bluuebunny/crossref_metadata_2025_split huggingface dataset:
Band tails in the density of states of mixed crystals
Authors: Monecke J. 
Published: July 2007

AbstractThe Saxon‐Hutner theorem proves the existence of band tails in the density of states for a wide class of models of mixed crystals. These band tails are discussed in detail by Lifshitz. They are not obtained, however, in self‐consistent theories like the coheren, potential approximation or in the theory of Klauder. The non‐existence of band tails in the self‐consistent theories is related to a wrong percolation behaviour of the self‐energy and it is proved that a recently proposed alternative theory results in a density of states which fulfils the Saxon‐Hutner theorem. Further it is shown that the density of states of binary mixed crystals exhibits all Van Hove singularities of both pure constituents.
Chromium centres in 3 CdSO4 · 8 H2O single crystals
Authors: Prasad P. Sathya Sainath , Radhakrishna S. 
Published: July 2007

AbstractThe optical absorption spectra of 3 CdSO4 · 8 H2O single crystals doped with Cr3+ is recorded at 300 and 80 K; the crystal field transitions are assigned and the B, C, Dq parameters evaluated. Polarisation investigations are undertaken to establish the exact electric dipole transitions and the exact magnetic dipole transitions. Splitting of the bands (differences between the parallel and perpendicular polarised spectra) due to the non‐cubic fields acting on the chromium (III) ion are not observed though two inequivalent cadmium atoms exist in the lattice. Also no lowering of symmetry is observed either from the low temperature spectra or the polarised spectra. Radiation damage studies are undertaken to study the mechanism of the formation of Cr3+ to Cr+ and the valence state effect on the electronic transitions. The effect of space charge compensating vacancies on the electronic transitions and its effect on the crystal field strength is studied using the radiation damage spectra. The formation of Cr+ from Cr3+ through Cr2+ is well explained. The theoretically calculated values coincide well with the experimentally observed values for the octahedral symmetry for both, Cr3+ and Cr+ ions in 3 CdSO4 · 8 H2O lattice.
Strong‐field scheme for C (d3) and the Spectra of Ruby and Cr2O3
Authors: Zhao Sang‐Bo , Zhou Kang‐Wei 
Published: July 2007

AbstractIn order to calculate the energy spectra of Cr3+ ions in a C3v symmetry crystal field, a radial orbit function is used for the d‐electrons in bounded ions having a form between the SCF wave functions of Richardson and Watson. In addition the complete strong field matrices of C(d3) are built up for the first time by a simplified strong‐field scheme, in which the Griffith standard bases of the O double group are taken as the starting point. Then the absorption spectra (including the spin‐allowed and spin‐forbidden spectra) of Cr3+ in ruby and Cr2O3 crystals are calculated. The theoretical results, with consideration of vibronic, are quite consistent with experiments. Thus the mechanism of the absorption spectra of Cr3+ in these two crystals is well explained. This scheme of calculating spectrum parameters by radial orbits greatly reduces the number of fitting parameters. This simplified strong‐field scheme can be extended to any dn system and any subgroup of Oh.
Theoretical calculation of the optical constants of transition metal silicides
Authors: Huang Tzu‐Yu , Lue Juh‐Tzeng 
Published: July 2007

AbstractA quantum theory of screening charges exploiting orthogonalized pseudowave functions to evaluate the conduction electron charge density due to d–p hybridization is used to solve the optical constants of transition‐metal silicides. The dependence of the complex refractive indices on photon wave vector, carrier relaxation time, valence charges, and core binding energies for TiSi2 is calculated. The results show much better agreement with the observed values than those from the classical Drude model.
Energetic and temporal characteristics of picosecond pulse self‐diffraction in silicon
Authors: Apanasevich P. A. , Asimova V. D. , Zaporozhchenko V. A. , Zaporozhchenko R. G. , Pilipovich I. V. 
Published: July 2007

AbstractSelf‐induced diffraction of ultrashort pulses in silicon crystals at high incident light intensities is studied. A theoretical model is presented which takes into account the band‐filling effect as a major mechanism of light‐induced grating anharmonicity. Experimental results on the energetic and temporal characteristics of four orders of diffraction are in good agreement with this theoretical model.
A new empirical many‐body potential energy function. Application to microclusters
Authors: Erkoç S. 
Published: July 2007

AbstractA new empirical many‐body potential energy function is proposed which comprises two‐ and three‐body interactions. The two‐body potential is a kind of hybrid function and the three‐body potential is expressed in terms of the two‐body interactions. The parameters of the potential energy function can be easily evaluated using dimer data and the bulk cohesive energy of the system considered. The proposed potential energy function is parameterized for several elements in f.c.c., b.c.c., and diamond structures and is applied for the investigation of structural stability and energetics of microclusters. The agreement between the present results and literature values is good.
Incommensurate–commensurate transition driven by concentration in rare gas mixtures adsorbed on graphite
Authors: Marti C. , de Beauvais C. , Ceva T. , Croset B. , Goldmann M. 
Published: July 2007

AbstractAn unexpected anomaly is observed in the phase diagram of argon‐xenon and krypton‐xenon mixtures adsorbed on graphite: less krypton than argon is needed to drive the incommensurate–commensurate transition. A mean lattice model is developed, which describes the krypton‐xenon mixture, however, local disorder terms must be added to obtain agreement with the argon‐xenon results.
Exciton‐grating induced metamorphoses of the degenerate four‐wave mixing spectra in the giant two‐photon resonances of the excitonic molecules in CuBr and CuCl
Authors: Mizutani G. , Nagasawa N. 
Published: July 2007

AbstractIt is demonstrated that the spectral shape of the DFWM generation in CuBr and CuCl show remarkable metamorphoses when the polarization of the incident two beams is set parallel to each other. According to the polarization character of the nonlinear polarization, these phenomena are concluded to be due to higher order non‐linearity than χ(3) where the really populated exciton grating contributes.
Double periodic peierls phases
Authors: Mertsching J. 
Published: July 2007

AbstractDouble periodic Peierls phases may arise in quasi‐one‐dimensional conductors containing two groups of electrons with different Fermi wave numbers, e.g. in very strong magnetic fields. For a nearly half‐filled conduction band, the Peierls distortion may be a kink lattice, a polaron lattice, or a nonlinear superposition of a kink lattice and a polaron lattice. The lattice distortion, the band structure, the magnetic moment, and the chemical potential in the ground state are calculated as a function of the magnetic field strength and the density of electrons.
An interpretation of the pressure dependence of EPR zero‐field splitting of Mn2+ in Na2ZnCl4 · 3 H2O
Authors: Lu Ke‐Qin , Guo Sheng‐Li , Wu Ping‐Feng 
Published: July 2007

AbstractThe relationship between the zero‐field splitting parameter D and the C3v crystalline potential components for Mn2+ ions is established by using the parametrization d‐orbital theory proposed by Zhao et al. The pressure dependence of D of Mn2+ in Na2ZnCl4 · 3 H2O is calculated. The results agree well with the values measured experimentally indicate that the D‐value increase with increasing pressure is caused most dominately by changing in the angle θ and next by the change in the bond length R under pressure.
Observation by ESR of electrons localized at intrinsic shallow traps in silver halide systems
Authors: Eachus R. S. , Olm M. T. , Janes R. , Symons M. C. R. 
Published: July 2007

AbstractElectrons shallowly trapped at intrinsic sites in single‐crystal and polycrystalline samples of AgBr, AgCl, and mixed iodohalides are observed by ESR. The results are consistent with a model in which the electron is localised by a silver ion in an effective mass state. The observed ESR linewidths are explained in terms of exchange narrowing. The effect of iodide on the free or nearly‐free electron g‐value is determined. Addition of iodide to AgCl or AgBr resulted in alloy line broadening. The amount of shallow trapping depended in part on dislocation density. In polycrystalline samples of AgBr, cyclotron resonance of the free electron polaron is observed simultaneously with the ESR signals from localized electrons. From the linewidth of the cyclotron resonance signal, the mobility of the free electron polaron in some polycrystalline samples is determined to be the same as that measured previously in very pure single crystals of AgBr.
Nucleation of superconductivity in ceramic oxides
Authors: Saif A. G. , Chela‐Flores J. 
Published: July 2007

AbstractThe nucleation of superconductivity in the interior of a bulk specimen, as well as at the surface of ceramic superconductors is discussed on the base of phenomenological equations, in which superconductivity coexists with antiferromagnetism. The prediction of the evolution of Hc2 with small variations on the coupling constant may serve to test the underlying phenomenological theory.
Dispersion properties of submicron‐thin CdS crystals
Authors: Reznichenko V. Ya. , Strashnikova M. I. , Cherny V. V. 
Published: July 2007

AbstractThe data are summarized, obtained by interference measurements at 4.2 K, on the dispersion of the refractive index n(λ) of submicron‐thin CdS single crystals. The series of the dispersion curves, n(λ), measured for crystals of different thickness, is approximated by theoretical dependences allowing for spatial dispersion. These data present clear evidence that the refractive index depends on the thickness of crystals provided their dimensions are comparable with the wavelength of light or smaller than the latter.
Frequency‐modulation optical spectroscopy of niobium. Theory and experiment
Authors: Magnitskaya M. V. , Kulikov N. I. , Shelekhov A. L. 
Published: July 2007

AbstractBoth, experimental and theoretical investigation are made of frequency‐modulated optical spectrum of Nb. The experimental spectra are measured in the range of light energy from 1 to 6 eV. The theoretical studies are performed in the framework of density functional formalism using the linearized hybridized KKR (LHKKR) method for self‐consistent calculations of band structure and wave functions. A reasonable coincidence between theoretical and experimental results is obtained.
Continuum Approximation of the General Inverse‐Power Lattice Sums in Cubic Crystals
Authors: Turner M. D. , Mohazzabi P. 
Published: July 2007

AbstractThe continuum approximation of Born and his collaborators for the calculation of simple lattice sums in cubic crystals is extended to the case of general lattice sums. The results show excellent agreement with the exact values across the board, thus providing a ground for further applications of the continuum model.
Stark Effect and the F‐Center Excited States
Authors: Ponnambalam M. J. 
Published: July 2007

AbstractUsing a simple model of the F‐center, it is shown that whether the |2Γ〉 state is above or below |2Γ〉 in emission is not quite clear from the existing Stark data. In light of this, the relative merits of the different Stark effects are critically analyzed. It is shown that fresh data on the field‐induced changes in the radiative life‐time can unambiguously settle the relative position of the |2Γ〉 state with respect to |2Γ〉.
The Theory of Elastic Wave Propagation in Inhomogeneous Media
Authors: Fokin A. G. , Shermergor T. D. 
Published: July 2007

AbstractThe theory of longitudinal and transverse elastic waves is considered within the framework of random field theory. A method is developed for solving problems associated with the scattering of waves by inhomogeneities of the density ϱ(r) and of the elastic modulus tensor λ(r) which is valid for the whole wavelength range. The scattering index γ, the phase v, and the group velocities c are computed using the Bourret approximation with allowance for spatial dispersion. Asymptotic expressions for γ, v, and c are obtained for the long (compared with the effective sizes of the scattering regions), short, and ultrashort wave ranges. In the latter case results can be obtained only by allowing for spatial dispersion.
Ferroelectric Phase Transition in (NH4)2BeF4. Possibility of Molecular Distortion Type of Transition
Authors: Bajpai P. K. 
Published: July 2007

AbstractThe possibility of molecular distortion type (MD‐type) microscopic mechanism (recently proposed for (NH4)2SO4) and the role of BeF ion in the phase transition of amonium fluoberryllate are examined by analysing crystal structural data in both, the paraelectric and ferroelectric phases. The results show that BeF ion attains a dipole moment in the FE phase and contribute significantly to the spontaneous polarisation (Ps). The computed value of Ps due to NH and BeF ions (0.21 μC/cm2) matches satisfactorily with the experimental results. The nature of the phase transition is found to be mainly of MD‐Type. The soft mode of the transition is proposed as a mixed mode having the internal mode of BeF ion and translatory modes of NH ions.
Spinodal Decomposition in Semiconductor Alloys
Authors: Dugaev V. K. , Petrov P. P. 
Published: July 2007

AbstractA generalization is proposed of the lattice gas model which takes into account the presence of free Fermions in the system. In the framework of this approach the Landau free energy expansion is constructed. The influence of the electron energy spectrum particularities on the spinodal decomposition in the semiconductor alloys is examined.
On the Band Structure of Ultrathin Layer Semiconductor Superlattices
Authors: Gushchina N. A. , Nikulin V. K. , Tzarev Yu. N. 
Published: July 2007

AbstractA band structure calculation of (GaAs)m(AlAs)m superlattices with m = 1, 2, 3, 4 is made by the recursion method in the Bloch sum basis. A dependence of the direct band gap width E on thickness m of the alternating layers is obtained which agrees well with other calculations and experimental photoluminescence data. The scheme of determination of the sp3s* Hamiltonian parameters proposed earlier is modified which affects significantly the results for the band discontinuities at the GaAs/AlAs heterojunction and for the “local” band gap width Eg of superlattices obtained from an analysis of the local density of electron states averaged over the layers parallel to the interface. A comparison of the lattice‐averaged band gap width E with the local width Eg shows that the latter yield an underestimated value for the gap width.
Polarons in Trans‐Polyacetylene and Polyyne Chains
Authors: Osipov V. A. , Bochnacka G. , Fedyanin V. K. , Malek J. 
Published: July 2007

AbstractThe polaron formation in trans‐polyacetylene as well as polyyne chains is investigated in the framework of the finite‐band scheme. The physical characteristics of polarons (spin, charge, formation energy, width, binding energy) are calculated. The bipolaron, tripolaron, and polarexciton states in polyyne are considered. A self‐consistent discrete analysis of polaron states is presented. Comparison between the finite‐band and discrete calculations is done.
Plasmon Dispersion in Trans‐Polyacetylene
Authors: Haase M. , Taut M. 
Published: July 2007

AbstractBy frequency momentum analysis, the plasmon dispersion of crystalline trans‐polyacetylene is calculated for q parallel and perpendicular to the chains. Both experimentally observed features: linear dispersion at medium q, and a drop for small q, are obtained. It is suggested that the latter feature is much more pronounced for q perpendicular to the chains (not investigated experimentally) than parallel.
Longitudinal Thermogalvanomagnetic Effects in Dilute Magnetic Semiconductors in a Quantizing Magnetic Field
Authors: Lyapilin I. I. , Karyagin V. V. 
Published: July 2007

AbstractThe temperature and magnetic field dependence of the longitudinal thermogalvanomagnetic coefficients in dilute magnetic semiconductors is calculated in a quantising magnetic field using Kubo's formula.
On the Mechanism of Vibrational Relaxation of Two‐Centre Excitions in Solid Neon
Authors: Fugol I. Ya. , Ratner A. M. , Rybalko Yu. I. , Steshenko Yu. L. 
Published: July 2007

AbstractThe population of vibrational levels of the lowest‐lying excimer term in solid neon is reproduced in the experimental luminescence spectra. The analysis of the kinetic equation suggests that the reproduced population can be caused by the vibrational relaxation only in the case of a great heat relase due to the two‐centre excitation jumps through the lattice.
Exotic Glassy Phase in the Site‐Diluted Transverse Ising Model at Zero Temperature ?
Authors: Busiello G. , de Cesare L. , Lukierska‐Walasek K. , Walasek K. 
Published: July 2007

AbstractA self‐consistent diagrammatic approach is used for studying the zero‐temperature properties of the three‐dimensional site‐diluted transverse Ising model via a path‐integral representation. It is found, that the peculiar competition between random and quantum fluctuations inhibites the occurrence of a second‐order phase transition and an exotic phase with some spin‐glass‐like characteristics appears. This should provide a plausible explanation of recent experiments on some mixed crystals.
Theoretical Description of Light Diffraction on Acoustic Pulses in Bragg's Region
Authors: Bodzenta J. , Kleszczewski Z. 
Published: July 2007

AbstractAs a result of theoretical analysis an equation is obtained describing the dependence of deflected light intensity on diffraction angle and time. Considerations are carried out for an isotropic, nonmagnetic dielectric medium and Gaussian light beam. The inverse problem is solved, too. Basing on its solution an acousto‐optic method for acoustic pulse parameter analysis is proposed. It allows to reconstruct the acoustic wave envelope basing on the diffraction pattern. This method may be used in investigations of acoustic properties of solids and liquids.
The Investigation of the Ferroelectric Phase Transition in Cluster Systems of Order–Disorder Type
Authors: Yukhnovskii I. R. , Korynevskii N. A. 
Published: July 2007

AbstractThe description of second‐order ferroelectric phase transitions in cluster systems of order–disorder type in the frames of the collective variables method is proposed. By means of the canonical Hubbard operator technique the Ising‐like form of the Hamiltonian is obtained. The partition function is represented as a functional integral over collective variables. The classification of collective variables according to their role in forming of the ferroelectric order parameter is made. For a consistent consideration of critical fluctuations of the order parameter a non‐Gaussian, quartic basic measure density is obtained.
Lineshape of Light Absorption by Thermalized Frenkel Excitons under Band‐to‐Band Transitions
Authors: Grigorchuk N. I. , Grechko L. G. 
Published: July 2007

AbstractIt is assumed that sublevels of the lowest exciton band in consequence of pumping are filled by excitons, which thermalize during their lifetime. The probability of throwing of such excitons to the next more higher lying band by means of another radiation source is investigated. By simple assumptions, when the distance between the exciton bands is much greater than the bandwidth difference and the damping parameter is independent of the frequency, the lineshape of light absorption under band‐to‐band transitions is calculated. For small damping in the case of broad bandwidth it is shown that the absorption is determined rather by temperature of the crystal than by bandwidth difference. In the case of narrow bands only that difference plays the essential role.
Nature of Hydrogen Bonding in Si‐A‐Center
Authors: Gutsev G. L. , Myakenkaya G. S. , Frolov V. V. , Glazman V. B. 
Published: July 2007

AbstractThe configurations containing one or two hydrogen atoms in a A‐center are calculated by the MNDO and Xα‐DV methods. It is established that the hydrogen atom is bound with the oxygen of the A‐center forming a new paramagnetic center. The electrical activity of the A‐center is decreased by hydrogen passivation of the two silicon dangling bonds. However, the defect states are not removed from the band gap.
Localized States in Crystalline Semiconductors
Authors: Kouimtzi S. D. 
Published: July 2007

AbstractHopping conduction is studied in crystalline Si, Ge, InSb, GaAs, and InAs. Sufficient degree of damage induced by electron irradiation allows the observation of conductance by nearest neighbour hopping, or variable range hopping. Evidence of electron‐electron interaction in the hopping conductance is presented.
Antiferromagnets with Random Anisotropy. Influence of the Dimensionality
Authors: Richter J. , Skomski R. 
Published: July 2007

AbstractThe influence of a small random anisotropy on the ground‐state properties of a classical antiferromagnet with an easy z‐axis in two, three, and four dimensions is discussed. The random anisotropy causes a slightly noncollinear magnetic structue, in which the tipping of the sublattice magnetisations varies over the system. The tipping is largest in two dimensions and decreases rapidly with increasing dimension. The magnetisation‐versus‐field behaviour is strongly influenced by the random anisotropy in the case of fields parallel to the easy z‐axis and close to the spin‐flop transition for dimensions two and three. A smearing out of the spin‐flop transition is indicated, which is particularly pronounced in two dimensions. The dimension four is the marginal dimension, where the small random anisotropy is almost negligible against the coherent part of anisotropy.
Hyperfine Fields at Implanted 12Boron in F.C.C. Metals
Authors: Tompa K. , Pirlot R. , Grenacs L. , Lehmann J. 
Published: July 2007

AbstractKnight shift data of implanted 12B are used to estimate hyperfine field, Hhf(s), and Knight's ξ factor for Al, Cu, Ag, and Au metals at the boron site. In the Rh, Pd, and Pt transition metals the Knight shift and the Korringa relaxation time T1e are used to estimate the s and d terms of the hyperfine field. In addition to the data from the literature T1e is measured in Rh metal, and it is proved experimentally that in Rh, Pd, and Pt over T1e there is no other spin–lattice relaxation mechanism around room temperature. The hyperfine fields at the boron are compared with those at the muon (+) in these metals.
Raman Spectroscopy of Soft and Rigid Modes in Ferroelectric TlInS2
Authors: Burlakov V. M. , Ryabov A. P. , Yakheev M. P. , Vinogradov E. A. , Melnik N. N. , Gasanly N. M. 
Published: July 2007

AbstractLow‐frequency Raman spectra of a TlInS2 single crystal in the vicinity of a ferroelectric phase transition are reported. In the ferroelectric phase a soft mode interacting with some rigid modes is observed. The temperature dependence of the soft mode frequency is found to be proportional to (Tc – T)1/2. An unusual behaviour of the rigid mode (ω = 20 cm−1) is observed. This fact is interpreted in terms of inherent lattice defects which cause nonhomogeneous broadening.
Triplet Molecular Excitations in Potassium Halide Cyanide Crystals. II. The K(CN)xCl1–x Mixed System
Authors: Camargo S. S. , von der Weid J. P. 
Published: July 2007

AbstractThe decay kinetics and luminescence intensity of the UV emission associated with the a3II → X1Σ+ electronic transitions of the CN– molecular ions in K(CN)xCl1–x mixed crystals are investigated between 10 and 450 K. At the lowest temperatures the emission lifetimes as functions of the CN– concentration x show a transition between localized and collective behaviours around the percolation threshold for the CN– sublattice. A low temperature non‐radiative decay process is observed and is attributed to the coupling of the relaxed excited states of CN– clusters to translational–rotational cyanide‐like phonon modes.