bluuebunny/crossref_metadata_2025_split huggingface dataset:
Crystal equilibrium and phonon dispersion in rare‐earth H.C.P. metals
Authors: Sinha H. P. , Upadhyaya J. C. 
Published: July 2007

AbstractThe phonon dispersionin two h.c.p. rare‐earth metals Tb and Ho are investigated on the basis of a model which uses a 5‐neighbour−central pair potential for close‐range forces and a screened Coulomb interaction for long‐range forces. The model considers completely the equilibrium of the ionic lattice in a medium of an uniform electron gas. Consequently two equilibrium conditions, necessary for the h.c.p. structure, are deduced and used in the study.
Optical lineshape for the A1−E transition − comparison of IOA with numerical method
Authors: Muramatsu S. , Nasu K. 
Published: July 2007

AbstractOptical lineshape functions for A1−E transitions coupled with phonon modes of a1 and e symmetries are calculated using the independent ordering approximation (IOA) and the numerical method of Longuet‐Higgins et al. (EXM). The two kinds of results are compared and it is found that the IOA well reproduces qualitatively the peculiar feature of the lineshape of EXM, as long as considering only the global profile of the lineshape and disregarding its possible structure within the range of the phonon frequency. The condition of the validity of IOA is discussed.
Ultraviolet absorption and emission of CN− centres in alkali halides
Authors: von der Heyden E. , Fischer F. 
Published: July 2007

AbstractThe ultraviolet absorption of CN− centres is studied in NaCl, KCl, RbCl, and NaBr single crystals, as well as the ultraviolet luminescence of NaBr:CN−. At low temperatures several CN− absorption bands are resolved from the low energy tail of the ultraviolet host absorption. These bands refer to the generation of valence vibrations of the excited CN− molecule. The ultraviolet luminescence of NaBr:CN− consists of well separated nearly equidistant bands (ΔE ≈︁ 0.26 eV) in the range between 213 and 374 nm. This structure is refered to valence vibrations of the ground state CN−. The valence vibrations are described by Morse potentials. The experimental data allow the determination of the potential parameters, especially of the bond dissociation energy and of the change of the internuclear distance due to the electronic transition.
Nichtparabolizität des valenzbandes von Bi2Te3 gefolgert aus transporteigenschaften
Authors: Stordeur M. , Kühnberger W. 
Published: July 2007

AbstractMessungen der galvanomagnetischen und thermoelektrischen Effekte an p‐Bi2Te3 werden im Rahmen eines nichtparabolischen Einvalenzbandomodells mit Vieltalstruktur interpretiert. Für dieses Modell werden die Ausdrücke für die galvanomagnetischen Koeffizienten und die Thermokraft angegeben. Für akustische Gitterstreuung werden die Streufaktoren der Hall‐ und Magnetowiderstandskoeffizienten theoretisch berechnet. Zur Ermittlung des reduzierten Ferminiveaus und der Breite der verbotenen Zone wird ein grafisches Lösungsverfahren angegeben. Der anomale Anstieg des Hallkoeffizienten bei steigender Ladungsträgerkonzentration wird durch den Einfluß des „nichtparabolischen”︁ Streufaktors erklärt. Entsprechend dem Erwartungswert für akustische Gitterstreuung ergibt sich der Temperaturgang der „isotropen”︁ Beweglichkeit proportional T−3/2 im Gegensatz zu den bisherigen Interpretationen mit parabolischem Band.
Antiresonance in vibronic absorption spectra of a two‐impurity system
Authors: Iida T. , Aegerter M. 
Published: July 2007

AbstractAntiresonance effect is studied in a system composed of two‐impurity centres in a crystal; one has a broad absorption band while the other has sharp phonon‐line structure in its absorption spectrum when no interaction occurs between the two defects. A general expression of the change in the absorption spectrum due to interaction between them is given. The antiresonance effect on a sharp zero‐phonon line is investigated in detail and the favourable conditions for the observation of such an effect are also discussed.
Study of the electric quadrupole interaction (EQI) in (Pb0.925Ba0.075)ZrO3 by perturbed angular correlations
Authors: Saitovitch H. , Fechner J. B. 
Published: July 2007

AbstractThe EQI in polycristalline (Pb0.925Ba0.075)ZrO3 has been investigated in the temperature range 22 to 240 to 22 °C by time differential perturbed angular correlation measurements. For the application of this technique (Pb0.925Ba0.075)ZrO3 was doped with small amounts of radioactive Hf181. According to the crystal structure studies this compound exhibits phase transitions at 175 °C (antiferroelectric → ferroelectric) and at ≈︁205 °C (ferroelectric → paraelectric); it exhibits also a large temperature hysteresis at the lower transition. It is shown that the electric field gradient (EFG) exhibits a sharp discontinuity at approximately 170 °C, corresponding to the first phase transition, and a slightly sharp discontinuity at approximately 200 °C, corresponding to the second phase transition. In the cubic phase a remaining EFG is observed, which is probably caused by lattice imperfections in the source. No any variation of the EFG following the hysteresis loop is found.
The path‐integral method and the motion of a phonon–impurity system in a magnetic field
Authors: Gifeisman Sh. N. , Malkoch Yu. G. 
Published: July 2007

AbstractIt is shown that the variational principle connected with a quadratic trial Lagrangian in Feynman's path‐integral representation can be applied for calculating the energy eigenvalues and thermodynamic functions of systems in a uniform arbitrary external magnetic field. As an example the ground‐state energy of a hydrogen‐like atom in a magnetic field is calculated. A theory of shallow F‐centres in the presence of an arbitrary external magnetic field is developed. The results are valid for arbitrary magnitudes of the polaron coupling constant.
Structure of the Impurity Band and Magnetic‐Field‐Induced Metal‐Non‐Metal Transition in n‐Type InSb
Authors: Ferre D. , Dubois H. , Biskubski G. 
Published: July 2007

AbstractSeveral samples of n‐type indium antimonide in the doping range 5.7 × 1013 to 3.9 × × 1014 cm−3 donors have been investigated. The electrical resistivity has been measured from 1.6 to 4.2 °K in magnetic fields up to 5 T. Activation energies ϵ1, ϵ2, ϵ3 which are characteristic of the resistivity versus temperature curves are measured and their variation with magnetic field are investigated. A transition from metallic conduction to an activated conduction process is observed for a critical magnetic field the value of which increases with the concentration of impurities. These features are interpreted with an impurity band structure which varies when the magnetic field is increased. A model of the impurity band and its changes with magnetic field are suggested. This model is consistent with the ideas of Mott and Davis on impurity conduction and the D− band model of Fritzsche suggested by Hubbard. These results are comparable with those which have already been obtained in germanium and silicon when the magnetic field or impurity concentrations are varied.
EPR of Non‐Kramers Rare‐Earth Ions in Tetragonal Crystals
Authors: Schwab G. , Hillmer W. 
Published: July 2007

AbstractElectric ΔM = 0 and magnetic ΔM = 0 and ΔM = 1 transitions were measured with X‐, K‐, and Q‐band frequencies within the ground state doublets of the rare‐earth ions in (Y, Tb)PO4, (Y, Tm)VO4, (Y, Tm)AsO4, and (Y, Ho)AsO4. The g‐factors and hyperfine constants were determined. The doublets show a zero field splitting Δ which can be attributed to random strain. The half width of the distribution of the splitting Δ, the most probable splitting, and the natural line width were evaluated from the line shape and line position. The intensities of the electric transitions were compared with those of a crystal field calculation.
Theory of Interband Resonance Raman Scattering in Small‐Gap Semiconductors
Authors: Enderlein R. 
Published: July 2007

AbstractA theoretical analysis is given for the interband resonance Raman scattering in small gap semiconductors. For a certain interval of incident photon energies the scattering spectrum shows a strong resonance peak. By measurements in the visible frequency region, especially the energy gap can be determined from the scattering spectrum. The possibilities of an experimental observation of the predicted effects are discussed for some representative small‐gap semiconductors.
Raman Scattering from Five Phases of Silver Iodide
Authors: Hanson R. C. , Fjeldly T. A. , Hochheimer H. D. 
Published: July 2007

AbstractThe Raman scattering is investigated from five phases of AgI that can be reached with moderate pressure and temperature. Particularly noteworthy is the strong negative pressure coefficient of the 17 cm−1 E2 mode in the wurtzite phase. Its mode gamma is −7.5. The intensity of this mode decreases above 1 kbar and shows hysteresis during pressure cycles. A possible interpretation of this hysteresis in terms of a sluggish phase transition from wurtzite to zinc blende is discussed. In the narrow phase between 3 and 4 kbar (IV) two strong modes are observed. At low temperature the sluggish phase transition does not occur and wurtzite transforms directly to rock salt at 3 kbar. The rock salt phase shows a second order spectrum similar to AgBr. The Raman spectrum of the disordered phase shows strong broad Rayleigh like scattering extending out to 50 cm−1 and a broad lattice like mode at 100 cm−1.
Born Model Calculations of the Properties of the Alkali Azides I. Cohesive Energies, Lattice Parameters, and Specific Volumes
Authors: Danemar Å. , Royce B. S. H. , Welch D. O. 
Published: July 2007

AbstractCalculations have been performed in which potentials developed for Born model calculations of the defect properties of KN3 have been used to evaluate the cohesive energies of the alkali azides, KN3, NaN3, RbN3, and CsN3. The stability of the lattices under small deformations about the experimental values of the lattice parameters has also been studied. Three forms for the azide repulsive potential are employed all of which give reasonable agreement with experiment for the body centered tetragonal structures but only one of which provides agreement across the series of alkali azides. Comparisons are made to previous calculations.
Monovalent Mercury‐Like Ion Dimer Centres in Alkali Halide Crystals
Authors: Ermoshkin A. , Evarestov R. , Gindina R. , Maaroos A. , Osminin V. , Zazubovich S. 
Published: July 2007

AbstractPolarized luminescence of (Ga+)2, (In+)2 and (Tl+)2 centres in KCl crystals is investigated experimentally. In the series of KCl, KBr, and KI crystals the (Tl+)2 centres are studied in order to clear up the influence of the anions on the (A+)2 centre properties. The quasimolecules [Tl2X10]8‐ and [T12X11]9‐, where X are Cl− or I− ions, with the symmetry D2h and D4h, respectively, were theoretically considered by a MO method. An attempt is made to prove the model of the (A+)2 centres basing on a comparison of the results of the experimental and theoretical investigations.
Magnetic‐Field‐Induced Energy Gap in HgTe Observed in Transport Measurements
Authors: Byszewski P. , Dziuba E. Z. , Gała̧zka R. R. , Szlenk K. , Szymborski K. , Walukiewicz W. 
Published: July 2007

AbstractExperimental results are given of galvanomagnetic measurements of p‐HgTe in strong pulsed magnetic fields performed up to 35 T in the temperature range 77 to 340 K. Co cen‐tration and mobility of holes in the intrinsic conductivity region were determined. To explain the experimental data it is necessary to introduce a valence and conduction band separation of 0.6 meV/1 T induced by magnetic field. The temperature dependence of the mobility shows that the hole mobility is limited by phonon scattering.
Charge‐Ordered State in Semiconducting Crystals of the Cs2SbCl6 Type and the Electronic Structure of Sb Ions
Authors: Makarov E. F. , Amelin I. I. , Ionov S. P. 
Published: July 2007

AbstractResults are presented of a calculation of the ground state energy for the various configurations of Sb ions. It is found, that the 5s25p2, 5s15p2, and 5s15p1 atomic configurations correspond to the SbCl, SbCl, and SbCl complexes, respectively. These configurations are near to occupations obtained in the LCAO‐MO terms. The nature of an effective electron attraction on the aig‐orbital in SbCl is discussed. In an atomic approach the energy gap value ΔE is determined. This quantity (ΔE = 0.043 a.u.) is found to be in good agreement with observations.
Symétrie du paramètre d'ordre de la transition de phase ferroélastique du phosphate de plomb
Authors: Torres J. 
Published: July 2007

AbstractOn examine d'un point de vue théorique la transition de phase ferroélastique du phosphate de plomb Pb3(P04)2 située à 180 °C. On remarque que le changement de symétrie spatiale R3m → B2/b qui se produit à la transition, s'accompagne d'un doublement du nombre d'atomes dans la maille élémentaire. Le phosphate de plomb est ainsi un matériau ferroélastique de type impropre. La symétrie du paramètre d'ordre de la transition est etudiee par des methodes classiques de theorie des groupes. On montre que le parametre d'ordre se transforme suivant une representation irreductible tridimensionnelle de R3m correspondant au point L de la frontiere de la premiere zone de Brillouin du reseau rhombo‐edrique. Toutefois deux representations irreductibles distinctes sont susceptibles d'induire la transition observee, laissant done subsister une ambiguite sur la symetrie reelle du parametre d'ordre. L'energie libre qui decrit revolution des proprietes physiques macro‐scopiques au voisinage de la transition prend la meme forme dans les deux cas.
Inelastic Neutron Scattering Study of the 2kF Instability in K2Pt(CN)4Br0.30 x D20 (KCP)
Authors: Comes E. , Renker B. , Pintschovius L. , Currat R. , Gläser W. , Scheiber G. 
Published: July 2007

AbstractBesides the modifications of the longitudinal acoustic dispersion in the c‐direction, ill‐elastic neutron scattering measurements of the 2kF instability in KCP between room temperature and 60 K reveal an additional excitation at a frequency of 0.6 THz for the wave vector 2kF. This excitation obviously corresponds to the additional structure earlier observed at low temperatures by infrared measurements but the extension in wave vector 2kF – 0.2c* < qc < 2kF + 0.1c*, the very small dispersion, and the fact that, though much weaker than at low temperature, it is still observable at room temperature, casts serious doubts on its interpretation in terms of the pinned charge density wave (pinned Fröhlich mode). The existence of a low frequency longitudinal optical phonon branch is more likely, despite the unexplained weak intensity of the corresponding phonons.
Low‐Temperature Galvanomagnetic Effects in n‐Type PbS
Authors: Finlayson D. M. , Johnson I. A. 
Published: July 2007

AbstractThe resistivity and Hall effect of lead sulphide single crystals containing 1016 to 1017 electrons cm−3 have been measured at temperatures down to 0.2 °K in magnetic fields up to 40 kG. The number of conduction electrons is independent of both magnetic field and temperature. A negative longitudinal magnetoresistance at low fields gives place to a positive effect at high fields and both are strongly dependent on electron concentration.
NMR Evidence for the Motion of Br−Ions in the One‐Dimensional Conductor K2Pt(CN)4Br0.3 nH20
Authors: Nagasawa H. , Miyauchi N. 
Published: July 2007

AbstractThe motion of Br ions in the one‐dimensional conductor K2Pt(CN)4Br0.3 2.6 H2O at room temperature is observed in the measurements of the NMR line width of Br81 nuclei. The temperature dependence of the NMR line width of H1 nuclei in K2Pt(CN)4Br0.3 × × 2.6 H20 shows that the rotational motion of water molecules is strongly correlated with the gradual metal‐to‐insulator transition in KCP.
On the Hc2 anisotropy in uniaxial superconductors
Authors: Teichler H. 
Published: July 2007

AbstractFor impurity‐free uniaxial superconductors the temperature dependence of the anisotropy of Hc2 is evaluated for the whole temperature range below Tc. In particular it is shown that the residual value of the relative anisotropy of Hc2 at Tc and the temperature dependences of the various angular momentum components of ΔHc2/H̄c2 reflect effects of Fermi surface and energy gap anisotropies.
Interactions hyperfines du centre F+ dans ZnO
Authors: Gonzalez C. , Galland D. , Herve A. 
Published: July 2007

AbstractDes mesures de RPE sur la lacune d'oxygène ayant piégé un électron (centre F+) dans ZnO, and permis de déterminer les paramètres des interactions hyperfines magnétique et quadrupolaire électrique, avec un noyau Zn67 adjacent à la lacune. Ceci dans les deux cas possibles de configuration: celui qui correspond à un Zn67 dans un site axial par rapport à la lacune, et l'autre, correspondant au noyau dans un des trois sites non‐axiaux. A partir des valeurs expérimentales du paramètre quadrupolaire P‖ = (3,13 ± 0,01) MHz (axial) et (3,1 ± 0,2) MHz (non‐axial) nous montrons que les quatre ions Zn++ premiers voisins, relaxent vers l'extérieur de la lacune.
Effects of excitation‐induced optical absorption in highly excited semiconductors
Authors: Kushida T. , Moriya T. 
Published: July 2007

AbstractOptical gain spectra are calculated for radiative exciton–exciton collision and biexciton recombination processes. The result well explains the red shift of stimulated emission bands of various semiconductors with increasing the pumping intensity or the excitation length. Several effects of excitation‐induced negative gain are also discussed.
Quasi‐cubic state and piezobirefringence of CdS and CdSe
Authors: Réza A. , Babonas G. , Šileika A. 
Published: July 2007

AbstractThe dependence of intrinsic birefringence Δ of CdS and CdSe on uniaxial stress X has been investigated at 77 K in the spectral range 0.6 eV to the absorption edge. The measurements are carried out up to stresses of 9400 and 6700 kp/cm2 at X ‖ c (2000 and 1900 kp/cm2 at X ⊥ c) for CdS and CdSe respectivitely. The dispersion of the linear stress coefficients of birefringence dΔn(E)/dX is determined. In the case X ‖ c the CdS and CdSe crystals are compressed up to the quasi‐cubic state of the upper valence bands at point Γ in the Brillouin zone. The experimental results of piezobirefringence are interpreted by the stress‐induced changes of the parameters of the optical transitions at the absorption edge and in the higher energy region.
Spectrum of collective electronic excitations in semiconducting crystals of the Cs2SbCl6 type
Authors: Tonov S. P. , Lubimov V. S. , Makarov E. F. , Ionova G. V. , Uimin G. V. 
Published: July 2007

AbstractCrystals of A2SbCl6 type with a very narrow half‐filled band are investigated. As the temperature is lowered it can undergo a transition to an electron‐charge ordered state. In this state alternate atomic sites along the (100) crystal direction are doubly occupied (SbCl63‐–SbCl6−)N. The compounds are diamagnetic in both the states (ordered and disordered). On the basis of an Hamiltonian that incorporates the intra‐site (I) and inter‐site (V) electron–electron interaction as well as the hopping energy the analysis of the two‐electron collective excitation spectrum is made. The conditions are found in which the two‐particle spectrum lies within the energy gap of the one‐particle spectrum. In a narrow band the transition from the charge‐ordered state to the delocalized one when there are low‐energy collective excitations will be either of second order or without a phase transition as a continuous one. The model of the transition to a delocalized state is discussed too.
A new current transport mechanism due to interband tunneling without and with photon assistance
Authors: Henneberger K. , Enderlein R. 
Published: July 2007

AbstractZener tunneling is shown to contribute in two different ways to the total current: firstly, by the intraband contribution of free carriers generated by tunneling and secondly, by an interband current resulting from charge transfer through the gap due to tunneling. The latter contribution is studied in more detail. The considerations are generalized to photonassisted tunneling, i.e. Zener tunneling which is followed by photon‐induced intraband transitions. The interband current is independent of concentration and mobility of free carriers and, consequently, dominates if those are extremely small.
Mössbauer study of FM sidebands produced by the RF magnetic field applied to an iron foil
Authors: Kopcewicz M. , Kotlicki A. , Szefer M. 
Published: July 2007

AbstractThe formation of rf sidebands in the Mössbauer spectra of metallic iron as a result of the application of an external rf magnetic field is studied. The dependence of the sideband intensities on the rf field intensity and the thickness of the sample is discussed. Experiments show that the formation of sidebands is connected with atomic vibrations induced within the foil by the rf field applied. Basing on the experimental spectra obtained, modulation indices are calculated in accordance with the FM theory. The results obtained are interpreted in terms of the modified magnetostriction model. The dependence of sideband formation on the coating of the foil with a damping medium is studied. It is found that covering of the sample surface with a silicon grease, adhesive tape, or metallic zinc causes a considerable damping of the sidebands and in some cases causes their complete quenching. This effect has been attributed to the dissipation of energy generated within the sample by the rf field. If the acoustic resistivity of the medium covering the sample is higher than that of air the energy transferred from the foil to the environment increases and the sidebands are damped.
On the measurement of the conductivity density of states of evaporated amorphous silicon films
Authors: Brodsky M. H. , Döhler G. H. , Steinhardt P. J. 
Published: July 2007

AbstractData are analyzed on the conductivity across the barrier between amorphous and crystal Si. The analysis assumes that variable range hopping near the Fermi level is the dominant conductivity mechanism in the evaporated amorphous Si film and band conductivity is dominant in the crystal. The density of states is found to be 1.2 × 1020eV−1cm−3at the Fermi level in amorphous Si. The barrier heights are found to be larger when the crystal is p‐type. This is in contrast to the somewhat analogous case of metal–semiconductor Schottky barrier diodes in which n‐type crystals give higher barriers. The possibility of applications in circuits is pointed out.
Monte Carlo Simulation of NMR Line Shapes in Distorted Non‐Metallic Solids
Authors: Baumhoer W. , Thiemann J. , Kanert O. 
Published: July 2007

AbstractThe Monte Carlo method is applied to calculate the quadrupole distortion of the shape of the NMR spin echo signal caused by randomly placed defects (point defects or dislocations) in a cubic lattice. Specific evaluations are carried out in the case of Na23Cl and Na23Br disturbed by Ca2+ (valence effect), by Ag+ (strain effect), and by a defined number of dislocations, respectively. The theoretical results are compared with XMR measurements on Na23Cl and Na23Br single crystals distorted by 0.01 at% Ca2+, 0.5 at% Ag+, 6 × 107 dislocations/cm2, and 1.8 × 108 dislocations/cm2, respectively. It is found that the calculations agree well with the experimental data in the case of doped crystals, whereas some deviations between measurements and theory exist if the crystal is strained by dislocations. These discrepancies may be explained by a non‐uniform distribution of the dislocations in the crystal.
Theory of Biexcitons Using the Boson Formalism The Ground State Binding Energy
Authors: Sheboul M. I. , Ekardt W. 
Published: July 2007

AbstractUsing the boson formalism of Usui for the Hamiltonian of the many exciton system, a coupled system of integral equations for the biexciton amplitudes is derived by means of the method of Gell‐Mann and Low. In lowest order, this system is then reduced to only one Schrödinger equation for the bound states of two ls‐excitons. With that the ground state binding energies of biexcitons in CuCl and CuBr is calculated in good agreement with experiment.