bluuebunny/crossref_metadata_2025_split huggingface dataset:
Electron Transport in Zincblende Semimetals
Authors: Rode D. L. , Wiley J. D. 
Published: July 2007

AbstractIterated solutions of the Boltzmann equation with Fermi statistics are presented for the zero‐gap semimetals α‐Sn, HgSe, and HgTe. Electron scattering operators in the first Born approximation arc derived for the T8c conduction band including piezoelectric and deformation potential scattering by acoustic phonons, polar optical mode Scattering, and Coulomb scattering. It is found that quantum corrections are, in many cases, comparable to RPA corrections but opposite in algebraic sign so that the overall corrections to the classical calculations are much smaller than previously indicated.
Electron Diffraction Study of the Local Atomic Arrangement in Amorphous Tellurium Films
Authors: Ichikawa T. 
Published: July 2007

AbstractAmorphous thin films of tellurium have been prepared by condensation on the substrate at liquid helium or nitrogen temperature in high vacuum, and a transmission electron diffraction study of these films has been undertaken. Diffraction patterns of such films show diffuse halos, which are characteristic of a highly disordered structure. A radial distribution analysis has been carried out in order to investigate the local atomic arrangement in the films. The result leads to the conclusion that the atoms in the films are arranged in short chains.
X‐Bay Photoelectron Spectra of Palladium–Silver and Nickel–Copper Alloys
Authors: Nemoshkalenko V. V. , Mindlina M. A. , Senkevich A. I. , Aleshin V. G. 
Published: July 2007

AbstractWith a Varian (IEE‐15) electron spectrometer the valence band photoelectron spectra and the binding energies of inner‐core electrons are measured for palladium‐silver alloys. For the nickel–copper alloys the photoelectron spectra known from literature are compared with the results of density‐of‐state calculations. Kβ2,5 emission bands of pure nickel and pure copper and from the alloy Ni–Cu (50 at%Cu)are also reported.
Pressure Dependence of Mossbauer Fraction and Energy Shift for Fe6' in Cu Lattice at 298 and 94 °K
Authors: Nandwani S. S. , Puri S. P. 
Published: July 2007

AbstractThe pressure variations of the Mössbauer fraction and the second order Doppler shift for Fe57 in Cn lattice at 298 and 94 °K have been calculated taking into account the effects of change of mass and force constant due to impurity atoms. Due to the large error in the experimental value of Williamson and Ingalls no conclusion regarding the change of force constant with temperature has been obtained. The pressure dependence of centre shift at the two temperatures enables one to calculate the explicit temperature dependence of isomer shift with pressure. It is shown that at 82 kbar the isomer shift at 298 °K becomes equal to that at 94 °K. This is explained using the band model of lattice.
The electronic structure of sns2 and snse2
Authors: Ch. Schlüter I. , Schlüter M. 
Published: July 2007

AbstractThe energy bands of SnS2 and SnSe2 are calculated using the local empirical pseudopotential method. The form factors of the pseudopotential were adjusted in such a way that the calculations reproduce the experimental values of the fundamental gaps. The space group D of these compounds is studied in detail and a comparison is made between the recent calculation by Fong and Cohen and the present work. Prom the pseudo wavefunctions the charge distributions of electrons and holes are calculated.
Uniaxial stress dependence of the fermi surface of zinc
Authors: Gerstein I. I. , Elbaum C. 
Published: July 2007

AbstractThe effect of uniaxial stress on the areas of several orbits of the zinc Fermi surface have been studied by measuring the phase shifts of the magnetoacoustic quantum oscillations of ultrasonic attenuation. The orbits studied were the two third‐zone electron orbits, i.e., the lens (ζ) and the needles (α), and four hole orbits on the second‐zone monster, i.e., two horizontal arm orbits (ß), with the magnetic field, H, along 〈1120〉 and 〈1010〉, and two junction orbits (Γ), with H along 〈1120〉, and the bow‐tie orbit (σ) with H along 〈1010〉. Calculations of the stress dependence were carried out on the basis of a non‐local pseudopotential model for the zinc Fermi surface and compared with the experimental results obtained. Good numerical agreement was thus obtained in half of the cases studied. Discrepancies of about a factor of two were found in the other cases, while the largest and smallest values of the stress derivatives (both measured and calculated) differed by as much as a factor of 100.
Temperature dependence of the hyperfine structure splittings of XO3 molecule‐ions in single‐crystal calcite
Authors: Serway R. A. , Chan S. S. L. , Marshall S. A. 
Published: July 2007

AbstractThe hyperfine structure splittings of three paramagnetic molecule‐ions formed in γ‐ir‐radiated single‐crystal calcite have been measured from 4.2 to 320 K. These molecule‐ions are CO, PO, and AsO Over this temperature range, they exhibit a decrease in hyperfine structure splitting with increasing temperature of between 1 to 2%. An analysis of the data suggests that the loss of unpaired electron spin‐density at the central atom is approximately proportional to the fractional increase in spin‐density at the oxygen‐orbitals. Furthermore, the fractional change in p‐character is about three times the fractional change in s‐character for these species. In all cases, calculated equilibrium bond‐angles are found to be insensitive to temperature. Estimates of the unpaired electron molecular orbitals are given using the hybridization ratios determined from the data.
Effect of localization on the temperature‐dependent impurity resistance in dilute non‐magnetic alloys
Authors: Dubey S. K. , Dayal B. 
Published: July 2007

AbstractA previous theory of the temperature dependence of the impurity resistance, is applied to those alloy systems where the constituent atoms have nearly equal masses. An expression is developed for the matrix element describing the coupling of the unperturbed phonons with the impurity electrons. Detailed calculations are made for a silver—cadmium dilute alloy, silver being the host metal. Satisfactory agreement with the experimental values is obtained. The results show that in this alloy system resonance states below the Fermi level are formed. Further it is shown that localized states are formed when the structure is h.c.p. and resonance states when the structure is cubic.
On the possibility of amplification of acoustic waves in the presence of plasma oscillations in strong electric fields in semiconductors Karnatak University, Dharwar, Mysore State
Authors: Krishnamurthy B. S. , Mulimani B. G. 
Published: July 2007

AbstractA kinetic method is developed of the acoustic wave amplification in a strong electric field in semiconductors with a simple parabolic band. A displaced Maxwellian distribution for electrons is assumed. It is found that the influence of the plasma oscillations on the acoustic wave amplification is significant and in the low electric field region the maximum value of the amplification factor is identical with the published result. In the strong field region the amplification factor takes a negative value because of the direct electric field term although the drift term may also contribute if the electron drift velocity exceeds the sound velocity.
Optical absorption associated with superlattice in silicon carbide crystals
Authors: Dubrovskii G. B. , Lepneva A. A. , Radovanova E. I. 
Published: July 2007

AbstractAbsorption of polarized light in the near IR and visible region has been measured in n‐type silicon carbide crystals of seven modifications: 4H, 6H, 8H, 15R, 27R, 33R, and 21R. All the samples showed clearly resolved polarized absorption bands at wavelengths characteristic for each crystal structure. It is shown that the energy position, temperature behaviour, and selection rules for these bands are in good agreement with those predicted theoretically for interminizone transitions in the Superlattice. The period of the super‐lattice is identified for several groups of SiC structures defined according to the principle of their unit cell formation.
Colour centres near ionic crystal surfaces
Authors: Bartczak W. , Sugier H. 
Published: July 2007

AbstractUsing the methods developed in part I the self‐trapping energy of the VK centre on and below the surface has been calculated for NaCl and KCl crystals. It is found that the energy decreases monotonously by approaching the external surface. Conclusions concerning the migration of VK centres towards the surface of the crystal are discussed.
On the Influence of Electronic Exchange and Correlation on Pseudopotential Calculations. III. Equilibrium Lattice Constants and Bulk Properties
Authors: Hafner J. 
Published: July 2007

AbstractThe equilibrium density, the corresponding binding energy, the equation of state at T = 0°K, the isothermal compressibility, and the pressure derivative of the bulk modulus of 11 simple metals are calculated by pseudopotential theory, using the Xα‐approximation for the exchange and correlation interactions. The agreement with experiment is satisfactory. It is shown that the best possible description of the atomic wave functions within the Xα‐theory is a good approximation for the core wave functions in the metal and that the magnitude of the conduction band‐core exchange interaction is strongly dependent upon the overlap of the conduction‐ and the core electron densities.
Non‐Adiabatie Calculation of the Binding Energy of the Exeiton–Neutral Donor Complex in Semiconductors
Authors: Munschy G. , Cababatos C. 
Published: July 2007

AbstractA new non‐adiabatic method of calculation is presented and applied t o the case of an exciton + − bound to a neutral donor ⊕ −. The one‐particle equation deduced is analogous to Born's nuclear equation, but non‐diagonal coupling terms are not involved. Moreover, as shown by the numerical results obtained, the ⊕ + − − complex becomes unstable for intermediate values of the electron to hole effective mass ratio.
Magnetic Moment Calculation in Disordered Systems: α‐Manganese
Authors: Röpke G. 
Published: July 2007

AbstractThe possibility to calculate magnetic moments in elemental disordered systems (amorphous state, lattice distortions, surfaces) using the inhomogeneous electron‐gas model is considered. Therefore a partial summation of the gradient expansion of the kinetic energy density functional is performed, which allows to obtain the Hund's rule. This model is applied to the calculation of the atomic magnetic moments in α‐Mn. The results are compared with recently measured values for the magnetic moments in this system.
½ 〈111〉 Stacking Faults in A15 (β‐W) Superconductors
Authors: Essmann U. , Zerweck G. 
Published: July 2007

AbstractIn A15 structures ½ 〈111〉 stacking‐faults break the linear chains of A atoms. This affects the electronic structure resulting e.g. in changes of the superconducting critical temperature Tc. Moreover the large pinning forces observed in these compounds are attributed to the described planar defects.
Dynamical Resonance Phenomena of the Optical JT‐Problem in Trigonal Systems
Authors: Sigmund E. , Wagner M. 
Published: July 2007

AbstractIf a degenerate high‐energy excitation is coupled to a low‐energy one, via the effective splitting of the former dynamical resonances may be expected. We confine us to the treatment of the optical absorption‐function of a so‐called E–e Jahn‐Teller system, appearing in trigonal symmetries. The calculation, which will be done by the use of a nonlinear canonical transformation, confirms our expectations. It is to be seen that each single excitation line displays a resonance behaviour. This also manifests itself in the total structural form of the optical spectra.
Exchange Narrowing in the ESR Spectra of Metallic GdxLa1–xB6 (x = 1 to 0.01)
Authors: Sperlich G. , Janneck K. H. , Buschow K. H. J. 
Published: July 2007

AbstractLinewidth measurements are reported of the ESR spectra of metallic GdxLa1–xB6 compounds (x = 1.0 to 0.01). This system is remarkable because contributions from the exchange narrowed linewidth ΔHex and the homogeneous linewidth ΔHhom can be estimated. The interpretation of ΔHex leads to values for the “exchange fields” He as a function of the Gd concentration.
Effect of Deuteration on the Davydov Splitting and on the Shape of the Absorption Band of OH Stretching Vibrations in Alcohol Monocrystals
Authors: Mikhailov I. D. , Savelev V. A. , Sokolov N. D. , Bokii N. G. 
Published: July 2007

AbstractA theoretical investigation has been made of the dependence of the shape and breadth of the absorption band for stretching vibrations vOH in hydrogen bonds of an alcohol crystal on the concentration of an isotopic impurity. It is shown that the structure of the VOH band is caused by Davydov splitting. The local mode frequencies arising on deuteration of an individual alcohol molecule are calculated using the Green's function method and the introuction of such impurity molecules into the crystal is found to lead to an effective disintegration of the hydrogen‐bonded chain to shorter chains. A method is proposed of constructing the absorption vOH band contour. The vOH absorption band contour is constructed for various concentrations of deuterated molecules under the assumption of their random distribution. The splitting of the vOH doublet decreases with increasing concentration of deuterated molecules, owing to the effective decrease of the lengths of the chain formed by hydrogen bonds in an alcohol crystal.
Spin‐Magneto‐Phonon Resonance and Nuclear Polarization by DC in Semiconductors
Authors: Kalashnikov V. P. , Karyagin V. V. 
Published: July 2007

AbstractThe enhancement of steady‐state nuclear magnetization due to the interaction of nuclear spins with hot conduction electrons in a semiconductor is investigated theoretically taking into account the effects of spin‐magneto‐phonon resonance (SMPR). It is shown that the stationary nuclear magnetization oscillates strongly in the vicinity of the SMPR points as a function of the magnetic field strength. The effect of nuclear de polarization in n‐type InSb observed by Clark and Feher [2] is considered as being conditioned by the SMPR transition.
On the Definition of the Current Operator Application to the Hubbard Model
Authors: Cabib D. , Kaplan T. A. 
Published: July 2007

AbstractA disagreement existing in the literature between various calculations of the electrical conductivity in the single‐band Hubbard model is resolved. The error, which occurs in a paper by Monecke, is pointed out and explained to be due to the assumption that the current operator, defined as the commutator of the Hubbard Hamiltonian with the polarization operator, is invariant under the lattice translations. The existence of ambiguity in the definition of a “good” current operator (which is translationally invariant) is pointed out and resolved in a large class of situations.
Conduction Band Parameters of Bi2See from Shubnikov‐de Haas Investigations
Authors: Köhler H. 
Published: July 2007

AbstractThe oscillatory magnetoresistance (Shubnikov‐de Haas effect) was observed on n‐type Bi2See single crystals between 1.6 and 4.2 K. The electron concentrations ranged from about 4 × 1017 to 4 × 1019 cm−3. Stationary magnetic fields up to 10.5 T were available. The angular dependence of the Shubnikov‐de Haas periods revealed an almost rotational symmetry of the Fermi surface around the kc = 0 a parabolic ε(k⊥) relation is found, parallel to the kc‐axis an increasing nonparabolicity is evaluated. Only above 1019 electrons/cm3 the deviation of the shape of the Fermi surface from that of an ellipsoid of rotational symmetry becomes significant. The cyclotron mass mc perpendicular to the kc‐axis (B ‖c) is determined to be 0.124 m0 in the whole concentration range. Fermi energies are evaluated up to 160 meV. The single‐valley model for the lowest conduction band of Bi2See is confirmed.
A Scanning Electron Diffraction Study of Vapor‐Deposited and Ion Implanted Thin Films of Ge (I)
Authors: Graczyk J. F. , Chaudhari P. 
Published: July 2007

AbstractThe structure of Ge films evaporated by several methods onto room temperature substrates of NaCl and films which have been ion implanted with 3 × 1015, 30 to 40 ke V Ge74 has been investigated via a scanning electron diffraction instrument with electron energy filtering. The radial distribution functions of all films are very similar and exhibit strong correlation peaks at 2.45, 4.00, and (4.85 ± 0.075) Å with coordinations of 4, 12, and ≈ 7, respectively. The remaining major peaks for higher r deviate substantially from the diamond cubic form of Ge. From the RDF analysis a density ratio ϱ0/ϱcryst of 0.86 to 0.95 is determined. Thermal anneal experiments showed that the films may be annealed to a density of ≈0.97 of crystalline density without crystallization. Amorphous films which have been ion implanted with the same energy and dose as the polycrystalline films show a considerable concentration of pores and voids of a maximum diameter of 100 Å. The RDF, however, is identical to the as‐deposited film with the exception of some changes in the correlation for r greater than 11 Å.
Phonon Dispersion and Phonon Densities of NaNO3
Authors: Plihal M. 
Published: July 2007

AbstractPhonon‐dispersion branches for specific directions of the wavevector, one‐ and two‐phonon densities, and the lattice specific heat Cv have been calculated for NaNO3 using the same lattice dynamical model which was applied recently to trigonal CaCO3. The results of the calculations are compared with available experimental data from inelastic neutron scattering experiments, the specific heat Cp, and the two‐phonon infrared absorption spectrum.
Magnetic Properties of the Ordered and Disordered CrPt3 and CrPt Phases
Authors: Besnus M. J. , Meyer A. J. P. 
Published: July 2007

AbstractThe structural and magnetic properties of cold worked and annealed Pt‐Cr alloys with Cr content 14 < c < 60 at% have been investigated. The annealed alloys show a spontaneous magnetization from 18 to 45 at% Cr with a maximum value for ferrimagnetic CrPt3. Above 17 at% Cr the appearance of a spontaneous magnetization follows the paramagnetic concentration range of Pt‐Cr alloys, and above 41 at% Cr there is a transition from non stoichiometric ferrimagnetic CrPt3 to non stoichiometric antiferromagnetic CrPt resulting in a pseudo critical concentration range. The cold worked alloys have a paramagnetic behaviour which is ascribed to an incoherent distribution of localized moments with prevailing antiferromagnetic exchange.
Pseudopotential Band Structure of ZnO
Authors: Bloom S. , Ortenburger I. 
Published: July 2007

AbstractThe empirical pseudopotential method is used to compute the band structure, density of states, and reflectivity of hexagonal zinc oxide. The local approximation is assumed, on the basis of recent photoemission experiments which showed that the zinc core 3d band lies deep below the valence band. The calculation succeeds in identifying the reflectivity peaks, but gives stronger amplitudes than are observed, and these identifications are shown to fit well into the systematics of the other three zinc chalcogenides. Reasonable agreement is also obtained with the experimental locations of the maxima in the density of states and with the large value of the valence bandwidth.
A Self‐Consistent Approach to the Problem of Bloch Electrons in the Electric Field
Authors: Henneberger K. , Röseler J. 
Published: July 2007

AbstractStarting from the concept of the “field‐modified model crystal”, a complete set of Bloch functions is self‐consistently defined. The Houston‐type functions constructed with the aid of this set are exact solutions of the time‐dependent Schrödinger equation. The equivalence of the model problem which is defined self‐consistently and the equation given by Wannier is shown. By appropriate choosing the phases of the Bloch functions a splitting of H into two commuting parts is found, the periodic part of which possesses a continuous, but limited spectrum, whereas the Stark‐ladder belongs to the remaining part.
Two‐Photon Excitation Spectra of Trivalent Rare‐Earth Ion Luminescence in Crystals
Authors: Apanasevich P. A. , Gintoft R. I. , Korolkov V. S. , Makhanek A. G. , Skripko G. A. 
Published: July 2007

AbstractTheoretical and experimental investigations are made of two‐photon absorption spectra of trivalent rare‐earth ions in crystals. Effective cross‐sections, selection rules, and relative intensities of the components are found. The most intensive two‐photon transitions are established. Two‐photon excitation spectra of luminescence of Er3+ and Ho3+ ions in CaF2 are obtained and effective excitation cross‐sections are measured using a tunable dye laser (715 to 850 nm). It is shown that the spectra have a peculiar structure which differs considerably from that of the one‐photon absorption spectra. The experimental results agree with theory. It is established that one of the levels in Ho3+ is the level 5G6 rather than 3K7 usually assumed.
Scattering probabilities for holes. II. Polar optical scattering mechanism
Authors: Costato M. , Reggiani L. 
Published: July 2007

AbstractThe integrated scattering probabilities per unit time for the hole‐polar optical scattering mechanism have been evaluated for a typical two‐band (Ev1 and Ev2) valence band structure (spherical and parabolic). The wave functions of the two bands are mostly p‐like, the first (P3/2, M±1/2), the second (P3/2, M±3/2). The symmetry properties of the valence band wave functions are shown to introduce important effects in the coupling and decoupling of the two bands by mixing of Bloch states. The apparent paradoxon of an infinity in the transition probability, for emission and absorption processes in a vertical transition between Ev1 and Ev2 if Ev1 ‐ Ev2 = hω0 the optical phonon energy, is removed by the symmetry of the valence band wave functions.
Optical absorption and Faraday rotation in yttrium iron garnet
Authors: Wettling W. , Andlauer B. , Koidl P. , Schneider J. , Tolksdorf W. 
Published: July 2007

AbstractOptical absorption and Faraday rotation of yttrium iron garnet have been investigated in the spectral range of 1 to 0.35 μm, at 300, 20, and 6 K. At wavelengths shorter than 0.7 μm the spectra were taken on thin films epitaxially grown on gadolinium‐gallium garnet substrate.
Intervalence band transitions in tellurium. II. Polarization E ⟂ c
Authors: Bangert E. , Fischer D. , Grosse P. 
Published: July 2007

AbstractFor the polarization E ⟂ c a weak absorption band dependent on hole concentration was found in tellurium in the spectral range 50 to 200 meV. This absorption is found at low temperatures and for hole concentrations > 1017 cm−3 It can be explained by intervalence band transitions H6‐H4 on the basis of the k·p perturbation treatment of part I. Further‐more the coupling between the valence bands H6, H4 and their energetic distance are determined. Other possible interpretations for the absorption band – the quadrupole and the forbidden transitions between the H5, H4 bands – are discussed.
The migration of vacancies in aluminium
Authors: Harrison E. A. , Wilkes P. 
Published: July 2007

AbstractA migrating vacancy has been simulated using the pair potential for aluminium derived from the pseudopotential of Heine and Animalu. In view of the continued use elsewhere of a kinetic criterion for truncating the structural relaxation, the method of relaxation is discussed and the case for the correct procedure clarified. It is pointed out that calculations of the barrier height which perform relaxation after placing the defect at the mid‐point of its path can be seriously in error. To avoid this it is essential to carry out a quasi‐dynamic relaxation, progressively moving the defect from the initial site to the energy saddle.