bluuebunny/crossref_metadata_2025_split huggingface dataset:
Calculation of the binding energies of doubly ionizable centres in II–VI compounds
Authors: Hagston W. E. , Sutherland H. H. 
Published: July 2007

AbstractThe ionization energies of a doubly ionizable centre are calculated on the basis of two different models. One of these is the effective mass approximation (i.e. shallow centre approximation) suitably extended so as to simulate central cell corrections, whilst the other, based on the concept of an electronic polaron, is more appropriate to the deeper centre regime. The results obtained provide a parametrization scheme which can be checked by experiment and thus lead to a possible means of identifying such centres.
A self‐consistent model for the electronic structure of the U‐center in alkali halides
Authors: Koiller B. , Brandi H. S. 
Published: July 2007

AbstractA simple one‐orbital per site model Hamiltonian for the U center in alkali halides with rock‐salt structure is presented, with correlation effects introduced via an Anderson type Hamiltonian. The Cluster‐Bethe lattice method is used to determine the local density of states, yielding both localized and extended states. A one‐electron approximation is assumed and the problem is solved self consistently in the Hartree‐Fock scheme. The optical excitation energy is in fair agreement with experiment. The present approach is compared with other models previously used to describe this center and the results indicate that it adequately incorporates the relevant features of the system indicating the possibility of its application to other physical situations.
Nonradiative multiphonon relaxation in Y3Al5O12:Nd3+
Authors: Perlin Yu. E. , Kaminskii A. A. , Enakii V. N. , Vylegzhanin D. N. 
Published: July 2007

AbstractAnalytical expressions are derived for the multiphonon decay rate of an isolated impurity level, when interaction with low‐frequency phonons appears as small perturbation. Both, the interaction with high‐frequency optical phonons and the contribution of Jahn‐Teller vibrations are taken into account in the framework of first cumulant approximation. In the temperature range 0 to 700 K the transition probability 4I11/2 → 4I9/2 of the states of Nd3+ ions in Y3Al5O12 crystals are calculated numerically. The results are in agreemnt with data obtained from laser genration kinetics.
Effect of uniaxial stress on free and bismuth‐bound excitions in InP
Authors: Weber G. , Rühle W. 
Published: July 2007

AbstractThe reduction of the shear deformation potentials of holes bound to the isolectronic impurity Bi in InP is determined by piezoluminescence. It is compared with the corresponding reduction for holes bound to the Coulomb‐type acceptors C and Zn. The theory for an effective mass acceptor describes well the cases of C and Zn. However, additional effects as local strain and Stark fields must be involved in the case of Bi leading to an extremely large reduction of the deformation potentials. No change in binding energy with applied stress as well as no exchange splitting of the Bi‐bound exciton can be detected within experimental accuracy. The stress dependence of the free exciton reflectance reveals values for the band deformation potentials and a value of 0.07 meV for the exchange splitting of the free exciton in InP.
Electronic Raman scattering on donor levels in three‐band semiconductors with direct band gaps
Authors: van Hieu Nguyen , Áiviet Nguyen 
Published: July 2007

AbstractA theory is presented of the electronic Raman scattering on shallow donor levels in three‐band semiconductors with direct band gaps. Explicit expressions of the matrix elements of the transitions from the ground state to the first excited state and to the states of the continuous spectrum are derived. It is shown that the most important contribution to these matrix elements comes from the intermediate states in the higher conduction band and in the valence band.
Conduction at low temperature in ion‐implanted silicon
Authors: Bourgoin J. C. , Frossati G. , Ravex A. , Thoulouze D. , Vandorpe M. , Waksmann B. 
Published: July 2007

AbstractThe electrical conductivity in a 4 × 1014 cm−2, 130 keV phosphorus implanted layer is studied, after annealing, in the temperature range 4.2 K to 6 mK. The annealing (at 600°C) is such that most of the phosphorus ions become electrically active and are only partially compensated by the remaining defects. The analysis of σ versus T indicates that three different regimes of conductivity are operating, depending on the temperature range. Between 4.2 K and ≈︁ 100 mK the results find a reasonable interpretation in terms of three‐dimensional variable range hopping (VRH), which follows Mott's law: σ ∼ exp (T−1/4). When T decreases, between ≈︁ 100 and ≈︁ 50 mK the hopping range becomes larger than the thickness of the implanted layer and a twodimensional VRH regime, in which σ ∼ exp (T−1/3), takes place. At low temperature, below ≈︁ 50 mK, σ varies as exp (T−1/2); a tentative explanation of this behaviour is proposed, in terms of correlation effects.
Spin polarization of a magnetic electron gas induced by a van Vleck ion
Authors: Palermo L. , da Silva X. A. 
Published: July 2007

AbstractThe mutual polarization of a magnetic electron gas and a van Vleck ion, interacting via exchange, are theoretically investigated using the double‐time Green function method. A pair of equations describing the dynamics of the electron gas and the ion are conveniently decoupled and an analytic expression for the electron gas polarization is obtained which depends on the square of the exchange parameter. Besides a RKKY‐like term, a new term associated to the process of formation of the magnetic moment of the ion appears.
The construction of central‐force interatomic potentials from whisker deformation data
Authors: Bowen D. K. , Vitek V. 
Published: July 2007

AbstractStress‐strain curves on single crystal whiskers can extend to the non‐linear region. It is shown that these provide data which can assist in the empirical construction or verification of central force potentials. Potentials constructed in this way are suitable for studying the atomic structure of lattice defects when large deviations from the ideal lattice positions occur in their cores. Furthermore, the effects of high external stresses on crystal defects can be investigated. An example of the latter may be found in the field‐ion microscope and as an application the non‐linear dilatation of the lattice under high hydrostatic tension is calculated, and the possible behaviour of dislocations in FIM specimens is briefly discussed.
Certain Features of Semiconductor Behaviour in Strong Parallel Magnetic and Electric Fields II. High‐Frequency Field Energy Absorption
Authors: Berezhkovskii A. M. , Ovchinnikov A. A. 
Published: July 2007

AbstractIt is shown that if in a semiconductor placed into strong parallel electric and magnetic fields the spin splitting energy in magnetic field is close to the energy of a Wannier‐Stark ladder step in an electric field, the high‐frequency field energy absorption occurs at two frequencies instead of one as in absence of an electric field.
Spin‐Wave Instability Theory in Cubic Single Crystal Magnetic Insulators II. Applications
Authors: Patton C. E. 
Published: July 2007

AbstractThe theory developed in Part I is used to calculate butterfly curves for parallel pumping in [001] and [110] magnetized yttrium‐iron garnet and transverse pumping in [001] magnetized YIG for comparison with available experimental data. The results are in good agreement with available experimental data and resolve several previously unexplained anomalies.
The Density of Unoccupied Electronic States in Tantal
Authors: Boiziau C. , Dose V. , Scheidt H. 
Published: July 2007

AbstractThe density of states in the unoccupied part of the conduction band of polycrystalline tantal is investigated using ultraviolet isochromat spectroscopy and soft X‐ray appearance potential spectroscopy (SXAPS). Density‐of‐state functions deduced from the two different measurements are quite similar and compare favourably to existing theoretical calculations.
Green's Theorem Calculation of Energy of Exciton near Hard Walls
Authors: Gallardo J. , Mattis D. 
Published: July 2007

AbstractThe method of Harper and Hilder is modified to obtain the energy levels of hydrogenic atoms or excitons near hard walls. The method is nonvariational, can be used with two or more bounding surfaces, and gives good results in various cases. It is only required to know the wave functions in the absence of such surfaces and to perform some elementary integrals.
Manetoelectronic Denisty of States for a Model Crystal
Authors: Wannier G. H. , Obermair G. M. , Ray R. 
Published: July 2007

AbstractAs shown previously, a first principles calculation of the quantum states of a crystalline electron in a magnetic field leads to a difference equation. The splitting of one Landau level by a particularly simple crystalline potential has been extensively studied. This paper proceeds further for this model case: All quantum numbers characterizing each individual state are exhaustively defined. One of them is discrete and the other two are contionous phases. It is shown that are ene gy eigenvalues depend only on the sum of the cosines of these phases. These properties permit the calculation of the density of states, which still shows as a function of the magnetic field the well known erratic behaviour. Physically understandable rusults are obtained, however, for the integrated density of states: at two magnetic fields which are numerically nearly equal, the intergrated densities of states of states are numerically almost indistinguishable although very different analytically.
Harrison's Method Electrical Transport Properties of Alkali Metals
Authors: Thakur J. , Srivastava P. L. , Mitra N. R. 
Published: July 2007

AbstractElectrical resistivity and thermo‐electric power of alkali metals are investigated in the structure of Harrison's first principle method. Slater's value of α in the Xα exchange with unmodified VOPW presents a good picture with Kleinman and Langreth exchange and correlation. The effect of different forms of exchange and correlation is discussed.
X‐Ray Thermal Diffuse Scattering Measurements of the [100] and [111] Phonon Dispersion Curves of Indium Arsenide
Authors: Orlova N. S. 
Published: July 2007

AbstractMeasurements of the thermal diffuse X‐ray scattering are performed from the (100) and (111) planes in indium arsenide single crystals. The intensities of the second‐ and third‐order scattering are calculated using the two‐atom chain model with different masses and four interaction parameters. The first‐order thermal diffuse scattering intensity is analysed and yields the acoustic and optic phonon dispersion curves in the [100] and [111] symmetry directions.
Spectral Distribution and Decay Times of the Luminescence of Mn2+ on Different Lattice Sites in ZnS
Authors: Busse W. , Gumlich H.‐E. , Geoffroy A. , Parrot R. 
Published: July 2007

AbstractThe spectral distribution of both, excitation and emission of luminescence of ZnS:Mn with manganese on different lattice sites is investigated by dye laser spectroscopy. An unambiguous correlation of zero‐phonon lines due to Mn2+ in cubic and different axial lattice sites is given. The relative oscillator strength of the fluorescent transition of Mn2+ in different crystal sites is determined by exciting within the zero‐phonon transitions of the absorption and by registering the zero‐phonon lines in emission, which belong to the same lattice sites, respectively.
Measurement of Mode Grüneisen Parameters in Si
Authors: Prechtel J. , Kalus J. , Lüscher E. , Pintschovius L. , Ghosh R. 
Published: July 2007

AbstractStress‐induced changes in energy of the phonons of the lowest acoustic phonon branch in the (q00) direction are investigated in Si by using inelastic neutron scattering. Applying uniaxial stress of 10 kbar causes energy changes in the order of 1%. A change in sign is found approximately in the middle of the Brillouin zone. Depending on the mutual orientation of the stress, the wave vector and the polarization vector of the phonons, different changes in energy are observed. From the observed energy changes general mode Grüneisen parameters are derived.
Ground and Excited States of the Biexciton and the M‐Band Luminescence in Highly Excited ZnO
Authors: Schrey H. , Klingshirn C. 
Published: July 2007

AbstractAdditional measurements on polarization properties and excitation intensity dependence are presented for the resonant two‐photon Raman scattering via biexcitons in highly excited ZnO at low temperatures reported earlier [1]. The binding energy of the biexciton ground state (symmetry Λ1) is determined to (19 ± 0.2) meV. An excited biexciton state (symmetry Λ5) is observed for the first time in II‐VI compounds. Moreover, the excitation spectra of the M‐band and of the bound exciton I9 are given for different polarizations of the exciting light. They indicate that the M‐band can be ascribed to a superposition of extrinsic and intrinsic recombination processes.
Local fields and electric dipole moment of localized impurities in crystals
Authors: Glinchuk M. D. , Deigen M. F. , Rozhko V. S. 
Published: July 2007

AbstractDipole transition matrix elements of impurity centres are estimated accounting for the “acting” electric field in the crystal Ea. Ea is shown to depend on the type of wave functions and radii of states among which the transition occurs. Some examples where Ea is essential are considered. It is found, for example, that the dipole moment of the localized electron is expressed via oscillator forces submitted to the sum rule only in the case when the radius of electron state is large enough. A corresponding criterion is given. The examination of matrix elements in the dipole transitions of off‐centre ions shows that in this case the acting field is near to the Lorentz field.
The exciton‐neutral donor and biexciton complexes in polar semiconductors
Authors: Mokross F. , Büttner H. 
Published: July 2007

AbstractFor a system of two different excitons interacting with LO‐phonons an effective Hamiltonian is derived. As a special example the exciton‐neutral donor binding energy is calculated using a variational procedure and discussed as a function of memh for different material parameters. The results are also compared to those of other authors and to experimental data. Corresponding calculations are done for the biexciton complex.
A hopping model for activated charge transport in amorphous silicon
Authors: Grünewald M. , Thomas P. 
Published: July 2007

AbstractA variable‐range hopping model is examined for transport in a band tail. For an exponential density of states the difference of the activation energies of conductivity and thermoelectric power, ΔE, is essentially determined by the steepness of the tail. ΔE varies slowly with tempera ture and depends little on the localization length α of the wave functions and on the magnitude of the density of states. From comparison of the results with experimental data it is suggested that this model applies to activated transport in n‐type amorphous silicon.
Frequency shift analysis of matrix isolated impurities
Authors: Jodl H. J. , Theysohn G. , Bruno R. 
Published: July 2007

AbstractA method is presented for calculating the shift of an impurity spectrum in the rare‐gas solids Ar, Kr, and Xe. The intermolecular potentials are approximated by Lennard‐Jones potentials for this purpose, the parameters of which are obtained from specially chosen combination rules. An expression for the lineshift in terms of these parameters, the host geometry, and the polarizability of the species is derived. If certain variables in this expression are appropriately grouped together there exists a linear relationship which is graphically demonstrated for various examples. It is shown that the consideration cannot be extended to neon as a host matrix.
On the phase diagram of itinerant magnets in the presence of unmagnetic electron bands
Authors: Bünger M. , Jelitto R. J. 
Published: July 2007

AbstractThe phase diagrams of itinerant magnets are strongly affected by the presence of additional bands of unmagnetic electrons. This feature is worked out by consideration of a simple model consisting of a single Hubbard band and a free electron band, which works as a source or sink for magnetic electrons.
Force‐correlation function method applied to the Hall coefficient of paramagnetic transition metals
Authors: Schiller W. , Christoph V. , Sellger R. 
Published: July 2007

AbstractUsing the formalism of force‐correlation functions for systems with two groups of charge carriers a formula for the Hall coefficient is derived. The formula is applied to the phonon‐assisted interband and intraband scattering of electrons and holes in paramagnetic transition metals. The experimentally observed maximum of the Hall coefficient at low temperatures can be understood by the different temperature dependences of the interband and intraband scattering terms in the expression for the Hall coefficient.
Polariton structure of interband transitions in semiconductors
Authors: Stahl A. 
Published: July 2007

AbstractA set of semiclassical wave equations is derived describing the interaction of virtual or real electron‐hole pairs with electromagnetic radiation. The solutions of these equations are the polaritons formed in an interband transition. They describe a renormalized photon surrounded by a cloud of electron hole pairs. The concept of interband polaritons is particularly useful for the understanding of effects that are sensitive to the structure of the electron‐hole cloud. As examples the phenomena of polariton free surface layers (similar to exciton free layers) and electronic Raman scattering in a depletion layer with distorted bands are discussed.
Double quantum external photoelectric effect in crystalline tetracene
Authors: Arnold S. , Pope M. , Hsieh T. K. T. 
Published: July 2007

AbstractThe subject effect (DQEPE) is confirmed in tetracene crystal and attributed to the interaction of a free electron and a trapped charge‐transfer (CT) state. The energy of the trapped CT state is 2.85 eV. The light intensity (I) dependence of the DQEPE yield Y is Y ∝︁ I1.5. Greatly improved experimental techniques for measuring photoemission rates and retardation potentials in a gaseous environment are described.
Temperature dependence of the electrical conductivity and thermoelectric power in MoTe2 single crystals
Authors: Conan A. , Delaunay D. , Bonnet A. , Moustafa A. G. , Spiesser M. 
Published: July 2007

AbstractThermoelectric power and de electrical conductivity measurements are made on MoTe2 single crystals in a wide temperature range (77 to 770 K). The results are analyzed on the basis of impurity conduction. It is shown that three processes contribute to the total conductivity: hopping conduction between impurity sites, scattering by optical modes, and, in the intrinsic domain, scattering by impurities. The thermal energy gap (0.99 eV) is approximately the same as the optical one (1.03 eV). The effective mass of electrons in the conduction band is not very different from the mass of the free electron (m* = 0.76m), and the dielectric constant of the medium is K ≈︁ 34. The agreement between theoretical and experimental results is quite good. A comparison with previous results performed on compact polycrystalline samples is given.
On the long‐wavelength behaviour of solids with fluorite structure
Authors: Bedi S. S. , Verma M. P. 
Published: July 2007

AbstractA rigid‐ion Lundqvist many‐body potential model is used to derive expressions of the second‐order elastic (SOE) constants and the principal Raman frequency for solids crystallizing in the fluorite structure. Application to CaF2, SrF2, and BaF2 clearly demonstrates the inadequacy of the Born potential and the importance of three‐body interactions in this system.
On the nature of U5+ centres in LiF
Authors: Lupei V. , Lupei A. 
Published: July 2007

AbstractEPR results on eight new U5+ centres of cubic, tetragonal, or lower symmetry obtained by X‐ or γ‐irradiation of LiF‐U6+ single crystals are reported. No trigonal U5+ centres are observed. From the analysis of the EPR spectra tentative models of charge compensation are proposed. The centres consist of uranate (+5) structures and not of uranyl UO complexes. From the structure of the U5+ centres that of the parent U6+ centres is inferred.
Sondheimer oscillation in aluminium single crystals
Authors: Sato H. 
Published: July 2007

AbstractThe Sondheimer oscillation is measured for the magnetic field in the (110) plane. For the field along the [100] and [110] axes, the periods, the phases, and the field dependences of the amplitude were carefully examined. When the field is tilted from the principal axes, a peculiar wave form is observed. Realistic calculations which include the exponentially decaying factor are made on the basis of the 4‐OPW Fermi surface (FS) model. The peculiar wave form and still unexplained field dependence of the oscillation amplitude are well explained when the exponential factor is taken into account.
F‐center photoionization in the semicontinuum model
Authors: Edwards A. H. 
Published: July 2007

AbstractThe L‐band calculation of Page, Strozier, and Hygh (PSH) is re‐examined. Using the semicontinuum model, the dipole strength and photo cross‐section are calculated for ground state to continuum state absorption of light. The results do not agree with those of PSH. The salient difference is that the dipole strength is structureless and leads to a cross‐section similar to that of hydrogen. From this it is concluded that this simple model does not account for the L‐band structure.
Determination of thermodynamical parameters of the EHD in silicon from luminescence data
Authors: Schmid W. 
Published: July 2007

AbstractThe usual lineshape calculation of the EHD emission in silicon by a convolution integral over the densities of states of electrons and holes results in a considerable deviation from the experimental photoluminescence spectrum on the low energy side. As shown in this paper, agreement between the experimentally determined and the calculated lineshape is considerably improved as lifetime broadening of the final states of the recombination is taken into account. As a consequence of this lineshape fit improved parameters for the EHD in Si are obtained (carrier temperature 5 K): carrier density n = (3.5 ± 0.05) × 1018 cm−3, work function Φ = − 9.3 meV. Furthermore, for the first time a lineshape analysis of the TA‐phonon assisted emission is given which allows to check the validity of the composition of the much stronger TO/LO phonon assisted luminescence out of the two components. From the carrier density within the EHD and the lifetime a value of the Coulomb enhancement factor is estimated and compared with published theoretical data.
Dynamical superhyperfine interaction of atomic hydrogen in KCl and RbCl
Authors: Hoentzsch Ch. , Spaeth J. M. 
Published: July 2007

AbstractWith ENDOR the shf and quadrupole interactions of the nearest Cl neighbours of atomic deuterium on cation sites in KCl and RbCl and of first‐ and second‐shell neighbours of interstitial deuterium in RbCl are measured. Comparison with previous data of atomic hydrogen shows a distinct isotope effect indicating a considerable influence of the zero‐point vibration on the shf interactions. Using an orthogonalization model including a Cl3pσ covalency, the vibrational potential is determined from the isotope effect. It is shown that this theoretical model cannot explain the measured spin density at the nearest Cl neighbours.