bluuebunny/crossref_metadata_2025_split huggingface dataset:
Analyticity breaking of wave functions and fractal phase diagram for simple incommensurate systems
Authors: Schellnhuber H. J. , Urbschat H. 
Published: July 2007

AbstractThe Aubry‐André transition for certain one‐dimensional quasiperiodic Schrödinger operators is discussed in terms of analyticity breaking for the states of the underlying periodic diamagnetic Ersatz‐Hamiltonian. The general concept is compared with recent developments in the theory cf non‐integrable Hamiltonian dynamics and illustrated by explicit calculations for the Harper model. It is shown that the latter is not structurally stable within the family of incommensurate systems derived from Bloch dynamics in irrational magnetic fields: A very simple non‐self‐dual quasiperiodic model is presented, which lies in the Harper universality class regarding critical behaviour but exhibits cascades of localization–delocalization transitions. The system has a “devil's fork” phase diagram, where localized and extended regions are separated by a fractal curve.
Physical properties of the TCNQ salts with 1‐methyl‐3‐alkylimidazolium derivatives
Authors: Nešpůrek S. , Koropecký I. , Šorm M. , Graja A. , Sopa E. 
Published: July 2007

AbstractElectrical conductivity and spectral properties (UV–VIS absorption and temperature dependence of IR absorption) are studied in the series of 1‐methyl‐3‐alkylimidazolium (MRI+) 7,7′,88′–tetracyano‐p‐quinodimethanes \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm (TCNQ)}^{\mathop {\rm - }\limits_{\rm .} } $\end{document} in the form of simple and complex salts. The poor electrical conductivity of simple salts (10−4 to 10−7 Sm−1) is influenced by the dimer arrangement of \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm TCNQ}^{\mathop {\rm - }\limits_{\rm .} } $\end{document} stacks. The magnitude of the gap energy Eg, (between 1.0 and 1.2 eV) depends on the size of the donor. Combining these salts with neutral TCNQ0 molecules gives complex salts with electrical conductivities increased by 3 to 7 orders of magnitude. Eg decreases to 0.4 to 0.5 eV, which is in a good agreement with 0.4 eV obtained from IR measurements. The electrical conductivities of 1‐methyl‐3‐propylimidazolium (MPI), 1‐methyl‐3‐butylimidazolium (MBI), and poly‐(1‐methyl‐3‐allylimidazolium) (MPaI) complex TCNQ salts are also influenced by the donor level located about 0.05 to 0.06 eV below the conduction band.
Phase transitions in ordered and disordered ferrimagnets. I. Correlated molecular field theory and Monte Carlo simulations
Authors: Fähnle M. , Haug M. 
Published: July 2007

AbstractThe uniform and the staggered paramagnetic zero‐field susceptibility χ of ordered and disordered ferrimagnets are calculated by means of the correlated molecular field theory and by Monte‐Carlo computer simulations. The results are similar to the case of disordered ferromagnets: site disorder gives rise to a wide transition regime from the asymptotic critical behaviour to the mean‐field behaviour, with strong upward curvature of the plot χ−1(T). In contrast, bond disorder has only a weak influence on χ−1(T). For the ordered S = 1/2 / 1 Ising ferrimagnet on a simple cubic lattice the Monte Carlo simulation yields a critical temperature consistent with that found by high‐temperature series expansons of Schofield and Bowers.
Infrared properties of TeEA(TCNQ)2
Authors: Železný V. , Petzelt J. , Swietlik R. 
Published: July 2007

AbstractPolarized reflectivity from three faces of TeEA(TCNQ)2 single crystals is measured in the frequency range 50 to 13500 cm−1 at room temperature. The spectra polarized closely to the TCNQ dimer axis are analyzed by means of Kramers‐Kronig relations to obtain the optical constants. They are also fitted to a model which has been previously applied to dimerized TCNQ salts. The model consists of an infrared active electronic oscillator (charge‐transfer mode) linearly coupled to the totally symmetric vibrations of TCNQ molecules. From the fit the microscopic electron–phonon coupling constants, transfer integral for the π‐molecular orbital t = 1864 cm−1, and the energy gap Δ = 938 cm−1 are evaluated. The most striking feature in comparison with other TCNQ salts is the low vibrational‐mode damping which leads to a very sharp and strong peak structure in the reflectivity and conductivity spectra.
Sensitized luminescence of pure and doped NaNO2 single crystals. I. Stationary spectra
Authors: Lisse F. , Köhlre J. , Pufahl H. , Schmid D. 
Published: July 2007

AbstractThe fluorescence and phosphorescence spectra of pure NaNO2 and of NaNO2 doped with KNO2 (up to about 2 × 10−3 mol KNO2/mol NaNO2) are investigated. Compared to the fluorescence spectra of pure crystals ten progressions of impurity‐induced lines are identified in the spectra of the doped crystals. The origin and the generating frequencies of these progressions are determined carefully, as well as the temperature and concentration dependence of their relative intensities with respect to those observed in pure crystals. A comparison of the shapes of impurity‐induced and unperturbed lines shows a striking difference: The unperturbed “zero‐phonon” lines (electronic transitions into intraionic vibrational levels of the NO2− without participation of interionic phonons) exhibit a pronounced asymmetry. The impurity‐induced lines, as well as the lines which are due to isotopically substituted NO2− are considerably narrower and Lorentzian shaped. A discussion of these observations will be presented in Part II.
Low‐temperature behaviour of the lithium modes in monoclinic Li2SO4
Authors: Cazzanelli E. , Fontana A. , Rocca F. , Frech R. 
Published: July 2007

AbstractPolarized Raman spectra of anhydrous monocrystalline lithium sulfate are studied from 90 K to room temperature. The analyzed frequency range, between 260 and 580 cm−1, includes the lattice modes of the Li+ cations and the internal bending of the sulfate anions. The observed temperature dependence of the frequency, linewidth, and intensity of the Raman peaks can be explained by a weak phase transition around 180 K.
Microscopic Models for Substitutional OH− and CN− Defects in Alkali‐Halide Crystals
Authors: Dick B. G. 
Published: July 2007

AbstractMicroscopic models for substitutional OH− and CN− defect ions in NaCl structure alkali‐halide crystals are used to calculate the preferred orientations, electric dipole moments, and tunneling matrix elements of these defects in various host crystals. Both Coulomb and short range interactions are included. The pressure induced transition of OH− in KI from preferred 〈110〉 to 〈100〉 orientations can be plausibly accounted for with the model. Vibration frequencies for translational motion of the defect predicted by the model are too high to be used to explain observed low lying excitations in the 10 to 30 cm−1 range.
Corrections from Electron‐Electron Interaction to the One‐Particle Density of States in Strongly Anisotropic Two‐Dimensional Systems
Authors: Firsov Yu. A. , Nakhmebov E. P. , Prigodin V. N. , Weller W. 
Published: July 2007

AbstractA simple model is proposed for the description of the one‐particle density of states ν(ε) of the degenerate electron gas in the grain boundary (inversion layer) of a semiconductor bicrystal or in a surface superlattice. The electron–electron interaction effect is calculated renormalized by scattering on the disorder in diffusion approximation. In the case of small tilt angles, where the grain boundary may be considered as a planar array of edge dislocation tubes (chains), a crossing‐over is obtained for ν(ε) from one‐dimensional (∼1/|ε|1/2) to two‐dimensional (∼ In2|ε|) behaviour in the neighbourhood of εcross ∼ w⟂2|ε|/h. Here ε is the difference of the energy from the Fermi energy, τ is the relaxation time due to scattering on the disorder, w⟂ is the transverse overlap integral characterizing the strength of the electron tunneling between dislocation tubes.
Correlation and Influence of Phonons in Calculations of the Density of States in Thin Films
Authors: Kierul J. , Stasiak J. W. , Kluczynski M. 
Published: July 2007

AbstractThe density of electronic states and its spatial distribution in thin films, based on the original adaptation of the coherent‐potential approximation (CPA) (Wojtczak and others) is obtained by including the phonon–electron interactions in the form proposed by Chen et al. This new approach allows to derive the line shape for electronic levels in which the broadening is also connected with lattice vibrations. The detailed calculations are performed for 4s copper and nickel thin films with f.c.c. lattice and (100) crystallographic orientations of the surfaces. The lattice vibrations are taken in pseudoharmonic approximation.
Dynamical Screening, Collective Excitations, and Electron‐Phonon Interaction in Heterostructures and Semiconductor Quantum Wells. Application to Double Heterostructures
Authors: Wendler L. , Pechstedt R. 
Published: July 2007

AbstractThe collective excitations of a double heterostructure are examined in detail. Including the important effects of the interfaces of the system the uncoupled modes are analysed, which are the long‐wave optical interface phonon modes, LO phonon modes, and intra‐ and intersubband plasmon modes. The electron‐phonon interaction is discussed and the coupling functions are calculated and discussed in graphical form. The resulting coupled modes, intra‐ and intersubband plasmon‐phonon modes, are calculated for different approximations of the polarization function, the random‐phase approximation, the plasmon‐pol approximation, and the long‐wave approximation. The dispersion curves of these modes are presented in graphical form for various cases. It is shown that the Landau damping of the modes strongly depends on the layer thickness and the concentration of the quasi‐two‐dimensional electron gas.
On the Theory of “Deep” Electronic Impurity States in Many‐Valley Semiconductors
Authors: Savvinykh S. K. 
Published: July 2007

AbstractFor many‐valley semiconductors a theory of electron states localized on short‐range point defects, i.e. defects with action ranges of the order of the lattice constant, is developed. Resonance electron scattering near the bottom of conduction band and a small value of the bound energy of the localized state are assumed. The transition from the general multiband formulation of the problem to the zero‐range potential approximation is accomplished. For crystals placed in crossed electric and magnetic fields the general expressions are derived determining the energy spectrum and wave functions of localized states.
On Trigger Properties of Molecular Organizates. II. Switch Waves in Donor‐Acceptor Systems with Strong Electron‐Deformation Interaction
Authors: Gaididei Yu. B. , Yakimenko I. I. 
Published: July 2007

AbstractThe charge transport is studied in the case of multilayer organizates consisting of donor and acceptor monolayers separated by dielectric molecular layers. It is shown that in such systems the charge can propagate as switch (trigger) waves. The velocities of these waves are calculated and their profiles are investigated as well.
Correlated Molecular Field Theory for the Ferromagnetic Regime of Amorphous Systems
Authors: Holey T. , Fähnle M. 
Published: July 2007

AbstractUsing the modified equation of state of Arrott and Noakes a self‐consistent correlated molecular field theory for the ferromagnetic temperature range of amorphous systems is developed. The temperature dependence of the spontaneous magnetization and of the width of Mössbauer lines is calculated, as well as the Arrott‐plots of amorphous ferromagnets.
To Applicability of Hamilton's Equations in Quantum Many‐Body Problems
Authors: Lindner U. 
Published: July 2007

AbstractThe connection between Schrödinger equation and Hamilton equations for interacting many‐particle systems is given and it is shown in which way the Hamilton function has to be constructed. Starting from an identity for the Hamilton function a criterion is derived which permits to check approximations. Applying this criterion to former calculations to the soliton problem in a modified Hubbard chain the consistency of the used approximation is shown.
Photon Recycling in Double Heterostructures. III. Variational Calculations
Authors: Enders P. 
Published: July 2007

AbstractThe influence of photon recycling onto the minority carrier distribution in double heterostructures is investigated by means of variational calculations based on the unified formulation of the construction of variational principles by Gerjouy, Rau, and Spruch. The time‐independent variational treatment by von Roos is examinated and shown to be actually one for the effective carrier lifetime. This approach is applied to finite samples and numerical results for dependence of the influence of photon recycling upon the sample thickness are presented.
Effect of Back‐Surface Reflection on the Electroreflectance Spectra of GaAs
Authors: Behn U. , Röppischer H. 
Published: July 2007

AbstractA detailed study of the influence of back‐surface reflection on electroreflectance spectra arising in an additional low‐energy peak is performed. Spectra with and without back reflection are measured on GaAs samples with various doping concentrations. First quantitative calculations on the basis of band‐to‐band related electroabsorption (Franz‐Keldysh effect) including field inhomogeneity reproduce the characteristic features and dependences of the experimental spectra. A new method for estimating the characteristic energy E0 of the exponential absorption tail of semiconductors is suggested.
Analysis of the Structural Phase Transition in Mixed Alkali Halide Crystals
Authors: Shanker J. , Sharma S. C. , Kumar M. 
Published: July 2007

AbstractAn analysis of structural transition in CsClKCl and CsClRbCl mixed crystals is presented by studying the lattice stability in terms of interionic potentials. The potential parameters are determined by fitting the experimental values of lattice energies in standard observed structure viz. CsCl structure for CsCl and CsBr crystals, and NaCl structure for RbCl and KCl crystals. It is found that CsClKCl mixed crystals remain stable in CsCl structure only for KCl less than 25%, and are transformed to NaCl structure when the proportion of KCl becomes equal to or more than 25%. For CsClRbCl mixed crystals, the transition from CsCl to NaCl structure is predicted when the RbCl component becomes equal to or more than 50%. These predictions are found to be in good agreement with experimental results. The lattice theory of structural stability is also applied to predict the transition temperatures for the mixed crystals viz. CsClKCl, CsClRbCl and CsClCsBr at which they transform from CsCl to NaCl structure.
Invariant Harmonic Oscillator Functions III. The Cubic Groups T and Th3)
Authors: Wöhlecke M. , Schöpp J. , Scherz U. , Jovanović A. 
Published: July 2007

AbstractTwo recently introduced methods, suitable to calculate symmetry adapted harmonic oscillator functions of excited states, are applied to the cubic point groups T and Th. Expressions for computational purposes and results for three‐dimensional excitation are presented.
Effect of Size Quantization on Field Emission from Ultrathin Films of Degenerate Wide‐Gap Semiconductors
Authors: Majumdar C. , Bose M. K. , Maity A. B. , Chakravarti A. N. 
Published: July 2007

AbstractAn attempt is made to investigate the effects of size quantization on the field emission from ultrathin films of degenerate wide‐gap semiconductors. It is found, taking n‐type GaAs as an example, that the presence of size quantization increases the field emission by several orders of magnitude as compared to that from bulk specimens of the same semiconductor. Under such quantization, the field emission may also show oscillatory behavior with decreasing film thickness, and is further found to be strongly dependent on the field strength and the carrier concentration.
X‐Ray Absorption Spectroscopic Studies of Chalcopyrite Mineral
Authors: Hemachandran K. , Chetal A. R. , Joshi G. 
Published: July 2007

AbstractThe X‐ray K‐absorption edge of Cu in chalcopyrite mineral is investigated using a 40 cm Cauchois‐type bent crystal X‐ray spectrograph. The study confirms the electronic configuration of chalcopyrite mineral as Cu1+Fe3+S22−. The near‐edge structures (XANES) B and C observed in the K‐absorption edge of Cu in the mineral are explained on the basis of molecular orbital theory and band structure.
Approximation of Electron Energy Bands by Cubic Splines
Authors: Neumann J. , Smrčka L. 
Published: July 2007

AbstractCubic spline functions are used to interpolate between the band energy eigenvalues evaluated on the regular cubic mesh of points in the irreducible part of the Brillouin zone (IBZ) making use of the knowledge of normal gradients of eigenenergies at the IBZ faces following from the crystal symmetry. The resulting approximate function has the full symmetry of the energy band and is represented within each cube by three‐dimensional Hermite splines which join together smoothly with continuity up to second derivative accross the cubes boundaries.
Phase Transition and Bipolaron Formation in Quasi‐One‐Dimensional Conductor β‐AgxV2O5
Authors: Onoda M. , Nagasawa H. 
Published: July 2007

AbstractThe electronic states of V4+ ions in β‐Ag0.40V2O5 are investigated by NMR and EPR. The structural phase transition is observed between 170 and 210 K. The 51V Knight shift results show that the spin‐singlet ground state of V4+ ion pairs is realized as bipolaron.
Flexibility Options in Valency‐Mixing Jahn‐Teller Systems
Authors: Weber C. , Wagner M. , Sigmund E. 
Published: July 2007

AbstractIn a previous study we have presented a novel species of a Jahn‐Teller system, which goes a good way to describe the unusual ESR behaviour in the system SmB6:Er3+. In the present study the “minimal” model is extended in the two most suggestive directions (additional states of the valency‐mixing surrounding and coupling dependence on nuclear motion). These models reduce the original ESR anisotropy of a crystal field calculation by a factor of five and come very close to the experiment.
Neutral Bound Excitons in a High Magnetic Field
Authors: Dujardin F. , Stébé B. , Munschy G. 
Published: July 2007

AbstractThe influence of a constant magnetic field on the energy of the ground state of an exciton bound to a neutral shallow impurity is studied in the high field limit. The Schrödinger equation is solved using the adiabatic approximation and considering the Coulomb potential as a perturbation with respect to the fundamental Landau level. The total energy is calculated by means of a combination of four Gaussian type variational wave functions. The results show that the magnetic field enhances the Coulomb interaction and allow to estimate the transition energies.
A Curved‐Wave Theory for EXAFS with Effective Scattering Amplitudes
Authors: Fritzsche V. , Rennert P. 
Published: July 2007

AbstractThe modified small‐scattering‐centre approximation (MSSCA) is applied to the multiple‐scattering theory of EXAFS. In the MSSCA the incoming spherical electron waves are approximated in the range of the scattering potential by an isotropic spherical wave. The scattering of these isotropic spherical waves can be described by effective scattering amplitudes, which are easy to evaluate. This method is a much better description than the plane‐wave approximation routinely used in EXAFS analysis. In comparison with the plane‐wave approximation the effort is some what increased by the distance dependence of the effective scattering amplitudes. The strength of the MSSCA is that it yields simple expressions for the multiple‐scattering contributions, which improve the accuracy especially for scattering pathways involving forward scattering events considerably.
On the Inconsistencies of Axially Symmetric Force Models for Noncubic Solids
Authors: Ramamurthy V. 
Published: July 2007

AbstractThe origin of the elastic inconsistency of a modified axially symmetric force model, proposed by Lehman, Wolfram, and De Wames, for noncubic solids and the circumstances under which its phonon frequencies become imaginary are analysed by making use of this model in the lattice dynamical study of face centred tetragonal indium. It is shown that the arbitrary differences in the tangential force constants along x and z directions destroy the compatibility between off‐diagonal and diagonal matrix elements, relatively stronger off‐diagonal elements give rise to imaginary frequencies at certain wave vectors along nonsymmetry directions while the failure of this model to comply with the rotational invariance conditions manifests itself as the elastic inconsistency. The distortions introduced by the deficiencies of this model into the phonon dispersion curves of f.c.t. indium, consequences of imposing additional invariance conditions on this model as well as its apparent equivalence with central and general tensor force models, are discussed.
Quantum Tunneling at First‐Order Phase Transitions in a Uniaxial Antiferromagnet with External Magnetic Field
Authors: Klamut J. , Prystasz W. 
Published: July 2007

AbstractThe formation of a new phase at or close to absolute zero cannot be due to thermal fluctuations and must be ascribed to a quantum mechanism. This means that the formation of the new phase can be reduced to tunneling movement of the system under the energy barrier separating the initial metastable state and the stable one. The probabilities of the transitions between the antiferromagnetic (AF) and ferromagnetic (F) states are obtained for the uniaxial two‐sublattice antiferromagnet by using quasiclassical approxamation (WKB fomalism).
Structural Stability and Phonon Dispersion of Arsenic
Authors: Shimamura S. , Shindo K. , Morita A. 
Published: July 2007

AbstractThe stability of the A7 crystal structure of As is studied using the third‐order pseudopotential expansion method. On the basis of model potentials fitted to the atomic energy levels in As4+, phonon frequencies of As in the A7 structure are calculated. It is shown that s–p hybridization plays a predominant role in stabilizing the A7 structure to the internal strain. An analysis of phonon dispersion curves of As in terms of the present method and additive short‐range force constants suggests that there are considerably strong covalent forces between neighboring atoms in As.
Chemical Processes on Semiconductor Electrode Interfaces and Distribution of Charge Transfer on the Orbital Energy Scale
Authors: Lorenz W. , Katterle T. 
Published: July 2007

AbstractAfter a look at the significance of total‐to‐orbital‐energy relations and of the tight‐binding scheme (in the sense of an independent‐particle model) for treating systems with a band gap, the orbital energy distribution of many‐electron partial charge transfer in chemical bond formation processes on semiconductor surfaces is discussed. Difference densities of states are evaluated for chemi‐sorption of water or its dissociation products, as well as for their displacement by an electrochemical model reactant (halide) on GaAs(111) surfaces.
Interaction of Semiconductors with a Strong Resonance Electromagnetic Field
Authors: Kruglov V. I. 
Published: July 2007

AbstractA procedure is developed of constructing an effective Hamiltonian, which makes it possible to reduce the nonstationary problem of interaction between a semiconductor and a strong resonance electromagnetic field to a corresponding problem of equilibrium statistical mechanics. Criteria are obtained when the proposed approach is valid. A corresponding effective Hamiltonian has been found taking into account the electron and hole acceleration by the field as well as different relaxation processes, which permits the investigation of both, the energy spectrum of a semiconductor in a strong field and its thermodynamical properties.