bluuebunny/crossref_metadata_2025 huggingface dataset:
Calculation of Compton Profiles of Tantalum and Tungsten
Authors: Papanicolaou N. I. , Bacalis N. C. , Papaconstantopoulos D. A.
Published: July 2007

Calculations of the Compton profiles for the transition metals Ta and W are performed, using electron wave functions obtained from self‐consistent augmented plane wave (APW) band structure calculations within the local density formalism of Hedin‐Lundqvist. Relativistic effects are included except for the spin‐orbit interaction. The observed structures of the Compton profiles in these metals are understood in terms of the topology of their Fermi surfaces.
Electron Energy Levels in GaAs/Ga1–xAlxAs Heterojunctions II. Optical Properties
Authors: Godwin V. E. , Tomak M.
Published: July 2007

The oscillator strength for electric‐dipole transitions and the photoionization cross‐section of impurities in GaAs/Ga1–xAlxAs heterojunctions are calculated.
Dependence of the Low Temperature EPR Spectrum of Cu2+ Ion on the Microwave Field Frequency and Temperature
Authors: Vasyukov V. N.
Published: July 2007

The EPR spectrum of the Cu2+ ion in octahedral environment is calculated with the account of the Jahn‐Teller effect within the cluster model. The study of the frequency dependence of the EPR spectrum is used as a basis for the estimation of parameters of the Hamiltonian describing the behaviour of the system. The appearance of an additional isotropic line and drop of intensities of the resonance lines of the low temperature spectrum with the temperature increase are explained on the basis of the population of a great number of excited states and their properties.
Thermoluminescence Study of CaF2:Nd Single Crystals from LNT to 400 °C
Authors: Subramanian Uma , Mukherjee M. L.
Published: July 2007

Thermoluminescence and X‐Ray fluorescence of single crystal of CaF2:Nd are studied earlier. Since the major emission is in the infrared, attention is denoted to this region only. Although, there are reports that strong emission in the visible is also observed, detailed results are not available in the literature. In this paper, thermoluminescence (TL) emissions in the UV and visible region are studied in the temperature range between liquid nitrogen temperature and 400 °C. Several parameters associated with the TL emission are also calculated. A tentative mechanism for concentration dependence of the 315 °C TL peak is suggested.
Thermopower in Quasi‐Two‐Dimensional Semiconductor Quantum Well Structures
Authors: Kubakaddi S. S. , Mulimani B. G. , Jali V. M.
Published: July 2007

Expressions for the thermopower in quasi‐two‐dimensional semiconductor quantum well structures are obtained in the extreme quantum limit when electrons are scattered by acoustic phonons via deformation potential coupling, polar optical phonons, and ionized impurities. Numerical results are given for the size dependence of thermopower. It is found to be enhanced over its bulk value for lower values of well thickness. The contributions from individual scattering mechanisms are found to increase with the increase of temperature.
X‐Ray Electron Density Distribution of GaAs
Authors: Pietsch U. , Tsirelson V. G. , Ozerov R. P.
Published: July 2007

Using ten X‐ray structure amplitudes of strong reflections and nine weak reflections both, the valence electron and the difference electron density distribution of GaAs, are calculated. The experimental data are corrected for anomalous dispersion using a bond charge model. The calculated plots are compared with up to now published band structure‐based and semiempirically calculated density plots. Taking into account the experimental data of germanium, measured on the same absolute scale, the difference density between GaAs and Ge is calculated. This exhibits the charge transfer between both the f.c.c.‐sublattices as well as both, the shift and the decrease of the bond charge, quite closely connected to the theoretical results published by Baur et al.
Electron Paramagnetic Resonance Analysis of Strain‐Induced Defects in Semi‐Insulating GaAs
Authors: Benakki S. , Goltzene A. , Schwab C. , Guangyu Wang , Yuanxi Zou
Published: July 2007

A series of plastically deformed GaAs samples is investigated by EPR at 9 GHz. The spectra show that the expected As quadruplet is correlated with a new spectrum over the whole strain range. These results are discussed within a model justifying the predominant role of different anionic antisite linked complexes according to the experimental generation conditions.
A New Correlation Energy Interpolation Functional for Many‐Electron Systems in the Homogeneous Electron Gas Model. The Ratio of Paramagnetic and Ferromagnetic State Energies versus Gas Density
Authors: Gritsenko O. V. , Zhidomirov G. M.
Published: July 2007

An interpolation method is suggested to calculated the correlation energies ϵ{ϱ} and ϵ{ϱ} of para‐ and ferromagnetic states of an homogeneous electron gas of any density ϱ. The functions ϵ{ϱ} and ϵ{ϱ} plotted in this method reproduce an exact dependence of correlation energy on gas, ϱ, in the limits within ϱ → infin; and ϱ → 0, as well as the empiric correlation energies of atoms. With the obtained functions, ϵ and ϵ, the possibility of appearance and suppression of ferromagnetism when varying the density of electron gas is investigated. Paramagnetic susceptibility of gas as a function of ϱ is calculated, and the results obtained are compared with the experimental data for Na and K.
Collective Magnetic Order and Intermediate Valence in the Anderson Model
Authors: Reddy G. Gangadhar , Ramakanth A.
Published: July 2007

The question of the coexistence of long range magnetic order and intermediate valence is investigated using the periodic Anderson model. The average occupation nf of the relatively well localized 4f level and the corresponding magnetization mf are selfconsistently calculated keeping the total number of electrons N per lattice site fixed. The Curie temperature TC is determined following the temperature variation of mf. The behaviour of TC as a function of the position of the localized 4f level Ef for a constant Bloch band width W and as a function of W for a constant Ef are studied for different values of N. The results are interpreted in terms of the interplay between the relative occupation of the f‐level and the conduction band and the fluctuations caused by the hybridization. Similarities with experimental results are pointed out. A phase diagram is constructed which indicates the constellations of model parameters which permit long range magnetic order.
The Application of the Differential Operator Method to the Calculation of Magnetization in Thin Ferromagnetic Films
Authors: Wiatrowski G. , Balcerzak T. , Wojtczak L. , Mielnicki J.
Published: July 2007

On the basis of differential operator method the critical temperature and magnetization vs. film thickness are calculated in the frame of the Ising model. The magnetization changes across the film, and the corresponding magnetization profiles for several values of reduced temperature are presented. All the results obtained are calculated for the particular case of S = ½ and for a film with s.c. lattice, although another crystallographic lattices may be considered as well.
Increasing Absorption Bistability of CdS at Room Temperature
Authors: Haddad I. , Kretzschmar M. , Rossmann H. , Henneberger F.
Published: July 2007

Visible‐wavelength increasing absorption bistability at room temperature is shown due to lattice heating of CdS in a fully cw‐regime. Cross talk of two beams and the switching behaviour of the bistable system are investigated. For the first time critical slowing down is demonstrated for this type of optical bistability. Quantitative theoretical investigations based on the heat flow equations yield an excellent agreement with the experimental data.
Correlations between Electron Paramagnetic Resonance and Bonding Parameters. Evidence of a Lattice Relaxation
Authors: Souiri M. , Goltzene A. , Schwab C.
Published: July 2007

The study of the correlations between bonding parameters (ionicity, bond length) of a crystal and some spin‐Hamiltonian parameters of a magnetic probe allows to demonstrate the occurrence of a lattice relaxation induced by the condition of a constant bond length between an identical pair of bonded ions, independently of the host matrix under consideration.
A Silicon–Gold Pair in Silicon Investigated by EPR
Authors: Höhne M.
Published: July 2007

A new gold‐related defect in silicon is observed after IR irradiation. Though a thermal treatment including additional doping with lithium is necessary for the production of this centre, the lithium obviously does not participate in the paramagnetic state. The paramagnetic state is mainly localized at a silicon atom and a gold atom, both forming a trigonal pair. The interaction with six groups of three equivalent silicon ligands is partly resolved. The g‐values are compared with those of other gold‐related defects in silicon. Models are discussed.
Lattice Dynamics of Transition Metals
Authors: Thakur V. K. , Singh T. N.
Published: July 2007

A phenomenological model for the lattice dynamics of face centred cubic transition metals is developed. The potential energy of the crystal lattice is considered as due to (i) ion–ion and (ii) ion–electron interactions. The force‐field involving ion–ion interaction is essentially a three body force model employing valence force field approximations. The contribution to the potential energy from ion–electron interaction is considered by a screened Coulomb potential. Phonon dispersion curves, specific heat, and Debye characteristic temperature of nickel, palladium, and thorium are computed on the basis of the model developed. Computed results are compared with the experimental ones.
The Electrostatic Lattice Energy
Authors: Olives J.
Published: July 2007

The limit volumic electrostatic energy of a crystal lattice of point charges is compared to the Born‐Landé expression and to the Ewald energy. Conditions are given about the existence of these energies, and the results are expressed in an integral form; a second integral form is obtained by application of Plancherel's theorem. The volumic electrostatic energy depends on the surface of the crystal (owing to the long‐range I/r dependence of the electrostatic energy). Information about the atomic configuration of the surface of the crystal, is obtained by minimization of the volumic energy (the minimum being the Ewald energy).
Lattice Vibrations in BiLiF4 and YLiF4
Authors: Schultheiss E. , Scharmann A. , Schwabe D.
Published: July 2007

Results of Raman studies of BiLiF4 and YLiF4 single crystals at 300, 77, and 4.2 K and powder pellets of these materials at 300 K are reported. The observed vibrations are assigned to the irreducible representations of the space group of the crystals.
Spin‐Wave Spectrum in Uniaxial Ferromagnetic Thin Films with Nearest‐Neighbour and Next‐Nearest‐Neighbour Exchange Couplings
Authors: Duda A.
Published: July 2007

The standing spin‐wave spectrum is analysed for the uniaxial ferromagnetic thin film with nearest‐neighbour and next‐nearest‐neighbour exchange interactions. The boundary conditions are described in terms of the uniaxial surface anisotropy. It is found that the nnn exchange interactions give rise to new types of bulk and surface spin‐wave modes. The properties of the new modes are discussed in their dependence on both, nnn coupling and surface anisotropy parameters.
Calculations on Relaxations Due to a Vacancy, Binding Energy of a Vacancy—Vacancy Pair, and Formation Energy of a Vacancy in Thorium
Authors: Ghorai A. , Sen S. K.
Published: July 2007

The lattice statics method is used to calculate the relaxations due to a vacancy created in a lattice. The measured phonon dispersion relations and the elastic constants are used as constraints to calculate the dynamical matrix considering interactions up to eighth neighbour. The calculation shows that the first three shells of atoms relax towards the vacancy. The divacancy binding energy is found to be 0.477 eV which agrees well with simpler model calculation. Considering the uncertainty in the experimental value the agreement between the calculated and experimental value of the monovacancy formation energy is fairly good.
Electron Momentum Density Distributions in Rhodium
Authors: Bonde H. P. , Shrivastava S. B.
Published: July 2007

Calculations of two photon momentum density distributions (TPMD) and the electron momentum density distributions (EMD) are made in the 4d metal rhodium. Results are presented and discussed in terms of band by band contributions, along important symmetry directions. A comparison of TPMD results is made in the metals Rh, Pd, and Ag.
The Long‐Wavelength Magnon Relaxation in Ferromagnetic Metals at T ⪅ Tc
Authors: Lutovinov V. S.
Published: July 2007

The spin wave (SW) relaxation processes in ferromagnetic metals are considered in the framework of the spin operator diagram technique in a wide range of temperatures. It is shown that at elevated temperatures T ⪅ Tc the process of magnon absorption on the thermal fluctuations of localized d(f) spins with conduction electron spin flip plays an essential role equally with the process of SW−conduction electron scattering. The results obtained are in qualitative agreement with the experimental data on FMR linewidth.
Deuteration Dependence of the Central Peak in KDP‐Type Ferroelectrics
Authors: Wesselinowa Julia M.
Published: July 2007

The Ising model in a transverse field is treated by means of the Green's function technique to calculate the dynamical structure factor below and above Tc in KDP‐ and DKDP‐type ferroelectrics. Deuteration causes a decreasing in the frequency of the soft‐ferroelectric mode and an increasing in the spin—spin damping. The underdamped character of the soft mode disappears on deuteration. In KD2PO4 the peak around the soft mode is absent and the ferroelectric mode spectra below and above Tc consist only of the central peak around E = 0. All obtained results are in very good agreement with the experimental data.
Local Virial Relations and Pressure
Authors: Ziesche P. , Lehmann D.
Published: July 2007

Using appropriately defined densities of kinetic and potential energies, of momentum current, and electrostatic stress local virial relations of finite clusters and extended crystals with nuclei kept fixed are easily derived both from the many‐electron Schrödinger equation and from the one‐electron Kohn‐Sham equations. Comparing them, a local version of the Averill‐Painter relation for exchange and correlation results. By means of the local virial relations rigorous formulae for the pressure follow. They need the knowledge of the momentum and the pair distributions or — within the local density approximation — the solutions of the Kohn‐Sham equation. This latter result — here derived from rigorous theorems — agrees essentially with that of Liberman and Hodges/Nieminen, additional terms arise from the electrostatic (Hartree) interaction between a unit cell and its neighbours.
The Behavior of Active Centers in a Laser Host. A Crystal Field Investigation on Sm3+ in LaF3 Single Crystal
Authors: Neogy D. , Purohit T.
Published: July 2007

The behavior of the Kramers ion Sm3+ in the widely used laser host LaF3 is studied in detail, theoretically. The results obtained with a crystal field of D3h symmetry which explains the absorption spectra quite well are in fairly good agreement with the available experimental data on this doped material. The crystal field and the spin—orbit interaction matrix set up in the ground term basis is diagonalized simultaneously to obtain the precise Stark energies and wave functions, and this automatically takes care of the crystal field mixing of different J‐multiplets so important for this ion. The nuclear level splitting of the isotopes of this ion due to the electric quadrupole and magnetic interactions which are strongly influenced by the crystal field and the consequences of the hyperfine splitting are worked out.
Magnetic Pinning Interaction of a Type‐II Superconducting Cylinder
Authors: Saif A. G. , Shehata L. N.
Published: July 2007

A model of the magnetic pinning interaction (i.e., a system of N‐curved flux lines (FLs) and a cylinderical inclusion) is developed. The field components inside and outside the inclusion are calculated. The energy of the system and the magnetic pinning force are completely determined from the field distribution inside the superconductor. The properties of the curved FLs near the surface of a type‐II superconducting cylinder are established. The energy of the system as well as the magnetic field and the current density are calculated. The force on a flux line (FL) element is completely determined by the total current density at the element position.
Nonlinear Excitation of Pure and Doped Rare Gas Crystals
Authors: Kessler T. , Markus R. , Nahme H. , Schwentner N.
Published: July 2007

The power dependence up to the destruction limit and the coefficient of two photon absorption in Xe and Kr crystals are derived from transmission and luminescence experiments. A temperature dependent reduction of the quantum efficiency for luminescence at high power densities due to exciton—exciton annihilation is observed.
Dyson and Bethe‐Salpeter equations for dynamical X‐ray diffraction in crystals with randomly placed defects
Authors: Holý V. , Gabrielyan K. T.
Published: July 2007

A new formalism is found for the description of the dynamical X‐ray diffraction in statistically disturbed crystals both, in the coherent and in the incoherent approximations. The formalism is based on Dyson's equation for the averaged wavefield amplitude in the crystal and on Bethe‐Salpeter's equation for the averaged mutual coherence functions. The equations are simplified assuming the single‐group approximation. Dyson's equation is solved analytically by the Fourier method, and the first iteration of the solution of Bethe‐Salpeter's equation is found. On the basis of these solutions reflection curves as well as angular intensity distributions are computed for a crystal with randomly placed microdefects. The connection is shown of the theory presented with Kato's dynamical statistical theory.
A simple cluster improvement to the coherent potential approximation
Authors: Eggarter T. P. , Troper A.
Published: July 2007

An extremely simple way of including cluster corrections in CPA calculations is presented. The procedure is tested on the one‐dimensional binary alloy density of states and gives an excellent agreement with Monte‐Carlo calculations.
Annealing of the F+ EPR centers and the 2.3 and 2.9 eV optical absorption bands in zinc sulfide crystals
Authors: Matsuura K. , Kishida S. , Tsurumi I.
Published: July 2007

The F+ EPR centers and the 2.3 and 2.9 eV optical absorption bands are introduced in ZnS crystals by electron irradiation, neutron irradiation, and Zn‐treatments, and then isochronal and isothermal annealings of these specimens are carried out. It is found that the predominant isochronal annealing stages in the electron‐irradiated, neutron‐irradiated, and Zn‐treated specimens occur at 150 to 360, 300 to 600, and 600 to 800 °C, respectively. However, the F+ centers and the 2.3 eV band are simultaneously annealed. Therefore it is established that the 2.3 and 2.9 eV optical absorption bands are due to the F+ centers. It is also described that the sulfur vacancies are stable below about 600 °C in the Zn‐treated specimens and the migration energy of the vacancies may be 1.4 eV.
Vibrational states of surface crystal atoms
Authors: Vikhrenko V. S. , Kulak M. I.
Published: July 2007

The momenta–time correlation functions and their spectral densities are studied for rare gas crystal atoms at the (100) and (110) surfaces. Their characteristics essentially differ from the bulk behaviour for particles lying in the surface plane, but already in the third subsurface atomic plane the differences from the bulk crystal spectrum are only slight. Distinct quasi‐resonance peaks observed in the spectral densities may be an information source for experimental analysis of the surfaces.
Beyond the LUC‐CNDO k = 0 approximation
Authors: Craig B. I. , Smith P. V.
Published: July 2007

In applying the periodic LUC‐CNDO method it has been customary to employ the so‐called k = O approximation to represent the rather complex Brillouin zone (BZ) density matrix summations which arise within that formalism. The inability of this simplifying approximation to accurately describe these terms has, however, led to somewhat disappointing results. In this paper the periodic LUC‐CNDO formalism is extended beyond the k = O approximation by employing LUC special k‐point sets of progressively increasing size to evaluate these BZ density matrix summations to essentially arbitrary precision. This enables one, for the first time, to actually assess the accuracy of this semi‐empirical formalism without the imposition of additional approximations. Carrying the calculations through to full convergence in the BZ density matrix summations it is found that the periodic LUC‐CNDO method provides insufficient flexibility within its parameterization scheme to result in quantitatively accurate values for all of the properties of the homopolar covalent solids which are of interest. Whilst extension of this work to incorporate the additional contributions of INDO produced little improvement, recent work employing the MINDO method within the LUC periodic formalism appears promising.
On trigger properties of molecular organizates. I. Tunnel transport in donor–acceptor systems with strong electron–deformation interaction
Authors: Gaididei Yu. B. , Yakimenko I. I.
Published: July 2007

A theory of tunnel transport of electrons from donor to acceptor through dielectric films is developed taking into account the interaction of electrons with the elastic degrees of freedom for donor and acceptor. The efficiency of the charge transport processes in such systems is shown to be characterized by a nonmonotonic dependence on the rate of electron supply to donor (pumping rate). At a well‐defined pump level the system tends to the non‐equilibrium phase transition from the monostable state to the bistable (trigger) one.
Structures and Energies of Symmetrical 〈001〉 Tilt Grain Boundaries in Silicon
Authors: Kohyama M.
Published: July 2007

The energies and atomic structures of a series of symmetrical 〈001〉 tilt grain boundaries in silicon are calculated using the tight‐binding type electronic theory (the bond orbital model). There exists a continuity of boundary structures in the ranges 0° ≦ θ < 53.13° and 53.13° ≦ 90°. The type of boundary structures changes at the Σ = 5(130) boundary (θ = 53.13°); for this boundary, the model by Bacmann et al. is shown to be more energetically favorable. At the Σ = 5(120) (θ = 36.87°) and Σ = 5(130) (θ = 53.13°) boundaries, there exist comparatively deep cusps in the energy against θ curve. The discrepancy between the present results in silicon and the experimental observations in germanium for the Σ = 25(170) and Σ = 41(190) boundaries is discussed.
(Sd)–f Hybridization in the Phonon Spectrum of Thorium
Authors: Onwuagba B. N.
Published: July 2007

It is observed that contribution from (Sd)–f hybridization associated with the local field correction can be approximated by a short‐range (Born‐Mayer) potential in the phonon spectrum of thorium in the framework of a rare‐earth metal model potential (REMMP) method. Calculated results agree reasonably well with experiment.
Optical Studies of Vanadium in Gallium Phosphide
Authors: Ulrici W. , Friedland K. , Eaves L. , Halliday D. P.
Published: July 2007

The results of optical absorption, luminescence, luminescence excitation, and temperature‐dependent Hall‐effect measurements on semi‐insulating n‐type GaP:V and n‐conducting GaP:V are reported. The VGa2+/VGa3+ acceptor level is found at Ec − 0.58 eV. Absorptions due to photoionization transitions from and into this level can be identified. The absorption bands due to the transitions 3A2 → 3T1(F) and → 3T1(P) of VGa3+ are measured, both absorptions include three zerophonon lines as well as phonon replica. At low temperatures the photoinduced rechargings VGa3+ ↔ VGa2+ are investigated and interpreted in terms of the three charge states of VGa and the excitation of electrons from the PGa4+P4 anti‐site centre.
The Detailed Investigation of the Critical Current Density of Optimized Nb3Sn Modified Jelly Roll Wire throughout Its Entire Superconducting Phase Including a Comparative Study with a Similar Non‐Optimized Composite
Authors: Hampshire D. P. , Jones H.
Published: July 2007

Data are given characterising the distribution in critical currents intrinsic to an optimized Nb3Sn wire as a function of field and temperature. The different functional forms of the component critical currents are discussed in terms of the Fietz‐Webb scaling law. It is demonstrated that the flux‐flow state is characterised by defect flow within the flux‐line‐lattice (F‐L‐L). A comparison is made both, between the critical current and also the flux‐flow state of optimized and non‐optimized composites.
Shape of Magnetic Reststrahlen‐Bands Caused by Magnon‐Polaritons in Uniaxial Ferrites
Authors: Lehmeyer A. , Merten L.
Published: July 2007

The magnetic reststrahlen‐bands for linearly and circularly polarized incident waves propagating parallel to the optical axis are calculated for uniaxial ferrites. From the shape of these spectra all the characteristic frequencies of the magnon‐polariton waves can be determined.
Optical Properties of the F‐Centre in Beryllium Oxide
Authors: Gorbunov S. V. , Kruzhalov A. V. , Springis M. J.
Published: July 2007

Optical anisotropy of absorption and luminescence of F‐centres in BeO crystals are investigated. It is established that the anisotropy of the absorption band of F‐centres in the 6.5 eV region is due to the splitting of the singlet excited state of the 1P type into the components 1A1 and 1E in the crystalline field of C3v symmetry. It is shown that the anisotropic band of F‐centre luminescence at 4.9 eV is determined by singlet‐singlet transitions 1A1 → 1A1. The more intense luminescence band of F‐centres at 3.4 eV with the lifetime 700 ms at 80 K and the insignificant anisotropy are due to the spin forbidden triplet‐singlet transitions 3E → 1A1. The characteristics of non‐radiative transitions in the F‐centre and the reasons for the absence of photoconversion of F → F+ centres are discussed.
Electron Spin Relaxation in Ferroelastic KH3(SeO3)2
Authors: Müller H.‐E. , Völkel G. , Brunner W. , Cevc P. , Kurkin I. N.
Published: July 2007

Measurements of the electron spin—lattice relaxation time T1 and the phase memory time TM of SeO2− centres in X‐irradiated single crystals of ferroelastic KH3(SeO3)2 are reported. At temperatures above 11 K the spin—lattice relaxation is governed by a two‐phonon process of optical phonons. Near the phase transition point two anomalies in the temperature dependence of T1 are found. The anomalous increase of T1 is explained by an increased damping of that mode which is responsible for the Raman‐process. The phase memory time TM decreases critically at Tc following a logarithmic temperature dependence.
Nematic Liquid Crystal in 2 + ε Dimensions
Authors: Trimper S.
Published: July 2007

The isotropic‐nematic phase transition is studied in 2 + ε dimensions. Using the elastic free energy and applying renormalization group approach for a fixed length system in analogy to magnetic systems it is shown that the system exhibits a fixed point which is related to a certain temperature T* above which the one‐constant‐approximation is correct. The critical exponents and the equation of state can be calculated near to T*. Under the influence of an external magnetic field the scaling laws have to be modified.
Angle Resolved Photoemission and Electronic Band Structure of MoS2
Authors: Mamy R. , Boufelja A. , Carricaburu B.
Published: July 2007

Angle‐resolved photoemission measurements are performed on the layer compound MoS2 at 21.2 and 40.8 eV excitation energies. It is shown the applicability of the E(k∥︁) method in the framework of a non‐direct transition regime. An experimental band scheme is proposed. Good agreement with band structure calculations is found except for some of them in the relative position of the d and p upper valence bands, which is here clearly ascertained.
Electron–Phonon Interaction in Semi‐Infinite Semiconductor Superlattices
Authors: Wendler L. , Haupt R.
Published: July 2007

In this paper the single‐particle Hamiltonian of the electron–(long‐wave optical) phonon interaction is discussed for semi‐infinite semiconductor superlattices. The dispersion relation of the (longwave optical) surface phonon modes is analyzed in detail. These modes are composed from ordinary interface phonons on adjacent interfaces coupling through their macroscopic electric fields to form a surface collective excitation of the whole structure with an electric field having an envelope function decaying exponentially from the surface of the semi‐infinite superlattice. The coupling function of the electron–phonon interaction is calculated using a continuum theory. This coupling function describing the modified Fröhlich interaction of a single electron with the continuous field of polarization of the surface phonons is discussed and presented in graphical form.
Investigation of the Phonon Sidebands of SH− and SeH− Centres in Cesium Halides and Potassium Bromide
Authors: Otto J.
Published: July 2007

Infra‐red spectra of SH− and SeH− centres in cesium halides show unusually strong phonon sidebands, whereas the intramolecular vibration ν0 itself is only weak. The effective charge of SH− centres is calculated from the intensity of the ν0 line and turns out to be five times smaller for cesium than for potassium and rubidium halides. Most of the fine structure in the phonon sidebands can be directly correlated with the phonon density of states of the unperturbed host lattices. LA and TA phonons appear alternately in the sidebands of the stretching vibration ν0 and the combination lines ν0 + νL and ν0 + 2νL with the librational mode νL of the centres.
Calculated Elastic Constants of Dilute Alloys
Authors: Ram P. N. , Semalty P. D.
Published: July 2007

The elastic constants of dilute alloys are studied using a Green's function technique. An impurity model with central and non‐central force‐constant changes extending upto second neighbours of the impurity is employed to describe the impurity in a f.c.c. lattice and explicit expressions for changes in elastic constants have been obtained in terms of the t‐matrix. The effect of volume changes on elastic constants is discussed. The contribution to the bulk modulus from the electron pressure is also included. Especially the changes in different elastic constants are calculated in a number of dilute alloys based on Cu, Ag, and Au. The calculated results are compared with available experimental measurements. The obtained force‐constant changes are found to be symmetry dependent.
Electronic Structure and Symmetry Properties of the Envelope Functions in PbTe‐Pb1−xSnxTe Superlattices
Authors: Gondar J. López , de Dios Leyva M.
Published: July 2007

In the framework of Dimmock's two band model and in the constant band edge approximation within each layer, the electronic structure for the PbTe–Pb1−xSnxTe SL is studied. The study is carried out for the 〈111〉 valley, ϰ⟂ = 0, and taking into account all the possible solutions for the effective Hamiltonian. A new dispersion relation and new zero energy gap conditions are derived. Numerical calculations reveal that the inclusion of the largest wave vector solutions do not substantially modify the energy spectrum obtained when such solutions are excluded.
Fluorescence‐Detected Low Field Resonances in T–T Annihilation in the A‐TCNB Single Crystal Lineshape and Dynamic Parameters
Authors: Konyaev S. N. , Shushin A. I. , Kolesnikova L. I. , Tribel M. M. , Frankevich E. L.
Published: July 2007

An investigation is made of the line shape of the low field resonances observed in the dependence of the fluorescence of a single A‐TCNB CT crystal on the external magnetic field. It is shown that the resonance is caused by avoided crossing of magnetic sublevels of a single T‐exciton arising when the direction of the field is close to the axis of the fine interaction tensor. An analytic expression for the resonance line shape is obtained. The spin–lattice relaxation rate of T‐excitons, τ−1 = (1.0 ± 0.3) × 107 s−1 as well as the rate of jumps between the planes of fast exciton migrations, ω1 = (5 ± 2) × 107 s−1, are determined.
A New Effective Field Theory for Dilute Ising Ferromagnets
Authors: Bobák A. , Karaba J.
Published: July 2007

A new type of effective field theory for a quenched site diluted Ising model is presented. As a result the general equation for magnetization is obtained. Particular emphasis is given to the honeycomb lattice for which the critical concentration and concentration dependence of the magnetization and critical temperature are calculated. The critical concentrations for a square and simple cubic lattice are also obtained.
Exciton Absorption and Luminescence of Indium Selenide Crystals
Authors: Gnatenko Yu. P. , Zhirko Yu. I.
Published: July 2007

By investigations of low‐temperature photoluminescence (PL) spectra of InSe crystals the nature of emission lines in the region of indirect exciton transitions is determined and the energy diagram of optical direct and indirect transitions is offered. The presence in γ‐InSe of regions containing stacking faults results in the appearance of a fine structure in the PL spectra of an n = 1 exciton state. Within the framework of a “resonant exciton” model the causes of the growth of integrated intensity in the absorption spectra of an n = 1 exciton state are discussed.
Electronic Band Structure and Optical Anisotropy in InS. I. Experimental Study
Authors: Takarabe K. , Kawamura H. , Wakamura K.
Published: July 2007

Optical properties of InS on (001) surfaces are investigated using polarized absorptions near the fundamental gap (1.5 to 3.0 eV) and polarized reflectivity in the range of photon energy from 2 to 20 eV using a synchrotron radiation source. Detailed analyses of polarized absorption spectra reveal that the fundamental band gap of InS is an allowed indirect transition for each polarization in the (001) plane. The lowest direct‐gap is allowed for b‐polarization, but forbidden for a‐polarization. Dielectric functions are derived from reflectivity spectra by Kramers‐Kronig analysis and some features in spectra are assigned to interband transitions.
A New Method for Numerical Calculations in Anisotropic Elasticity Problems
Authors: Gundersen S. A. , Lothe J.
Published: July 2007

In anisotropic elasticity theory it is of major importance to calculate a certain matrix N and its orientational derivatives. On the basis of existing theory, a new iteration scheme is developed. The efficiency of the scheme is tested by application to a few examples.
Electronic Transfer and Thermal Vibration Parameters in Titanium Carbide an X‐Ray Diffraction Study
Authors: Field D. W.
Published: July 2007

An X‐ray diffraction study of titanium carbide powder of composition TiC0.90 is carried out at room temperature. The intensity data for 48 reflections to sin θ/λ = 13.7 nm−1 are compared with theoretical intensities obtained using various models. An electron transfer from metal to non‐metal resulting in a net charge of (2.2 ± 0.3) charges is found. There is no suggestion of covalent character of the bonding. The values of the r.m.s. vibration amplitudes of the atoms uTi = (6.36 ± 0.04) pm and uC = (5.9 ± 0.3) pm, and the Debye temperature is (610 ± 4) K. These results largely support recent work on the material; however, a recent suggestion of distortion of the titanium electron density towards the carbon atoms is not supported.
Photoinduced Recharging Phenomena and Vanadium‐Related Centres in GaAs:V
Authors: Ulrici W. , Kreissl J. , Vasson A. , Vasson A. M. , En‐Naqadi M.
Published: July 2007

Photoinduced recharging phenomena are studied at low temperatures (T < 80 K) on n‐type and semi‐insulating GaAs:V by optical absorption, C‐EPR, and TD‐EPR. Illumination with hvexc > > 1.05 eV into the photoionization absorption αII excites electrons into the conduction band and the recharging V + eecb → V takes place monitored by optical absorption and EPR. The centre responsible for αII appears to be a V‐containing complex of unknown structure, rechargable under illumination from (V–X) into (V–X)+. The V2+(II) centre measured by TD‐EPR is shown to be a second V‐containing complex different from (V–X). The interpretation of all experiments does not require a V‐related mid‐gap level.
A Simple Model of Re‐Entrant Magnetism in Amorphous Alloys
Authors: Kamberský V. , Kalva Z. , Závěta K.
Published: July 2007

A phenomenological model involving two kinds of self‐consistent interaction fields is shown to simulate the “re‐entrant” magnetic behaviour (i.e., mixed ferromagnetic and spin glass‐like ordering). Besides the Weiss field, it postulates fields of random directions and magnitude proportional to the mean absolute value of the local magnetic moment. Simple qualitative results are discussed and numerical results are compared with recent experiments on amorphous Fe8Ni72P10B10 alloys.
Two‐Atom Cluster Approximation for Ising Model (S = 1/2)
Authors: Balcerzak T. , Bobák A. , Jaščur M. , Mielnicki J. , Wiatrowski G.
Published: July 2007

The cluster containing two spins and their neighbourhood is taken into account in the frame of a new effective field approximation. As the result, two coupled equations describing the magnetization and correlation function are derived. The numerical calculations of the Curie temperature, magnetization, correlation function, and magnetic specific heat for the case of s.q. and s.c. lattices are discussed.
A Comparative Study of the Phenomenological Potentials for Ionic Crystals of Alkali Halides
Authors: Khwaja F. A. , Naqvi S. H. , Razmi M. S. K.
Published: July 2007

A comparative study of some well‐known interionic model potentials is carried out by computing anharmonic properties of alkali halides. The importance of including the zero point energy and the Van der Waals contributions properly is emphasised. Recently reported values of the Van der Waals term are employed to redetermine the unknown parameters of the potential. A comparison with experiment is made. It is concluded that the potential form proposed by Born and Mayer comes closest to the experimental situation.
Field Theory of a Viscoelastic Medium Subjected to a Phase Transition
Authors: Olemskoi A. I. , Panin V. E. , Petrunin V. A.
Published: July 2007

Evolution of a medium, which is subjected to the transition of crystallisation, martensitic type and so on, is realised as the interaction of a Higgs field, that describes a reconstruction of atomic system (transformation of potential relief), and a gauge field of displacements. It is shown, that the soliton type distribution of the fields is connected with one‐ and two‐dimensional defects. The conditions of the existence of defects are analyzed.
Contribution from the Lattice Vibrational Term and Pressure Dependence of the Phase Diagrams for Alkali Alloys
Authors: Soma T. , Iwafune K. , Kagaya H.‐Matsuo
Published: July 2007

The lattice vibrational contributions to the internal energy and Helmholtz free energy of alkali metals such as K, Rb, and Cs are studied in the dynamical treatment using the previously developed electronic theory based on pseudopotentials. The pressure effect on the phase diagrams of the CsK, CsRb, and RbK systems are obtained quantitatively considering lattice vibrational contributions. A region of phase mixture is decreased under pressure, and the melting curves under compression show an increase in temperature.
Optical Study of Phase Transition from Tetrahedrally into Octahedrally Coordinated MnS
Authors: Goede O. , Heimbrod W. , Weinhold V. , Schnürer E. , Eberle H. G.
Published: July 2007

MnS thin films on glass substrates prepared by thermal vacuum evaporation show zincblende/wurtzite and rocksalt structure, respectively in dependence of the substrate temperature. The thermal‐treatment induced transition from the tetrahedrally (ZB/W) into the octahedrally (RS) coordinated phase is studied optically by photoluminescence, excitation, and absorption spectroscopy and by X‐ray diffraction measurements. Emission bands in the red and infrared spectral region are observed being characteristic for the tetrahedrally and octahedrally coordinated phase, respectively. The excitation due to energy transfer by Frenkel excitons is studied in various stages of the ZB/W → RS phase transition. As a result of this transition a shift of the absorption edge by about 300 meV to lower energies is found ascribed to a corresponding energy‐gap difference.
Electronic Band Structure and Optical Anisotropy in InS. II. Theoretical Study
Authors: Takarabe K. , Kawamura H. , Wakamura K.
Published: July 2007

The electronic band structure of InS is calculated for the first time using the empirical pseudopotential method. A group‐theoretical study of the symmetry properties of InS is included. The resulting energy bands are then used to calculate the imaginary part of the dielectric function for each polarization along the principal axes of InS. The total and partial electronic densities are mapped on the (110) plane. Comparisons are made with previous experimental studies.
First Principles Prediction of Structural Properties and Pressure Dependence of the Charge Density and Energy Gaps in Diamond
Authors: Rodríguez C. O. , Casali R. A. , Blanć E. L. Peltzer Y , Cappannini O. M.
Published: July 2007

The possibility of predicting from first principles structural properties of solids has always been an aim of quantum theory of solids. These predictions are possible at present, and one also obtains a detailed description of many other microscopic properties. Using the ab‐initio pseudopotential approach a determination of the total energy and structural properties of diamond are made showing good agreement with experimental values. A detailed study is also given of the volume dependence of the forbidden X‐ray structure factor F(222) and of the pressure dependence of real space charge density and of different energy gaps. An analysis of the importance of transferability (norm‐conservation) of the input potentials is made.
Correlation between Chemical Shift, Plasmon Energy, and Partial Charge
Authors: Sinha S. H. , Chetal A. R.
Published: July 2007

X‐ray chemical shifts in copper and manganese compounds are correlated with the product of partial charge and plasmon energy. A linear relation between the chemical shifts and the product is observed, with the chemical shift increasing when the product increases. The constant of proportionality for copper and manganese is of different numerical value. The relationship is used to predict the chemical shifts for other copper and manganese compounds. When correlating chemical shifts with plasmon shift alone, it is seen that the chemical shifts do not vary linearly with plasmon shifts.
On the Bleaching of the A‐Bound Exciton Absorption in GaP: N. An Example for an Electron–Hole Liquid Induced Optical Nonlinearity
Authors: Woggon Ulrike , Henneberge F. , Weinert H.
Published: July 2007

The intensity dependence of the A‐line absorption in GaP:N is investigated at various nitrogen concentrations and at different excitation conditions, i.e. for resonant and band‐to‐band excitation. For the intensity levels, which are necessary to saturate the absorption, simultaneous luminescence measurements have clearly shown the formation of an electron‐hole liquid in the excited region. An explanation is given of the experimental findings which takes into account the presence of an electron–hole liquid in the sample.
Charge Transfer in Nickel–Hydrogen System
Authors: Badirkhan Z. , Khalifeh J.
Published: July 2007

The local environment is considered of a hydrogen interstitial in ferromagnetic transition metals. The electronic structure of dilute hydrogen in nickel is described by a simple tight‐binding approximation. The interstitial is mainly characterized by an extra “s” effective energy level and hopping integrals between the hydrogen ls orbital and its nearest s, p, and d orbitals. The solution of such a problem requires the use of Friedel's screening rule and the equation coupling the physical parameters relevant to both spin directions. Charge transfer from metal to metalloid is present for reasonable values of the Coulomb correlation between the two electrons in the ls orbital. The change in the total saturation moment per added impurity atom and the local moment at the hydrogen site are also calculated.
Interaction of a Localized Spin Moment with Phonons Due to the Exchange Scattering of Virtual Carriers in Semiconductors
Authors: Semenov Yu. G.
Published: July 2007

A new theory of the spin‐lattice interaction mechanism is developed for localized spins in semiconductors. In this mechanism, the coupling with phonons results from exchange scattering on a localized spin of the electron‐hole pairs accompanying the phonons. The process leads to a relaxation flip of the localized spin, provided the intermediate‐state carrier spins are flipped by spinorbit interaction. A detailed analysis of the mechanism is carried out in the approximation of the isotropic band structure of the semiconductor and the deformation electron‐phonon interactions. The experimental manifestations of the mechanism are discussed.
Stress Space and Strain Space in Continuum Mechanics
Authors: Kröner E.
Published: July 2007

Both, the kinematics and the statics of the mechanical state of a solid can be represented in the language of differential geometry. If the state is defect‐free then the geometry is, in general, Riemannian. The above statements are proved for the general nonlinear case. In particular it is argued that stress function tensor and stress tensor play the role of the metric and Einstein tensor, respectively, of the stress space whereas the equilibrium conditions for forces and moments (in absence of volume forces and moments) are the Bianchi identies of the stress space. Extension to solids with defects is possible.
Self‐Consistent MAPW Calculation with a Warped Muffin‐Tin Potential. I. The Electronic Structure of Al and Its Pressure Dependence
Authors: Bross H. , Eder R.
Published: July 2007

In the framework of the MAPW‐formalism the warped‐muffin‐tin approximation is discussed in detail. It turns out that the usually neglected terms are not only small as a consequence of wellknown facts of electrostatics but that the MAPW‐formalism has the advantage that the dominant multipole densities vanish with zero slope at the surface of the APW sphere. Using this approximation the electronic structure of Al is evaluated at seven different values of the lattice constant. This information enables the determination of the equation of state at zero temperature, the pressure dependence of the shape of the Fermi surface as well as the compressibility. At low pressures the agreement with experiments currently available is considerable. For higher pressures we expect a drastic change of the Fermi surface which should be seen by de Haas‐van Alphen experiments.
On the Anomalous Self‐Diffusion in B.C.C. Titanium
Authors: Köhler U. , Herzig Ch.
Published: July 2007

Self‐diffusion of 44Ti is measured in β‐Ti under UHV conditions in the whole range of existence of the b.c.c. phase. The Arrhenius plot shows a strong upward curvature in agreement with previous investigations of Murdock et al. The anomalous diffusion behaviour is related to the experimentally observed softening of the LA ⅔〈111〉 phonon mode and is explained by a monovacancy mechanism with a temperature‐dependent migration enthalpy. When separating the phonon related diffusion contribution the analysis yields a frequency factor and an activation enthalpy consistent with normal vacancy diffusion parameters.