bluuebunny/crossref_metadata_2025_split huggingface dataset:
N‐Interface Problem Revisited
Authors: Davison S. G. , Sulston K. W. 
Published: July 2007

AbstractThe general Dyson equation is derived for an N‐interface system within the tight‐binding approximation. An iterative procedure is developed, by means of this equation, which enables closed, well‐defined expressions to be found for the interfacial Green functions at atomic sites on either side of any interface in an N‐interface system.
Studies on Quantum Percolation
Authors: Chaturvedi Meena , Srivastava Vipin 
Published: July 2007

AbstractStudies on the localisation in binary alloys (commonly termed as ‘quantum percolation’ problem) are reviewed highlighting the special features that this simple model has and which are absent in other models — the most prominent among them being the existence of extended states at infinite disorder. Some new scaling arguments are also reported that enable to predict qualitatively the behaviour of the participation ratio as function of concentration of one of the constituents of the alloy. These are substantiated by numerical simulation results. After summarising all'important approaches and their results, one of the important conclusions drawn is that in two‐dimensional binary alloys not all states are localised at any disorder, contrary to a recent belief.
Study of Optical Relaxation and Inhomogeneous Distribution Function of Impurity Organic Molecules by Site‐Selective Laser Spectroscopy
Authors: Sapozhnikov M. N. , Alekseev V. I. 
Published: July 2007

AbstractSite‐selective excitation of luminescence and hole burning in the absorption spectra are used for a study of the electronic and vibrational relaxations and inhomogeneous distribution function for coproporphyrin III molecules in solid ethanol and n‐octane matrices in the temperature range from 3.2 to 26 K. From the structural luminescence spectra obtained at the site‐selective excitation the vibrational frequencies of coproporphyrin in the ground and excited electronic states are measured. The temperature broadening of the homogeneous, purely electronic zero‐phonon line investigated by hole burning is mainly determined by the two‐phonon Raman scattering of low‐frequency phonons with the effective frequency 35 cm−1 while its residual width at 0 K results from the anharmonicity of the matrix vibrations. The pure dephasing time T obtained from the homogeneous, purely electronic zero‐phonon linewidths changes from 17.6 to 53.0 ps at T = 3.5 K to 2.8 ps at T = 25 K. The phase relaxation time T2 measured from the homogeneous linewidth of the vibronic level in the excited electronic state is equal to 2.4 ps at T = 3.5 K.
Te Formula for Strong‐Coupling Superconductivity in Random Narrow‐Band Alloys
Authors: Beckmann A. , Kolley E. , Kolley W. 
Published: July 2007

AbstractThe transition temperature Tc of strong‐coupling superconducting alloys AcB1‐c is determined with emphasis to tight‐binding. Local random Eliashberg‐type equations are configuration averaged by means of an effective mass operator on the basis of the CPA. Contrary to the McMillan form the resulting Tc formula involves two different phonon‐mediated coupling parameters. The electron‐phonon mass enhancement is originated from a complex renormalization factor.
Einbau und Diffusion von Cu(I)‐Ionen in CsI anhand von NMR‐Messungen
Authors: Budde K. , Richtering H. 
Published: July 2007

AbstractEs werden die Ergebnisse von Kernresonanz‐Untersuchungen zur Diffusion in reinem und CuI dotiertem CsI vorgestellt. Ein Einfluß der Dotierung auf die Linienverschmälerung der beiden Kerne 127I und 133Cs wird nicht beobachtet. Aus dem Verlauf der Linienverschmälerung folgt, daß zwischen 200 und 360 °C die mittleren Sprungfrequenzen beider Wirtsteilchen von gleicher Größenordnung sind. Die mittlere Sprungfrequenz der Cu+‐Ionen kann aus der Lebensdauer‐Verbreiterung der 127I Kernresonanz‐Absorptionslinie ermittelt werden. Sie ist nur unwesentlich größer als die der Wirtskationen und zeigt eine ähnliche Temperaturabhängigkeit wie diese. Aus den Resultaten der Kernresonanz‐Messungen wird der Schluß gezogen, daß Cu+‐Ionen in CsI substitutionell eingebaut werden und dem gleichen Diffusionsmechanismus wie die Cs+‐Teilchen folgen.
On the Influence of the Magnetic Ordering on Thermodynamic and Electrical Properties in the Hubbard Model
Authors: Schumacher W. 
Published: July 2007

AbstractThe specific heat and the electrical conductivity are calculated in the Hubbard model in Hartree‐Fock approximation (HFA) for an antiferromagnetic ordering and for arbitrary band filling using the antiferromagnetic solutions which are found in HFA and which are established with respect to the existence of double solutions of the Néel temperature in the framework of a theory taking into account fluctuations of the spin.
Multiphonon Structure of Optical Transitions to Impurity Resonance States. The Influence of Anharmonicity
Authors: Suisky D. 
Published: July 2007

AbstractExpressions are derived for the absorption coefficient of substitutional impurities taking into account resonant impurity states and anharmonicity of lattice vibrations. In both the cases the lineshape of the absorption band is modified due to broadening effects. It can be shown that the contribution due to anharmonicity is not only remarkable, but dominates under certain conditions, for example, in the case of strong electron‐phonon interaction.
Calculation of the Exoelectron Energy Spectrum for NaCl
Authors: Gerasimov A. B. , Merkin M. M. , Tsertsvadze A. A. 
Published: July 2007

AbstractA quantum‐mechanical calculation of the probability of an elementary exoelectron emission (EEE) act from a NaCl crystal is made. The mechanism previously suggested by the authors is used, according to which the emission takes place at the expense of the energy released at exoenergetic reactions between defects. The calculations are made for the particular case of annihilation of the F‐centre with a negative halide atom. There is good agreement between theory and experimental results.
Thermodynamics of Superconducting Alloys with Localized States in the Energy Gap
Authors: Schossmann M. , Schachinger E. 
Published: July 2007

AbstractA general formula for the energy difference between superconducting and normal states of an alloy with paramagnetic impurities is developed on the basis of the Shiba‐Rusinov theory. The result is used to calculate the thermodynamics of the alloys In‐Mn, In‐Cr, and Pb‐Mn. It is shown that the deviation function is particularly sensitive on the position and number of localized states for all possible impurity concentrations. Finally, a comparison of theoretically calculated specific heat values for In‐Mn with experimental results demonstrates a satisfactory agreement.
Resonances and Averaged Forces in Bounded Semiconductor Plasmas
Authors: Nikolov N. A. , Malinov P. N. 
Published: July 2007

AbstractThe density distributions of the current carriers and their velocities in a bounded semiconductor plasma are found on the basis of the two‐component MHD. The semiconductor plasma is placed between two metal electrodes. The averaged forces of Miller's type, which act on the current carriers, are found. The resonance frequencies are found at which the averaged forces increase and the densities have a modulation maximum. The possibility of experimental observation of “hole sound”‐type resonances is discussed.
FIR Studies of OCN−, SCN−, and SeCN− Centre Gap Modes in KI Single Crystals
Authors: Otto J. , Fischer F. 
Published: July 2007

AbstractSeveral sharp absorption lines within the frequency range of the phonon gap of KI are shown to be due to the chalcogenocyanate centres. A resonance mode occuring near the low‐frequency gap boundary is also ascribed to the SeCN− centre. The experimental data are compared with a three‐dimensional model calculation for a monoatomic isotopic impurity centre and with a simple model for the centre of a linear molecular ion. A characterization of the gap and resonance modes is given.
FMR Linewidth in Bulk Metals in Parallel Configuration
Authors: Fraitová D. , Půst L. 
Published: July 2007

AbstractA formula for the ferromagnetic resonance (FMR) linewidth is presented for the case of isotropic bulk ferromagnetic metals in the parallel configuration, free surface magnetization motion being assumed. The numerical evaluation of the formula agrees with the relative accuracy −0.5 × 10−2 to +1.5 × 10−2 with exact results based on macroscopic FMR theory. The influence of surface magnetization pinning on the linewidth value is also discussed.
Field Ionization of Phosphorus Atoms in Silicon
Authors: Žurauskas S. , Dargys A. 
Published: July 2007

AbstractElectron tunneling from phosphorus atoms into the silicon conduction band is investigated at cryogenic temperatures in metal—insulator—semiconductor (MIS) structures. To observe field ionization and, at the same time, to exclude other competing processes, such as the impact ionization and the electric‐field‐assisted thermal ionization, the experiments are performed with electrical pulses of several ns duration. Field ionization dynamics after the application of a voltage step, when the tunneling time is comparable to the electron transit time through the structure, is analysed theoretically and compared with the experiment. Since the tunneling time is very sensitive to the parameters associated with the impurity it is argued that field ionization experiments may appear valuable in the investigations of shallow impurity states in semiconductors.
The FH‐Centre Energy Structure in KCl and KBr
Authors: Salomatov V. N. , Parfianovich I. A. 
Published: July 2007

AbstractThe energy parameters of the FH(Br−)‐, FH(O−) — centres in KCl and FH(O−) — centres in KBr are calculated within the framework of perturbation theory. From the comparison of calculated and experimental data the following conclusions are drawn: (1) the long‐wave shift of the F‐centre absorption band in KCl with increasing Br− concentration may be due to the formation of FH(Br−)‐centres whose components are a \documentclass{article}\pagestyle{empty}\begin{document}$ a\sqrt 2 $\end{document} apart (a is the shortest interionic distance); (2) the decay of impurity excitons in KCl‐Br leads to the creation (or the manifestation in the stimulation spectrum) of the FH(Br−)‐centres with components being 2a rather than a \documentclass{article}\pagestyle{empty}\begin{document}$ a\sqrt 2 $\end{document} apart; (3) the change in the optical characteristics of the FH(O−)‐centre as compared to those of the F‐centre in KBr is consistent with the experiment assuming that an O− off‐centre position in the lattice site exists. The possibility of F‐centre RES life‐time lowering is mentioned.
Dielectric Properties of Ice in the Presence of Space Charge
Authors: Petrenko V. F. , Ryzhkin I. A. 
Published: July 2007

AbstractThe effect of the space charge at the contacts on the low‐frequency dispersion of the electrical properties of ice is theoretically investigated. It is shown that in general case there are four characteristic frequencies related to four Maxwell relaxation times of four partial conductances of defects. The real part of the dielectric permittivity has dispersion “steps” at characteristic frequencies. An analysis of the step heights and their position in the dielectric spectrum gives valuable information on concentrations and mobilities of charge carriers in ice.
Evaluation of Photoelastic Constants and Strain Derivatives of the Static Dielectric Constant of Silver and Thallium Halides
Authors: Verma T. S. , Kumar V. , Shanker J. 
Published: July 2007

AbstractA method for calculating the photoelastic constants and strain derivatives of static dielectric constant for silver and thallium halide crystals, which crystallize in NaCl and CsCl structures, respectively, is developed. The shell model formulation, which takes into account the polarizability of positive as well as negative ions and considers also the effect of Lundqvist's three‐body interaction, is used in the present calculation. The short‐range overlap repulsive interactions between first and second neighbours as well as the van der Waals dipole—dipole interactions are also considered in evaluating the short‐range force parameters which are used for the calculation of the photoelastic constants and the strain derivatives of the dielectric constant. The results are found to compare well with available experimental data.
The Contribution of Zero‐Point Vibration toward the Static and Thermodynamical Properties of Potassium Halides
Authors: Singh R. P. , Rana J. P. S. , Varshney G. B. 
Published: July 2007

AbstractThe cohesive energy, molecular force constant, reststrahlen frequency, third‐order elastic (TOE) constants, van der Waal's coefficients, bulk modulus, and its pressure dependence are evaluated for potassium halides using a generalised‐shell model (GSM) in which the zero‐point energy is estimated from a relation used by Narayan and Ramaseshan, and van der Waal's (vdW) coefficients are evaluated by the Slater‐Kirkwood‐variational (SKV) method. The Hafemeister‐Flygare (HF) type short‐range overlap repulsive potential, effective up to second neighbours, is used. The results obtained are in excellent agreement with the experimental data.
Longitudinal Nernst‐Ettingshausen Effect in Heavily Doped EuO
Authors: Auslender M. I. , Karyagin V. V. , Zolotovitskii A. B. , Kalashnikov V. P. , Gizhevskii B. A. 
Published: July 2007

AbstractTemperature and magnetic field dependences of the Nernst‐Ettingshausen effect in heavily doped ferromagnetic semiconductors over a wide temperature interval embracing the Curie point are calculated numerically for the material parameters of Eu0.99Gd0.01O. It is assumed that usual Born scattering of current carriers by spin fluctuations dominates. The results obtained agree semiquantitatively with the experimental data.
Warm Electron Coefficient of Two‐Dimensional Electron Gas in Silicon Inversion Layer at Low Temperatures
Authors: Basu P. K. , Roy J. B. 
Published: July 2007

AbstractWarm electron coefficient of a two‐dimensional electron gas in Si‐MOSFET's is calculated at low temperatures by assuming that the distribution function is characterised by an electron temperature. Bulk acoustic phonon, Rayleigh wave, impurity, and surface roughness scattering mechanisms are considered and the phonon numbers are taken exactly. The present values of β are of the same order as those obtained by other workers, but differ widely from the experimental data. Both positive and negative values of β are obtained in the present calculation, while earlier workers obtained only positive values. Possible reasons for the discrepancies are discussed.
Pinning of a Curved Flux Line by Macroscopic Inclusions in a Type II Superconductor
Authors: Shehata L. N. , Saif A. G. 
Published: July 2007

AbstractThe pinning force is calculated as a function of the distance between a curved (or straight) flux line and the centre of a macroscopic superconducting (or normal) ellipsoidal inclusion. When the ellipsoidal tends to a spherical inclusion the results agree with those previously obtained.
A New Technique for the Evaluation of Densities of States in ab initio Calculations of Periodic Systems
Authors: Angonoa Giuliana , Dovesi R. , Pisani C. , Roetti Carla 
Published: July 2007

AbstractA recently introduced expansion technique for calculating densities of states (DOS) of crystalline systems is applied for the first time in conjunction with ab initio HF calculations. Graphite, lithium, and beryllium are chosen as test systems; Legendre polynomials are used as the orthogonal expansion set. The quality of the results depends both on the density of the sampling net used for the evaluation of the expansion coefficients, and on the number of terms used in the expansion; the influence of these two parameters is discussed. It is shown that the new technique provides a substantially accurate description of the DOS and related quantities (Fermi energy, density matrix), although it is not able to reveal the fine structure of the spectrum. The computing time is about ten times less than required by conventional techniques of comparable accuracy.
Effects of Excitation Intensity on Photoluminescence of Pure CdTe
Authors: Kim Q. , Langer D. W. 
Published: July 2007

AbstractThe photoluminescence of high purity n‐type CdTe single crystals (n ≈ 2.9 × 1014 cm−3) at liquid helium temperature is studied at different excitation intensities. Emissions due to the recombination of free excitons and excitons bound to neutral donors, ionized donors, and neutral acceptors are discussed as well as the transitions of free carriers to various impurities. Other impurity related spectral features are observed within the range of 120 meV from the band edge and their origin is described in analogy to the present knowledge of the spectra of III‐V and other II‐VI compounds.
On the Optic Vibrational Modes in Amorphous Arsenic
Authors: Lottici P. P. 
Published: July 2007

AbstractThe Raman, infrared, and inelastic neutron spectra on bulk amorphous arsenic are reviewed and compared. The main peak in the polarized Raman spectra does not correspond to a maximum in the neutron density of states and some kind of vibrational selection rules is observed. This behaviour is interpreted in terms of a simple continuous random network model for the a‐As structure in which symmetric stretch (SS) motions, highly correlated through the network, exhibit high Raman activity.
Metallic Quenching of Exciton Luminescence in Anthracene
Authors: Ya. Glushko E. 
Published: July 2007

AbstractThe peculiarities of the molecular crystal luminescence spectrum shape are considered within the framework of the polariton theory; in particular the anthracene luminescence spectrum shape caused by external phonon modes of the crystal is described. Exciton‐phonon interaction including the anisotropy of the anthracene crystal, exciton energy, and phonon modes are taken into account in the microscopic model. Determination of the radiation transmission coefficient of the crystal bordering on metallic films of various widths is performed within the framework of classical crystal optics. The results of computations of the luminescence spectra dependence on temperature, metallic film width, and crystal orientation allow to define the limits of applicability of the anthracene luminescence isotropic model. Qualitative agreement of calculated spectra with experimental data known in literature is received.
EHP Luminescence of GaP:N under Resonant Free‐Exciton Excitation
Authors: Schwabe R. , Staehli J. L. , Streit I. , Thuselt F. 
Published: July 2007

AbstractThe electron‐hole plasma (EHP) luminescence of thin nitrogen doped GaP layers is investigated using a resonant free‐exciton excitation which ensures an absolute homogeneous excitation of the crystals. Spatially resolved measurements of the EHP luminescence give hints that the impurities in a certain doping range induce a phase separation into two degenerated plasma‐like phases whose densities are close together. The results are compared with theoretical phase diagram calculations for an acceptor doped material. An increase in doping level as well as in pump power favours an EHP expansion. Moreover first results of highly nitrogen‐doped GaP (nN = 3.1 × × 1019 cm−3) are presented using the same experimental procedure.
Electron Scattering Interaction and Elementary Excitations in Lead Chalcogenides
Authors: Giese B. 
Published: July 2007

AbstractDielectric properties and elementary excitations are discussed in lead chalcogenide semiconductors on the base of the RPA‐dielectric function using a Kane‐band model. Numerical and analytical results are presented for the dielectric function and the elementary excitation spectrum and compared with results for a parabolic model. A sum rule for the spectral function of the phonon propagator is given to calculate the phonon strength of elementary excitations.
Jahn‐Teller Effect in EPR and Optical Absorption Spectra of Cu2+ in LiNbO3 Single Crystals
Authors: Petrosyan A. K. , Khachatryan R. M. , Sharoyan E. G. 
Published: July 2007

AbstractOptical and EPR spectra of LiNbO3 single crystal doped with copper ions are measured in the range of 200 to 6000 nm and in the X‐band, respectively. In the temperature range 60 to 200 K a transition is observed from the low‐temperature EPR spectra with Cs symmetry (g𝒵 = 2.403, gy = 2.121, gx = 2.095 and = 51°) to the high‐temperature spectrum with C3v symmetry (g′∥ = 2.22, g⟂ = 2.17 and 𝒵 ∥ C3) whose parameters are given by the average of the corresponding parameters of the low‐temperature spectra. EPR spectra of LiNbO3:Cu2+ are interpreted taking account of the static Jahn‐Teller effect in trigonal field and formation of non‐equivalent minima on the adiabatic potential surface. In case of the static Jahn‐Teller effect in trigonal field formulas for the g‐factors of d9 ions are derived theoretically. A new model of Cu2+ substitution in LiNbO3, i.e. formation of a Cu  VLi complex, is suggested. In optical spectra an absorption band at 5000 cm−1 is detected due to Jahn‐Teller splitting of the 2Etr ground state. The Jahn‐Teller stabilization energy EJT = 1250 cm−5 and crystal field parameters 10Dq = 8200 cm−1, ν = −1200 cm−1, and ν− = 600 cm−1 are determined.
Analysis of the Hyperfine Interactions of the Vacancy‐Iodine Complex in ZnSe
Authors: Schrittenlacher W. 
Published: July 2007

AbstractThe ESR line multiplicity of iodine containing ZnSe single crystals obtained after optical excitation is analysed by means of a spin Hamiltonian. A good fit is obtained considering Zeeman energy, hyperfine energy, quadrupole energy, and (pseudo)‐nuclear Zeeman energy with S = ½ and I = 5/2. The fact that iodine consists to 100% of the isotope 127I with I = and that the spectra are described by I = is proof that iodine is an integral part of the complex centre. This is the first time that a ligand hyperfine structure of A‐centres in ZnSe is observed and numerically analysed. Therefore, also the orientations of the different tensors in the spin Hamiltonian are determined with respect to the orientation of the complex centre. Besides the 127I ligand hyperfine structure the 77Se hyperfine and the 77Se ligand hyperfine structure are observed. From the different hyperfine parameters the distribution of the hole wave function is derived and yields ≈ 90% localisation in the sp3‐hybrid lone pair orbitals directed to the zinc vacancy.
Electron Paramagnetic Resonance of Tetravalent Praseodymium in Zircon
Authors: Harris E. A. , Mellor J. H. , Parke S. 
Published: July 2007

AbstractThe electron paramagnetic resonance of Pr4+ in the tetragonal crystal field of ZrSiO4 is measured at 9.9 GHz at temperatures near to 15 K. Hyperfine constants and g‐values are reported which, unlike most other rare‐earth ions in this material, show only weak anisotropy. The spectra are interpreted in terms of a 2F5/2Γ ground state with evidence of mixing to 2F7/2 states.
The Magnetic Field Distribution in Deformed FLL in Type II Superconductors
Authors: Przełożny Z. , Kozłowski G. 
Published: July 2007

AbstractThe elastic properties of the flux line lattice (FLL) in type II superconductor are calculated from the Ginzburg Landau theory for large induction Hc1 ≪ H ⪅ Hc2. It is obtained that the elastic response of FLL to the localized perturbation field is non‐local generally. The change of magnetic field caused by the deformation of FLL is expressed by the integral with kernel vanishing in the distance . It leads to the effective interaction between flux‐lines with range and amplitude proportional to −2. The influence of the surface of the superconductor on FLL deformation caused by the normal inclusions is obtained.