007

The microwave absorption in the submillimeter range is investigated in semimetallic bismuthantimony alloys, Bi(1–x)Sbx (x = 0.0275, 0.050). The objects of measurement are hybrid resonances, the dielectric anomaly, and the plasma cyclotron resonance. In the alloy, Bi0.95Sb0.05 the electron‐hole hybrid resonance is found to be a quadratic function of the frequency. In the frequency range 136 to 587 GHz the resonance shift is more than 50%.
E–e Jahn‐Teller system: Optical response studies
Authors: Rueff M. , Sigmund E.
Published: July 2007

The E‐e Jahn‐Teller system is considered. An exact Fourier transformation of the optical response, as calculated by an operator method, is given. The absorption functions depend on the coupling strength and on temperature. Their behaviour is discussed. Comparisons are made with other theoretical investigations.
Superexchange field and intense magnetic field dependences of the Faraday rotation induced by the electric dipole transitions in YIG
Authors: Guillot M. , Le Gall M.
Published: July 2007

The influence of the superexchange field on the Faraday rotation induced in YIG at 1.15 μm wavelength by electric dipole transitions is analyzed in both the octahedral and tetrahedral sites where the contributions of the strong allowed transitions and the weak “forbidden” transitions are determined. It is shown that the temperature evolution of the magneto‐optical coefficients associated with the electric dipole transitions, as deduced from experiments on YIG, is well described by an effective field model which uses the superexchange and the applied magnetic fields. From this model it is shown also that under high (≈ 105 Oe) and intense (> 106 Oe) magnetic fields, Ha, the total Faraday rotation depends on Ha, firstly through the direct influence of the field on the sublattice magnetization and secondly through the magnetic field dependence of the “electric” magneto‐optical coefficients in the a and d sites.
The electron states associated with the core region of the 60° dislocation in silicon
Authors: Alstrup I. , Marklund S.
Published: July 2007

A geometrical arrangement of silicon atoms corresponding to a cylinder of infinite length with a 60° dislocation core along the axis is constructed using linear elasticity theory. The one‐electron energy bands of this cylinder are studied using extended Hückel theory with parameters optimized to give best fit to the absolute bulk energy bands of finite silicon crystals. Electron states localized at the atoms in the dislocation core have a profound dangling bond character and form a band in the bandgap with a width of about 0.7 eV.
Anisotropy of lattice vibrations of layered compounds
Authors: van der Valk H. J. L. , Haas C.
Published: July 2007

The polarizable ion model is used to explain the observed anisotropy of the lattice vibrations of layered compounds with the Cd(OH)2 or CdCl2 structure. The electronic polarizabilities of the ions, the Szigeti effective charge, and the contribution of the short‐range forces to the frequencies of the optical modes are deduced from optical data for the lattice vibrations of PbI2, CdI2, SnS2, and SnSe2. From the analysis it is found that the contribution of the short‐range forces is rather isotropic. The large anisotropy of the optical modes is caused mainly by static dipoles of the anions induced by local electric fields. For the semiconductors SnS2 and SnSe2 the reduction of the ionic charges and static dipoles is larger than for the more ionic compounds PbI2 and CdI2.
The pseudopotential method and the problem of ordering in alloys. III. Intermetallic compounds LiAl, LiTl, and NaTl
Authors: Makhnovetskii A. B. , Krasko G. L.
Published: July 2007

A method, developed in previous papers is applied to the a priori analysis of the thermodynamical stability of the crystal structures of the compounds LiAl, TiTl, and NaTl. Allowing for only pairwise interaction (second order of the pseudopotential perturbation theory), it is found that the structure B‐2 (of CsCl type) is the most stable one for LiAl and LiTl, while in NaTl a spinodal decomposition must arise. Inclusion of multi‐ion interaction, using some higher‐order terms of the Brillouin‐Wigner perturbation theory results in a stabilization of the B‐32 structure in NaTl and LiAl while in LiTl the B‐2 structure is left stable. The structures obtained are experimentally observed. The thermodynamical evolution of the structures is also discussed.
Analysis of lattice thermal conductivity of solid argon at low temperatures
Authors: Gupta I. J. , Trikha S. K.
Published: July 2007

An attempt is made to analyse the lattice thermal conductivity of solid argon at low temperatures, using Holland's model. The dispersion relation q = C sin―1 (ω/ωmax), for transverse phonons, is used to determine vg/v2p in the conductivity integrals. A fairly good agreement is obtained between the calculated and the experimental results of Clayton and Batchelder, in the temperature range 1.5 to 20 K. The dislocation density and the average grain size of the polycrystalline specimen are determined to be 2.5 × 1011 m―2 and 0.05 mm, respectively.
Fluctuations of Order Parameter and Anharmonic Interaction in the Vibronic Model of Ferroelectrics
Authors: Mailyan G. L. , Plakida N. M.
Published: July 2007

The free energy for the vibronic model of a ferroelectric is calculated taking into account the fluctuations of the order parameter (soft phonons) defined by the electron‐phonon and anharmonic interactions. As a result, a considerable lowering of the phase transition temperature Tc in comparison to its mean field value is obtained. Both the anharmonic and electron‐phonon interactions define this reduction of Tc, the latter being more important for narrow‐gap ferroelectrics.
Pseudocubic Angular Dependence of the M = −1/2 to +1/2 EPR Transitions for Ions with S = 3/2 by Small Distortions of the Cubic Crystal Field
Authors: Gehlhoff W.
Published: July 2007

The line positions of the EPR transitions — determined by the generalized spin Hamiltonian ℋ︁ = gβBS + ∫β{S Bx + S By + S Bz − 1/5 (SB) [3S(S + 1) − 1]} for cubic symmetry and S = 3/2 — are calculated to the second order of perturbation theory taking into account small rhombic distortions of the crystal field. In the case of the transition M = −1/2 ⟷ +1/2 — frequently the only one experimentally observed — it is shown that under certain conditions such distortions of the crystal field apparently cause the same cubic angular dependence as the term ∫βS3B does. Therefore, the parameters f and g determined from the experiment may contain contributions of non‐cubic fields. These contributions, which can be determined by measuring at two microwave frequencies, are calculated for four different systems of the rhombic principal axes.
The Dielectric Relaxation of Impurity—Vacancy Complexes in KI Doped with Cl+ Anions
Authors: Zílio S. C. , De Souza M.
Published: July 2007

Using the ITC technique the dielectric relaxation of KI doped with divalent ions and small amounts of Cl− or Br− anions is studied. New low temperature ITC peaks are found at temperatures as low as 120 K. Also a strong effect is found in the aggregation kinetics of the divalent ions. A model for the trapping of the divalent ions by the Cl− or Br− anions is proposed.
Random One‐Dimensional Classical Magnet
Authors: Krzemiński S.
Published: July 2007

For the thermodynamic quantities (specific heat, spin‐spin correlation functions, magnetic susceptibility) of an impure one‐dimensional system of classical spins of arbitrary dimensionality with arbitrary, isotropic nearest‐neighbour interactions rigorous expressions are found in the thermodynamic limits. The quenched approximation is considered for both, site and bond impurity models. The present theory is an extension of Liu and Joseph's work for the pure case.
The Influence of Lattice Vibrations on the Parametric Resonance in Hydrogen‐Bonded Ferroelectrics by Means of Parallel Electric Microwave Pumping
Authors: Stamenković S. , Stojanović S. D. , Žakula R. B.
Published: July 2007

The pseudospin–phonon formalism is used to describe the influence of lattice vibrations on the occurrence of a parametric resonance in the hydrogen‐bonded ferroelectrics. The theoretical results obtained show that such a resonance is considerably stabilized by the strong coupling between protons and heavy ions.
Concentration Dependence of Exchange Field in Dilute Metals
Authors: Khalyullin G. G.
Published: July 2007

The dependence of the exchange field on the paramagnetic impurity concentration in dilute metals is investigated. The consideration of the difference in the occupation probability of sites at different coordination spheres results in a variety of concentration dependences of the exchange field instead of a linear dependence. The concrete type of this dependence is determined by the conduction electron density. Numerical calculations are made of the paramagnetic Curie temperature change with dilution for a simple cubic crystal.
Dynamical Properties of NO Impurity Molecules in Alkali Halides. II. Vibrational Spectra
Authors: Rebane L. A. , Zavt G. S. , Haller K. E.
Published: July 2007

The first‐order Raman scattering induced by the NO molecule in KI and RbCl is measured. The spectral features are compared with those observed in the ultraviolet and infrared spectra. The spectral properties are interpreted within the models which take into account the librational motion of the molecule. The force constants connecting the molecule with its neighbours are found to possess high anisotropy. The main spectral features are explained as the result of the modification of the local densities of states and as the manifestations of librational motion.
Fermi Liquid Effects in Ferromagnetic Metals
Authors: Carneiro G. M. , Pereira P. R. Rodrigues
Published: July 2007

Microscopic Fermi‐liquid theory is used together with the s–f or s–d exchange model to discuss Fermi‐liquid effects in ferromagnetic metals at zero temperature. The contribution from exchange of virtual magnons to the quasiparticle scattering amplitude and the Landau quasiparticle inter‐action are calculated in the Migdal approximation. It is shown that exchange of magnons lead to strong forward electron–electron scattering. It is found that the quasiparticle effective mass and the spin susceptibility of the conduction electrons are strongly enhanced, whereas their compressibility is unaffected by electron–magnon interactions.
Anomalous Mössbauer Lineshapes in the Magnetically Ordered Ga2O3–Fe2O3 System
Authors: Nagarajan R. , Srivastava J. K.
Published: July 2007

Mössbauer measurements show that an incomplete annealing of the magnetically ordered Ga2O3–Fe2O3 system gives rise to anomalous Mössbauer spectra which are characterised by an enhancement in the intensity (or percentage absorption) of their central portions as compared to the intensity of outer absorption peaks. Measurements carried out in an external magnetic field confirm that the observed anomalous Mössbauer lineshapes are due to ionic spin fluctuations (either due to the motion of individual spins, i.e. electronic relaxation effects, or due to the collective motion of large number of spins in a small region of material, i.e. superparamagnetic effects) and are not a result of any distribution of hyperfine field or the presence of critical superparamagnetism in the incompletely annealed solid solutions.
Dynamical Response of Electrons in GaAs at 300 K
Authors: Brauer M.
Published: July 2007

Numerical calculations are made on the time response of the high‐field electron distribution function at T = 300 K in GaAs both for instantaneously and periodically varying electric fields. According to Rees the method of calculation is an iterative process due to Kellogg for solving a homogeneous Fredholm integral equation of the second kind derived from the Boltzmann equation. The time evolution of the average drift velocity, the mean energy of the electrons in the central valley, and the fraction of electrons in the satellite valleys is presented for an instantaneous application E(t) = E · θ(t) of the electric field. Finally the time dependence of the average drift velocity and the satellite valley population fraction is calculated for a sinusoidal electric field E(t) = Eac × sin ωt with Eac = 5 kV/cm and ω = 2.2 × 1011 rad/s. The results obtained are discussed, taking into account the band structure and the effective scattering processes.
Numerical Results of the Hubbard III Approximation for Arbitrary Values of the Correlation Energy and the Electron Density (with Application to Disordered Alloys)
Authors: Kammler F. , Elk K.
Published: July 2007

For the Hubbard model the density of states and the damping are calculated numerically for arbitrary values of U and n. The magnetic properties of the ground state are studied by a self‐consistent calculation of the magnetization m. It is shown, that the ferromagnetic state is unstable for each value of U and n. Using the same procedure binary alloys are considered, too.
The Boson Field Analysis of the Critical Temperature Region in Ferromagnets
Authors: Tošić B. S. , Marinković M. M. , Berar S.
Published: July 2007

A new method is proposed which makes it possible to apply the boson picture to ferromagnetics at high temperatures. A result of such an approach is the appearance of an additional level that leads to a phase transition from the ferromagnetic to the antiferromagnetic phase which takes place in the majority of rare earths. It is also shown that the boson picture of the ferromagnetics yields a richer physical content than the other, usual ones. Its main consequence leads to the conclusion that the Heisenberg model of ferromagnets works best to weak ferromagnetics (mainly rare earths).
Effect of Crystal Field on the Inelastic Neutron Scattering Cross‐Section
Authors: Sugawara K.
Published: July 2007

The magnetic inelastic scattering of neutrons by paramagnetic rare‐earth compounds where the rare‐earth ion has a substantial crystal‐field splitting is studied theoretically. Using the time‐dependent spin correlation functions, the effects of the crystal‐field and exchange to the first and second moments of inelastic neutron scattering cross section are investigated. The results are applied to the singlet ground‐state Pr‐ and Tm‐compounds. We also discussed the relationship between the temperature dependence of the intensity of quasi‐elastic scattering and those of longitudinal relaxation rates of NMR and EPR.
The Effects of Coordination Polyhedron Structure on Rare‐Earth Ion Spectra
Authors: Korolkov V. S. , Makhanek A. G.
Published: July 2007

Investigations are made of some regularities in the position of Stark components and a number of conclusions are drawn on the nearest surrounding structure rare‐earth (RE) ions. Since the splitting of the J‐manifold is generally defined by the overlap of RE ions and ligand orbitals, it is possible to establish a relation between the phenomenological crystal field parameters \documentclass{article}\pagestyle{empty}\begin{document}$ B_{t_p \overline {r^t}} $\end{document} (CFP) and the structure of the nearest surrounding. It is important that the various multipolarity CFP (t = 2, 4, 6) in the overlap model depend identically on R while their values in the CF theory are proportional to \documentclass{article}\pagestyle{empty}\begin{document}$ \overline {r^t } /R^{t + 1} $\end{document}. The dependence on the ligand angular coordinates is similar for the two models.
Raman Scattering from Tunnelling and Hindered Rotational States of CN− Molecules in KCl
Authors: Durand D. , Luty F.
Published: July 2007

The low lying tunnelling and hindered rotational states of dilute (≈ 10−4) systems of substitutional CN− ions in KCl are studied by Raman techniques. The tunnelling splitting of the ground state could be directly observed as a resolved side‐band structure of the CN− stretching vibration. The observed splitting is in quantitative agreement with the previously derived value for the tunnelling splitting, while the appearance of this splitting only in the T2g scattering geometry confirms definitely the 〈111〉 dipole model. Hindered rotational structure (in the 10 to 30 cm−1 range), which is partially resolved, is detected, both in the low energy and stretching‐side‐band spectrum in Eg and T2g symmetry. The observed Raman data can be fitted to the Raman positions and intensities calculated by Beyeler, using the V4 + V6 Devonshire model parameters derived from high resolution IR work.
Crystal Field Parameters for Gd3+ in Gd2(MoO4)3
Authors: Guttel C. , Antic E. , Caro P. E.
Published: July 2007

The absorption spectrum of Gd3+ in orthorhombic Gd2(MoO4)3 single crystal is measured at temperatures from 4 to 453 K. Nd3+ (10% and 50%) and Dy3+ (23%) substituted to Gd3+ give rise to little shifts of the absorption spectrum. The positions in the energy scale of the Stark components of the 6P levels of the 4f7 configuration of Gd3+ are obtained. A parametric computation of part of the C2v crystal field parameters yields the following values: B = − 222, B = +489 cm−1. Ground state 8S7/2 zero field splitting is predicted as a result of the calculation.
Comments on the Static Dielectric Function of Jellium
Authors: Brosens F. , Lemmens L. F. , Devreese J. T.
Published: July 2007

The equation of motion for the Wigner distribution function in a homogeneous electron gas, linearized to first order in the applied external field, and decoupled using the Hartree‐Fock prescription, rigorously describes the dynamical exchange effects in the dielectric response to a ‐weak perturbation. This equation of motion can approximately be solved with a variational principle, and a trial solution for the Wigner distribution function can be found, yielding a density that exactly satisfies its equation of motion. The dielectric function ϵvar obtained in this way thus includes dynamical exchange interactions. Comparing ϵvar with the dielectric function ϵit obtained from an iterative procedure, where exchange effects are supposed to be small compared to the Hartree terms, it turns out that ϵit provides the terms to order e4 in the geometric progression of ϵvar in powers of e2. In the static limit ϵit is the dielectric function calculated by Geldart and Taylor from a diagrammatic expansion. Thus a theoretical justification is given for Sham's approximation that the static susceptibility including exchange is obtained by considering the susceptibility from the diagrammatic expansion as the first two terms in a geometric progression.
Localized States on Imperfections and Red Shift of the Absorption Edge in Some Ferromagnetic Semiconductors
Authors: Čápek V.
Published: July 2007

A theory is presented for the red shift of the absorption edge of some ferromagnetic semiconductors as being due to localized electronic states on lattice imperfections influenced by the usual s–d coupling. A good correspondence with the experiment on some chromium chalcogenide spinels is obtained.
Infrared Absorption by an Optical Polaron in a Magnetic Field
Authors: Huybrechts W. J.
Published: July 2007

The infrared absorption by an optical polaron in an external magnetic field is discussed for weakly polar semiconductors at low temperatures. The broadening of the cyclotron resonance and the anomaleous behaviour of the cyclotron mass are evaluated to first order in the electron‐phonon coupling using a well‐known perturbational approximation.
The Resonant States of the Ti(d2) Impurity in CdSe
Authors: Kocot K. , Baranowski J. M.
Published: July 2007

Optical and electrical investigations show that Ti introduces a shallow donor in CdSe. The character of this donor is determined by the well localized 3d2shell of the Ti impurity substitutional on cadmium sites. The energy position of the Ti(d2) level depends on temperature and hydrostatic pressure. It is demonstrated that at high temperatures the Ti (d2) ground state becomes degenerate with the conduction band of CdSe. It is also shown that the excited 3T1 (F) and 3T1(P) states of the Ti (d2) are resonant states. Autoionization of the excited Ti (d2) impurity is observed in photoconductivity measurements.
Quantum Theory of the Order–Disorder Transition Energy in AuCu3
Authors: Kozlov E. V. , Emelyanov V. N. , Antonov V. A.
Published: July 2007

The stability conditions of the short‐ and long‐range orders are formulated and numerical calculations are made of the order‐disorder heat of transition as well as the total ordering energy of a AuCu3 solid solution having the Ll2 superstructure.
Coherent Ladder Approximation for the Random Hubbard Model
Authors: Kolley E. , Kolley W.
Published: July 2007

Dynamical effects of the electron–electron interaction in binary alloys with off‐diagonal disorder are described in a self‐consistent theory obtained by unifying a local ladder approximation for the random Hubbard model and a modified CPA. Numerical results are presented for partially averaged densities of states, self‐energies which fulfil the Luttinger theorem, and effective two‐particle vertices. The totally averaged density of states exhibits tails with strongly damped correlation humps.
Magnetooptical Investigation of Hg1‐xCdxTe Mixed Crystals II.Semiconducting Configuration and Semimetal → Semiconductor Transition
Authors: Guldner Y. , Rigaux C. , Mycielski A. , Couder Y.
Published: July 2007

An investigation is made of the interband magnetoabsorption at photon energies 120 to 370 meV on semiconducting Hg1‐‐xCdxTe alloys (x ≦ 0.3). Magnetooptical spectra obtained in the Voigt (ϵ ∥ H) and Faraday (σ+, σ‐) geometries are interpreted in the framework of the Pidgeon and Brown model. The band parameters are estimated for each composition by fitting the transition energies. First observations are reported of polaron effects inducing interband magnetooptical anomalies. By extending the magnetoabsorption measurements to alloys of very small interaction gaps, the evolution of Γ8, Γ6 levels in the region of the semimetal → semiconductor transition is described.
The One‐Dimensional Fourier Transform of Compton Profiles
Authors: Sciiülke W.
Published: July 2007

Theorems on the one‐dimensional Fourier transform of directional Compton profiles are given within the frame of the one‐electron approximation. The theorems relate the one‐dimensional Fourier transform of Compton profiles with the three‐dimensional Fourier transform of the momentum density, with the off‐diagonal elements of the first‐order density matrix, with the translation invariance of the lattice, and with the density of Bloch k‐states (Fermi surface) respectively. Possible applications of these theorems are discussed and demonstrated by means of the Fourier transform of experimental Compton profiles of Si and Li.
On the Polymorphic Phase Transition in Alkali Halides
Authors: Charabarti S. K.
Published: July 2007

Earlier calculations of the equation of state and phase transition data at 298 K for a potassium chloride crystal are extended to include the other alkali halides. It is shown that both the elastic and phase transition data are well reproduced by the three‐body potential model (TBPM). Since the calculations tend to become lengthy, a simpler procedure of calculating the equation of state and transition pressure with the help of the Murnaghan's equation is also suggested. The procedure gives reasonably good agreement with experimental results.
Diffusion Correlation in Random Primitive Cubic Alloys
Authors: Buin H. J.De , Bakker H. , Van Der Mey L. P.
Published: July 2007

Correlation effects for diffusion in random cubic alloys are calculated by Monte Carlo computations. Using two independent models the parametersfB,fA,fv, the correlation factors, and ‐ tB, the net probability that a B‐tracer will return to its original lattice position, are obtained and analyzed. Evidence is presented that the relation, fB = (1+‐tB)‐ /(l − tB), is not strictly valid in these alloys where symmetry around the vacancy jump vector does not normally exist. However deviations are not large for realistic vacancy‐atom exchange frequencies WA/WB> 0.1).
Spin‐dependent recombination at exchange‐coupled dislocation centres in silicon
Authors: Wosiński T. , Figielski T.
Published: July 2007

The recent experimental results on spin‐dependent recombination at dislocations in Si are reviewed. A theoretical model including an exchange interaction between unpaired electrons in the dislocation core is proposed. The numerically calculated exchange integral appears to have a positive value. The model presents a dislocation as consisted of segments of exchange‐coupled paramagnetic centres. The magnetization of the segments, calculated in Ising approximation is compared with the experimental results.

Kürzliche experimentelle Ergebnisse von spinabhängiger Rekombination an Versetzungen in Si werden erneut diskutiert. Ein theoretisches Modell wird vorgeschlagen, das Austauschwechsel‐wirkung zwischen ungepaarten Elektronen im Kern der Versetzung annimmt. Das numerisch berechnete Austauschintegral scheint einen positiven Wert zu haben. Das Modell liefert eine Versetzung, die aus Abschnitten von Austausch‐gekoppelten paramagnetischen Zentren besteht. Die Magnetisierung der Abschnitte, die mit der Ising‐Näherung berechnet wird, wird mit den experi‐mentellen Ergebnissen verglichen.
The “extra” phase transition in TTF‐TCNQ
Authors: Phillips J. C.
Published: July 2007

High‐resolution heat capacity data show an “extra” phase transition at 46 K in TTF‐TCNQ powders in addition to the five phase transitions observed in bulk samples between 38 and 54 K. The “extra” phase transition in powders can be explained as a surface phase transition which corresponds to the bulk phase transition at 48 K. In powders the latter is shifted to 49 K by ferroelastic interactions between the “bulk” phase in grain interiors and the compressed surface phase.
Optical properties of cuprous halides in the 4 to 30 eV range
Authors: Lewonczuk S. , Gross J. G. , Khan M. A. , Ringeissen J.
Published: July 2007

The reflection spectra of CuCl, CuBr, and CuI monocrystals are measured in the 4 to 30 eV range, mainly with synchrotron radiation of ACO in Orsay. The band structure of CuCl and CuBr are calculated. The highest valence band is predominantly d‐like, as already stated, the second band is p‐like. Information about the band structure is also obtained by recent photoemission measurements which permit an evaluation of the densities of valence states. A disagreement appears when the results of the two methods are compared, in particular for the shape of the second valence band. The experimental features are discussed taking into account theoretical and photoemission results.
A New Approach to the Theory of X‐ray Spectra of Metals with Allowance for the Finite Lifetime of the Deep Hole
Authors: Sokolov O. B. , Grebennikov V. I. , Turov E. A.
Published: July 2007

The effect is analyzed of the deep hole forming on the inner level during X‐ray transition on the form of the corresponding emission and X‐ray photoelectron spectra of metals. The intensity of both the types of spectra is calculated in one common approach within the framework of the theory of scattering of the exciting photon on the electronic metal system. A generalization of the Wigner‐Weisskopf theory of radiation damping of excited atomic state is proposed for the case of a many‐particle system. The new approach permits to make allowance for the effect of the process of readjustment of valence electrons on the rate of radiation decay. It is shown that these phenomena can be taken into account formally if an effective non‐Hermitean Hamiltonian of a definite type is introduced into the theory. The general formulae obtained permit comparison of the results of different approaches in the theory of the spectra under investigation. The spectra can be analyzed numerically not only near the excitation threshold but also over the whole energy interval on the basis of simple models.
Magnetic susceptibility anisotropy of holes in tellurium
Authors: Vorontsov S. A. , Dolgopolov D. G. , Poltoratskii V. I. , Svechkarev I. V.
Published: July 2007

An expression for the spin contribution to the magnetic susceptibility anisotropy of holes in tellurium is derived. The total hole susceptibility anisotropy including spin and orbital terms is calculated with scattering taken into account. The complete quantitative description of the experimental data for hole concentrations of 3.5 × 1016 ≦ n < 3.5 × 1018 cm−3 and T = 4.2 K is obtained by means of selection and more precise definition of the spectrum parameters which determine the spin contribution. The discrepancy between calculated and experimental temperature dependences of the hole magnetic susceptibility anisotropy at temperatures above 60 K appears to be due to the thermal variation of the spectrum parameters.
Frequency spectra of disordered chains with short‐range order
Authors: Wu Shi‐Yu , Cocks J. A. , Chiu V.
Published: July 2007

The frequency spectra of five binary chains with equal atomic concentrations but various strengths of short range order are computed using Wu's approximate method. The configurations associated with the pseudolocalized resonance and localized modes are identified and the probabilities of their appearance are correlated to the short range order parameter Pij.
Resonance scattering of X‐rays in metals
Authors: Sokolov O. B. , Grebennikov V. I. , Turov E. A.
Published: July 2007

A theory is proposed of resonance scattering of X‐ray radiation on the electronic system of a metal which reasonably takes into account the damping of the intermediate states with a hole on the inner level. In virtue of the formulae obtained for the cross‐section of photon scattering, expressions are derived for absorption and threshold emission spectra. Adequate allowance for the finite lifetime of the deep hole permits the description of the re‐emission process. Investigated are the emission spectra arising in the event of transition of an electron between the inner levels of the atom of the metal when excited by a radiation whose frequency is less than the ionization threshold of the corresponding level.
On the theory of parametric excitation in quantum electron–phonon systems
Authors: Anh Vo Hong , van Trong Nguyen
Published: July 2007

The problem of parametric excitation of electromagnetic vibrations of a quantum electron‐phonon system is studied using a formalism based on the equation of motion for the quantum distribution function of an electron gas interacting with phonons in the presence of high‐intensity radiation field and the complete system of Maxwell equations. Calculations of the growth rates and the threshold values of the external electric field E0 are presented for both, uncoupled electron and electron‐phonon systems in different regions of wave number κ for κ ‖ E0 as well as for κ ⊥ E/0.
Asymptotic oscillations of the radial distribution function in a quasi‐crystalline model of liquids
Authors: Medvedev N. N. , Naberukhin Yu. I.
Published: July 2007

The radial distribution function (RDF) behaviour at large R in a quasi‐crystalline model of liquids (crystal lattice with lattice sites smeared out by the Gaussian distribution) is studied by numerical calculations. RDF asymptotic oscillations are found to be describable by the Fisher formula obtained from general statistical laws, if the model is based on b.c.c. and f .c.c. lattices, and not to be describable by this formula for hexagonal close packing. It is also established that the parameters of experimental RDF asymptote for liquid argon differ from those for the three above‐mentioned lattices.
On F‐ and FH‐centres in cesium halides
Authors: Vandekhaeghe A. , Jacobs G.
Published: July 2007

Fg‐centres are formed in CsI doped with foreign halogen ions, by irradiation in the F‐band at 180 K. They are observed in CsI:Br−, CsI:Cl−, and CsI:F−. The lifetime of the relaxed excited state of the F‐centre in pure CsI and of the FH‐centre is determined by measuring the repopulation of the ground state after depletion with laser light. The results are τR = 3 μs for the F‐centre in CsI, 360 ns for CsI: Br−, 400 ns for CsI: Cl−, 290 ns for CsI: F−. The luminescence decay time of the F‐centre in CsCl is found to be 2 μs, the relaxed excited state lying 0.07 eV under the conduction band. The results on the FH‐centre suggest that the lowest emitting level is 2s with a large admixture of 2p character. Simultaneously with the formation of FH‐centres, new absorption bands appear in the M‐band region, possibly due to MH‐centres.
Wave‐vector dependence of the electron energy losses of PbS, PbSe, and PbTe
Authors: Büchner U.
Published: July 2007

The wave‐vector(q‐)dependence of electron energy losses of cubic PbS, PbSe, and PbTe up to q‐values near the first Brillouin zone boundary and up to energies of 40 eV is given. Anisotropic effects of the derived energy loss functions Im [−ε(ω, q(ijk))]−1 and dielectric functions ε2(ω, q(ijk))[(ijk) = (100), (110), (111)] are observed and discussed in terms of present band structure calculations.
Ladungszustand von Bor in Boriden der Übergangsmetalle
Authors: Aleshin V. G. , Serebryakova T. I. , Kharlamov A. I.
Published: July 2007

Mit der Methode der Röntgen‐Photoelektronen‐Spektroskopie werden die Bindungsenergien von Rumpfelektronen in einer Gruppe von Boriden der ersten Übergangsperiode gemessen. Es wird gezeigt, daß in Boriden der Metalle, die am Anfang der Periode stehen, die Elektronendichte an den Bor‐Atomen größer und in Boriden der Metalle, die am Ende der Periode stehen, kleiner ist als die Elektronendichte in reinem Bor. Das Übergangsmetall ist in alien Fällen ein Donator. Die beobachtete Änderung des Ladungszustandes der Bor‐Atome befindet sich im Einklang mit den vorhandenen Vorstellungen über den Typ der chemischen Bindung in Boriden.
Deviations from Matthiessen's rule in silver containing low‐density defects
Authors: Goodarz M. , Barnard R. D.
Published: July 2007

The parameters obtained in an earlier paper by Barnard on the low field Hall effect in Ag alloys are used to calculate the contribution to the deviation from Matthiessen's rule (DMR) Δ1 due to anisotropy in the relaxation times in the systems AgAu, AgCd, and Ag + dislocations. Comparison is made with new experimental data of DMR on AgCd and Ag + dislocations between 4 and 300 K and pre‐existing data on AgAu. Whilst anisotropy in the relaxation times can account for most of the observed DMR in AgAu and Ag + dislocations, it makes only a minor contribution in Ag‐Cd (a charged impurity in Ag) because this impurity scattering is nearly isotropic. AgCd is discussed in terms of a second contribution Δ2 arising from inelastic coherent scattering (Kagan and Zhernov) and Δ3, a new contribution, developed in this paper arising from the energy dependence of the resistivity of the host metal and related to its diffusion thermopower. A discussion is also made of the applicability of Δ3 to the anomalous system MgAl where negative values of Δ exist at high temperatures.

Die in einer früheren Arbeit von Barnard über den Halleffekt in niedrigen Feldern von Ag‐Legie‐rungen erhaltenen Parameter werden benutzt, um den durch die Anisotropie der Relaxationszeiten hervorgerufenen Beitrag zur Abweichung von derMatthiessen'schenRegel(DMR), Δ1 inden Systemen AgAu, AgCd und Ag + Versetzungen zu berechnen. Ein Vergleich mit den neuen experimentellen Werten der DMR an AgCd und Ag + Versetzungen zwischen 4 und 300 K und den vorher existierenden Werten an AgAu wird durchgeführt. Während die Anisotropie der Relaxationszeiten fast die gesamte beobachtete DMR in AgAu und Ag + Versetzungen erklären kann, wird für AgCd (eine geladene Störstelle in Ag) gefunden, daß sie nur einen kleinen Beitrag liefert, well diese Störstellenstreuung nahezu isotrop ist. AgCd wird mit einem zweiten Beitrag Δ2 diskutiert, der von der inelastischen kohärenten Streuung (Kagan und Zhernov) herrührt und mit Δ3 einem neuen Beitrag, der in der Arbeit entwickelt wird und aus der Energieabhängigkeit des Widerstands des Wirtsmetalls stammt und mit dessen Diffusions‐Thermospannung verknüpft ist. Die Anwendbarkeit von Δ3 auf das anomale System MgAl, wo negative Δ‐Werte bei hohen Temperaturen auftreten, wird ebenfalls diskutiert.