bluuebunny/crossref_metadata_2025 huggingface dataset:
Photogalvanic effect in crystal with dislocations
Authors: Efanov A. V. , Entin M. V.
Published: July 2007

The photoelectrical properties of a crystal with identically orientated straight edge dislocations are considered. Such a medium has a preferable direction due to the absence of axial symmetry of the dislocation potential. Hence, the photogalvanic bulk effect may occur. A generalization of the Rhead model is obtained taking into account the deformation potential. Scattering on a dislocation in the classic limit is considered for this case and for the case of an unscreened deformation potential. The tensor of the photogalvanic effect in the ranges of direct interband transitions and of light absorption by free carriers is obtained using the results.
Spectroscopic manifestation of self‐trapping excitons in ionic insulators
Authors: Plekhanov V. G. , Shepelev V. V. , Grinfelds A. U.
Published: July 2007

The luminescence and excitation spectra of free and self‐trapped excitons, whose states are separated by a small potential barrier, are investigated experimentally on an example of NaI and RbI crystals. The height of the self‐trapping barrier is established to be independent of the kinetic energy of an exciton, but it is inversely proportional to its first quantum number. The spectroscopic manifestation of the self‐trapping barrier in the excitation spectra of the steady‐state luminescence of self‐trapped excitons is shown. The value of barrier height obtained experimentally coincides best of all with the value calculated from the theoretical model of the polarizing exciton. The evolution of the luminescence excitation spectra of self‐trapped excitons in a temperature interval 4.2 to 80 K is studied. If the relaxation mechanism of free excitons is reflected in the oscillating structure (the oscillation period is equal to the energy of LO phonon) of luminescence excitation spectra, then the further exciton relaxation along the adiabatic sheet is manifested most directly in the structure of hot luminescence spectra of the self‐trapping excitons.
Domain Wall Stabilization in Crystals with Complicated Magnetic Phase Diagram
Authors: Mitsek A. I. , Sirota D. I. , Kolmakova N. P.
Published: July 2007

The static and dynamic properties of a many‐domain magnetic with a complicated magnetic phase diagram are considered, the domain walls in the magnetic are fastened with plane defects. Near orientational phase transitions the potential pit of a wall may have a fine structure. It results in the anharmonicity of domain wall oscillations, their spectrum depends strongly on the ratio of anisotropy constants. The temperature dependence of the coercive force, magnetic and magnetoelastic hysteresises, and the dynamic susceptibility are discussed.
Polaronic Effects on the Verwey Transition in Fe3O4
Authors: Ihle D.
Published: July 2007

On the basis of a band model for the extra B‐site electrons in Fe3O4 a detailed estimate of the relevant small‐polaron (SP) parameters of Fe3O4 is given taking into account the interatomic Coulomb interaction, the formation of SP due to the interaction with phonons, and the SP correlation. The isotope and pressure effects on the Verwey transition temperature are explained as SP effects.
Evidence of Electromagnetic Quantum 1/f Noise Found in Gold Thin Films
Authors: Kilmer J. , van Vliet C. M. , Bosman G. , van der Ziel A. , Handel P. H.
Published: July 2007

Photonic quantum 1/ƒ noise is identified in Au metal films below the Debye temperature. The low values of the Hooge parameter predicted by Handel's theory (i.e., αtrue ≈ 10−6 to 10−8) are arrived at by realizing that only the fraction ≈ 3kT/2ΔϵF of the total number of carriers is available for scattering at a given temperature.
Activation Energy of Substitutional Defects in Alkali Chlorides
Authors: Bandyopadhyay S. , Neogy C. , Deb S. K.
Published: July 2007

Based on a semi‐continuum model, the electrostatic, the polarisation, and the repulsive energy change of a lattice are calculated numerically, as functions of four different types of relaxations for the first fourteen ions of a substitutional defect in the saddle point position in an alkali chloride crystal. It is found that for a particular value of displacement, the total energy change of the lattice is minimum. A study of variation of the angle for the relaxed ions suggests further lowering of the lattice energy corresponding to a particular value of the angular displacement. These results are utilised in calculating the saddle point energy, the migration energy, and the activation energy for the motion of a host ion and a defect ion in NaCl, KCl, and RbCl crystals.
Indirect‐Forbidden Exciton Transitions in AgBr
Authors: Sliwczuk U. , Stolz H. , von Dee Osten W.
Published: July 2007

Observation of low temperature resonant Raman scattering in AgBr involving the TA(L) momentum‐conserving phonon for the first time, allows symmetry‐forbidden indirect exciton transitions to be studied in silver halides. From analyzing the energy dependence of scattered intensity, in terms of impurity trapping and intra‐ and intervalley exciton scattering, relative scattering probabilities are determined for these relaxation processes. The exciton‐TA(L)‐phonon matrix element obtained with respect to that for the allowed TO(L) process is 5.5 × 10−3 (meV)−1. Taking into account the TA(L)‐assisted component, from a lineshape analysis of the indirect exciton edge a value of 28 meV is derived for the Is exciton binding energy.
Impurity States in the Presence of an Interface
Authors: Godwin V. E. , Tomak M.
Published: July 2007

A modification of the effective mass approximation in the Sham‐Nakayama approach is discussed. Binding energies are calculated as functions of electric field, scattering length, and distance of impurities localized at the interface between SiO2, and an n‐type inversion layer on Si (001).
Photochemical Hole Burning in Polycrystalline and Neutron Irradiated NaF
Authors: Ortiz C. , Afonso C. N. , Shelby R. M. , Tropper A. C. , Bjorklund G. C.
Published: July 2007

Spectroscopic properties of aggregate color centers in polycrystalline NaF thin films are measured for the first time by photochemical holeburning. A comparison with single crystals shows that the density of the color centers, and both the inhomogeneous linewidth and holewidth are increased in the polycrystalline material. Also studied are the effects of two different irradiation sources (neutrons and X‐rays) in single crystal samples. The excited state lifetime T1 of the 6070 Å centers is found to be very similar in all the samples.
Mössbauer and Positron Studies of Superconducting Oxides BaPb1−xBixO3
Authors: Groznov I. N. , Ionov S. P. , Kevdina I. B. , Lubimov V. S. , Makarov E. F. , Marchenko O. V. , Mikhailov N. N. , Onischuk V. A. , Shantarovich V. P.
Published: July 2007

Mössbauer spectra and lifetime positron distributions are studied for BaPb0.99−xSn0.01BixO3 samples with 0 ≦ x ≦ 0.4 containing Sn119 as Mössbauer label. A correlation is observed between the dependence of room temperature parameters of Mössbauer and positron spectra on x and transition temperatures to superconducting state Tc(x). The data obtained are interpreted in terms of bielectron transfer over bismuth centers.
Influence of SiSi Bonds on the Local Electronic Density of States of a‐SiO2
Authors: Grafe T. , Strehlow R.
Published: July 2007

Results of cluster‐Bethe‐lattice calculations for complexes of Si—Si bonds in a‐SiO2 are presented. The influence of such Si04(ySi, [4 − y]O) defects on the local electronic density of states (LDOS) of SiO2 is discussed. For all values of y = 1, 2, 3, 4 localized occupied and empty defect states are found in the SiO2 gap. From cluster calculations using a bond‐orbital representation the defect functions are calculated. The local gap of these defects is distinctly changed only for y = 1, reflecting the x dependence of the SiOx gap for higher x values.
Analysis of Anharmonic Properties of Some Partially Covalent Crystals
Authors: Singh R. K. , Khare P.
Published: July 2007

The anharmonic properties of silver, thallium, and copper halides are analysed by means of a new interionic potential model which incorporates theeffects of the long‐range Coulomb and three‐body interactionsand the short‐range van der Waals (vdW) attraction and overlap repulsion extended up to the second‐neighbour ions. The model potential is applied to investigate the third‐order elastic constants and the pressure derivatives of second‐order elastic constants of the crystals. Additively some thermodynamic and thermoelastic behaviours of these solids are calculated. The results agree fairly well with the available experimental data and show a consistent trend throughout.
The Effect of Relaxing Defects on the Spin—Lattice Relaxation at Ferroelectric Phase Transitions
Authors: Geppert U. , Kühnel A.
Published: July 2007

Spin—lattice relaxation times are calculated near the phase transition for a uniaxial ferroelectric containing defects. The defects are assumed to couple linearly to the order parameter. Defects and order parameter are of relaxator type. The corresponding Langevin equations are given and solved with help of perturbation theory for small anharmonicity and weak influence of the randomly located defects on the Curie temperature. It is found that the experimentally observed opposite anomalies of the spin—lattice relaxation times in TGS can be understood for definite values of the defect parameter.
Application of the Quadratic Response Theory to the Screening of a Positron in an Electron Gas of Metallic Density
Authors: Rubaszek A. , Stachowiak H.
Published: July 2007

The screened Coulomb potential following from the quadratic response theory is modified and applied to the Kahana equation for a positron in an electron gas. Electron—electron correlations are taken into account in a local way, proposed by Shaw. For the first time within this formalism no divergence of the total annihilation rates occurs in the low density region. Self‐consistency, according to the total screening charge around the positron, is approached. The momentum dependent enhancement factors are found to be in good agreement with the experimental data.
Calculation of the Jahn‐Teller Coupling Forces for ZnS:Cu2+ and GaP:Ni+
Authors: Welnert C. M. , Scherz U.
Published: July 2007

The Jahn‐Teller coupling forces for the deep d level impurities ZnS:Cu2− and GaP:Ni+ are calculated with a cluster model. The calculation consists of a self‐consistent LCAO calculation of a cluster of 17 atoms with the impurity in the center. The Jahn‐Teller active modes of ω and τ2 symmetry are modelled by the corresponding small distortions of the ligands nearest to the impurity. Coupling forces to the ω and τ2 modes are found to be of similar strength. There is only weak coupling to optical and localized modes in contrary to what has been assumed so far. A strong Jahn‐Teller effect which could account for the strong quenching of the ground state g factor observed in these centers is only possible by coupling to the acoustic modes.
A Dynamic Percolation Approach to the Andrade Creep
Authors: Schönhals A. , Donth E.
Published: July 2007

A new approach to the Andrade law of creep relaxation is given. Starting points are the theory of linear response and the fluctuation‐dissipation theorem (FDT). According to the FDT the macroscopic shear complianceis determined by the correlation function of shear angle fluctuation of a functional subsystem. An investigation of the shear pulse response leads to the conclusion that the subsystem must be considered as a temporarily inhomogeneous solid. A dynamical percolation model is developed resulting in a power law for the short‐time behavior of creep compliance. The relevant exponent lies between 0.3 and 0.47, definitely lower than 1/2. The experimental value for the Andrade exponent is about 1/3.
Anharmonicity Effects in IR‐Reflection Spectra of Sheelites
Authors: Efendiev Sh. M. , Nagiev V. M. , Burlakov V. M.
Published: July 2007

Reflection spectra of PbWO4 crystals vs. the temperature are studied over the 700 to 1000 cm−1 frequency region. On the basis of an invertibility criterion of the oscillator obtained in the present paper, the anomaly in the reststrahlen band in the reflection spectrum is found to be connected with a strong frequency dependence of the damping Γ(Ω) of the transverse optical vibration. A possible decay channel for an intramolecular excitation corresponding to the peak of the function Γ(Ω) is proposed.
On Correlation between Structural Features of Liquid Metals and the Effective Ion–Ion Potential
Authors: Gelchinskii B. R. , Ryskulbekova R. M.
Published: July 2007

A comparison of ion–ion interaction potentials obtained by various methods is performed. A certain similarity of potentials using empirical information and their distinction from priori potentials are noted. A correlation is found of the short‐range part of the effective ion–ion potential obtained by the Percus‐Yevick equation with radial distribution function form. It is suggested to use this correlation both, for developing methods of a theoretical estimation of ion–ion potentials and for revealing some specific features in the structure of melts.
Interionic Forces and Elastic Properties of Na2S
Authors: Agnihotri Neeta , Singh R. K. , Sanyal S. P.
Published: July 2007

An interionic potential model is proposed for crystals with antifluorite structure which consists of long‐range Coulomb and three‐body interactions (TBI), and short‐range dispersive and repulsive interactions up to second‐neighbour ions. This potential is used to calculate the cohesive energy, second‐order elastic constants, and their pressure derivatives of Na2S. The calculated values of elastic constants and cohesive energy agree well with their measured data which shows that the TBI contribute significantly to these properties.
Properties of the Exciton–Phonon System in a Magnetic Field
Authors: Gu Shi‐Wei , Zhou Yu‐Kui
Published: July 2007

The properties of excitons for a polar crystal in a weak magnetic field are discussed by using a perturbational method. When the interaction between phonons with different wave vectors in the recoil effect is neglected and a slow motion of the exciton is assumed, the electron–hole effective potential, the self‐trapping energy of an exciton, and the renormalized masses are derived.
Vibrational Spectra of Crystals with Sheelite Structure and the Solid Solutions on Their Basis
Authors: Nagiev V. M. , Efendiev Sh. M. , Burlakov V. M.
Published: July 2007

IR‐reflection spectra of sheelite‐type crystals, XMeO4, where X = Ca, Pb: Me = Mo, W, and solid solutions on their basis are investigated. The obtained spectra are treated under the program: dispersion oscillator model – Kramers‐Kronig analysis. Frequency evolution and the decay of natural vibrations by substituting the metal atoms both inside the MeO tetrahedron and beyond of it are also studied. It is shown that the IR‐active vibrational spectrum of sheelite‐type crystals considerably depends on X‐type atoms (Ca or Pb). In solid solutions, while substituting Ca or Pb, some of vibrations in the spectrum reveal two‐ or three‐mode character of rearrangement. But the replacement of Mo by W does not lead to the formation of local vibrations, and the spectrum is found to be rearranged as a spectrum of single‐mode character.
Off‐Symmetry Phonon Frequencies of Copper
Authors: Chopra K. K. , Bouarab S.
Published: July 2007

A simple phenomenological model is applied to interpret the experimentally measured off‐symmetry phonon frequencies of copper. It is emphasized that a truly acceptable theoretical model should not only give good results in the symmetry directions but must also be capable of a satisfactory reproduction of frequencies in the off‐symmetry directions.
Delocalized Positronium in Alkali Halides
Authors: Boev O. V. , Arefiev K. P.
Published: July 2007

The Bloch state of positronium in alkali halide crystals is considered. Interactions of positronium with the crystal field and with acoustic phonons are taken into account using perturbation theory. The effective mass of positronium in alkali halides is determined theoretically for the first time. Influence of these interactions on the positronium features in a crystal is discussed. The results obtained are in good agreement with available experimental data.
X‐Ray Photoelectron Spectra of Ag, Ga, In, and β‐Sn Metals Multielectron Excitations
Authors: Scrocco Marisa
Published: July 2007

Information on the final‐band energies of metals to relate to theoretical models can be usefully obtained from high‐energy photoemission spectra (XPS). The satellites present in the valence and core regions of Ag, Ga, In, and β‐Sn are assigned to multielectron excitations and compared with transition energies extracted from band structure calculations.
Optical Detrapping in Molecular Crystals. II. Second Conduction Band
Authors: Petelenz P.
Published: July 2007

A possibility of optical detrapping to the second conduction band is investigated. A simple model is proposed to account for the coupling between the trap and band states. The coupling (when operative) is shown to shift the apparent distribution of trap depths towards greater values. Conclusions are utilized to propose a new experiment to locate the second conduction band of the anthracene crystal, and to probe its properties.
Phonons in Face‐Centred Cubic Calcium and Strontium
Authors: Singh S. P. , Rathore R. P. S.
Published: July 2007

The axially symmetric and unpaired forces are employed to analyse the phonon dispersion and elastic behaviour of face centred cubic calcium and strontium which have so far not been studied adequately. The model with three parameters predicts the results which agree marvellously with the recently measured data.
Magnetic State of Crystals with Dislocations
Authors: Karnaukhov I. N. , Zhuravlev A. F.
Published: July 2007

The inhomogeneous elastic fields of linear dislocations can lead to the formation of the noncolinear magnetic structure in the magnetic crystals under consideration. This structure is calculated in the frame work of the phenomenological approach; its localization region is determined and its formation criteria are discussed. The influence of the dislocation dilatation on the line width of the FMR and NMR is calculated also.
On the Damping of the Excitonic Polaritons
Authors: Cam Hoang Ngoc , van Hieu Nguyen , Viet Nguyen Ai
Published: July 2007

The general properties of the damping constants of polaritons in the two‐branch and three‐branch models are considered in the framework of the Green's function method. In particular, the expressions for the damping constants of the polaritons in terms of those of the excitons are established.
EPR Powder Spectra of Low‐Symmetric Mn2+ Complexes in Aragonite Lattice
Authors: Lech J. , Ślęzak A. , Bójko I.
Published: July 2007

Electron paramagnetic resonance of Mn2+ ions in polycrystalline samples of natural aragonite containing about 100 ppm Mn impurities is studied at X‐ and K‐band. The parameters of the rhombic spin Hamiltonian estimated from the “powder” spectrum are found to be in a good agreement with the parameters obtained with single crystals. It is shown that satisfactorily accurate values of the spin Hamiltonian parameters can be extracted without the use of a simulating method, even in the case of the rather complex “powder” spectrum recorded at X‐band.
Analysis of Photoelastic Behaviour of Fluorite‐Structure Crystals
Authors: Dutt N. , Sharma O. P. , Shanker J.
Published: July 2007

An analysis of the photoelastic behaviour of fluorite‐structure crystals is performed by considering the existing theories of electronic polarizabilities of ions. On the basis of experimental and theoretical information available for electronic polarizabilities it is assumed that the change in polarizability due to strain under the effect of hydrostatic pressure is mainly arising from the change in anion polarizability. Values of strain polarizability parameters and volume derivatives of refractive index or electronic dielectric constant are evaluated and compared with experimental data for CaF2, SrF2, BaF2, PbF2, Sr(NO3)2, Ba(NO3)2, and Pb(NO3)2 crystals.
General Theory of Secondary Radiation in Condensed Matter
Authors: Lang I. G. , Pavlov S. T. , Prokaznikov A. V. , Goltsev A. V.
Published: July 2007

A general theory is given accounting for the secondary radiation which is excited in condensed matter exposed by light at finite temperatures, T ≧ ħωs, where ωs is the radiation frequency. The formula which is derived for a light scattering tensor of rank four, is similar to that obtained by Kubo for the conductivity tensor. It allows for all types of interactions possible within the scattering medium. The obtained results are compared to conclusions in the cases of either low, T ≪ ħωs, or T ≥ ħωs temperatures.
Calculation of the Change in Knight Shift Due to Zn, Ga, and Ge Impurities in Copper
Authors: Gerbeth G. , Mrosan E. , Zeller R. , Dederichs P. H.
Published: July 2007

Starting from a self‐consistent determination of the scattering properties of localised substitutional impurities the change in Knight shift in dilute alloys is calculated. The free‐electron theory of Daniel and Blandin is generalized to the case of the spherical band approximation. Numerical results are presented for Zn, Ga, and Ge impurities in a Cu host.
The Theory of Auger Spectra from Alloys. The Effect of Electron Correlations in Partially Filled Narrow Bands
Authors: Drchal V. , Kudrnovský J.
Published: July 2007

The effect of electron correlations on the Auger spectra from the substitutionally disordered narrow‐band metal alloys with partially filled bands is studied within the degenerate Hubbard model. Perturbation theory is used limited to the second order in U/w (U Coulomb integral, w bandwidth) for the calculation of the one‐particle Green function, and the ladder approximation for the two‐particle Green function. The effect of disorder is included within the single‐site approximation. The theory is illustrated on a simple model of the copper‐nickel alloy.
Spin Anisotropy and Critical Exponents for a Heisenberg System A Renormalization Group Approach
Authors: Fakioǧlu S.
Published: July 2007

Firstly the renormalization group technique is applied to an isotropic Heisenberg spin system with long‐range interaction and a set of critical exponents are calculated. These exponents are expressed in terms of a potential parameter s̀. All critical exponents except β, the magnetization exponent, depend on s̀. Secondly, the anisotropy is considered and the related crossover exponent φ is evaluated. This later parameter turns out to be equal to γ, the susceptibility exponent, as predicted by some authors.
The Surface or Interface Polaron in Polar Crystals. III. The Phase‐Transition‐Like Transition for the Surface Polaron
Authors: Jin‐sheng Pan
Published: July 2007

The behaviour of the surface polarons in polar crystals is taken into account by making use of the Bogolyubov inequality. The results show that the ground state energy, effective mass, and the effective potential energy of the surface polarons are dependent on the temperature. For the strong coupling surface polaron, when the temperature approaches a certain critical value T0, there exists a phase transition from the polaron to the free electron; but for the weak coupling case, such a phase transition does not exist.
Structure and Bonding in Cubic IV–VI Crystals VI. Acoustic and Optical Deformation Potentials
Authors: Enders P.
Published: July 2007

Within the six‐band p‐model by Volkov et al. the acoustic and optical deformation potentials for the band‐edge states at the L‐points of the Brillouin zone are derived. Numerical results are obtained by means of geometrical arguments and chemical trends of tight‐binding parameters. These agree well with experimental and other theoretical results for the optical deformation potentials, but not for the acoustic ones. The conclusion in II on the smallness of the average interband‐optical deformation potentials is confirmed.
Electronic Properties of the Liquid TlGeTl2Te4 and TlSnTl2Te4 Systems
Authors: Ishikawa H. , Aoyama M. , Uemura O. , Satow T.
Published: July 2007

Measurements of the electrical conductivity, the magnetic susceptibility, and the thermoelectric power for the liquid TlGeTl2Te4 and TlSnTl2Te4 systems are made in wide temperature and composition ranges. It is observed that the conductivity for both systems falls near the composition of 80 mol% Tl and the diamagnetic susceptibility also shows a maximum at the corresponding composition. The thermoelectric power changes its sign around this composition. The ratio of real and free electron density of states at the Fermi level for both systems is close to 0.3 around the above mentioned critical composition, and at other compositions the value rises up to more than that. These electronic properties are discussed in the light of current transport theories employed in liquid semiconductors.
Transient Ie Centres in Alkali Halides
Authors: Jacobs G.
Published: July 2007

Temporary infrared absorption bands are created in NaCl, KCl, RbCl, and KBr when nominally pure X‐ray coloured crystals are irradiated in the F band at low temperatures. This absorption shows a zero‐phonon line and a very detailed phonon structure. Some properties such as thermal decay, optical bleaching with polarized light, influence of impurities, and shape of the zero phonon line are studied.
One‐Particle Crystal Field Hamiltonians
Authors: Adam S. , Adam Gh. , Corciovei A.
Published: July 2007

Systematic derivation of the one‐particle crystal field Hamiltonians is given for all possible site symmetries in crystals. Distinct parametrizations are found to occur only for the eleven Lauesymmetry groups, 1, 2/m, mmm, 4/m, 4/mmm, 3, 3m, 6/m, 6/mmm, m3, and m3m. The functional dependence of the Hamiltonian on the choice of the coordinate axes is also investigated. Its importance in proving, by numerical means, the correctness of the computed f‐electron energy levels in crystals is illustrated on an example.
Real‐Space Properties of Transition Dipole Matrix Elements in Semiconductors
Authors: Czajkowski G. , Balslev I.
Published: July 2007

The real‐space properties of the transition dipole matrix elements in semiconductors are studied theoretically. The results are expressed in terms of conventional band edge characteristics (such as the momentum matrix element and the band structure) and used in the coherent wave approach developed recently by Stahl. Simple isotropic bands lead to a real‐space behaviour of the dipole density described by a spherical evanescent wave. Anisotropic band extrema and saddle points are also studied.
Local‐Density‐Functional Approach to the Electronic Structure of Rhodium under High Pressure
Authors: Petrů J.
Published: July 2007

The electronic structure of f.c.c. rhodium at three lattice constants corresponding to an ambient pressure up to 650 kbar is derived using self‐consistent density‐functional calculations by the quadratic‐augmented‐plane‐wave method. Comparisons are made for the pressure‐dependent behaviour of the energy bands and the charge distribution, as well as the total and angular‐momentum‐decomposed densities of states inside the muffin‐tin spheres. Harrison's semiempirical parametrisation is tested against these first principles results.
Nonlinear Theory of the Photomagnetoelectric Effect with a Square‐Root Relationship between Carrier Densities
Authors: Augelli V. , Vasanelli L. , Leo M. , Leo R. A. , Soliani G.
Published: July 2007

The theory of the photomagnetoelectric effect (PME) is studied in the case in which the recombination mechanism gives rise to a square‐root relationship between carrier densities. The nonlinear continuity equation is solved and analytical expressions of short‐circuit PME current IPME and photoconductance ΔG are found in the case of strongly absorbed light. The dependence of IPME and ΔG on the light intensity is studied by assuming as an example a three level recombination model. The main results of the analysis is that the IPME vs. ΔG behaviour shows the same power law as the charge carrier do.
On the Magnetic Properties of Gd1−xRExAl2 Alloys
Authors: Witański K.
Published: July 2007

Disordered alloys of RE metals are considered and a general formula for paramagnetic susceptibility and the equation for Curie temperature are derived. The previously derived effective exchange interaction is assumed and the crystal electric field is taken into account. Molecular field and Hart‐ree‐Fock approximations combined with the coherent potential approximation are used. The results obtained are applied to Gd1−xRExAl2 (RE = Dy, Ho, Er) and discussed together with the experimental data.
Microscopic Model for the Relaxation and Excitation of Localized Spin Waves
Authors: Lin J. T. , Li Z. Y.
Published: July 2007

A microscopic Hamiltonian with long‐range spin‐spin interactions showing the host‐spin‐induced energy relaxation and frequency shift of the impurity spin is studied within a Markovian process. The localization conditions and the associated dispersion laws of spin waves in ferromagnetic and antiferromagnetic systems containing one or two impurities are investigated at various domains of the exchange integrals and the spin amplitudes. The correspondence between the localized spin waves and lattice vibrational modes is analyzed. Finally, the energy absorption and the possible mechanism for selective excitation of a localized magnon are discussed based on a quantized Hamiltonian which includes the impurity‐host coupling and their interactions to an external magnetic field with frequency near resonance to that of the localized active mode.
A Dynamical Theory for a Disordered Hubbard Chain far from Equilibrium. II. The Low‐Field Case
Authors: Heiner E.
Published: July 2007

For a finite chain of strongly correlated electrons a nonlinear transport theory is treated. The time dependent behaviour of the expectation values for singly and doubly occupied states and the local and total current densities are calculated for oscillating boundary conditions in the asymptotic limit (t → ∞).
51V NMR of Amorphous and Crystalline V‐Zr Alloys
Authors: Bakonyi I. , Han K.‐S. , Schone H. E.
Published: July 2007

Results of 51V NMR Knight shift and linewidth measurements are described for thin films of V100−xZrx b.c.c. crystalline (x = 6.4 and 8.4) and amorphous (x = 17.2, 28, and 46.4) alloys prepared by rf sputtering onto copper substrates. The field dependence of the linewidth and, for x = 28 and 46.4, heat‐treatment effects were also considered. Based on these experimental data, quadrupole effect, electronic structure, and chemical short‐range order of amorphous V‐Zr alloys are discussed.
Effects of the Crystal Field in the Spectra of Iron Group Impurities in ZnSe
Authors: Biernacki S. W.
Published: July 2007

The many‐electron crystal field term states are calculated with account of the symmetry dependent deformation of the 3d orbitals and of the dependence of one‐electron energies on the spin orientations. It is shown that the one‐electron 3d orbitals of symmetry t2 are extended with respect to orbitals of symmetry e by 1 to 4%. The relative deformation depends on the ratio of a σ‐type resonant integral to a π‐type resonant integral.
Atomic Ordering in Multicomponent Alloys
Authors: Dabrowski L.
Published: July 2007

The pair interaction model of binary alloys is generalized to cover the case of an arbitrary number of components. Both, the interaction radius and the number of short‐ and long‐range ordering parameters are unlimited. The problem is solved by applying the high‐temperature series expansion method, using a new diagram technique, to calculate the fluctuation potential.
Many‐Body Contribution to the Energy of Metals with B.C.C. Lattice
Authors: Bogdanov V. I. , Fuks D. L.
Published: July 2007

The Fourier transforms of covalent charge density and the contribution of the third and fourth order of perturbation series for the energy (E) of alkali and some transition metals are calculated on the basis of self‐consistent Brillouin‐Wigner pseudopotential perturbation theory. The scattering of electrons on the planes of the first and second Brillouin zones in the b.c.c. lattice is taken into account. It is shown that the value E is of the same order as the heat of polymorphic transition. The convergence of perturbation series in pseudopotential theory for the calculation of transition metal energy with Animalu's form‐factors is investigated.
Wavelength Modulated Spectra of α‐Ag0.7Zn0.3 near the Optical Absorption Edge
Authors: Stearns R. , Braunstein R. , Muldawer L.
Published: July 2007

The optical properties of α‐phase Ag 0.7Zn0.3 are determined near the optical absorption edge. This alloy composition dampens the sharp Ag‐plasma resonance. The band shifts which are observed are in qualitative agreement with calculations which are performed for the similar alloy, α‐Cu0.7Zn0.3.
Photoinduced Optical Absorption of Cr4+ in Semi‐Insulating GaAs:Cr
Authors: Ulrici W.
Published: July 2007

The optical absorption of Cr4+ created during illumination with hv > 0.75 eV in semi‐insulating GaAs:Cr is investigated at low temperatures (≤ 150 K). Analyzing the concentrations of Cr2+, Cr3+, and Cr4+ during illumination and measuring the excitation spectrum of Cr4+, the creation mechanism of photoinduced Cr4+ conclusively proved to be the two step process Cr3+ + hv → Cr2+ + holevb and holevb + Cr3+ → Cr4+. The concentration of photoinduced Cr4+ is measured in dependence on the contents of Cr2+ and Cr3+ present in the samples before illumination, on temperature, and on illumination intensity. Its time dependence of rise after switching on and of decay after switching off the illumination is measured under various conditions. The results are interpreted using dynamic equations for the concentration of Cr2+, Cr3+, and Cr4+ during illumination basing on the assumption that only excitation and capture processes via the valence band contribute to the formation of photoinduced Cr4+ and that the tunneling process Cr4+ + Cr2+ → 2 Cr3+ is responsible for its decay.
Electroabsorption for Deep Level to Band Transitions Accompanied by Multiphonon Processes
Authors: Schenk A. , Enderlein R. , Suisky D.
Published: July 2007

The electroabsorption spectrum for optical transitions from a deep level to a band accompanied by multiphonon processes is calculated within the Lucovsky model. The line shape turns out to be highly sensitive to the Huang‐Rhys factor and to the ratio of electrooptical and phonon energy.
The Sextic Polynomial of Crystal Elasticity
Authors: Head A. K.
Published: July 2007

It has previously been proved that the sextic polynomial of crystal elasticity is not explicitly solvable for arbitrary elastic constants and directions except for hexagonal symmetry. In the case of cubic symmetry there are special elastic constants known for which the polynomial is solvable for all directions. A search is made over the range of physically significant elastic constants for any further special cases. It is conducted with an extension to Galois theory that gives a measure of how far any particular polynomial is from being solvable rather than just a yes‐no result. No further special elastic constants are found and it appears very probable than none can exist although there is not a strict proof of this.
Photoelectron Diffraction and Band Structure Effects in ARXPS from the Valence Bands of GeS
Authors: Chassé T. , Berg U. , Brümmer O.
Published: July 2007

X‐ray photoelectron spectra of the valence band region of GeS are measured in dependence on polar and azimuthal angle. The anisotropy of the valence band structures is due to both, influences of initial state wave function and photoelectron diffraction. By these means in addition to the symmetry character of initial states the atomic nature of different valence band peaks can also be explained.
The Electronic Configuration of 121Sb in Semiconductors
Authors: Weyer G. , Andreasen H. , De Waard H.
Published: July 2007

Isomer shifts of the 37 ke V Mössbauer transition in 121Sb are determined for 121Sb constituents and impurities in III‐V and II‐VI compound semiconductors. Radioactive 121Xe isotopes decaying to 121Te, the 121Sb‐parent isotope, were implanted at the ISOLDE facility at CERN. The nature of the electronic configuration of Sb‐isoelectronic and Sb‐donor and ‐acceptor impurities in semiconductors is discussed in terms of bond hybridization and ionicity. The influence of structural relaxation is pointed out.
Carrier drift mobilities in some organic solids. A search for organic photovoltaic materials. I. Charge transport calculations in 2–2′ bipyridine and pyridazino [4,5‐d] pridazine
Authors: Kumar B.
Published: July 2007

Excess hole and excess electron mobilities are studied in 2–2′ bipyridine and pyridazino [4,5‐d] pridazine using tight binding approximation. With suitable molecular orbitals for band structure and using a potential given by Silbey et al. the energy bands are calculated. The applicability of band model and the suitability of these materials for organic photovoltaic devices are discussed in the light of existing theories.
Temperature dependence of structural and transport properties of less‐simple liquid metals
Authors: Rahman S. M. M. , Sarker D. K.
Published: July 2007

Shear viscosity and self‐diffusion coefficients are calculated for certain less‐simple liquid metals at various temperatures. The basic assumption undertaken is that these properties of a liquid metal resemble those of an appropriate hard sphere fluid. The temperature dependence of the basic ingredients, i.e. the hard sphere diameter and packing fraction is considered via a full thermodynamic perturbation formalism. The essential features inherited by these metals are included in the relevant electron‐ion interactions. A variational procedure leading to a minimization of the free energy is employed to determine the optimum values of the hard sphere diameters and packing fractions. These optimal and self‐consistent ingredients are employed in computing the shear viscosity and self‐diffusion coefficients of Ag, Hg, Ga, and Sn. The calculated results are found to be in agreement with the experimental and the available theoretical results for most of these metals.
Non‐linear optical susceptibilities of molecular crystals in the region of vibronie excitations. III. Non‐totally symmetric vibrations
Authors: Stoychev K. T.
Published: July 2007

The quadratic optical susceptibility of molecular crystals is calculated in the frequency region of vibronic excitations consisting of an electronic exciton and a non‐totally symmetric vibration. An one‐dimensional model with nearest‐neighbour interactions is used. Intermolecular and intramolecular exciton phonon interactions are considered and the former is shown to play a dominant role in nonlinear optical spectra. The sign of the exciton effective mass is shown to affect the spectrum inside the two‐particle exciton‐phonon band but not the bound state resonance.
Linearised screened pseudopotential and superconducting state parameters of a number of metals
Authors: Sharma R. , Sharma K. S. , Dass L.
Published: July 2007

A linearised form for the screened form factors of electron‐ion interaction is proposed and applied for the prediction of superconducting state parameters viz. electron‐phonon coupling strength λ, Coulomb pseudopotential μ*, transition temperature Tc, isotope effect exponent α, and the interaction strength N0V. Good agreement between the computed results, experimental data, and the results of Allen and Cohen based on the HA potential, supports the proposition.
Symmetry analysis of the low‐temperature domain structure in ferroelastic LiKSO4
Authors: Balagurov A. M. , Popa N. C. , Savenko B. N.
Published: July 2007

The domain structure appearing in ferroelastic LiKSO4 at T < 190 K is analysed starting from the principle of macroscopic symmetry conservation. The transitions from, the point groups 6mm or 6 into mm2, 2, or 1 are considered in detail. It is shown that by the measurement of the split of reciprocal lattice node it is possible to determine the point group of the para‐ and ferroelastic phase in LiKSO4.
Effect of forced vibrations on the scattering of X‐rays and mössbauer radiation by a crystal. II. Dynamical effects
Authors: Dzyublik A. Ya.
Published: July 2007

A dynamical theory for Raman scattering of γ‐quanta in crystals under forced vibrations is given. The pendellösung‐effect, the anomalous transmission of γ‐quanta through a crystal as well as suppression of inelastic scattering and reactions are shown to exist in the two‐wave case. A general theory of γ‐acoustic resonance for arbitrary geometry of Laue diffraction is developed. An anomalous transmission of Mössbauer radiation through a vibrating crystal far from the Bragg condition is predicted due to arising of electromagnetic wave packets in the crystal, which do not interact with nuclei.
Photon‐phonon interaction influence on the external vibration spectra of molecular crystals
Authors: Botvich A. N. , Shabanov V. F. , Vtyurin A. N. , Pozdnyakova T. A.
Published: July 2007

A method is developed to determine the parameters of electromagnetic and elastic excitations in molecular crystals including the polariton resonance region. The dependence of eigenvectors and eigenfrequencies on the wavevector of elementary excitations is calculated numerically for m‐chloronitrobenzene crystals. The conditions are found when the photon‐phonon resonance effect becomes observable in the Raman scattering (RS) spectra of this crystal.
Surface states – an effect of overlap integrals
Authors: Stankiewicz Barbara
Published: July 2007

The effect of overlap integrals on the electronic structure of a simple cubic crystal is analysed using the LCAO method. Interaction between first, second, and third neighbours are taken into account. Surface and volume bands are determined. The width of energy bands as well as the number of surface states depend strongly on the value of overlap and resonance integrals. As a result, the location of the surface band with respect to the volume band is very sensitive to values of overlap integrals between nearest neighbours.
Magnetic Moments and Initial Susceptibilities of f‐Electron States Experiencing a Crystal Field of Cubic Symmetry
Authors: Fischer G. , Herr A.
Published: July 2007

The effect of perturbation to the second order caused by a magnetic field H on the energy levels of an f‐electron situated in a crystal field of cubic symmetry is calculated. This development is of particular interest in the understanding of magnetic properties of f‐electrons: the term in H gives the individual magnetic moment of the considered sub‐level and the term in H2 the corresponding Van Vleck susceptibility. The cases of H parallel respectively to the three principal crystallog‐ raphic directions are considered. The three terms of the energy development are tabulated for all J from 2 to 8 in the cases of purely fourth and sixth order crystal field.
Three‐Phonon Interactions in Bismuth Germanium Oxide
Authors: Krzesinska M.
Published: July 2007

The anharmonic interactions of hypersonic waves with thermal phonons in bismuth germanium oxide (BGO) will be discussed. The effect of elastic anisotropy, temperature, and chromium impurity on the allowed three‐phonon processes is treated in detail. Allowed processes where hypersonic waves interact with thermal phonons on the same acoustic branch of the phonon spectrum as themselves are predicted to exist. Measurements of velocity at low temperatures in BGO are used for calculations.
On the Functional Integral Method to the Hubbard Model
Authors: Wosicki P.
Published: July 2007

Magnetic properties of nickel are studied with use of the single‐site coherent potential approximation in the functional integral method. For comparison various field models are considered. Interband interactions in the first approximation are taken into account.
Magnetic Properties of Rb2MnxCr1−xCl4 Mixed Crystals
Authors: Grieb Th. , Wacker K. , Naumann E. , Treutmann W. , Heger G. , Geick R.
Published: July 2007

The mixed crystal system Rb2Cr1−xMnxCl4 is studied by magnetization measurements at liquid helium temperatures and for orientations of the external magnetic field H parallel and perpendicular to the crystallographic c‐axis. The concentration x of the samples is in the range 0≦x≦≦0.3 on the Cr‐rich side and 0.9≦x≦1.0 on the Mn‐rich side. The experimental results are analysed and discussed by means of an average model calculation for the magnetic x‐H phase diagram at low temperatures (T = 4.2 K). The experimental data confirm the predictions of the model with respect to the influence of the single‐ion anisotropy of the Cr2+ ions on the spin‐flop field in the region of high Mn concentration and of the antiferromagnetic exchange coupling between Mn2+ and Cr2+ ions on the magnetization for high Cr concentration. In addition, the experimental results are in agreement with those from magnetic resonance measurements.
Induced Magnetic Form Factors for 3d Transition Metals and 3d‐3d Alloys III. Diamagnetie Form Factors
Authors: Pabst J. , Röll H.
Published: July 2007

Diamagnetie scattering is discussed for transition metals and transition metal alloys. The same concept as applied for the description of induced spin scattering is used. It is shown that diamagnetic susceptibility and form, factors obtained from band structure calculations greatly differ from those calculated from Hartree‐Fock‐Slater densities for the free atom. Differences induced by a charge transfer between the alloy atoms arise also between the quantities of pure metals and those of alloys; however, the differences between pure metals and alloys are less than those with induced spin scattering. Calculated diamagnetic form factors are indicated by their Fourier coefficients.
Non‐Monotonous Behaviour of the Nernst‐Ettingshausen Effect in Conductive Films in a Strong Magnetic Field
Authors: Askerov B. M. , Kuliev B. I. , Figarova S. R. , Eminov R. F.
Published: July 2007

The Nernst‐Ettingshausen effect is studied in thin conductive films in a strong transverse magnetic field. The expression is obtained for the NE coefficient Q for arbitrary charge carrier statistics and film thickness, assuming dimensional quantization and piezo‐acoustic phonon scattering. It is shown that in the case of films with degenerate electron gas the NE coefficient oscillates with the variation of the thickness of the film d. The oscillation period is determined as a function of the concentration of the conduction electrons. Taking account of the surface scattering a detailed analysis of the NE coefficient dependence on the film thickness is given including films of thickness comparable to the mean free path of the charge carriers. Computer calculations show that under these conditions the function Q(d) is non‐monotonous as well.
Quantum Oscillations of Magnetoresistance and Thermomagnetic Power and the Fermi Surface of As‐Sb Alloys
Authors: Muntyanu F. M.
Published: July 2007

Quantum oscillations of magnetoresistance and thermomagnetic power of AsxSb1−x (0 ≦ x ≦ 1) alloys in stationary magnetic fields up to 15 T at low temperatures (1.9 ≦ T ≦ 17 K) are investigated. In the alloys, with x ≦ 0.3, the quantum oscillations of thermomagnetic power with a “giant” amplitude are observed. The peculiarities of the energy spectrum reconstruction are determined and the composition range in which a break of the hole necks occurs is defined. It is established that AsSb alloys are semimetals in which overlapping of the hole and electron terms in the first approximation increases linearly with increasing x.