bluuebunny/crossref_metadata_2025_split huggingface dataset:
On the Influence of Amorphization on Atomic Diffusion in Condensed Systems
Authors: Milchev A. , Avramov I. 
Published: July 2007

AbstractA simple theoretical model which examines the effect of structural disorder on the mobility of diffusing particles in amorphous materials is suggested. So, following Anderson's ideas, it is assumed that structural disarray results in a probability distribution of energy barrier heights for diffusion around some mean value, Eer, with a given dispersion δE, used as a measure of disorder. In the framework of the mean field approximation and using the concept of random walks, it is shown that the impact of dispersion δE on the mean stay time of the diffusing particles leads to corrections of several orders of magnitude, as compared to mean stay time values, calculated traditionally in terms of the average activation energy Ecr only.
On the Connection between Isofrequency Temperature Dependences of Inelastic Light Scattering and Dielectric Anomalies in Lithium Niobate Crystals
Authors: Gorelik V. S. , Umarov B. S. , Umarov M. 
Published: July 2007

AbstractThe isofrequency temperature dependence of inelastic light scattering intensity in ferroelectric LiNbO3 crystals at frequencies of Ω = 15 to 100 cm−1 and at different scattering geometries is discussed. The parameters of an effective soft mode are obtained. A comparison is made of the experimental results with the simplest variant of the light scattering theory near the phase transition point. The Curie‐Weiss constant and temperature shift coefficient of the soft mode frequency are determined. The applicability is shown of the approximation of one effective soft mode in the region of low frequencies near the phase transition point in the crystal examined.
Theory of Free‐Carrier Magnetoabsorption in Mixed Zincblende Narrow‐Gap Semiconductors
Authors: Szatkowski J. , Sierański K. 
Published: July 2007

AbstractThe influence of chemical disorder on the magneto‐optical properties of mixed semiconductors with zincblende structure and dispersion relations typical of III‐V and II‐VI compounds is considered theoretically. The magneto‐optical transitions between Landau levels are described, treating the potential due to the chemical disorder as a perturbation. It is found that all transitions between any two Landau levels are allowed (Δn δ 2). The absorption coefficient is non‐vanishing for any polarization and frequency due to the presence of chemical disorder. For parallel and perpendicular light polarization additional Kohn or logarithmic‐like divergencies of the absorption coefficient are obtained at photon energies equal to hω = E – E.
Spin‐Polarized Compton Profile of Nickel
Authors: Rennert P. , Carl G. , Hergert W. 
Published: July 2007

AbstractThe expression for the spin‐polarized Compton profile is calculated using relativistic corrections in a nonrelativistic time‐dependent perturbation theory. The spin polarization of the Compton profile for ferromagnetic materials can be measured by circularly polarized X‐rays. The calculated spin‐polarized Compton profile of nickel is presented. The anisotropic profiles and the isotropic one are considered. The curves show a characteristic shape caused by a positive spin polarization of the d‐electrons and a negative one of the s, p‐electrons.
Structure and Thermodynamics of the Liquid Noble Metals from the Generalized OPW and Resonant Model Approaches
Authors: Regnaut C. , Fusco E. , Badiali J. P. 
Published: July 2007

AbstractThe influence of the d electrons on the structure factor, entropy, and heat capacity of liquid noble metals is analyzed. This is done by using the generalized orthogonalized plane wave (OPW) and resonant model potential (RMP) approaches in connection with the optimized random phase approximation technique. The results of the OPW and RMP equally well compare to the data on Cu and Ag. In the case of gold, only very qualitative OPW results are obtained.
Role of Thermal Transport in the Non‐Equilibrium Behaviour of a Cylindrical Ferromagnetic Superconductor
Authors: Chashoo G. J. , Dharmadurai G. 
Published: July 2007

AbstractThe steady state temperature distribution in a long current carrying cylindrical wire of a ferromagnetic superconductor at bath temperatures below the magnetic transition is obtained using some simplifying approximations. It is found that dissipation in this ferromagnetic resistive state would lead to the onset of a non‐equilibrium intermediate resistance state almost simultaneously in the entire cross‐section of the wire at a critical power level. The results indicate the dominant role of surface thermal transport in deciding the gross electrical behaviour of this non‐equilibrium reentrant superconductor under various thermal environments involving gaseous and liquid helium. The significance of these findings is discussed.
Luminescence of Ga‐Doped α‐Al2O3 Crystals
Authors: Jansons J. L. , Kulis P. A. , Rachko Z. A. , Springis M. J. , Tale I. A. , Valbis J. A. 
Published: July 2007

AbstractThe introduction of Ga3+ ions into α‐Al2O3 crystals results in a new complex luminescence band at about 5 eV. The main optical excitation maximum is observed at 8.5 eV indicating the bound exciton nature of the excited state. In the cathodoluminescence spectra at 80 K three sub‐bands can be detected with maxima at 4.61, 5.15, and 5.58 eV. The luminescence decay in all the three bands has two exponential components — a short one with τ = (15 ± 1) ns and a long one with τ about 1 ms. The Ga‐related luminescence can be observed under the excitation of X‐rays up to 600 K; a drop in intensity takes place at about 210 K corresponding to the Ga‐related TSL peak. The activation energy of the release of electrons at this peak as determined by the fractional‐glow method is (0.70 ± 0.02) eV and the frequency factor 1014 s−1.
Oscillations of Local Magnetization in the Non‐Ideal Antiferromagnetic Chain
Authors: Gildenblat G. 
Published: July 2007

AbstractA Green's function technique is used to obtain the exact form of the Friedel type oscillations of local magnetization in the spin 1/2, XY antiferromagnetic chain induced by the presence of a boundary or impurity. It is shown that, in addition to the amplitude, the functional form of the oscillations is determined by the strength of the perturbation caused by the impurity and intensity of the external magnetic field. Comparison is made with the earlier perturbation theory treatment in the free‐fermion approximation.
Correlations between OH(OD) Stretching Vibrations and Structural Characteristics of Hydrogen Bonds in K4Fe(CN)6 · 3 H2O Crystal
Authors: Savatinova I. , Anachkova E. 
Published: July 2007

AbstractThe OH and OD uncoupled stretching vibrations of the K4Fe(CN)6 · 3 H2O (KFCT) crystal obtained by isotope dilution technique are discussed and connected with the H bond structural characteristics. The force constants Fo‐H and the anharmonicity constants 2XoH of the different OH oscillators in KFCT are calculated using the uncoupled Raman frequencies. No significant differences are found between the correlations of spectroscopic and crystallographic data in the case of weak O‐H …︁ N and O‐H …︁ O hydrogen bonds.
Study of a Bound Surface Optical Polaron by a Non‐Perturbative Method
Authors: Bhattacharya M. , Mukhopadhyay S. , Mitra T. K. 
Published: July 2007

AbstractThe problem of an extrinsic surface optical polaron, bound to an impurity atom, near the surface is investigated for the first time in the framework of a recently developed canonical transformation method. Energy and wave function for all ranges of the coupling constant (α) and the impurity parameter (β) are obtained numerically following the canonical transformation method. For a strong impurity the relatively unimportant effect due to the image potential is neglected. The dependence of the energy, the wave function, and the induced potential on α, β are obtained and shown graphically.
Picosecond Recombination of Photoexcited Carriers in Glow Discharge a‐Si:H Films of Different Deposition Temperature
Authors: Bergner H. , Brückner V. , Dietrich D. , Nowick W. 
Published: July 2007

AbstractThe temporal behaviour is studied of photoexcited charge carriers in GD‐a‐Si: H in the ps range, the amorphous films are produced at different substrate temperatures up to 200°C. The recombination is characterized by a two‐step relaxation process. The relaxation times are 32 to 165 ps and 0.75 to 1.4 ns, respectively. The sample prepared at 200°C shows a superposition of linear and bimolecular recombination. The recombination rate was found to be γ = 3,3 × 10−10 cm3 s−1.
Non‐Linear Optical Susceptibilities of Molecular Crystals in the Region of Vibronic Excitations. II. Totally Symmetric Vibrations
Authors: Lalov I. J. , Stoychev K. T. , Penchev S. P. 
Published: July 2007

AbstractThe quadratic non‐linear optical susceptibility of molecular crystals in the vibronic region (one Frenkel exciton + one totally symmetric phonon) is calculated. A one‐dimensional model is used to find an analytic expression for the non‐linear susceptibility and numerical calculations of its frequency dependence are made. The two mechanisms of exciton‐phonon interaction — frequency shift of the vibration and shift of the equilibrium positions — have: (1) a cummulative action for excitons of positive effective mass (one‐particle resonances of the non‐linear susceptibility appear); (2) a compensating effect for excitons of negative mass (many‐particle resonances appear).
Acoustic Phonon Anomaly in Mixed‐Valent TmSe
Authors: Ichinose S. , Tamura I. 
Published: July 2007

AbstractThe excitation spectrum of mixed‐valent TmSe is investiagted in terms of the Sherrington‐Riseborough model. The numerical calculations reproduce the anomalous feature of the acoustic phonon band, provided that the d‐f electronic excitation energy is comparable to the energy of the LA phonon.
Screening of a Proton Moving through the Electron Gas
Authors: Stachowiak H. 
Published: July 2007

AbstractThe problem is considered of a positively charged particle moving through the electron gas with a velocity comparable to the Fermi velocity vF or smaller. The problem is solved in the static RPA approximation. It is found that up to a velocity of about 0.8vF the positive particle is completely screened. For higher velocities oscillations appear in the screening charge distribution — different from the Friedel oscillations — and complete screening does not occur. For velocities lower than about 0.8vF the anisotropy of the screening is studied. The relevance of this problem to positron annihilation in metals is pointed out.
Structure and Bonding in Cubic IV–VI Crystals. III. On the Cubic to Rhombohedral Phase Transition
Authors: Enders P. 
Published: July 2007

AbstractThe cubic to rhombohedral phase transition is considered within the Girshberg‐Tamarchenko approach for the vibronic anharmonicity of the soft TO modes and a Landau free energy expansion for the strictive coupling of optic and acoustic modes. It turns out, that one needs a not too simple model for the lattice repulsion forces for a comprehensive description of the phase transition. The spontaneous rhombohedral shear below Tc appears as secondary (induced) order parameter. The relation to the work of Littlewood is discussed.
Spin Waves in an Easy‐Axis Ferromagnet with a Finite Concentration of Impurities with Competing Anisotropy
Authors: Lukanin A. I. , Medvedev M. V. 
Published: July 2007

AbstractThe spin‐wave spectrum is investigated of a Heisenberg ferromagnet with an easy‐axis single‐ion anisotropy in which a number of host atoms is substituted by impurities with an easy‐plane singleion anisotropy. It is shown for both, the case of a weak local perturbation (when one impurity atom does not break the stability of the ground state with completely parallel spins) and the case of a strong local perturbation (when a single impurity creates one or even several localized spin deviations in the ground state) that there is a gap in the spectrum of low‐lying spin excitations and the spin‐wave damping Γk is proportional to the wave vector k near the bottom of the quasicontinuous band. The critical concentration up to which the ferromagnetic state possessing a gap in the spin‐wave spectrum remains stable is estimated.
Thermodynamical Behaviour of the Uniaxial Crystals of “Easy‐Axis” Type with Diverse Origins of Magnetic Anisotropy
Authors: Kazakov A. A. , Kleshev S. M. 
Published: July 2007

AbstractInstead of solving the set of the 2s equations for the Green function of a ferromagnetic with singleion and two‐ion anisotropy of arbitrary order, it is suggested to solve a single equation for the parametric Green function. Green's function, low‐temperature spectrum, and magnetization are calculated for an anisotropic ferromagnet with arbitrary spin. In the low‐temperature region one spin wave branch is excited and as a consequence the thermodynamical behaviour of the system is particularly simple.
Magnetic Anisotropy of Disordered Magnetics with Jahn‐Teller Ions
Authors: Ivanov M. A. , Mitrofanov V. Ya. , Fishman A. Ya. 
Published: July 2007

AbstractThe influence of random strain fields on the magnetic anisotropy of systems with Jahn‐Teller (JT) ions of the iron group is investigated. The averaging of the free energy over the randomly distributed sources of the strain fields is carried out using two‐ and three‐dimensional distribution functions obtained in the paper. It is shown that the value and sign of the first and second cubic anisotropy constants are determined by the ratio of the molecular field parameter to the width of the random field distribution.
Wannier Functions from Landau Functions?
Authors: Wannier G. H. 
Published: July 2007

AbstractIt is well known that the set of functions in a Bloch band is equivalent to copies of a single function placed on a lattice. The possibility of establishing a similar relation in the presence of a magnetic field is investigated. Landau ground state wave functions for the symmetric gauge placed on a square net serve as trial objects. The result is equivocal. It is proved that the standard procedures of the Bloch—Wannier transformation are feasible for some fields, but impossible for other fields. Both sets of fields are infinite and all members of the second set are smaller than those on the first. The resulting situation is discussed.
Positron Annihilation in Zinc. Theory and Experiment
Authors: Pawłowska Zoja 
Published: July 2007

AbstractThe electron—positron pair momentum density distribution in zinc is computed in the independent particle model (IPM) approximation on the basis of band structure calculations and the positron wave function. Some additional results of the application of the selection rule for positron annihilation to the h.c.p. structure are given. The angular correlation curves are calculated along three main crystallographic directions [100], [110], [001]. The overall shapes of the angular correlation curves can not be well explained in terms of the IPM approximation. Introducing the enhancement factor proposed recently by Arponen and Pajanne and the momentum independent enhancement for the core states and the umklapp components, the disagreement between IPM theory and experiment is reduced.
Computer Simulation of Glancing Scattering of a Fast Proton Beam by a Crystal Surface
Authors: Vyatkin E. G. , Taratin A. M. , Vorobiev S. A. 
Published: July 2007

AbstractWith the help of the binary collision model the glancing scattering of 10 MeV protons incident at the (100) and (110) surfaces of a tungsten crystal is investigated. The angular distribution and the dependence of the angular spread of the reflected protons on the incidence angle and crystal temperature are calculated.
Thermal Expansion and Mode Grüneisen Parameters in Lithium
Authors: Prasad B. 
Published: July 2007

AbstractThe mode Grüneisen parameters γqj, the mean value of Grüneisen parameter γM, and the thermal expansion coefficient γM are computed for b.c.c. lithium employing the model potential proposed by Krasko and Gurskü. The present results are compared with available experimental data. Reasonable agreement between theory and experiment is obtained.
Thermal Conductivity and Optical and Paramagnetic Absorption Spectra of Reactor Irradiated MgO Crystals
Authors: Abramishvili M. G. , Altukhov V. I. , Kalabegishvili T. L. , Kvachadze V. G. 
Published: July 2007

AbstractThe effect of reactor irradiation on thermal and optical properties of MgO is studied experimentally and theoretically. Optimum regimes of irradiation and annealing are selected, which promote the accumulation of a great number of F‐centres in the crystal and allow to reveal a relevant bend on the thermal conductivity curve x(T) at T ≈ 10 K. A general expression for the resonance inverse relaxation time of phonons' on F‐centers is obtained. Parameters of the model and basic mechanisms of thermal resistance of n,γ‐irradiated MgO crystals are determined. It is shown that the low temperature irradiation leads to more effective accumulation of F‐ and F+‐centres and hence to a stronger radiation change of the thermal conductivity.
Investigation of Z Center Conversions in KCl:SrCl2. II. Dielectric Relaxation Caused by Mutual Conversions of Z1, Z2, and F Centers
Authors: Kessler A. , Kizler P. 
Published: July 2007

AbstractLoss angle measurements in the course of linear heating are carried out during a mutual conversion of F, Z1, and Z2 centers in KCl:SrCl2 one into the other and of KCl:SiCl2 containing no colour centers. It is found that besides the known losses caused by reorientation of impurity vacancy complexes, point defect surface polarization, and conductivity, also the Z2 → F conversion causes losses. A thorough analysis of the results leads to the conclusion that a transport of electrons takes place during the Z2 → F conversion whereas the other conversions are realized by a „transport”︁ of ions or neutral components.
The Validity of the Low‐Temperature Expansions for the Anisotropic Heisenberg Models
Authors: Škeinjar M. T. , Kapor D. V. , Šetrajčić J. P. 
Published: July 2007

AbstractThe low‐temperature expansion of the relative magnetization of two anisotropic Heisenberg models is discussed. It is shown that due to the existence of the temperature independent energy gap, the dimensionless temperature cannot be applied as the small parameter. In other words the low‐temperature expansion is completely invalid for the Heisenberg model with the Ising anisotropy. For the anisotropic model proposed by Belorizky et al. one can make calculations in the first order in the anisotropy parameter, but there is no term of order T3 as previously stated.
Evaluation of the First Relaxed Excited State Energy of the Free Fröhlich Polaron
Authors: Lépine Y. , Charbonneau M. 
Published: July 2007

AbstractThe first relaxed excited state energy of the free Fröhlich polaron is evaluated using the Fock approximation of Matz and Burkey. From a discussion of a variational‐type expression of this energy, it is concluded that a singularity in the space of variational parameters separates the ground state from the first relaxed excited state and that other singularities separate the other excited states. From this interpretation, this energy is evaluated, using two complete model spectra; a Gaussian spectrum and a second one involving an internal magnetic field in addition to the Gaussian part. It is found that for α ≦ 1.2 no excited state is observed. For 1.2 ≦ α ≦ 4.2, a two‐dimensional excited state is obtained while for α ≦ 4.2 a Gaussian excited state is obtained. These results are, however, limited by the choice of the model spectrum. For large α's, an asymptotic limit is obtained of ‐0.053α2ħω, a value close to that obtained from the best product ansatz calculations.
Control of Carrier Concentration by Stimulated Emission in Highly Excited Direct Gap Semiconductors
Authors: Egorov V. D. , Müller G. O. , Weber H. H. , Jacobson M. A. , Dite A. F. 
Published: July 2007

AbstractStimulated recombination may result in orders of magnitude reduction of lifetime of photo‐excited carriers depending on the length over which optical amplification of (spontaneous) emission can occur. This effect is verified in the excitation spot dependence of photoconductivity in CdS, in qualitative agreement with model calculations.
EPR Studies of Cu2+ in Anhydrous Lead Tartrate
Authors: Korkmaz M. , Bessege R. , Gavaix A. 
Published: July 2007

AbstractEPR of Cu2+ doped single crystals of anhydrous lead tartrate grown from silica gel are carried out at 300 K. Four Cu2+ lattice sites, labeled A, B, C, and D are identified. These sites exhibit four sets of four hyperfine lines in all directions except some particular directions. The g‐factor, the hyperfine splitting, the mixing parameters, and Fermi contact interaction constant are calculated for each site and they are compared with those found for other tartrate crystals in the literature. The spectra are found to have different intensities for different sites suggesting a preferential occupation of the sites by the Cu2+ ions.
The Ni Donor and Acceptor Levels in CdSe
Authors: Baranowski J. M. , An Phuong 
Published: July 2007

AbstractThe charge transfer spectra of Ni impurity in CdSe are reported and discussed. It is shown that they consist of the photoionization spectrum of the donor Ni2+ (d8) and the spectrum connected with the transition of an electron from the valence band to the Ni in result of which the Ni1+(d9) charge state is created. An analysis of the charge transfer spectra allows to determine the N2+ (d8) donor level at 0.32 eV and the Ni1+(d9) acceptor level at 1.81 eV above the top of the valence band. These results and other transition metal levels established previously in CdSe allows to discuss chemical trends in their position within the gap.
The Improved Point‐Ion Potentials for the F+‐Centers in LiNbO3 and LiTaO3
Authors: Ho Fat Duen 
Published: July 2007

AbstractThe validity of the point‐ion potentials is very essential and even critical for the study of the F+‐centers in lithium niobate and lithium tantalate. Earlier calculations are based on the assembly of 810 ions of the crystal‐lattices. In order to address to this important subject in much greater detail new potentials are developed by including 3750 ions instead of 810 ions. It is found that the 3750 point‐ion potentials are almost in accord with those of 810 point‐ions for each crystal. This is also true for the resulting values of the transition energies. Thus the convergence of the lattice sums is further demonstrated, and the validity of 810 point‐ion potentials is more convincingly shown.
Photostimulated Uneven Magnetoresistance at Inelastic Scattering of Electrons in Semiconductors
Authors: Tsurkan G. I. , Shmelev G. M. , Shon Nguyen Hong 
Published: July 2007

AbstractThe magnetoresistance (MR) of a nondegenerated polar semiconductor in the presence of linear polarized laser radiation (frequency Ω) is estimated. At low temperatures (k0T ≪ hω0, ω0 is the optical phonon frequency), the contribution in MR is made by two groups of carriers with energies 0 < ε < hω0 and hω0 < ε < ε < 2hω0. In strong magnetic fields besides usual (anomallously large) MR an uneven MR (UMR) appears (due to the laser radiation) depending on the orientation of the wave field relative to the dc electric field. The UMR value may be governed by the difference |Ω – ω0|.
Fluctuation Theory of Magnetic Superconductors
Authors: Savchenko M. A. , Stefanovich A. V. 
Published: July 2007

AbstractA fluctuation theory of ternary and pseudo‐ternary superconducting compounds of rare‐earth metals is constructed on the basis of phase lamination in complex magnetic systems during phase transitions. It is shown that a high‐temperature superconducting phase may appear in these compounds. The criterion for the emergence of such a phase is obtained.