bluuebunny/crossref_metadata_2025_split huggingface dataset:
Distribution Functions and Thermodynamical Properties of KD2PO4 and ND4D2PO4 Type Crystals
Authors: Levitskii R. R. , Korynevskii N. A. , Stasyuk I. V. 
Published: July 2007

AbstractIn the cluster approximation, taking into account long‐range correlations, the distribution functions of deuterated ferroelectric compounds of the orthophosphate type are calculated. The behaviour of the single and pair function near the phase transition point for both the KD2PO4 and ND4D2PO4 type structures is analysed. It is shown that expressions for the longitudinal and transversal components of the dielectric susceptibility tensor are in a qualitative coincidence with the experiment in the phase transition region. Phase transition and some thermodynamical properties of deuterated orthophosphates are studied on the basis of the results obtained. It is shown that the long‐range interaction is necessary to form antipolarization states.
Solitary Excitations in One‐Dimensional Ferromagnets with Biquadratic Exchange
Authors: Pushkarov Kh. I. , Pushkarov D. I. , Vlahov J. P. 
Published: July 2007

AbstractThe existence of solitary excitations (“magnolitons”) in one‐dimensional ferromagnets with biquadratic exchange is shown. Such excitations appear as solutions of a nonlinear „Schrödingerlike”︁ equation with higher nonlinearity.
Influence of Exchange Interaction on the Quantum Transport Phenomena in Hg1−xMnxTe
Authors: Jaczyński M. , Kossut J. , Gałązka R. R. 
Published: July 2007

AbstractA series of anomalous features of the Shubnikov‐de Haas effect in n‐type Hg1−xMnxTe mixed crystals is detected, e.g., strong temperature dependence of the ShdH peak positions, large values of electronic g‐factors, non‐monotonic behaviour of the amplitude of ShdH oscillations as a function of temperature. These features cannot be explained with the help of usual theoretical models. They are explained within the modified Pidgeon‐Brown model including the exchange interaction between conduction electrons and electrons from 3d shell of Mn ions. The quantum oscillations of the thermoelectric power are also observed. The behaviour of amplitude and peak positions of thermoelectric power are compatible with those of magnetoresistance.
The Semiconductor–Semimetal Transition in Bi1−xSbx Alloys with x ≧ 0.22
Authors: Kraak W. , Oelgart G. , Schneider G. , Herrmann R. 
Published: July 2007

AbstractIn Bi1−xSb, alloys with x = 0.13 to 0.25 the electrical transport properties (electrical resistance, magnetoresistance, and Hall effect) in the temperature interval T = 1.8 to 77 K in weak magnetic fields ( μB ≪ 1) are investigated. In alloys with x = 0.19 and x = 0.23 the dependence of the galvanomagnetic properties on the hydrostatic pressure are also investigated. The rapid increase of the charge‐carrier concentration in alloys with x > 0.22 and the qualitatively different pressure dependence of the gelvanomagnetic properties for this two alloys are explained by the overlapping of the conduction band at L with a valence band at an other point of the Brillouin zone, which begins at x ≈︁ 0.22. A semimetal‐semiconductor transition is detected in Bi1−xSb, alloys with x > 0.22 under high hydrostatic pressure.
Atomic Motions Corresponding to Zone Center Phonons in Paratellurite
Authors: Lemos V. , Cerdeira F. , Cardona M. 
Published: July 2007

AbstractBy using standard group theory techniques the symmetrized atomic motions are obtained corresponding to the various irreducible representations of the factor group of paratellurite (TeO2). This material can be treated as a molecular crystal. Thus the various symmetrized atomic motions of the same symmetry which correspond to molecular vibrations of different symmetry should not mix much if the dynamical matrix for the zone center phonons is diagonalized. Simple rules are developed for the identification of the various modes in the observed Raman and infrared spectra. These rules are based on the magnitude and ratios of the observed frequencies, their infrared strength, and their Raman cross‐sections. Strong Raman cross‐section and infrared strength result only if the corresponding molecular vibrations are allowed and if these vibrations are fully symmetrized over the four molecules per unit cell. In this manner a consistent assignment of all the observed infrared and Raman modes is achieved.
Inelastic Scattering of Electrons by Optic Phonons in InSb‐Type Semiconductors
Authors: Pfeffer P. , Zawadzki W. 
Published: July 2007

AbstractInelastic scattering of electrons by optic phonons in III–V semiconducting compounds of InSb type is described, taking into account consistently nonparabolic band structure of these materials both in the ε(k) dependence and the electron wavefunctions. The calculations are based on the Kane band model, including explicitly admixture of p‐like components and spin mixing in the conduction band. A variational procedure is used to derive explicit expressions for electric conductivity in case of optic phonon scattering. It is indicated how to generalize the procedure for an arbitrary spherical energy band. Numerical values of electron mobility in n‐InSb at various temperatures and electron concentrations are presented and compared with mobilities calculated in the relaxation time approximation, thus examining the validity of the latter. It is demonstrated that even at room temperature the nonelastic character of electron–phonon collisions has a pronounced effect on the conductivity.
Oscillator Strength of Excitons in Highly Excited PbI2
Authors: Iwasaki T. , Goto T. , Nishina Y. 
Published: July 2007

AbstractAbsorption and emission spectra are measured in highly excited states of evaporated films of PbI2 at 10 K. The spectra show that the oscillator strength of the 1s exciton decreases with the increase in the excitation intensity. This change is related to the decrease in the exciton binding energy in the highly excited state.
Nonadiabatic Quantum Theory of Interstitial Diffusion in Crystals
Authors: Pavlovich V. N. , Rudko V. N. 
Published: July 2007

AbstractThe influence of the nonadiabaticity of interstitial motion on the quantum underbarrier diffusion is discussed. The wave functions of crystals with an impurity, localized in initial and final positions, are obtained and used for the calculation of the probability of interstitial transitions from one interstitial to another per unit time. The temperature dependence of this transition probability is analysed, taking into account the nonadiabaticity of impurity motion and the deviation from the Condon approximation which is used for the calculation of transition matrix elements.
Electron Paramagnetic Resonance Study of Cu2+ in K2Zn(ZrF6)2 · 6 H2O
Authors: Petrashen V. E. , Yablokov Yu. V. , Davidovich R. L. 
Published: July 2007

AbstractAn EPR study of Cu2+ ions in K2Zn(ZrF6) · 6 H2O in the temperature range 4.2 to 300 K at X and Q bands is carried out on single crystals and powders. The presence of the two conjugated Cu(H2O)62+ complexes is discovered and the angles between respective axes of the rhombic crystalline field are determined. The temperature dependence of the Cu2+ EPR spectrum tensor parameters is discussed in terms of dynamic Jahn‐Teller effect. The additional arguments in favour of the dynamic nature of the observed phenomena are given and the values of the energy splittings between three possible Jahn‐Teller configurations δ1,2 ≈︁ 280 cm−1, δ1,3 ⪆ 1000 cm−1 are obtained. The necessity of the “dynamic” approach to the study of “static” Jahn‐Teller EPR spectra of Cu(H2O)62+ complexes in similar low‐symmetry crystals is shown.
On the Calculation of Superhyperfine Structures
Authors: Gehlhoff W. 
Published: July 2007

AbstractThe calculation of SHF structures is studied, which are caused by the interaction with several ligand nuclei if the simultaneous occurrence of electronic spin transitions with and without nuclear flips must be taken into consideration. The connection is shown between two formulas given in the literature for the calculation of SHF structure produced by ligand nuclei with I = 1/2.
Inelastic Light Scattering of the VK Centers in the Alkali Halides
Authors: Goovaerts E. , Schoemaker D. 
Published: July 2007

AbstractThe Raman spectra of the “self‐trapped hole” or VK center are measured in LiF, KCl, and RbCl. The localized vibrational modes induced by these centers are situated at 437, 241, and 244 cm−1, respectively. The vibrational modes of the VK center in the alkali halides and fluorides are calculated, making use of a semi‐empirical energy function. These calculations are discussed and compared with the experimental data.
Photoconduction in Polydiacetylene Multilayer Structures and Single Crystals. Evidence for Band‐to‐Band Excitation
Authors: Lochner K. , Bässler H. , Tieke B. , Wegner G. 
Published: July 2007

AbstractSteady state photoconduction action spectra for polydiacetylene multilayer structures and single crystals (TCDU) are reported. Interpretation is given in terms of a valence‐to‐conduction band transition which is buried under the vibronic sidebands of the dominant exciton transition. The associated absorption coefficient follows a (αb ħω) ˜ (ħω − Eg)2 law which indicates either an indirect transition or a direct transition between non‐parabolic bands. The general validity of this relationship is supported by literature data for PTS, DCHD, and polyethylene. Gap energies are (2.5 ± 0.1) eV and (2.6 ± 0.1) eV for two different multilayer forms, (2.6 ± 0.1) eV for TCDU, (2.1 ± 0.1) eV for PTS, and (2.30 ± 0.05) eV for DCHD. The transition is three‐dimensional indicating finite valence and conduction band dispersion perpendicular to the polymer chain direction.
NMP‐TCNQ: A Realization of the Disordered Hubbard Model
Authors: Papatriantafillou C. 
Published: July 2007

AbstractSeveral quantitative models have been proposed for the electronic structure of the organic charge transfer salt NMP‐TCNQ. They range from the periodic Hubbard model that emphasizes the role of electron correlation in the material, to models that emphasize the role of its intrinsic static disorder. A detailed study is made of the dielectric properties of the material, and it is found that the intrinsic static disorder depends on the electronic density of states at the Fermi level. Then, considering the system as a realization of the one‐dimensional disordered Hubbard model and using available experimental data, the intrinsic disorder and other band parameters are calculated.
Charge Transfer Spectra of Transition Metal Ions in Cadmium Halide Lattices
Authors: Coutts A. G. , Day P. 
Published: July 2007

AbstractThe near ultraviolet spectra of CdCl2 and CdBr2 crystals doped with Fe2+, Co2+, and Ni2+ at 4.2 K and the magnetic circular dichroism spectra of Fe2+, Co2+, and Ni2+ doped in CdBr2 are measured. The intense bands observèd in the spectra are assigned to charge transfer transitions between the halide ions of the crystal lattice and the 3d orbitals of the guest ion.
Transient Infrared Absorption of Bound Polarons in NaCl
Authors: Carlier F. , Jacobs G. 
Published: July 2007

AbstractWhen NaCl crystals containing F and M centres are irradiated in the corresponding absorption bands with laser light pulses a transient induced absorption band is found with a maximum at 0.29 eV. This band, caused by bound polarons, shows a structure due to phonon emission. The average energy separation between the maxima is 0.0297 eV at LHT. This is equal to 0.89ℏωLO. The decay of the induced infrared absorption is logarithmic. The source of the attractive field for the polaron is not known.
Mean Free Paths by Inelastic Interactions, Stopping Powers, and Energy Straggling for Electrons of Energies up to 20 ke V in Various Solids
Authors: Akkerman A. F. , Chernov G. Ya. 
Published: July 2007

AbstractFor the elements C, Be, Mg, Al, Si, K, Ge, Sb, Bi calculations of the mean free paths and stopping powers of low energy electrons are performed. In the computational model Lindhard's formalism of the dielectric response function for pair and plasmon excitation and the classical cross‐section for ionization processes are used. Anomalously high mean free paths and small stopping powers in potassium are found. This behaviour which is connected with low electron concentration in the valence band is expected to hold for all alkali metals. For energies above 10 ke V the calculated dE/dχ agree well with values calculated from the Bethe‐Bloch formula. A Monte‐Carlo method is used for the calculation of the energy loss distribution of electrons passing through thin targets. It is noted that Blunck‐Leisegang's theory fails to render the energy straggling at electron energies below 10 ke V.
Theory of the Anomalous Bulk Photovoltaic Effect in Ferroelectrics
Authors: von Baltz R. 
Published: July 2007

AbstractA model is presented for the bulk photovoltaic effect (BPVE) in ferroelectrics which is due to an asymmetry in the ionization cross‐section for polarized impurities. This asymmetry is related to a quantum‐mechanical interference effect and explains the dependence of the BPVE on frequency and polarization of light, and it gives reasons for a possible sign change of the current, as it is observed, e. g., in BaTiO3. Numerical results agree nearly perfectly with experimental data for Fe‐doped LiNbO3.
Stimulated Intrinsic Recombination Processes in II–VI Compounds
Authors: Koch S. W. , Haug H. , Schmieder G. , Bohnert W. , Klingshirn C. 
Published: July 2007

AbstractThe intrinsic recombination processes are investigated in highly excited II–VI compound semiconductors which involve the following scattering processes: the exciton‐exciton scattering (P2 line), the exciton‐electron or ‐hole scattering, and the sattering of an exciton by emission of a longitudinal optical phonon. From the stationary rate equations the laser threshold and the maxima of the spontaneous and stimulated emission for the various processes are determined. Experimental investigations of these emission processes are carried out for CdS platelets, ZnO and ZnTe crystals. Good agreement between experimental results and theoretical predictions for the temperature dependences of the laser thresholds, and of the emission maxima is obtained.
Two‐Centre Exchange Interactions between Orbitally Degenerate Ions. I. One Ion in Orbitally Degenerate State
Authors: Eremin M. V. , Kalinenkov V. N. , Rakitin Yu. V. 
Published: July 2007

AbstractA multielectron theory of exchange interactions in transition metal ion pairs in cubic matrices and ions in orbitally degenerate states is developed. The orbitally dependent part of the exchange Hamiltonian is expressed by Pauli operators determined in the orbital space for the case of an orbital doublet and by fictitious orbital operators L̃ = 1 in the case of a triplet state. It is shown that the anisotropic exchange parameters may be estimated from isotropic ones. The theory described is compared with experiment.
Temperature Dependence of the Resistivity in Semimetals of the Bismuth Type
Authors: Kuka G. , Kraak W. , Gollnest H.‐J. , Herrmann R. 
Published: July 2007

AbstractThe resistivity of semi‐metallic bismuth‐antimony alloys and tellurium‐ or tin‐doped bismuth specimens is studied in a temperature range from 1.8 to 77 K. Typical dependences of the specific resistivity ϱ(T) as a function of Fermi energy are conceivable on the basis of an electron‐phonon scattering theory.
Ultrasonic studies of the structural phase transition in squaric acid
Authors: Rehwald W. , Vonlanthen A. 
Published: July 2007

AbstractThe elastic stiffness functions c11, c66, c33, and c44 are determined by ultrasonic velocity measurements as a function of temperature below and above the phase transition at Tc = 373 K. Their variation below Tc is discussed in terms of critical exponents. From their value of the order of 0.5 no unique decision can be made whether the elastic critical behaviour is determined by the crossover exponent for the stress acting as a “modifying field”, is due to a tricritical point, or is the consequence of a weakly first‐order transition.
Two‐centre exchange interactions between orbitally degenerate ions. II. Two ions in orbitally degenerate states
Authors: Eremin M. V. , Kalinenkov V. N. , Rakitin Yu. V. 
Published: July 2007

AbstractThe semiempiric theory of anisotropic exchange interactions developed earlier within the framework of the strong crystal field scheme is applied to describe pair exchange interactions between orbitally degenerate transition metal ions lying on a fourfold axis and having approximately Oh site symmetries. The effective Hamiltonians, with orbitally dependent parts expressed in terms of ficitious orbital moments, are obtained for all possible combinations of orbitally degenerate states (doublet–doublet, doublet–triplet, and triplet–triplet). These include relatively small numbers of anisotropic exchange parameters which can be estimated from the values of isotropic exchange parameters. The theory described is compared with experiment.
Optical absorption study of iron trifluoride thin films
Authors: Lachter A. , Salardenne J. , Barrière A. S. 
Published: July 2007

AbstractThe optical absorption of crystallized thin films of iron trifluoride is investigated. The energy gap in FeF3 thin films is about 5.96 eV. The six peaks characterizing the different spin transitions between the 3d states of iron and two excitonic peaks are obtained. Furthermore, an optical absorption edge corresponding to an energy of 1.1 eV is observed. It can be interpreted by electronic transitions from localized states in the forbidden band due to a lack of fluorine to the delocalized states of the conduction band.
Auger recombination in PbSnTe‐like semiconductors
Authors: Ziep O. , Mocker M. , Genzow D. , Herrmann K. H. 
Published: July 2007

AbstractIn semiconductors with PbSnTe‐like band structure the Auger coefficient Cn is investigated for most probable eeh transitions taking into account a nonparabolic approximation (NPA). Considering mirror‐symmetric hyperbolic bands, singularities in the so‐called “activation energy” appear which are removed if deviations from the hyperbolicity are included. At high temperatures Tl the value of Cn in NPA has the same order of magnitude as the value C proposed by Emtage and is nearly independent of temperature; if Tl < 77 K the value of Cn strongly decreases and differs by orders of magnitude from C. The obtained results are compared with experimental data.
Optical phonons in PdHxand PdDxby superconducting tunneling measurements
Authors: Dumoulin L. , Nédellec P. , Arzoumanian C. , Burger J. P. 
Published: July 2007

AbstractTunneling data on phonon spectra for some superconducting PdHxand PdDxcompounds withx≈ 0.95 are presented. The main observed structures correspond to the optical vibrations of H and D indicating that these phonons are basic for the occurrence of superconductivity in these compounds. The position and width of these structures are discussed and compared: anharmonicity effects are observed which indicate that the H force constant is 14% higher than the D one.
A new off‐center defect system, RbCl:Li+, studied with dielectric techniques under hydrostatic pressure
Authors: Thörmer K. , Lüty F. 
Published: July 2007

AbstractRbCl crystals with Li+ doping, spanning a concentration range of nearly three orders of magnitude, are systematically studied in their real and imaginary dielectric response under hydrostatic pressure (up to 7 kbar). A dielectric constant anomaly and loss peak around 40 K is found, which can be fitted to a Langevin‐Debye behavior of classical dipoles with an activation energy for reorientation of 510 K. For small Li+ doping (N < 1018 cm−3), this dielectric response scales with the Li+ concentration, yielding (for Lorentz corrected fields) a dipole moment of 〈p〉 = 0.52 e Å. The potential barrier for the Li+ dipole reorientation is found to be drastically reduced under hydrostatic pressure, shifting the observable relaxation to low temperatures. Though this pressure tuning process is interrupted by the NaCl → CsCl structural phase‐transition at 4.6 kbar, it can be extrapolated that for about 8 kbar (i.e., 2% compression) RbCl:Li+ should become a tunneling system similar to KCl:Li+. Consequences of the observed behavior for the theoretical understanding and host‐lattice trends of Li+ off‐center defects and for the behavior of FA(Li) centers are discussed.
Inversion of the Γ and L conduction bands of GaSb under uniaxial stress
Authors: Noack R. A. 
Published: July 2007

AbstractWith photoluminescence experiments under high uniaxial stress in 〈111〉 crystallographic direction it is possible to observe the inversion of the Γ and L conduction bands of GaSb directly in the spectra at 6.5 kbar. From the line shifts the uniaxial deformation potential constant of the L conduction band E2 = (15 ± 1) eV is determined. Also the energy separation between the two conduction bands at zero stress is obtained from the experimental data: ΔE = (93 ± 3) meV. A donor level assosiated with the L conduction band is seen in the spectra at higher stresses. The ionisation energy of this donor is determined to Ei = 33 meV.
Effect of the mixing between Frenkel excitons and charge transfer states on charge carrier transfer in a linear molecular crystal
Authors: Petelenz P. 
Published: July 2007

AbstractThe previously proposed model of the mixing between Frenkel excitons and CT states is generalized for a linear model crystal to include the effect of the CT states from the immediate neighbourhood of the charge carrier in the direction of its propagation. The transfer of the charge carrier to one of the molecules involved in the CT state is taken into account. In contrast to the influence of more distant CT states, the effect yields the reduced value of the effective mass of the charge carrier. Some crude numerical estimates are given, and the possible experimental consequences are pointed out.
Frequency‐ and wave‐vector‐dependent dielectric function of a model semiconductor
Authors: Milchev A. 
Published: July 2007

AbstractClosed analytical expressions for the real part ϵ1(q, ω) and the imaginary part ϵ2(q, ω) of the frequency‐ and wave‐vector‐dependent dielectric function are obtained including a gap Eg in an appropriate manner in the spirit of the nearly‐free electron approximation, and requiring that these functions will exactly satisfy the Kramers‐Kronig relations and the f‐sum rule. In the long wavelength limit the classical Lorentz oscillator result comes out, whereas for ω = 0 the static screening function is decisively improved with regard to earlier model calculations. The results also yield the plasmon dispersion relations ωL(q) and ωT(q) for Si, Ge, GaAs, and ZnSe in good agreement with previous detailed computations. With the average gap width Eg going to zero the expressions obtained transform into the well‐known RPA (Lindhard) formulae for a free electron gas.
Study of the charge exchange process of iron impurity atoms in GaAs and GaP by Mössbauer spectroscopy
Authors: Seregin P. P. , Nasredinov F. S. , Bakhtiyarov A. Sh. 
Published: July 2007

AbstractThe iron impurity atom state in GaAs and GaP is studied by emission Mössbauer spectroscopy. The iron atoms substitute for gallium atoms and have a tetrahedral surrounding. The electron configuration for a neutral state of these centres (Fe)° is 3d54s0.52p1.56 (in GaAs) or 3d54s0.79p2.37 (in GaP), while in the ionized state the population of the 3d shell of iron is increased (3d6). The process of fast electron exchange via the valence band between the (Fe)° and (Fe)− centres at 295 K is observed in slightly overcompensated GaP. For E(Fe) – E(Co) a value of – (0.035 ± 0.002)eV is obtained where E(Fe) and E(Co) are the iron and cobalt levels in GaP, respectively.