bluuebunny/crossref_metadata_2025_split huggingface dataset:
Dispersion curves of stimulated Raman effect in piezoelectric cubic crystals
Authors: Schulz V. , Merten L. 
Published: July 2007

AbstractIt is shown that Stokes and anti‐Stokes waves for general directions of propagation in piezoelectric crystal couple anharmonically both with transverse and longitudinal polaritons (stimulated Raman effect). Only for special directions in the crystal pure transverse polaritons are excited. The dispersion functions for such a special direction in GaP are calculated numerically. If the damping of the polariton waves is neglected the wave vectors of the coupled waves are either real quantities or pairs of conjugate complex quantities. The complex wave vectors are represented in the complex plane. The results show that exponentially amplified polariton waves exist. The properties of these waves are discussed in detail.
Triplet exciton trapping in p‐terphenyl crystals studied by delayed fluorescence and phosphorescence
Authors: Takase T. , Morikawa E. , Kotani M. 
Published: July 2007

AbstractTriplet exciton trapping in p‐terphenyl crystals is investigated by delayed fluorescence and phosphorescence. Trap depth ((2800 ± 100) cm−1) and concentration (10−6 mol/mol) are deduced from the temporal behaviour of delayed fluorescence. The same trap is also found in the phosphorescence spectrum. The bimolecular annihilation rate constant between free and trapped excitons (1 × 10−13 cm3 s−1) is found to be orders of magnitude smaller than that for free—free annihilation.
Optically detected magnetic resonance in Zn1−xMnxTe
Authors: Malyavkin A. V. 
Published: July 2007

AbstractOptically detected magnetic resonance (ODMR) due to ESR of Mn in Zn1−xMnxTe is observed. The resonance is displayed in reconstruction of recombination spectra of free exciton, exciton bound to a neutral acceptor, and donor‐acceptor pairs in magnetic field. Two cases are treated: when electron and hole spin‐splitting energies are less or comparable to their spin temperatures (at Mn concentration x = 0.0025), and when spin‐splitting energies many times exceed spin temperatures (x = 0.08).
Donor‐related edge luminescence in ion‐implanted ZnTe
Authors: Verity D. , Nahum J. , Bryant F. J. 
Published: July 2007

AbstractSingle crystal samples of ZnTe are implanted at 77 K with chlorine, bromine, copper, or silver ions of 100 keV energy. The low temperature cathodoluminescence spectra of the sample are recorded as a function of post‐implantation isochronal (30 min) annealing temperature in vacuum in the range 50 to 500 °C and compared with the spectra of similarly‐annealed unimplanted and argon‐implanted reference samples. Chlorine, bromine, and copper each induce similar changes in the emission spectrum and, in addition to enhancing strongly donor‐acceptor pair bands at 547.3 (CII) and 553.6 nm (BII), produced new edge emission bands at 530.2, 535.2, and 530.6 nm, respectively. These three new bands are each assigned to a transition from a deep donor level to the valence band. The deep donor defects are attributed to the complexes (VZn2ClTe), (VZn2BrTe), and (VZn2Cui) or (VZn 2CuTe), with electron binding energies of 65, 88, and 69 meV, respectively. In contrast, annealing of silver‐implanted ZnTe causes emission spectrum changes comparable to those induced by argon ion bombardment and produces no effects which can be attributed to the silver impurity.
Conduction electron self‐energy effects in ferromagnetic semiconductors
Authors: Eränen S. , Sinkkonen J. 
Published: July 2007

AbstractThe interaction between conduction electrons and localized lattice spins is studied. The problem is considered in broad conduction band ferromagnetic semiconductors at low temperatures using spin‐wave approximation to obtain the lattice moment correlation functions. Calculating the self‐ energies in generalized Born approximation for both the conduction electron spin directions it is shown that a spin gap does not exist i.e. even at zero temperature the spin down band has a tail extending down to the spin up band edge. Consequently the relative conduction electron spin polarization does not reach the ideal value 100%, but ‐ with parameter values appropriate for EuS ‐ remains always smaller than 93% and further keeps practically constant at low temperatures. At T = 10 K the value 93% exactly coincides with the known experimental result for EuS. In addition the mobility including self‐energy terms only is evaluated. For spin down electrons the mobility is found to be several orders of magnitude smaller than for spin up electrons. Moreover, due to the non‐existence of the spin gap the spin flip scattering is always present, which tends to reduce the mobility of spin up electrons from the ordinary Boltzmann result.
On the interaction between a vacancy and an interstitial impurity atom in B.C.C. transition metals
Authors: Masuda K. 
Published: July 2007

AbstractThe binding energies are calculated between a vacancy and an interstitial impurity (like carbon) atom in b.c.c. transition metals (α‐Fe, Mo, and W). The changes in the total energy due to the introduction of lattice defects are calculated using a tight‐binding type electronic theory and the Born‐Mayer repulsive potential. A comparison is made with previous theoretical calculations as well as with recent experimental observations (positron annihilation experiments). In addition the detailed electronic structure is investigated of the impurity atom, assuming both, interstitial and substitutional occupations and using the recursion method by Haydock et al. It is shown that there are marked differences in the local p‐orbital density of states between the octahedral and substitutional impurity (carbon) atoms. These calculations enable one to understand the stability of the vacancy‐interstitial impurity pair in b.c.c. transition metals.
A microscopic interpretation of the spin‐lattice coupling coefficients for S‐state 4f7 ions
Authors: Pastusiak W. 
Published: July 2007

AbstractA previously reported model for spin–lattice coupling for 4f7 electrons, based on the assumption that intraionic interactions are perturbed by relativistic interaction with crystal lattice, is developed. Analytical formula for second‐ and fourth‐order spin‐lattice coefficients are derived. Using these formula and the concept of the relativistic crystal field in the point charge approach the values of the spin‐lattice coefficients for Gd3+ in CaF2 are calculated. These values are in much better agreement with the experimental values than those calculated so far. To the best of our knowledge the fourth‐order spin–lattice coefficients are calculated the first time and their values are about ten times smaller than the experimental ones.
Second‐order perturbation treatment of correlations in transition metal alloys
Authors: Drchal V. , Kudrnovský J. 
Published: July 2007

AbstractCorrelation effects in disordered transition metal alloys are studied within the degenerated Hubbard model using the perturbation theory limited to the second order in U/w (U Coulomb integral, w bandwidth). The influence of disorder is included within the coherent potential approximation. The theory is illustrated on a simple model of the copper–nickel alloy.
Parameters of bound multiexciton complexes in direct polar semiconductors
Authors: Haufe A. , Henneberger K. , Röseler J. , Wünsche H.‐J. 
Published: July 2007

AbstractUsing a generalized density‐functional method, which takes electron–phonon interaction into account, the ground state energies of donor BMEC's D0Xm(m = 1,…, 20) are calculated for the polar semiconductors ZnS, CdS, and CdSe. The highest stability is obtained for complexes possessing filled electron shells (m = 1, 7, 19), whereas gaps of instability are located between these complexes. The spectral locations of luminescence lines connected with the radiative decay of BMEC's are predicted and found to be concentrated between the luminescence lines of the bound exciton and the free exciton. Furthermore, analytic approximate expressions for the electron and hole densities are obtained and their shapes are extensively discussed.
Theory of coherent quasi‐steady states in NQR multipulse experiments
Authors: Ermakov V. L. , Ya. Osokin D. 
Published: July 2007

AbstractOn the basis of the average Hamiltonian theory the influence of the pulse sequence t — (τ — t — 2τ — t — τ)n on a system of two dipolar coupled equivalent spin‐1 nuclei each subject to local electric field gradients is studied. Using a fictitious spin‐1/2 formalism a general method is developed for solving the Liouville equation for such spin systems, leading to results which reproduce the experimentally observed quasi‐steady state of magnetization in nitrogen‐14 pulse experiments. Expressions for the density matrix of the system in terms of the effective time n4τ and the parameters characterizing the quadrupolar and dipolar interactions are obtained.
Forbidden luminescence and resonance Raman scattering of bound exciton states in CdS
Authors: Baumert R. , Broser I. , Gutowski J. , Hoffmann A. 
Published: July 2007

AbstractA series of six energy levels is found at energy distances 2.5, 3.8, 4.7, 6.1, 7.0, and 8.3 meV on the high energy side of the neutral‐acceptor bound exciton I1 in CdS. They appear in the emission and absorption spectra of some freshly grown virgin crystals and of some crystals damaged by laser‐irradiation. Resonance Raman scattering (RRS) establishes the new levels as intermediate states in every high quality crystal. These levels are interpreted as excited states of the bound exciton I1. The direct radiative recombination is forbidden due to parity selection rules. These selection rules are removed in symmetry disturbed crystals, at high excitation intensities, or by recombination with phonon participation. In consequence they are detected as forbidden luminescence, as LO phonon replica, or as 1‐LO‐ and 2‐LO‐Raman lines. The 2‐LO scattering cross section of the energy region of bound excitons in CdS is determined.
Anomalous transient‐time dispersion in amorphous solids: Oxadiazole
Authors: Crisa N. 
Published: July 2007

AbstractHole transport in thin films of an organic disordered solid (oxadiazole) is studied by time‐of‐flight techniques, as a function of sample thickness and applied field. The experimental data are analyzed in terms of the theory of stochastic non‐Gaussian transport by Scher and Montroll, showing the validity of this model. The last section is devoted to an evaluation of the hole drift mobility: its resulting values are extremely low (<10−6 cm2/Vs).
A new semiempirical formula for superconducting transition temperatures of metals and alloys
Authors: Surma M. 
Published: July 2007

AbstractA new formula describing the superconducting transition temperature is presented. The electron–phonon coupling constant λ and the phonon frequency spectrum parameters of a material are the quantities which define the transition temperature Tc of superconductors. A comparison between the experimental and calculated values of Tc for metals and alloys confirms the validity of the new formula presented in this paper.
Far‐infrared photoconductivity spectroscopy of shallow acceptors in InSb
Authors: Meisels R. , Kuchar F. 
Published: July 2007

AbstractAcceptor excitation as well as ionization spectra are observed in InSb doped with Ge and Cd using Fourier transform spectroscopy and photoconductivity techniques. Best agreement with theoretical results is obtained with the following values for the Luttinger parameters: γ1 = 36.13, γ2 = 16.24, and γ3 = 17.34 which were recently deduced by Littler et al.
Spin‐lattice relaxation theory of excited triplet‐state impurities in molecular crystals
Authors: Sugakov V. I. , Shtepa Yu. D. 
Published: July 2007

AbstractThe processes of spin‐lattice relaxation of the excited local triplet states in molecular crystals at low temperatures are investigated. The coupling of the translational and rotational motion of the molecule (TRC relaxation mechanism) is chosen as the major phenomenon, leading to the coupling of the spin system with acoustic vibrations. The general expressions for the spin‐lattice relaxation time of the triplet centre in molecular crystal with impurities are derived taking into account the change of force constant due to the impurities. The angular, field, and temperature dependences of SLR time are calculated for an isotopic impurity in naphthalene crystal. The results of calculation are in accordance with available experimental data.
Study of various approximations for the continuum planar potentials at channeling I. Monoatomic crystals
Authors: Dedkov G. V. , Gorshokov A. M. 
Published: July 2007

AbstractA detailed analysis of different approximations for the continuum planar potentials under the channeling conditions is given. The continuum potentials for positrons (electrons) channeled in (110) and (100) planes in crystals of diamond, silicon, and tungsten are calculated in different approximations to the screening function. The model of an atom with a piecewise exponentially decaying electron density is discussed. The influence of the thermal vibrations and the atomic shell structure on the potentials is investigated. Some estimates of the photon energy radiated at channeling of 56 MeV electrons in (110) planes of C are given.
Magnetooptical study of the fundamental absorption edge in Cd1−xMnxTe
Authors: Khoi Nguyen The , Ginter J. , Twardowski A. 
Published: July 2007

AbstractThe fundamental absorption edge in Cd1−xMnxTe for x = 0.01, 0.05, 0.10, 0.20 in the Faraday configuration, at magnetic fields up to 5 T and in the temperature range 1.8 to 293 K is studied. Moreover the exciton spectrum of extremely thin samples (of less than 1μm) is measured. An additional structure on the σ‐edge is found. The appearance of that structure is supposed to be the effect of the mixing of exciton states in the zincblende structure.
Quantum transport in quasi‐one‐dimensional systems
Authors: Arora V. K. , Prasad M. 
Published: July 2007

AbstractThe results of quantum transport investigations in quasi‐one‐dimensional systems assumed to be of cylindrical geometry are presented. Quantum size effect is important when the de Broglie wavelength (λD) of confined electrons becomes comparable to radius R0 of the cylindrical geometry. In the extreme quantum‐limit, λD ≫ R0, the resistivity is found to be proportional to λ2D/A, where A = πR20 is the area of cross‐section. Similar behavior is found for electrons confined to a strong magnetic field, λD ≫ λ = (hc/eB)1/2, when A = πλ2 is the area of the cyclotron orbit of radius λ in a magnetic field of strength B. The quantum transport behavior of electrons confined in thin wires is found analogous to those confined in a magnetic field.
Localization effect in CrRh alloys
Authors: D˘adålat D. , Petrişor T. , Giurgiu A. , Pop I. 
Published: July 2007

AbstractMagnetic susceptibility measurements of CrRh alloys are reported. Below the Néel temperature a temperature independent magnetic susceptibility is observed for the samples containing 10.9 and 14.5 at% Rh. A decrease of the magnetic susceptibility as a function of temperature is observed for samples containing between 5.14 and 14.5 at% Rh in the paramagnetic region. A slight localization, induced by Rh impurities on the host Cr atoms, is proposed in order to explain these peculiar behaviours. The magnetic phase diagram is also given. The Néel point rapidly increases at the beginning, with increasing Rh concentration, and then slowly decreases, giving rise to a large maximum at about 6 at% Rh.
On the schrödinger spin‐exchange ferromagnet
Authors: Brown H. A. 
Published: July 2007

AbstractThe thermodynamic behavior of a ferromagnet whose interactions are described by the Schrödinger spin‐exchange operator is investigated. The transition temperatures, magnetization, susceptibility, exchange energy, heat capacity, and entropy are calculated for general spin and lattice coordination number using the constant‐coupling approximation. Both first‐ and second‐order phase transitions are found. Comparison with some results of the high‐temperature expansion method shows some qualitative agreement.
Quantumchemical studies of chemisorption at anion or cation sites of the GaP (110) surface. Coverage dependence of adsorption energy and equilibrium in cases of positive and negative partial charge injection
Authors: Lorenz W. , Engler C. , Nechwatal A. , Adler G. 
Published: July 2007

AbstractChemisorption of electronegative or electropositive atoms at anion or cation sites of a relaxed GaP (110) surface is investigated in the TB approximation, with parameters corresponding to fluor or lithium adsorption. Local densities of states and the dependences of the surface Fermi energy, partial charge injection, adsorption energy, and adsorption equilibrium upon the adsorption density are reported.
Electromagnetic wave propagation in the uniaxial antiferromagnetic crystals FeF2, CoF2, and MnF2
Authors: Brandmüller J. , Lehmeyer A. , Häussler K. M. , Merten L. 
Published: July 2007

AbstractIn the most general form the matter equations of electrodynamics contain the magneto‐electric tensor in addition to the electric and magnetic permeability tensor. By group‐theoretical methods, however, it is shown that for crystals belonging to the magnetic point group 4′/mmm′ the magneto‐electric tensor vanishes. Important examples for this point group are the antiferromagnets FeF2, CoF2, and MnF2. Regarding this essential simplification a generalized Fresnel's equation of the wave normals is derived for these antiferromagnetic crystals. The Fresnel's equation has two solutions describing the magnitudinal and directional dispersion of the refractive index for the two corresponding waves. The limiting cases of these two solutions agree with results already known from literature. Besides, the polarization of both waves is determined.
Low‐temperature fluctuational motion of dislocations in crystals I. Quantum and dissipative effects
Authors: Osetskii A. I. 
Published: July 2007

AbstractA mechanism underlying fluctuational bending of dislocation segments is considered which is based on periodical ordering in the thermal motion of atoms near the dislocation core. Basic principles of calculating the probability of dislocation unpinning from local obstacles due to the fluctuations are formulated. As found, the interaction of dislocation segments experiencing fluctuational bending with phonons and/or conduction electrons, described in the framework of the usual dissipation model, can result in a reduction of the energy of atoms near the dislocation core during the fluctuation. Consequently, the effective activation energy of the dislocation unpinning from local obstacles is increased, i.e. the mean velocity of the activated dislocation motion drops. Activated dislocation motion at low temperatures is analysed with an account of the possible quantum mechanical fluctuations which can arise in condensed structures owing to the correlation of atomic zero point vibrations. An expression is derived for the probability of low temperature fluctuational dislocation with allowance for quantum mechanical effects.
Spin dependence and the interrelation between staggered and uniform field properties in the exact solution of one‐dimensional mixed‐spin ising ferrimagnets
Authors: Yousif B. Y. , Bowers R. G. 
Published: July 2007

AbstractAn exact statistical mechanical calculation of certain properties of a one‐dimensional mixed‐spin Ising model is presented. Particular attention is given to the behaviour at very low temperatures. Investigations are centred on questions of spin dependence and of the relation between uniform and staggered field properties.
Nonlinear Excitation of New Emission Bands in Kcl Crystals Containing Color Centers
Authors: Casalboni M. , Francini R. , Grassano U. M. , Pizzoferrato R. 
Published: July 2007

AbstractNew luminescence bands are observed in KCl containing F and F‐aggregate centers under strong excitation with an infrared laser. All these emission bands occur at energies higher than those of the pumping beam. These „up‐conversion”︁ emissions are assigned to transitions from higher excited states of color centers populated by means of multiphoton absorption. Specific relations between the centers and the emission bands are also discussed.
Kumakhov Radiation Energy Losses of Ultrarelativistic Electrons and Positrons
Authors: Kanloev A. M. 
Published: July 2007

AbstractThe process of spontaneous radiation from ultrarelativistic electrons and positrons in planar channels (the Kumakhov effect) is studied by means of computer modelling. The energy loss for radiation is investigated depending on the angle of particle in the crystal. A significant difference in the absolute energy losses of electrons and positrons is noted.
Investigation of the Electronic Structure of VFeH Alloys by Positron Annihilation
Authors: Szuszkiewicz M. , Chojcan J. , Ostrasz A. 
Published: July 2007

AbstractThe angular distributions of annihilation quanta (AD) coming from the two‐photon annihilation of a positron‐electron pair are measured for V0.96Fe0.04Hx alloys. The results are discussed in view of application to the description of the electronic structure of the system under consideration within the rigid band approximation. It is found that the explanation of results obtained requires the assumption of d‐like electron states in the vicinity of the Fermi energy capable to be occupied, beginning from a certain concentration of (4s + 3d)‐like electrons.
Investigation of Structural Defects in the Amorphous Ferromagnetic Alloy Fe40Ni40P14B6
Authors: Grimm H. , Kronmüller H. 
Published: July 2007

AbstractStructural defects in the amorphous ferromagnetic alloy Fe40Ni40P14B6 are investigated by measuring the magnetic polarization in the region of approach to ferromagnetic saturation. From the field dependence of the high‐field susceptibility it is concluded that the main source of internal stresses may be characterized as quasi‐dislocation dipoles. These structural defects are shown to be rather stable under annealing treatments and may be produced by small plastic deformations.
Optical Phonons in Amorphous Silicon Oxides. I. Calculation of the Density of States and Interpretation of LoTo Splittings of Amorphous Sio2
Authors: Lehmann A. , Schumann L. , Hübner K. 
Published: July 2007

AbstractUntil now there exists no calculation of the phonon density of states of amorphous SiO2 and related materials, which could interpret the experimentally detected splittings between longitudinal and transverse modes in their optical phonon spectra. This problem is solved by taking into account the influence of the vibrationally induced polarization on the motion of atoms. A simple model for the description of this polarization in non‐crystalline SiO2 is developed and used for the calculation of the density of states of LO and TO phonons in the framework of a coherent potential approximation for structurally disordered systems. This new method leads also to the determination of the IR response function and to simple analytical expressions for the microscopic parameters of the model, i.e. the bond angle at the oxygen atom and transverse dynamic effective charges. The values of these parameters are determined from IR transmission spectra of thin SiO2 layers prepared with the help of different methods. The calculated density of states and IR response function are in good agreement with corresponding experimental results.
Manifestation of Spin–Rotation Coupling in Intersystem Crossing in a Rotating Impurity Molecule
Authors: Sildos I. , Sild O. , Dolindo I. 
Published: July 2007

AbstractThe dependence of the probability of the singlet‐triplet S1–T1 radiationless transition on the total angular momentum J is observed for an NO impurity molecule in the KCl matrix. This dependence disappears in the presence of a magnetic field (H ≧ 0.2 T), which breaks the spin‐rotation coupling.