bluuebunny/crossref_metadata_2025_split huggingface dataset:
Dipole Forbidden Transmission of Magnetopolaritons in CdSe
Authors: Kochereshko V. P. , Röseler J. , Uraltsev I. N. , Henneberger K. 
Published: July 2007

AbstractTransmission spectra of the well‐known dipole forbidden excitonic lines AF and AL are studied in magnetic fields up to 18T in Faraday and Voigt configuration. Magnetic field induced shifts are observed and carefully interpreted within a theoretical model including mixingof A‐ and B‐valence bands. The unusual shift of line AF in the Voigt configuration is explained as a polariton effect. Furthermore, the absence of any doublet structure in both geometries is confirmed by theoretical investigations.
Diffusion and Localisation in Random Systems
Authors: Elyutin P. V. , Hickey B. , Morgan G. J. , Weir G. F. 
Published: July 2007

AbstractDirect computer experiments are conducted on electron diffusion in a simple cubic lattice where the disorder corresponds to the Anderson model. Results for the onset of total localisation are in good agreement with other numerical estimates and it is found that the critical value of the parameterW/ZV is (17.7/6). A random structurally disordered system is also investigated with hopping integrals given by V(r) = ‐V0 exp (‐r/a) and found that localisation occurs at the critical value a = 3 ± 0.3. Thisis in agreement with the only other numerical estimate but is substantiallydifferent from theoretical calculations.
Ground and Excited States of Tl+ Impurity in KCl Crystal by the Use of the Green's Function Method
Authors: Moretti P. , Ranfagni A. , Agresti A. 
Published: July 2007

AbstractThe problem of determining the position of impurity levels in ionic crystals is considered in the framework of the Green's function method which allows the location of these levels with respect to the valence and conduction bands of the host crystal. The case of KCl:Tl+ is examined both, in the ground (a21g) and first‐excited(a1gt1u) state configuration, in order to make possible acomparison between the theoretical predictions and the experimental absorption energies. The calculation is first performed in the one‐electronscheme; the Coulomb (G ≈︁ 0.3 eV) and the spin—orbit (ζ ≈︁ 0.7 eV) interactions are considered later perturbatively since the one‐electron energy difference (W0 ≈︁ 6 eV)is sufficiently high. In such a way a more plausible energy‐level scheme is obtained with respect to molecular‐orbital computations.
Vibrational Relaxation and Hot Luminescence of Ne*2 Centers in Solid Neon
Authors: Gaethke R. , Gürtler P. , Kink R. , Roick E. , Zimmerer G. 
Published: July 2007

AbstractHot luminescence of Ne*2 centers (molecular type self‐trapped excitons) in solid Ne is measured under state selectiveexcitation using synchrotron radiation. The luminescence spectra are analysed with the aid of a new theory on vibrational relaxation of the Ne*2 centers. It is possible to show that the rate of relaxation is slower for centers located at the surface than for centers in the bulkof the Ne solid. In combination with a direct measurement of the lifetimes (1 ns for 1∑+u; 5 μs for 3∑+u), absolute values for the relaxation rates are obtained. They range between 6.6 × 104 s−1 (bulk) and 6.6 × 103 s−1 (surface).
Electric Field Gradient at Gd in Gadolinium and Rare Earth Trifluoride Single Crystals
Authors: Budzynski M. , Goremychkin E. A. , Kochetov O. I. , Latuszynski A. , Mikolajczak P. , Mühle E. , Muminov A. I. , Subotowicz M. 
Published: July 2007

AbstractThe electric field gradient at the Gd nucleus in gadolinium and rare earth trifluoride single crystals, LaF3, CeF3, PrF3, NdF3, SmF3, EuF3, and GdF3 are measured by the method of integral perturbed angular correlation. The experimental data are compared with those of point charge model calculations and withthe results of other experiments such as Mössbauer spectroscopy, electron paramagnetic resonance, nuclear quadrupole resonance, and optical absorption. The results obtained for Gd in trifluorides of the light rare earth elements allow to conclude that the origin of the field gradient cannot be explained by the point charge model.
Spectral Diffusion and Triplet Exciton Localization in an Organic Glass
Authors: Jankowiak R. , Ries B. , Bässler H. 
Published: July 2007

AbstractPhosphorescence spectra of glassy 2‐bromonaphthalene films prepared by vapor deposition at 4.2 K are recorded under site‐selective excitation. The Stockes shift between absorption and emission origins gradually vanishes as the excitation energy is scanned across the inhomogeneouslybroadened profile of the T1 ← S0 OO transitionindicating a continuous decrease of the exciton diffusivity with exciton energy. The effect is rationalized in terms of stochastic hopping transport across a Gaussian density of states. A Monte Carlo computer simulation provides the basis for quantitative data interpretation. A criterion for excitonimmobilization is established.
Exact Density Functionals for Ground‐State Energies II. Details and Remarks
Authors: Englisch H. , Englisch R. 
Published: July 2007

AbstractStatements utilized or mentioned in the Part I are proved or discussed in detail. Especially it is shown that for finite‐dimensional state spaces the strictly positive densities being strictly less than two are E‐V representable and that the density functional by Lieb is differentiable at the E‐V densities.
Dependence of the Total Mobility in a One‐Band Model Applicationto n‐Type MoTe2
Authors: Conan A. , Bonnet A. , Zoaeter M. , Ramoul D. 
Published: July 2007

AbstractIn a one‐band model, the total carrier mobility relations, deduced from the Debye‐Conwell formula and Mathiessen's rule, are compared. With the help of these two laws the resultant mobility and the thermoelectric power (TEP) kinetic term variations are given. For n‐type MoTe2 single crystals, it is shown that a classical compensated semiconductor model can explain all the experimental results (electrical conductivity, TEP). A good accuracy is obtained by the use of Mathiessen'srule with exponents departing not much from the theoretical values. The model adopted is in good agreement with dichalcogenides band structure calculations. A donor level arising from the presence of bromine impurities, is located at 9.5 meV from the conduction band.
Two‐Spin Cluster Approximation in the Blume‐Capel Model
Authors: Lock S. L. , Lee B. S. 
Published: July 2007

AbstractA two‐spin cluster approximation based on a perturbation expansion of the free energy in powers of the order parameter is applied to calculate the properties of the Blume‐Capel model. The results obtained for the tricritical point are comparable to those of other two‐spin‐type cluster approximations.
Molecular Cluster‐INDO Calculations of Substitutional Defects inAlkali Halides
Authors: Matos Maria , Maffeo B. 
Published: July 2007

AbstractThe one electron level structure of LiF, NaF, LiCl, and NaCl crystals containing F and U centers and of NaCl crystal containing U3 centers are calculated using the INDO method and the molecular cluster (MC) approximation, with special emphasis in parameterisation. Spin polarisation is considered in the unrestricted Hartree Fock formulation of the method. The Fand U band transition energies are estimated using a limited configuration interaction (CI) calculation, and the electronic mechanism involved in the U3 absorption band are also examined. A rough estimation is made of the spin density at the substitutional H atom nucleus in NaCl.
Non‐Equilibrium Population of Fe3+ Electronic States after the Electron Capture I. 57Co in LiNbO3 and LiTaO3
Authors: Doerfler R. , Nagy D. L. , Pfannes H.‐D. , Putzka A. , Ritter G. , Zeman N. 
Published: July 2007

AbstractAll Zeeman levels of Fe3+ ions contribute intense and narrow lines to the Mössbauer emission spectra of LiNbO3:57Co and LiTaO3:57Co in 2 T ≤ Hext ≤ 7 T at 4.2 K. To explain the electronic spin and magnetic field dependence of the line intensities irreversible processes like the decoupling of electrons from the lattice or a field‐dependent slow relaxation should be involved. The existence of a long‐lived heated localized mode is ruled out.
Superconducting Properties of the Hexagonal‐Close‐Packed Alloy System TcZr
Authors: Chatterjee Parsathi 
Published: July 2007

AbstractThe theoretical formula of McMillan, modified via the multiple‐scattering theory of Gomersall and Gyorffy, is very successful in computing the electron—phonon coupling constant (λ) and the superconducting transition temperature (Tc) of elements and compounds from quantities readily obtainable from band structure work or approaches based on the scattering theory. However, for disordered solids this theory fails because of the breakdown of the translational symmetry used in the multiple scattering theory. In the particular case of substitutional alloys, the problem can still be solved however if, at each lattice point, the t‐matrix of an individual scatterer is replaced by a configurational average of the t‐matrices of the alloying materials (average t‐matrix approximation). This modified theory, which has already been successfully applied to some cubic substitutional alloys, is herein used to predict λ and Tc for the h.c.p. TcZr alloy system. The results indicate that this system has good superconducting properties.
Two Kinds of Self‐Oscillations and the Flip‐Flop Effect in a Semiconductor with Shallow Donors
Authors: Voronin I. N. 
Published: July 2007

AbstractSome non‐equilibrium electronic processes are considered which may take place in a homogeneous semiconductor at low temperatures. Conditions are found of the excitation of two kinds of self‐oscillations—those of electron temperature and electric field strength and of electrontemperature, density, and electric field strength — as well as the conditions under which a flip‐flop effect is to be expected. An adiabatic approximation is used assuming the energy and electric field relaxationtimes to be far smaller than the recombination time. The concentration of the free charge carriers (electrons) is regulated by an extrinsic illumination and impurity breakdown. Frequencies and amplitudes of the self‐oscillations as well as a flip‐flop time are estimated.
Angular Dependence of SSWR in Thin Metallic Films Approximate Analytical Solution
Authors: Jirsa M. 
Published: July 2007

AbstractThe spin‐wave resonance spectrum characteristics, namely the mode position, linewidth, and intensity, for a thin homogeneous conducting film with an uniaxial surface anisotropy and an arbitrarily oriented external magnetic field are determined analytically using the spin‐wave approximation. Comparison with the numerical data computed in the “full” model shows good agreement for all spin‐wave modes including the lowest‐order ones.
Kink Lattice Solution in a Quasi‐One‐Dimensional Peierls‐Fröhlich System with a Nearly One‐Third‐Filled Band. II. Thermodynamic Considerations
Authors: Fischbeck H. J. 
Published: July 2007

AbstractThe thermodynamic meaning of the kink lattice solution derived in the first part of this work is analyzed. To this end the grand potential of this solution is calculated at zero temperature. Its minimum is self‐consistent only if a special relation between the external parameters is realized. In general this solution describes the incommensurate phase only approximately. The phase transition into this approximate phase is for the most part discontinuous but in a certain region of the parameter plane continuous. This picture is expected to be essentially correct.
ESR Study of Cu2+ Diffused into Sodium β″‐Alumina
Authors: Abello L. , Schwerdtfeger S. J. , Schwerdtfeger C. F. 
Published: July 2007

AbstractESR spectra due to Cu2+ ions diffused into sodium β″‐alumina are studied. The symmetry of the spectra place the Cu2+ ions at the mid‐oxygen sites of the conduction planes. The complex spectra are a superposition from several different configurations of ions around this site which change as a function of the amount of annealing time. The angular variations of the spectra can be divided into two main types; an anisotropic site symmetry with spin‐Hamiltonian parameters g∥ ≈ 2.355, g⟂ ≈ 2.087, A∥ ≈ 12.0 mT, A⟂ ≈ 2.0 to 4.0 mT, and a more isotropic site symmetry with g∥ ≈ 2.003, g⟂ ≈ 2.240, A∥ ≈ 9.9 mT, A⟂ ≈ 8.8 mT. These spectra are only visible at liquid‐helium temperatures. In addition an anisotropic, random‐type spectrum is observed to replace the Cu2+ spectra at the temperature of annealed crystals is increased. This is attributed to thermal motion of the Cu2+ ions due to their weak binding to the site.
Multimode Pseudo Jahn‐Teller Effect for Off‐Centre Impurities in Crystals
Authors: Bersuker G. I. , Polinger V. Z. 
Published: July 2007

AbstractSystems with off‐centre impurity in the orbitally nondegenerate ground state are discussed. The off‐centre position of the impurity is shown to result from the mixing of the ground state and one of the excited electronic states by odd crystalline vibrations, displacing the impurity from the lattice point (pseudo Jahn‐Teller effect, PJTE). At high enough temperatures transitions of the impurity between the equivalent off‐centre positions occur due to the coupling with the PJTE active phonons. The qualitative estimation of the transition probability obtained for this process is in agreement with the line broadening data for the Li+ :KCl.
Dielectric Relaxation at the Glass Transition as a Free Volume Process. II. A Continuous Distribution of Relaxation Times
Authors: Alegráa A. , Barandiarán J. M. , Colmenero J. 
Published: July 2007

AbstractA previous work describing the α dielectric relaxation in glasses by means of a single, free volumedependent, relaxation time, is generalized by allowing for a distribution of relaxation times. Such a distribution is assumed to arise from differences in free volume within the glass. A phenomenological parameter is introduced for describing the interaction among the different zones. By using a temperature independent, symmetric, distribution in the inverse of the free volume expansion coefficient the experimentally found, asymmetric and temperature‐ as well as thermal‐story dependent distribution of dielectric relaxation times is reproduced. The physical meaning of the assumed distribution is discussed together with some implications on the dielectric response of a glass. Comparison with measurements performed on PVC shows good agreement.
Generation of Hot Free Electrons Due to the Interaction between Charge‐Transfer Excitons and Thermalized Free Electrons in Molecular Crystals
Authors: Andreev V. , Pope M. 
Published: July 2007

AbstractThe interaction of a free, thermalized electron with a CT exciton (nearest‐neighbor hole–electron pair) in an anthracene crystal is discussed theoretically. The rate constant for the annihilation of the CT exciton by the electron, in which an Auger electron is produced in a plane‐wave crystal state by the decay of an intermediate excitonic ion state is estimated to be about 10−10 to 10−9 cm3 S−1.
Determination of Valence Band Parameters in ZnTe
Authors: Fröhlich D. , Nöthe A. , Reimann K. 
Published: July 2007

AbstractThe fine structure of the 2P exciton in ZnTe is studied by two‐photon‐absorption. The energy splitting into four states, caused by the envelope–hole coupling, allows the determination of the Luttinger parameters γ2 and γ3, which describe the complex valence band. γ2, 0.8 and γ3 = 1.7 are obtained. These values will be compared to results of other experiments mainly on 1S excitons.
Exciton Drops in One‐Dimensional Molecular Chains. New Method of Solving of Gap Equation
Authors: Tošić B. S. , Šetrajčić J. P. 
Published: July 2007

AbstractA new method of solving the gap equation for exciton drops is proposed. By the use of this method the elementary excitation spectrum is found. It is shown that this spectrum satisfies the superfluidity condition.
Excitation Spectra of Photoluminescence Bands in Cd1–xMnx Te
Authors: Ambrazevičius G. , Babonas G. , Rud Yu. V. 
Published: July 2007

AbstractThe excitation spectra of photoluminescence bands B (2.0 eV), C (1.2 eV), and D (1.4 to 1.6 eV) are investigated at 5 and 78 K in Cd1–xMnxTe single crystals for 0.40 ≦ x ≦ 0.70. The data for the B‐band are interpreted in terms of the model of Mn2+ intra‐ion d–d transitions. The disagreement of some experimental results with this model is discussed. The photoluminescence band C, in contrast to B, is excited by several different temperature‐dependent processes. The models based on the common excitation mechanism for the B and C photoluminescence bands are shown to be insufficient to interpret the experimental results.
Zero‐Phonon Lines in the Excitation Band Centred at 23200 cm−1 Due to Mn2+ in Polymorphic ZnS
Authors: Pohl U. W. , Gumlich H.‐E. , Busse W. 
Published: July 2007

AbstractA system of zero phonon lines is observed within the 23200 cm−1 excitation band of Mn2+ in ZnS. By site selecting laser spectroscopy four zero phonon lines are identified due to Mn2+ at cubic lattice site (AN) and also at the main polymorphic lattice sites (AS, PN). A similar structure is registered due to the nearly hexagonal site (PS). The zero phonon lines of Mn2+ at polymorphic sites are shifted in energy with respect to those of Mn2+ at the cubic site. The energy shift is correlated to the shift of zero phonon lines observed within the three lower energy excitation bands.
Positron Age–Momentum Correlation in Ultrafine Particles of Silver and Gold
Authors: Matsuoka Y. , Terakado S. , Tanigawa S. 
Published: July 2007

AbstractAnnihilation characteristics of positrons in ultrafine particles of silver and gold are studied by the dual parameter measurements between the positron age and the momentum of annihilating pairs. The momentum dependence of the mean lifetime in the fine particles examined shows a maximum at zero momentum and minima at intermediate values of the momentum. This momentum dependence can be attributed to the positronium formation and the conversion of ortho‐positronium at the surfaces.
Temperature Dependences of Third‐Order Elastic Constants of CsCl, CsBr, and CsI Crsystals
Authors: Varshney R. K. , Shanker J. 
Published: July 2007

AbstractExpressions for third‐order elastic constants (TOEC) of CsCl‐structure solids are derived taking the thermal contribution into account. Six distinct values of TOEC for CsCl, CsBr, and CsI crystals are calculated at 0 K and at room temperature (300 K). Values of pressure derivatives of second‐order elastic constants are also calculated corresponding to both the temperatures. The phonon‐pressure contribution is incorporated within the framework of the three‐body potential model. The results are discussed and compared with other investigations.
Calculation of Grüneisen Constants in Si
Authors: Mayer A. P. , Wehner R. K. 
Published: July 2007

AbstractLattice dynamical calculations of the Grüneisen constants for general strain components are performed using the bond charge model of Weber with additional assumptions on anharmonic forces. The model is adjusted to fit data available at the Γ, X, and L points from various experimental techniques. The results along the main symmetry axes indicate that the Grüneisen constants depend sensitively on those model parameters which were originally determined from the phonon dispersion in the harmonic approximation. It is concluded that for a consistent description of phonon dispersion and anharmonic properties the model has to be revised.
Measurement of Phonon Energies in Silicon under Uniaxial Stress
Authors: Estel J. , Kalus J. , Pintschovius L. 
Published: July 2007

AbstractStress‐induced changes in phonon energies of the TA (ξ, ξ, ξ) branch are investigated in silicon by using inelastic neutron scattering. With stress in the [111] direction of 1.01 GPa the energy shift of the phonons changes from 0.5% near the Γ‐point to −1.2% at the zone boundary. Comparison with theoretical calculations of Mayer and Wehner [1] shows good agreement.
Critical Study of the Static Functional Integral Method in the Hubbard Model
Authors: Lorenz B. , Fehske H. 
Published: July 2007

AbstractThe effect of the static approximation in the functional integral representation of the paramagnetic Hubbard model is critically investigated. The exactly solvable two‐site model is treated within the one‐ and two‐field static functional integral method and some thermodynamic properties (local magnetic moment, specific heat cv) are compared with the exact solution for various interaction strengths and electron densities. It is shown that the static functional integral theory yields unphysical results for cv in the strong interacting system at small densities. The two‐field and one‐field methods are preferable in the low‐ and high‐temperature regions, respectively.
Electronic Band Structure of CdF2. Photoemission Experiment and Pseudopotential Calculations
Authors: Orlowski B. A. , Plenkiewicz P. 
Published: July 2007

AbstractEnergy distribution curves (EDC) of electrons photoemitted (hv1 = 21.22 eV and hv2 = 40.8 eV) from the valence band (F− 2p) and the Cd 4d band of a CdF2 crystal are measured and the valence and conduction band structures are calculated using the local empirical pseudopotential method (EPM). Comparison of the measured and calculated data show that the three main maxima measured in the valence band correspond well to the maxima in X5, L3, and X5 obtained in the calculated histogram of the valence band density of states. The influence of the final‐state structure on the position of peaks in the valence band is not observed on EDCs obtained for both, hv1 and hv2 photoemission exciting energies. For Cd 4d band the wide splitting of 1.46 eV is obtained only for hv1 = 21.22 eV while it is not obtained on EDC for hv2 = 40.8 eV. This Cd 4d band splitting may be caused by the influence of the final density‐of‐states maximum obtained in conduction band in X1‐ point. The results obtained are compared with reflectivity data available in the literature.
The Spin Density and Optical Properties of Amorphous Thin Arsenic Silicate Films
Authors: Al‐Ani S. K. J. , Hogarth C. A. 
Published: July 2007

AbstractThe spin density of amorphous As2O5/SiO thin films is found to be lower than that of SiO films deposited under similar conditions. The measurements show a decrease in the spin density of an amorphous As2O5/SiO film with increasing temperature which can be explained in terms of some annealing of dangling bonds. The fundamental absorption edge of these films at different temperatures is investigated and analysed assuming optical absorption by indirect transitions. The infrared absorption spectra indicate some chemical bonding between the two oxides. Experimental data on the wavelength dependence of the refractive index are presented. The dispersion of the refractive index follows a single‐oscillator model. Some effects of room temperature aging of the films are also presented.
Temperature Dependence of the Exciton Lineshape of GeO2
Authors: Fröhlich D. , Weber H.‐J. , Wille R. , Francini R. 
Published: July 2007

AbstractTwo‐photon measurements are presented of the IS exciton lineshape in GeO2 between 4.5 and 150 K. With a frequency‐doubled dye laser and a Raman‐shifted Nd:YAG laser the excitonenergy around 4.65 eV can be scanned. The temperature dependence of the total line width can be explained by a theoretical model of exciton‐phonon coupling. Furthermore the results reveal an unexpected asymmetry, which seems to originate from a non‐uniform contribution of optical phonons.
Optically Induced EPR of Conduction and and Donor Band Electrons in Zinc Sulphide
Authors: Backs D. , Hertrampf A. 
Published: July 2007

AbstractConventional EPR of mobile electrons as well as optical EPR excitation and quenching spectra of variously doped ZnS single crystals are reported. The different kinetic behaviour and the EPR parameters of the resonance lines are discussed involving donor and conduction band electrons. From the optical EPR excitation and quenching spectra and from ac‐microwave photoconductivity measurements a simple band model is proposed for the optical transitions.