bluuebunny/crossref_metadata_2025_split huggingface dataset:
Polaron state of an electron near a structural instability
Authors: Batyev E. G. , Efanov A. V. 
Published: July 2007

AbstractThe formation of a Pekar polaron‐type self‐trapped state by an electron in ferro‐ and antiferroelectrics near the phase transition point is shown to be possible in the case when there is no strong coupling polaron far from the transition. This feature is due to the “soft mode” in the phonon spectrum. The properties of the polaron strongly depend on the proximity to the phase transition point.
On the interband absorption in lead chalcogenides
Authors: Genzow D. , Mironov A. G. , Ziep O. 
Published: July 2007

AbstractThe optical absorption coefficient K for direct allowed interband transitions between states L and L, respectively, is calculated on the basis of the six‐band model for lead chalcogenides, taking into account the k‐dependence of optical matrix elements. Comparisons are made between theoretical results of the six‐band and two‐band models and experiments. Good agreement is obtained between the calculated and experimental absorption spectrum in the vicinity of the absorption edges. For photon energies ħω > 1.5EG the experiments give higher K than theory. The disagreement is stronger for the six‐band model. The temperature‐ and composition‐dependence of K near the absorption edge are described better by the two‐band than by the six‐band model.
Nucleation phenomena in electron–hole drop formation in Ge and Si. III. Experimental results for Ge
Authors: Westervelt R. M. , Staehli J. L. , Haller E. E. 
Published: July 2007

AbstractA systematic experimental study and theoretical analysis of hysteresis and threshold phenomena in the luminescence of electron–hole drops (EHD) and free excitons (FE) in volume‐excited crystals of ultrapure Ge is presented. Data are given between 1.2 and 2.0 K for 1) hysteresis curves for the EHD and FE luminescence intensity obtained by cycling the excitation; 2) metastable time development of the EHD signal for times ≈ 4 × 103 s; and 3) a calibrated phase diagram for the FE density thresholds n+ and n− for the creation and destruction of EHD vs. T. Excellent agreement between these data and nucleation theory is found. The principal experimental results are: 1) reproducible hysteresis curves for EHD exhibiting well‐defined excitation thresholds; 2) logarithmic variation of the EHD signal with time and direct evidence that individual EHD can exist for times ≈ 6 × 104 s; 3) the first measurement φ0 = (1.9 ± 0.2) meV of the EHD condensation energy from threshold data which correctly accounts for non‐equilibrium effects, resolving previous discrepancies with spectroscopic data; and 4) an accurate measurement of the EHD surface energy w = (2.6 ± 0.3) × 10−4 erg cm−2.
An optimized LCAO version for band structure calculations application to copper
Authors: Eschrig H. , Bergert I. 
Published: July 2007

AbstractAn LCAO version for band calculations is presented which is conceptional simple, highly effective, and satisfies any reasonable accuracy demand. Due to the very convenient way of representing the results for wave functions it can easily be carried out self‐consistently and e.g. can be used to calculate Wannier functions. For illustration, numerical results for copper are given.
The influence of interatomic potentials on the interaction of He with a \documentclass{article}\pagestyle{empty}\begin{document}$ \frac{1}{2}\left\langle {111} \right\rangle $\end{document} {110} edge dislocation in molybdenum
Authors: van Heugten W. F. W. M. , van den Berg F. , Caspers L. M. , van Veen A. , de Hosson J. Th. M. 
Published: July 2007

AbstractThe binding of clusters of up to four helium atoms to a \documentclass{article}\pagestyle{empty}\begin{document}$ \frac{1}{2}\left\langle {111} \right\rangle $\end{document} {110} edge dislocation in Mo is calculated, using two sets of interaction potentials. The first set contains MoMo, MoHe, and HeHe potentials derived by several authors between 1970 and 1974. The second set contains potentials recently fitted to phonon curves and helium desorption experiments. Both sets give binding energies between He and the dislocation of respectively 1.6 and 1.8 eV and binding energies between dislocation bound helium of 0.7/0.9 and ;0.2/+0.1 eV, respectively. The migration energy of helium along the dislocation is found to be equal to that in the bulk.
The magnetic moment of Cr0.6Mn0.4
Authors: Williams D. E. G. , Spraget H. W. G. , Perrin R. 
Published: July 2007

AbstractThe results of a neutron diffraction experiment on a b.c.c. single crystal of Cr0.6Mn0.4 are analysed in terms of a spherical atom form factor to give a mean magnetic moment per atom of (0.82 ± 0.04) β. The deviations from spherical shape of the spatial distribution of the magnetic moment are explained in terms of a predominantly t2 symmetry.
Absorption, excitation, and fluorescence spectra of thallium‐activated ammonium bromide
Authors: Sharan V. B. , Srivastwa D. N. S. , Sen S. C. 
Published: July 2007

AbstractThe optical spectra of Tl+ ion in a CsCl‐like environment is found to differ considerably from those of a Tl+ ion in NaCl‐like environment. Absorption, fluorescence, and excitation spectra of ammonium bromide which has a CsCl‐like structure at room temperature, activated by various amounts of thallium are investigated at room temperature in order to ascertain the nature of the electronic states involved in the luminescence centres in a CsCl‐like host lattice. The A and B absorption bands are obtained at 259 and 224 nm even at low thallium content. With increasing thallium concentration additional absorption bands are obtained at 234, 242, 265, 275, and 285 nm. The emission bands are obtained at 390, 428, 490, and 570 nm. The absorption and fluorescence bands are assigned to the electronic transitions with Tl+ in cubic symmetry and in dimer centres having D4h site symmetry. The pattern of luminescence spectrum is compared to that of NH4Cl:Tl reported earlier.
Infrared absorption of silicon irradiated by protons
Authors: Gerasimenko N. N. , Rollé M. , Cheng Li‐Jen , Lee Y. H. , Corelli J. C. , Corbett J. W. 
Published: July 2007

AbstractHydrogen implantations into silicon samples at room temperature and at 190°C are carried out. Infrared studies are performed on these samples before and following annealing. Previously observed divacancy and hydrogen vibrational bands are found as well as higher‐order‐bands not previously found in proton irradiation. In addition new hydrogen vibrational bands and other bands are observed and discussed.
Channeling and a semistatistical model for the interatomic potential
Authors: Pathak A. P. , Srivastava M. P. 
Published: July 2007

AbstractA semistatistical model is used for neutral and ionized atoms to calculate channeling parameters like critical angles. The variation of interatomic potential with interatomic distance based on this model, is compared with that obtained with other approximations of the Thomas‐Fermi model. It is found that the interatomic potential itself and the channeling parameters obtained compare well with predictions of TF model and with experiment.
Spin diffusion and spin–lattice relaxation in paramagnetic crystals
Authors: Vugmeister B. E. 
Published: July 2007

AbstractThe spin diffusion effect on the paramagnetic relaxation due to fast relaxing paramagnetic centres is investigated theoretically. The derived expressions for the relaxation rate take into account peculiarities of the Zeeman energy migration in a disordered spin systems and are valid for an arbitrary relation of the paramagnetic particle interaction between themselves and with the fast relaxing centres. The homogeneously and inhomogeneously broadened EPR spectra are considered and compared with the experiment.
Superconductivity originating from quasi‐orbital electrons. III. Quasi‐orbital conduction electrons in non‐adiabatic systems
Authors: Krüger E. 
Published: July 2007

AbstractQuasi‐orbital conduction electrons as defined in Part I are considered in non‐adiabatic systems. It is shown that for any interaction in such systems the “crystal spin” of the electrons and phonons is a conserved quantity, with phonons possessing the crystal spin quantum number one. Furthermore, it is shown that a spin–phonon exchange interaction may occur in the non‐adiabatic system. According to Part II, this spin–phonon interaction yields a coupling of the electrons to Cooper pairs.
Localization of additional screening charge around 3d‐transition metal impurities in Al
Authors: Lautenschläger G. , Mrosan E. 
Published: July 2007

AbstractThe additional screening charge around 3d‐transition metal impurities in Al which is localized inside the muffin‐tin sphere around the impurity is calculated. From the results it is concluded that the greatest part of the charge perturbation due to the impurity is screened within a spherical region of radius rMT. This result is in agreement with the assumption of strongly localized impurities usually applied in the theory of substitutional impurities in metals.
Interaction between a metal surface and an external molecular complex
Authors: Alfred L. C. R. 
Published: July 2007

AbstractThe long and intermediate range interaction between a metal surface and an external molecular complex is investigated. The calculation is based on a simplified model where the complex is represented by an ensemble of point multipole fields and the metal by a semi‐infinite jellium of smeared out ionic cores and free electrons. The response of the metal electrons to the external field is obtained in closed form by a linearized Thomas‐Fermi treatment. The energy of the complex in the metal surface response field is determined from perturbation theory. Applications to the effective multipole moments of the complex and to the changes in its internal couplings are discussed.
Effect of three‐body interactions on the electronic polarizabilities and photoelastic behaviour of alkali halides
Authors: Shanker J. , Lashkari A. K. G. , Gupta V. P. 
Published: July 2007

AbstractThe effect of three‐body interactions which are responsible for the Cauchy breakdown in ionic solids, is investigated on the electronic polarizabilities and photoeleastic behaviour of alkali halides. A new set of electronic polarizabilities of alkali and halogen ions is produced. The strain derivatives of electronic polarizabilities are evaluated by considering the influence of the crystalline potential on the polarizabilities of ions. The photoelastic behaviour is studied by determining the strain derivatives of electronic dielectric constant. Results obtained agree closely with experimental data.
Hopping conductivity in heavily doped strongly compensated GaAs
Authors: Arnaudov B. G. , Domanevskii D. S. , Yanchev I. Y. 
Published: July 2007

AbstractThe hopping conductivity in heavily doped and closely compensated LPE gallium arsenide is investigated in the temperature range 4.2 to 250 K. It is found that the resistivity in n‐type samples increases with lowering the temperature as In Q ∼ (T★/T)α where α takes successively the values 1, 1/2, and 1/4. The values of T★ in the corresponding temperature ranges are in a good agreement with theoretically calculated ones provided one takes into account the correlation in the impurity distribution. The resistivity in analogous p‐type closely compensated samples depends on temperature as In Q ∼ T−1/2 as a rule.
The electrical conductivity of bismuth chalcogenides in the liquid state
Authors: Satow T. , Uemura O. , Sanzyo M. 
Published: July 2007

AbstractThe electrical conductivities of liquid BiTe and BiSe systems are measured as a function of temperature. Plots of the electrical conductivity and its temperature derivative versus composition for liquid BiTe system give a relatively smooth curve near the stoichiometric composition of Bi2Te3. The electrical conductivity of the liquid BiSe system is considerably small compared with liquid BiTe system. The temperature dependence of the electrical conductivity indicates that the liquid BiSe system becomes metallic rapidly with increasing Bi content beyond the composition of Bi2Se3. The impurity doping (Bi, Ga, and In) effects are investigated on Bi2Se3 melt using both the electrical conductivity and the magnetic susceptibility. The results of Bi‐doped melts suggest that a complete ionization occurs of the excess Bi atoms, whereas an appreciable non‐localization of valence electrons is seen in alloys containing excess Ga and In atoms.
121Sb mössbauer spectroscopy in some mixed‐valence antimony hexachlorides
Authors: de Jesus Filho M. F. , Sanchez J. P. , Friedt J. M. 
Published: July 2007

AbstractThe 121Sb Mössbauer spectra of (NH4)2Sn1−xSbxCl6 (x = 0.13, 0.21, 0.28, and 0.33) and Cs2SbCl6 are reported in the temperature range from 4.2 to 140 K. The spectra consist in the whole temperature range of two lines with isomer shifts characteristic for SbIII and SbV ions. Not observed is the thermal activation of a fast electron transfer between the SbIII and SbV ions suggested previously.
Ionization of low donor levels and recombination of hot electrons in n‐Si at low temperatures
Authors: Asche M. , Kostial H. , Sarbey O. G. 
Published: July 2007

AbstractThe concentration of electrons and the decay time of carriers additionally excited from the donor states are measured in dependence on the electric field strength in n‐Si in the temperature region of partial freezing out. From these data the parameters characterizing the processes of phonon assisted and impact ionization and recombination are determined. It is shown that at not too low temperatures the Auger recombination and the impact ionization at weak electric field strength are noticeable and are determined by the contribution of the highly excited states of the donors. The phonon assisted recombination is described by the improved model of the cascade process including intervalley scattering of the electrons.
Calculation of the transition temperature Tc of superconductors
Authors: Nowotny H. , Hittmair O. 
Published: July 2007

AbstractAn iterative solution of the Eliashberg equations for isotropic superconductors is approximated by an analytical expression and gives as a result an equation for the superconducting transition temperature Tc. For small Tc (Tc ≪ mean phonon energy) a formula is derived, which agrees within a few per cent with the well‐known McMillan formula, if in this formula the mean logarithmic phonon energy ωlog is taken as pre‐factor, a correction which was already proposed earlier. For large Tc the (λ < ω2)1/2 behaviour of Allen and Dynes is found. Numerical results are presented for 0.5 < λ < 8, where the α2F(ω)‐shapes are taken corresponding to Hg, Pb, In, and Nb.
Excitons in WS2 films pressure and temperature effects
Authors: Brothers A. D. , Brungardt J. B. 
Published: July 2007

AbstractA technique for producing thin film samples WS2 is reported. Exciton peak positions are measured as a function of hydrostatic pressure to 3500 atm at 90 K and temperatures in the range 90 to 300 K. Values for (∂E/∂P)T for the A‐ and B‐peaks are 5.9 × 10−6 and 7.2 × 10−6 eV/atm, respectively. Peak C shifts 0.3 × 10−6 eV/atm, while values of (∂E/∂T)P are −1.8 × 10−4, −2.8 × 10−4, and −0.3 × 10−4 eV/K for peaks A, B, and C, respectively. The value of (∂E/∂T)V is estimated at 1 × 10−4 eV/K. A comparison of these results with those for MoS2 is made, and comments are made concerning the nature of the band structure of WS2.
Calculation of the dielectric function of the one‐dimensional Hubbard model
Authors: Gasser W. , Höfling R. 
Published: July 2007

AbstractThe dielectric function of the one‐dimensional Hubbard model is evaluated in the strong correlation limit for small wave numbers and arbitrary electron concentrations in the paramagnetic phase. Expressions are given for the plasma frequencies, the plasmon stiffness, the critical wave number and for the real and imaginary part of the dielectric function in the whole frequency region. The results are compared with recent experimental studies of K‐TCNQ (potassium‐tetracyanoquino‐dimethane) performed by Tanner et al.
Calculation of first‐order and second‐order Jahn‐Teller coupling constants in MgO:V2+ and KMgF3:V2+
Authors: Bacci M. 
Published: July 2007

AbstractThe Jahn‐Teller coupling constants for the systems MgO:V2+ are computed up to the second order, following a new parametrization method, which is based on the angular overlap model. The results are then discussed in respect of the interpretation of the zero‐phonon line splitting (4A2g → 4T2g) in MgO: V2+, previously given.
Atomic configuration of a ½ 〈111〉 screw dislocation in pure Mo and in Mo containing He interstitials
Authors: van Heugten W. F. W. M. , Caspers L. M. , de Hosson J. Th. M. 
Published: July 2007

AbstractThe atomic configuration around a screw dislocation with ½ 〈111〉 Burgers vector is calculated using two different sets of interatomic potentials for Mo. The boundary conditions are given by anisotropic elasticity theory. A narrow dislocation without a distinct stacking fault region results. Two different molybdenum‐helium potentials are used to calculate the positions with maximum energy gain for helium atoms near the ½ 〈111〉 screw dislocation in Mo. The strongest binding energy of the helium atom of ≈︁ 1.6 eV is found for the dilatational sink close to the dislocation line. The present calculations confirm earlier results on the interaction between a helium atom and a ½ 〈111〉 {110} edge dislocation that elasticity theory gives a reasonable description far away from the dislocation core but fails in the neighbourhood of the core region.
Dynamic properties of [X] centres in cesium halides
Authors: Pilloud J.‐J. , Jaccard C. 
Published: July 2007

AbstractIn thallium doped cesium halides, the evolution of the number of self‐trapped holes with different orientations is monitored by measuring EPR spectra intensities. With a linearly polarized excitation in a suitable geometry, the relative absorption dichroism of the individual centre is determined, i.e. the absorption cross‐section ratio with polarization parallel/perpendicular to the centre axis. It amounts to 8 ± 2 at 436 nm and 10 ± 2 at 604 nm in CsI, and to 16 ± 2 at 406 nm in CsBr. Measurements with increasing temperature indicate that the first thermoluminescent peak is due to recombination following the movement of the centres along their axis only, whereas the second peak results of 90° jumps. The critical temperatures are 58 and 86 K in CsI, 106 and 130 K in CsBr, and 146 and 167 K in CsCI.
First and second order Raman scattering by pair modes in silicon
Authors: Jouanne M. , Morhange J. F. , Balkanski M. 
Published: July 2007

AbstractIon implanted silicon with two types of impurities is studied using Raman scattering. The splitting of the localized modes into two pair modes is observed. In the case of 10B31P pairs the two modes are ω ∥ = 650 cm−1, ω ⊥ = 620 cm−1, and for 11B31P pairs, ω ∥ = 628 cm−1, ω ⊥ = 605 cm−1. Results for BAs pairs in silicon are also reported. It is believed that for the first time the second order Raman scattering by pair modes is observed. The second order spectrum gives information about the density of states of these modes.
Off‐center Cu+ in mixed crystals
Authors: Li M. Siu , de Souza M. 
Published: July 2007

AbstractPerturbed off‐centre Cu+ ions by Cl− ions in KI and by I− ions in KCl are studied using uniaxial stress induced dichroism on the Cu+ uv absorption band and ionic thermocurrent (ITC) technique. Barrier height for the Cu+ reorientation is found to have a small decrease as compared with pure KI crystal. The symmetry of the multiwell potential minima changes from 〈111〉 orientation in KI to 〈110〉 in mixed KI + KCl crystals. When I− ions are added to KCl the off‐centre behaviour of the Cu+ is found to degenerate in a single deep potential well.
Optical and vibronic spectra of MnO in cesium bromide
Authors: Radhakrishna S. , Hariharan K. 
Published: July 2007

AbstractOptical absorption spectrum of cesium bromide doped with MnO ion shows five bands. All these above bands are interpreted in terms of transitions within molecular orbital levels using the Ballhausen‐Liehr scheme. It is observed that, superposed on the electronic transition associated with the band at 6000 Å, there is a vibrational fine structure which arises due to the coupling between the electronic transition and the totally symmetric stretching vibration of the ion. The IR absorption spectrum of specpure CsBr:MnO shows four lines which are interpeted on the basis of different local symmetries of MnO ion in the lattice.
Anomalous magnetoresistance and band crossing in uniaxially compressed HgTe
Authors: Takita K. , Onabe K. , Tanaka S. 
Published: July 2007

AbstractResistivity at helium temperatures of uniaxially compressed slightly p‐type HgTe decreases greatly by application of a magnetic field along the stress direction. It increases again above a certain magnetic field HM showing a large resistance minimum. The minimum position HM increases proportionally to the applied compression. These properties are investigated using a magnetic field up to 55 kOe under a uniaxial compression up to about 7 × 108 dyn/cm2. By comparison with the magnetic sub‐band scheme calculated by the effective mass theory, it is concluded that the resistance minimum is due to a band‐crossing HM between the lowest Landau levels of the conduction and the valence bands. A second band‐crossing point is also observed by using a magnetic field modulation technique. A shear deformation potential constant of the Γ8‐band b is deduced; b = (−1.5 ± 0.2) eV. Further, an acceptor impurity band in the stress‐induced band gap is found by the analysis of the temperature dependence of weak field Hall coefficient.
Effect of crystal field on the inelastic neutron scattering cross‐section (II)
Authors: Sugawara K. 
Published: July 2007

AbstractThe linewidth of magnetic inelastic neutron scattering in metals is studied theoretically. In particular the linewidth due to the sf interaction is investigated on the basis of the Hirst theory for magnetic ions with substantial crystal‐field splitting. The theory is applied to the quasi‐elastic and the inelastic neutron scattering cross‐sections due to Ce3+. The experiments of Loewenhaupt and Steglich on the (CexLa1−x)Al2, considered to be the first to demonstrate the non‐vanishing values of the linewidths associated with excited states near zero temperature, can be qualitatively explained by the present theory.
Polarized luminescence and EPR study of Sn+ centres in KCl:SnCl2 crystals
Authors: Egemberdiev Zh. , Seeman V. , Zazubovich S. , Jaanson N. 
Published: July 2007

AbstractThree types of Sn+ centres, recently found by Delbecq et al. in KCl:SnCl2 crystals irradiated at 77 K and warmed up to certain temperatures, are investigated by absorption, EPR, and polarized luminescence methods at 25 to 450 K. The intra‐centre luminescence peaks at 2.03, 2.06, and 2.02 eV are observed for all types of Sn+ centres under excitation in the most intensive absorption bands of Sn+ in the region from 6.4 to 5.6 eV and also in weak absorption bands at 5.1 to 3.1 eV. The connection of the observed absorption and emission bands with the Sn+ centres of a certain structure is established by comparing the thermal stabilities of the Sn+ centres obtained by the EPR and optical methods. The emission of all three types of Sn+ centres is polarized along the C4 crystal axis, which is probably caused by the orientation of the SnCl molecular ion in the crystal. The spectral bands of Sn+ centres are connected with the electronic transitions between the fully occupied ground state and two groups of excited states of the SnCl molecular ion whose energies depend on the location of v with respect to SnCl. The connection of the geometrical structure of Sn+v centres with that of Sn2+vc centres in KCl:SnCl2 crystals is discussed.