bluuebunny/crossref_metadata_2025 huggingface dataset:
Stochastic Dynamics Crossover From 1/ƒ3 to Flicker Noise
Authors: Canessa E. , Nguen V. L.
Published: July 2007

Finite time processes within the limits of the Newton equation and zero inertia motion (i.e., road to chaos) are studied by numerically solving the ordinary, stochastic Langevin equation in 1D for a free particle with inertia moving in a medium with viscosity γ. In these simulations, the scaling behaviour of particle trajectories x(t) and velocities v(t) with time are derived and the inclusion of non‐zero particle masses is shown to define the asymptotic time limit τc at which — independently of γ — the system evolves into the well‐known statistically stationary state characterized by x2(t)> æ t and flicker noise. The time τc is further analysed from the correlation length given by the two‐point autocorrelation function of the particle velocity at each value of γ. It is found that the noise power spectrum of v(t) is characterized by flicker noise for frequencies ƒ ≦ ƒc ≈ 1/τc, whereas for ƒ > ƒc, the noise power spectra behaves as 1/ƒv, where v varies between the limits of Newton's equation (i.e., v = 3) and road to chaos (i. e., v = 1). Furthermore, at times τ < τc and 0 < γ < ∞, an ad‐hoc exponent for the scaling of the variance of particle velocities with time is shown to characterize a subset of multifractal dimensions df(γ) while the single particle trajectories are shown to display a rather different subset of exponents on increasing γ. Generic features of this transition are nicely given by Poincaré maps in the velocity space.
Electrical Conductivity of Hot Electrons in Narrow‐Gap Semiconductors in the Extreme Quantum Limit at Low Temperatures
Authors: Bhaumik S. , Sarkar C. K.
Published: July 2007

The conductivity of hot electrons in narrow‐gap alloy semiconductors at low temperatures is calculated in the extreme quantum limit assuming a displaced Maxwellian distribution. The model includes the non‐equipartition of phonons and the Landau‐level broadening due to electron impurity interactions. It is assumed that the energy relaxation of electrons is governed by the inelastic acoustic phonon scattering via deformation potential and the mobility is limited by the acoustic phonon, ionized impurity, and alloy disorder scattering. The effect of the modified free carrier screening due to magnetic quantization is considered. The magnetic and electric field dependences of the conductivity have also been investigated.
Origin of Superelectrons
Authors: Fukuhara M.
Published: July 2007

The origin of superelectrons lies in the atomic nature. Superelectrons are derived from four special electron pair sets of 1s2, 2p6, 3d10, and 4f14, which can be represented as 1So of s‐type spin‐singlet pairing in the Russel‐Saunders term symbol. Tc increases with the increase of the compressive pressure against these spherical electron clouds by the pinch effect due to excess oxygen in cuprate oxide superconductors and the outermost electrons in the superconducting elements, suggesting the increase of the attractive interaction between electrons.
Subband Effects on High‐Field Electron Transport in Quasi‐One‐Dimensional Systems
Authors: Wang X. F. , Lei X. L.
Published: July 2007

A detailed calculation of electron transport in AlxGa1‐xAs/GaAs quantum wires by the use of a balance‐equation approach, considering all possible acoustic and optical phonon scattering and taking fifteen subbands into account, is reported. Crossover from one dimension (1D) to three dimensions (3D) in both low‐ and high‐field regimes is studied by investigating mobility and electron temperature as functions of the radius of quantum wire. At low temperatures, the linear mobility of a quasi‐1D electron system may be ten times higher or ten times lower than that of a 3D system depending on the relative position of the Fermi energy to subbands. At very high electric field, the difference in the transport behavior of quantum wires with differing radii and that of a 3D system disappears as a result of high electron temperature and drift velocity.
Optical Nonlinearities and Carrier Transport in GaAs: EL2 at High Excitation Levels
Authors: Jarasiunas K. , Delaye Ph. , Roosen G.
Published: July 2007

Laser induced picosecond transient gratings are used to study carrier transport via free carrier and photorefractive nonlinearities in semi‐insulating undoped GaAs bulk crystals. Carrier lifetime (τR = 1.5 ns), hole and ambipolar mobilities (μh = 410 cm2 V−1 s−1, μa = 760 cm2 V−1 s−1) are measured directly and an electron mobility equal to 5200 cm2 V−1 s−1 is calculated. The optical properties of highly excited GaAs reveal deep donor EL2 transformation and intracenter absorption under picosecond excitation. Rotation of the diffracted beam polarization is observed for the first time in orientation of the grating vector along the crystallographic axis [001]. This signal is attributed to a strain field at dislocations in LEC‐grown GaAs wafers.
Monte Carlo Study of the Order of the Phase Transition in Ising Systems with Multispin Interactions
Authors: Zhang Guo‐Ming , Yang Chuan‐Zhang
Published: July 2007

By analyzing the finite‐size behavior of the maxima of the specific heat near the phase transition temperature, the order of phase transition of two‐dimensional Ising systems with multispin interactions in the horizontal direction and two‐body interactions in the vertical direction are determined. The results strongly support the Turban conjectures.
Compton Profile Studies of CrxNi1−x Alloys
Authors: Pal D. , Padhi H. C.
Published: July 2007

Compton profile studies of CrxNi1−x alloys are made for concentrations x = 1.0,0.58, and 0.20. Present measurements indicate peaking of the Compton profile around x = 0.5, which is very similar to that of TixNi1−x alloys. The model of electron rearrangement between 3d and 4s states of individual metals with a transfer of about 0.25 electrons seems to explain the observed peaking of the profile at x = 0.58.
Energy Transfer Between AT and AX Minima in KBr: TI, Quantitative Four‐Level‐Model
Authors: Hlinka J. , Mihoková E. , Nikl M. , Polák K. , Rosa J.
Published: July 2007

The decay kinetics of the A‐luminescence in KBr : TI is investigated in the wide temperature region from 4 to 500 K. In the decay of AT emission up to four components with different decay times can be resolved and in AX emission rise time components are found. For the first time the energy transfer between AT and AX emission bands is observed separately between metastable levels (T = 30 to 40 K) and between radiative ones (T = 60 to 120 K). The set of experimental data obtained is sufficient to determine the rate constants for radiative and nonradiative transitions introduced in the semiempirical four‐level model proposed.
Measurement of Planar Channeling Radiation from 19.2 MeV Electrons in Silicon Using a Microtron
Authors: Poturaev S. V. , Kumakhov M. A. , Ognev L. I. , Iskandarian V. M. , Khatkov T. A. , Stirin A. I.
Published: July 2007

An experimental set‐up for studying radiation of channeled relativistie electrons in single crystals is designed. The source of electrons is a 19.2 MeV microtron. With the help of a mirror‐symmetric achromatic magnetic system a beam of electrons wih an angular divergence less than 0.3 mrad is transported to a single crystal target. The measured radiation spectra at planar channeling of 19.2 MeV electrons in silicon single crystals 3, 7, and 18 μm thick are presented and compared with the calculated spectra. Theoretical calculations are based on a newly developed method using a complex potential for describing the line broadening.
Expansion of Free Energy in Terms of Correlation Functions within the Landau‐Ginzburg Model. II. Calculation in Two‐Dimensional and Three‐Dimensional Cases
Authors: Madzhulis I. , Kaupužs J.
Published: July 2007

The asymptotics of correlation functions and critical exponents are investigated within the Landau‐Ginz‐burg phase transition model for ferroclectrics. The new method proposed is based on a subsequent account for fluctuations. Both analytical and numerical calculations are performed showing that the method gives nontrivial critical exponents. Moreover, precise values are obtained in the two‐dimensional case below the phase transition point. The first‐order phase transition is observed in the three‐dimensional case.
Study of Phonon Eigenfrequencies in Metallic Glasses
Authors: Gupta N. , Jain K. C. , Saxena N. S.
Published: July 2007

The density fluctuations in terms of phonon eigenfrequencies are studied in Ni50Zr50 and Cu66Ti34 metallic glasses using two different theoretical approaches. The calculated results of phonon eigenfrequencies show all the main characteristic features of the dispersion curves. The effective interatomic interactions are studied in terms of a pair potential using the extended theory of the Wills‐Harrison potential which includes the effect of d‐band electrons. Finally, from the low wave‐vector transfer region of the dispersion curves, some thermodynamical properties are also calculated which are in agreement with each other.
Computation of Elastic Moduli and Dispersion in (s–d) Interactive Atomic Liquids. The Example of Liquid Pt and Pd Metals
Authors: Venkatesh R.
Published: July 2007

A form of Wills‐Harrison's potential is used to derive the longitudinal and transverse phonon frequencies of Pt and Pd through the use of Takeno and Goda's equations. The low k‐values of phonon frequencies are found to be linear with k and from the slopes of these linear plots the elastic constants are calculated for both metals. The potential functions are also used to calculate the elastic constants of these liquid metals through the use of Schofield's equations. Structure factors in excellent agreement with experiment are generated treating the liquids as square‐well fluids. The paramenters are used to calculate S(0), the structure factor in the long‐wave limit. From the computed S(O) the compressibility and hence C11 are calculated. Because of the well‐known caging effect that occurs due to back scattering, effective masses are used in the calcultion of phonon frequencies. It is gratifying to note that the elastic constants calculated by different methods are in satisfactory agreement with each other.
Temperature Dependence of the Interface Polaron in Polar Crystals
Authors: Xiao Jing‐Lin , Sun Bao‐Quan , Xiao Wei
Published: July 2007

There is weak bulk but strong surface coupling between the electrons and phonons for many polar crystals. Here some properties of the interface polaron in polar crystals, which is a weak coupling with bulk longitudinal optical (BO) phonons and a strong coupling with surface longitudinal optical (SO) phonon, are studied. The temperature dependence of vibration frequency, induced potential, image potential, the effective interaction potential, and mean number of interface polarons is obtained by using a linear‐combintion‐operator method proposed by Huybrechts. Numerical calculations, for the AgCl/Kl crystal interface, as an example, are performed and some properties of these quantities of the interface polarons in polar crystals are discussed.
Hamiltonian and Boundary Conditions for Electrons in Semiconductor Heterostructures
Authors: Schnittler Ch. , Kirilov M.
Published: July 2007

In using the equivalent Hamiltonian approach for the simulation of semiconductor heterostructures two aspects are discussed controversially in the present literature: firstly the form of the equivalent Hamiltonian and secondly the appropriate boundary conditions. In this paper both aspects are investigated in the framework of the envelope‐function formalism especially for non‐parabolic band structures. Appropriate forms of the equivalent Hamiltonian and the boundary conditions are suggested and compared. The expected deviations are presented using theoretical calculations for type I and type II heterostructures. In accordance to theoretical evidence, the differences may be important in the case of type II heterostructures. From a theoretical point of view the use of the energy mass should be preferred. But for final evidence further experimental investigations and comparison with calculations based on different models are necessary.
Electronic Structures of Fe in La1–xCaxFeO3–y
Authors: Li Jiangong , Cai Xiaohong , Wang Tianmin
Published: July 2007

The isomer shift of La1–xCaxFeO3–y decreases gradually with increasing x, indicating the gradually increasing average intermediate valence state of iron, which is interpreted as being due to electron delocalization among iron ions on identical octahedral sites. The Mössbauer spectra of La0.50Ca0.50‐FeO3–y and their theoretical treatment show that electron delocalization slows down with dropping temperature. Two magnetic hyperfine patterns in the spectrum of this compound at 80 K may be assigned to Fe3+ and Fe5+ by assuming a charge disproportionation according to the scheme 2Fe4− → Fe3+ + Fe5+.
Electronic Structure and Superconductivity of NbN under High Pressure
Authors: Palanivel B. , Kalpana G. , Rajagopalan M.
Published: July 2007

The band structure and superconductivity of niobium nitride in the NaCl structure under pressure is theoretically calculated. The effect of pressure on the band structure is obtained by means of the self‐consistent linear muffin‐tin orbital method. The calculated equation of state is in good agreement with experimental results. The calculated value of the cell parameter is 0.4475 nm which is in agreement with the experimental value. McMillan's formula is used to calculate the values of the superconducting transition temperature (Tc). The parameters necessary to calculate Tc are taken from the band structure outputs. The theoretically calculated value of Tc under ambient condition is 14.594 K which compares well with the experimental value. Further increase in pressure increases the Tc values which may be due to sp → d electron transfer from nonmetal to metal atom.
Monte‐Carlo Simulation in a Total Energy Scheme for Classical and Quantum High‐Field Transport in Semiconductors
Authors: Poli P. , Rota L. , Reggiani L. , Bertoncini R. , Ferry D. K.
Published: July 2007

A microscopic deseription of transport properties in a nondegenerate semiconductor is presented which makes use of a novel total energy scheme. The semi‐classical kinetic equation is solved through an original Monte‐Carlo simulation which gives the distribution functions of the turing points, the new quantities devised to deseribe transport properties. Then, this semi‐classical scheme is generalized by including genuine quantum features such as collisional broadening and intra‐collisional field effects. Numerical results for the case of a simple model semiconductor are presented for illustrative purposes.
Electromagnetic Waves in Anisotropic Multilayer Ferrite Structures with Trigonal Symmetry under Parallel Magnetization
Authors: Bobkov V. B. , Zavislyak I. V.
Published: July 2007

The dispersion relations of retarded modes in recurrent form and the energy flux distribution for waves propagating in multilayer ferrite‐dielectric structures magnetized in the plane are obtained by using an impedance matching technique. The structures examined are arbitrary combinations of dielectric layers and (111)‐oriented ferrite films with basic cubic anisotropy. The applied bias magnetic field is assumed to be directed along the 〈110〉 ferrite film axis. The waves propagating perpendicular to the applied field direction are considered. The permeability tensor of a layer with trigonal symmetry is obtained to describe the dynamic magnetic properties of the ferrite layers. As examples of the described algorithm numerical calculations for some structures are carried out.
Structure Factor of Liquid Alkali Metals by the Integral Equation Theory
Authors: Jakse N. , Bretonnet J. L.
Published: July 2007

The pair correlation function g(r) and the structure factor S(q) of liquid alkali metals are calculated using an integral equation developed by Madden and Rice, which is based on the soft core mean spherical approximation. It is found that this closure relation is particularly well adapted to the treatment of the Friedel oscillations of the pair potential, which are seen to be most influential in determining the peculiarities of S(q). A good agreement is obtained with experimental data for Na and Li.
On the Relaxation Energy of Vacancy Formation and the Jellium Model for the Alkali Metals
Authors: Maganta L. F. , Vázquez G. J.
Published: July 2007

Within the jellium model we write the vacancy formation energy Ef as the sum of several terms: Ef = ΔT + ΔExc + ΔEc + Er, where ΔT is the change in kinetic energy of the electrons, ΔExc is the change in exchange and correlation energy, ΔEc is the change in electrostatic energy, and Er is the contribution because of lattice relaxation. Each term in this equation, except Er, is calculated using the density functional formalism for Li, Na, K, Rb, and Cs, respectively. To obtain Er we used the corresponding experimental values of Ef and subtracted from each of them the corresponding calculated values of the other terms. The resulting values for Er are all positive and relatively large, varying from about 0.1 to 0.23 eV.
Nonequilibrium Phonon Scattering on Impurity States of Co in CdTe
Authors: Beisyuk P. P. , Sadykov N. R. , Khabibullin B. M. , Shegeda A. M.
Published: July 2007

The mechanisms of interaction of nonequilibrium phonons with electron donor states localized on Co2+ impurities in monocrystals of CdTe are investigated by the heat pulse technique. There is no impurity scattering for phonons of longitudinal mode propagating along one of the fourth‐order axes q ∥ [100], where I‐phonons are nonpiezoactive. Therefore, the piezoelectric mechanism of electron phonon interaction predominates over all other scattering mechanisms.
A Detailed Investigation of the Dynamic and Thermodynamic Properties of Liquid Germanium
Authors: Rao R. V. Gopala , Venkatesh R.
Published: July 2007

Using Rao‐Joardar's equation the potential energy of interaction in liquid germanium at a density of 46.5 nm−1 is derived. The potential function shows a kink at 0.29 nm and an attractive minimum at 0.46 nm corresponding to the first and second nearest‐neighbour distances. The values calculated by other methods is found to be in good agreement with the present values. The derivatives of the potential function are used to calculate the phonon frequencies using Bhatia‐Singh's (BS) method and also by that of Hubbard and Beeby (HB). The agreement between the two methods is fair. Using Bhatia‐Singh's method the elastic constans are calculated. They are also calculated through the use of velocities in the long‐wave limit as obtained from the equations of Takeno and Goda and are from the phonon frequencies as obtained from Hubbard and Beeby's equations. The elastic constants calculated by different methods are found to be in good agreement with each other. Using the third and second derivatives of the potential the Grüneisen constant yg is evaluated. It is also calculated through pressure and energy of the vibrations. The values obtained by different methods are interconsistent. An average value of 1.39 for yg is obtained. The Grüneisen constant is used to evaluate the pressure derivative of the diffusion coefficient.
A Contribution to Friction between Solids
Authors: Gerlach E.
Published: July 2007

It is shown that the interaction of charge density fluctuations leads to a contribution to sliding friction, which is not negligible. In particular we have a finite friction force even if there is no direct contact between the materials. These concepts may be of interest for an understanding of the new friction microscope.
Feynman Path‐Integral Quantum Monte‐Carlo Simulations of One‐Dimensional Chains in the Presence of Attractive Intersite Interactions
Authors: Böhm M. C. , Schulte J. , Utrera L.
Published: July 2007

Feynman path‐integral quantum Monte‐Carlo (QMC) simulations are employed to investigate the ground‐state properties of the one‐dimensional Hubbard chain in the presence of attractive intersite interactions V. With increasing magnitude of the V elements the formation of domain structures causing a violation of the translational symmetry within the ID chain is observed. Domain structures differ from on‐site charge density wave (CDW) configurations in so far as their charge distribution shows random behaviour. The on‐site CDW is highly ordered. It is suggested that condensation transitions are position‐space concomitants of superconducting configurations of the ID chain. The formation of symmetry‐breaking domains is attenuated in ID chains with an average electron density 〈n〉 of 1.0. The dynamics of the electronic and spin degrees of freedom is studied by the fluctuations of the electronic charges 〈(Δn2)〉 and the local magnetic moments 〈(Δs2)〉.
Two‐Dimensional Galvanomagnetic Transport in GaAs Quantum Wells
Authors: Ghosh P. K. , Chattopadhyay D. , Ghosal A. , Mulimani B. G.
Published: July 2007

Hall mobility, Hall ratio, and magnetoresistance coefficient of the electrons two‐dimensionally itinerant in a square quantum well of GaAs are calculated in the regime of dominant lattice scattering. A numerical iterative solution of the Boltzmann equation is used considering Fermi‐Dirac statistics. The variation of the galvanomagnetic coefficients is studied with temperature, 2D carrier concentration, channel width, and magnetic field in the classical region.
Modification radiativement induite du spectre de luminescence de l'ion Ce3+ dans les solutions solides Ca1–xSrxS
Authors: Belsky A. N. , Krachni O. , Mikhailin V. V.
Published: July 2007

Les differences observées entre les spectres d'émission de l'ion Ce3+ dans les solutions solides Ca1–xSrxS, mesurés sous excitation dans la bande de l'activateur et dans le domaine de l'absorption fondamentale ont été expliquées. On a montré que le spectre de luminescence de ces phosphores lors de l'excitation interbande est la somme de deux spectres: le premier obtenu lors de l'excitation de l'activateur et le second de forme identique au précédent mais déplacé par rapport s̀ lui vers les grandes longueurs d'onde. On a attribué ce dernier spectre à la midification radiativement induite de la symétrie d'une certaine proportion de centres Ce3+ lors de l'excitation interbande. On a également considéré cet effet dans le cas de l'excitation par rayons X. Le modéle proposé a permis d'obtenir de nouveaux renseignements sur la structure spaciale locale des solutions solides Ca1–xSrxS.
On the Role of High‐Order Multiple Scattering Terms in Br K‐Edge XANES of the Ionic Conductor AgBr
Authors: Soldatov A. V. , Ivanchenko T. S. , Longa S. Della , Bianconi A.
Published: July 2007

The role of the multiple scattering terms in the Br K‐edge X‐ray absorption near edge structure (XANES) spectrum of AgBr is studied. In this system, in spite of the arrangement of atoms in collinear geometry, the first term in the expansion of the absorption coefficient (the single‐scattering term) is shown to account for the main features of the experimental spectrum in the range of 80 eV above the absorption threshold. The role of both the large Br‐Ag distance 0.289 nm and the short core hole lifetime in reducing the amplitude of multiple scattering terms is discussed. The size of the cluster of neighbor atoms probed by the XANES spectrum is studied: the second shell consisting of twelve Br atoms is shown to give the main contribution to the observed experimental features showing the minor role of the first coordination shell.
Raman Light Scattering Due to Collisions of Wannier‐Mott Excitons with Impurities and between Them
Authors: Vlasov G. K. , Prokhorov D. V. , Chizhikova E. I.
Published: July 2007

The theory of Raman light scattering due to Coulomb (exchange) interaction of an exciton in an intermediate state with neutral impurities in semiconductors is developed. The consideration is based on the third‐order perturbation theory. The possibility of such an approach is proved even for conditions of resonant Raman light scattering in direct‐gap semiconductors. The theoretical estimations for scattering cross‐section and scattering efficiency are well fitted with experimental data obtained by Ulbrich et al. on CdTe crystals. However, full explanation of these data must involve exciton scattering on bound excitons or biexcitons.
Magneto‐Optical Properties of F Center in KCI:SH−
Authors: Donatti D. A. , Aegerter M. A. , Iida T.
Published: July 2007

The magnetic circular dichroism (MCD) of F centers in KCI:SH− has been measured in absorption in the 1sσg → 2pyπu transitions at 493 and 509 nm, with fields up to 5 T and in the temperature range 1.5 K < T < 77 K. Within the limit of detection, no MCD is observed in the near infrared transition 1ss̀g → 2ps̀u as well as in both emissions 2pσu → Iss̀g and 2ps̀g. The optical detection of EPR in the F ground state presents an isotropic single band with g = 1.965 ± 0.007. The spin‐lattice relaxation measured at H = 0.32 T is typical of a direct process T−1 = 4.3 × 10−2 coth (gμBH/2kBT). The spectral variation of the MCD is calculated using perturbation theory to first order. The Hamiltonian includes the spin‐orbit interaction in the 2pπu excited state and the orbital molecular wave functions are obtained by a linear combination of 1s and 2p atomic orbitals. The calculated MCD is in good agreement with the observed one, for the spin‐orbit interaction strength σz = 3.6 meV.
Lattice Dynamics of the Orientationally Ordered Crystal C60
Authors: Lipin A. S. , Mavrin B. N.
Published: July 2007

A calculation of the vibrational spectrum of intermolecular modes of the low‐temperature orientationally ordered crystalline phase of fullerene C60 is carried out in the approximation of an intermolecular potential which includes two contributions: the atom‐atom Lennard‐Jones (12–6) potential and a noncentral interaction. This model has allowed to approximate satisfactorily the experimental data on neutron scattering, temperature dependence of specific heat, and bulk modulus. Phonon dispersions, sound velocities, elastic constants, and densities of vibrational states are calculated. It is shown that in the centre of the Brillouin zone librational modes which are Raman active should be located in the region 20 to 30 cm−1 and infrared active translational modes should be in the range 40 to 60 cm−1.
Helicons in the Presence of an AC Field in a Superlattice Plasma of Finite Layer Thickness
Authors: Misra K. D. , Pandey M. K. , Haile Tigistu
Published: July 2007

Helicon propagation in superlattices is examined in the presence of an externally applied ac electric field. Particle trajectories in perturbed and unperturbed coordinates in the presence of the applied ac field are determined and used for evaluating the perturbed distribution function, conductivities, and dielectric tensors. These results are used to find the dispersion relation for a superlattice structure. Illustrations are given for a superlattice structure subjected to various ac field amplitudes and frequencies. The earlier results for helicon mode propagation are recovered when the externally applied ac field is reduced to zero along the superlattice growth axis. It is observed that the ac field frequencies significantly affect the branch‐folding and propagation characteristics rather than the amplitudes of the signal. Application of this study for visualizing many observable effects through experiments and computer simulations are suggested.
The Infrared Absorption and Electron Spin Resonance of (MT)2(TCNQ)3 · 2H2O
Authors: Sekretarczyk G. , Olejniczak I. , Graja A. , Abashev G. G.
Published: July 2007

Infrared absorption and electron spin resonance studies are presented for (MT)2(TCNQ)3 · 2 H2O. It is shown that the IR spectrum of the salt is dominated by the Ag modes of TCNQ activated by electron molecular vibration (e mv) coupling; the coupling in (MT)2(TCNQ)3 · 2H2O is stronger than the coupling in other trimerized TCNQ salts. The donor vibrations are particularly susceptible to the temperature variation, which reflects the T‐evolution of the hydrogen bonds. From the ESR study it follows that the spin interactions in (MT)2(TCNQ)3 · 2 H2O are of one‐dimensional character.
Electronic Structure of Interfaces and Extended Defects in Ionic Covalent Crystals
Authors: Prosandeev S. A. , Teslenko N. M.
Published: July 2007

A consistent description is given in terms of the Green function method of electronic states associated with interfaces and extended defects in ionic covalent crystals. Closed expressions are derived for calculating the density and dispersion of impurity states. These expressions do not require the knowledge of wave functions of electrons, rather they operate with a limited number of Fourier transforms of Green functions of an ideal crystal. Formulas are given for calculating the electrostatic part of the potential at the defect and on the surface allowing an effective summation of lattice sums. The theory is illustrated by the example of an ideal chain of oxygen vacancies in AMO3‐type oxides.
Dissipative Charge Transfer Dynamics in an Asymmetric Double Quantum Well
Authors: May V. , Kühn O. , Thomas P. , Vaupel H.
Published: July 2007

Charge oscillations in an asymmetric double quantum well structure are described in terms of a density matrix theory for a coupled three‐level system. Including the phonon modes of the quantum well structure both an exact and a perturbational treatment with respect to the electron‐phonon coupling is presented. In additional, the physical meaning of the approximations leading to the perturbational approach is clarified. The exact treatment is used to calculate the temporal evolution of the charge distribution over the various levels. Furthermore, the influnence of dissipation on the dynamics is studied.
Intensity Dependent Effects in Silver Chloride: Bromine‐Bound Exciton and Biexciton States
Authors: Schulz M. , von der Osten W.
Published: July 2007

Varying the excitation power density over twelve orders of magnitude, the broad band recombination luminescence of AgCl containing 10 to 300 ppm of bromine impurities is investigated. Resonant excitation in the impurity‐induced and the free exciton absorption enables to discriminate recombination of the bromine‐associated self‐trapped exciton (STE(Br)) and intrinsic contributions. At very high powers a new band emerges which, on the basis of its nonlinear behaviour and lineshape, is ascribed to a bromine‐bound biexciton. The spectral features, including a zero‐phonon line of the STE(Br), allow a detailed analysis of all states in terms of binding energies and exciton radii. The results are compared with corresponding data in AgBr: I− and AgCl: I−.
Shell Structure Potential for Channeling in Solids
Authors: Kumar V. Hari , Pathak A. P.
Published: July 2007

The position dependence of the stopping power in planar and axial channels using the shell model charge density is established. The corresponding shell atomic potential is derived from the shell charge density using Poisson's equation. By using the continuum model approximation, axial and planar potentials are calculated. A comparison with other frequently used statistical potentials established the possibility to apply this shell potential usefully and analytically to various problems of atomic collisions in solids.
The Separable Potential Method and Its Connection with the Embedded‐Atom Method
Authors: Idiodi J. O. A. , Obodi G. N.
Published: July 2007

A detailed comparison of the separable potential method (SPM), recently proposed by one of us, with the embedded‐atom method (EAM) allows a characterization of the embedding function F through a nonlinear differential equation. The complete solutions of the nonlinear differential equation are given, and as a demonstration of the applicability of the method, one of the solutions is employed to calculate various physical quantities for some f. c. c. metals. The applicability of the unified approach discussed here, goes beyond f. c. c. metals. We illustrate this important point by comparing some of our results obtained for b. c. c. metallic vanadium with similar results obtained recently by Adam and Foiles in 1990.
Effective Phonon Coupling in Tunneling System
Authors: Ye Z.
Published: July 2007

This paper is devoted to the study of the renormalization of wave functions and coupling constant in dissipative two‐state tunneling systems, where the quantum effects of the tunneling particle on the phonon bath, as we will show, cannot be simply ignored. Through a general discussion of the extended objects of quantum origin, the renormalization factors are calculated in a simple approach. The effective phonon coupling constant is obtained. The possible improvement on the calculation of the renormalized tunneling parameter is briefly discussed.
Study on the Three‐Dimensional Electron Momentum Density and the Fermi Surface in Cu by Positron Annihilation
Authors: Kondo H. , Kubota T. , Nakashima H. , Murakami Y. , Tanigawa S.
Published: July 2007

The electron momentum density and the Fermi surface in Cu are studied by a two‐dimensional angular correlation of positron annihilation radiation (2D‐ACAR). The three‐dimensional electron momentum density is reconstructed using the image reconstruction technique. The electron momentum density obtained in the extended zone scheme is reduced to that in the reduced zone scheme by using the Lock‐Crisp‐West (LCW) folding procedure. The Fermi surface in Cu is determined in the reduced zone scheme. The enhancement parameters and the autocorrelation function are compared with the theoretical calculations.
Reference System Approach in the Electron Liquid Theory. III. Dynamic Function of Local‐Field Correction
Authors: Vavrukh M. , Solovyan V. , Vavrukh N.
Published: July 2007

The dynamic local‐field correction function G(q, ν) (q is the wave vector, ν = 2πnβ−1 the Bose‐Matsubara frequency) for the interacting degenerated electron gas is suggested. For easy handling the correction is given in the form of two‐and three‐dimensional integrals. The allowance for this correction makes it possible to perform computations of various energetic and structural characteristics in a wide range of the coupling parameter (0 ≦ rs ≦ 10) with the highest precision.
Two‐Photon Spectroscopy of Excitons and Polaritons in Strained ZnTe
Authors: Fröhlich D. , Kubacki F. , Schlierkamp M. , Mayer H. , Rössler U.
Published: July 2007

Two‐photon absorption is measured in ZnTe single crystals with uniaxial stress applied along [001] and [111] crystal directions. Using different polarization configurations, two‐photon selection rules, and the polariton fusion model all observed resonances in the region of the 1S exciton are identified as longitudinal excitons or transverse polaritons. A quantitative interpretation of the experimental data becomes possible by calculating the exciton and polariton dispersion in the eightfold space of the 1S exciton. This calculation takes full account of the applied stress, electron‐hole exchange interaction, and finite wave vector. Values for the deformation potentials Dd = 5.47 eV, Du = 1.89 eV, D = 3.63 eV and for unstrained ZnTe the transverse exciton energy ET = 2.3809 eV and the longitudinal transverse splitting ΔLT = 0.5 meV are derived.
Modified Thomas‐Fermi Approximation. A Surprisingly Good Tool for the Treatment of Semiconductor Layer Structures Including Various Two‐Dimensional Systems
Authors: Trott S. , Trott M. , Nakov V.
Published: July 2007

In this paper the calculational procedure of the electronic structure of δ‐doped quantum well HEMTs is studied with emphasis on the calculation rather than on the results. It will be shown that a modified Thomas‐Fermi approximation yields very accurate results which differ from the exact solutions of the Kohn‐Sham equations by only percents while the CPU time is reduced drastically and convergence problems are avoided. The question hinges on the point of an appropriate ϱ(V(r), r) in the Poisson equation. The construction of this charge density is discussed in detail. Care is taken on the nonseparability of the Schrödinger‐like equation with a position dependent mass.
Effect of Finite Energy of Deformation Potential Acoustic Phonons on the Low‐Temperature Breakdown Characteristics in n‐Ge
Authors: Pramanik T. K. , Bhattacharya D. P.
Published: July 2007

The effect of the finite energy of acoustic phonons on the breakdown characteristics is investigated here for a sample of n‐Ge at lattice temperature 5K. Impact ionization and thermal recombination are the two kinetic processes which need be taken into account for the phenomenon phenomenon of impurity breakdown in n‐Gc. The electric field dependence of impact ionization coefficient A1(E) and thermal recombination coefficient B1(E) is investigated here using the newly developed field dependence of electron temperature where the effect of finite energy of the acoustic phonons is taken into account. Then the impurity breakdown characteristics of the material are investigated. The calculations are carried out for a parabolic law of dispersion and a scalar effective mass. In comparison with other calculations and with available experimental data, the results obtained here show a better agreement in some of the characteristics.
Description of the Electrical Resistivity in Aluminium Alloys with Spherical Precipitates
Authors: Brzezinski A. , Gläser U. H.
Published: July 2007

Using an effective‐medium model for the electrical resistivity the Boltzmann equation is solved for binary systems including spherical precipitates. The model reproduces the behaviour of the resistivity of aluminium alloys during ageing and particularly provides the correct position of the characteristic resitivity maximum. Compared to the former generalized‐effective‐medium theory the two parameters mean free path and extra‐resistivity caused by clustering are involved in a more realistic way.
Electron Transport and Superconductivity in Transition Metal‐Containing Diamond‐Like Films
Authors: Bozhko A. D. , Chudinov S. M. , Rodichev D. Yu. , Pypkin B. N. , Stizza S. , Berrettoni M. , Briggs A.
Published: July 2007

The electron transport in W‐, Mo‐, and Nb‐containing diamond‐like films with specific resistance of 10−4 to 1014 Ω cm is investigated. It is shown that for most dielectric films (with low metal concentration) at room temperature the electric conductivity is in agreement with the Poole‐Frenkel model and tends to be activationless following Shklovskii's mechanism at low temperatures. The transition to a low‐resistance state is observed as an electric field of about 5 × 105 V/cm is applied. At high metal concentrations (more than 18%) evidence of superconductivity with Tc ≦ 4 K is observed. At temperatures below Tc one or two reentrant transitions to the resistive state are revealed. The influence of the magnetic field on the superconducting and reentrant transitions is studied. Possible mechanisms for the reentrant transitions are also discussed.
A Semi‐Infinite Space Type‐II Superconductor in the Presence of an Alternating Current
Authors: Saif A. G.
Published: July 2007

The exact analytical solutions for the electromagnetic equations governing the dynamics of a type‐II superconducting semi‐infinite space in the presence of an alternating current are obtained. The electromagnetic power losses on the surface of the superconductor are given.
Nonlinear Magnetic Response of the Highly Correlated Anderson Lattice
Authors: Rao T. Venkatappa , Reddy G. Gangadhar , Ramakanth A.
Published: July 2007

The periodic Anderson model (PAM) has, apart from other features, interesting magnetic properties. Depending on the model parameter values, it has both ferromagnetic and paramagnetic ground states. Earlier calculations where the localized electrons were assumed to be weakly correlated have shown that in the neighbourhood of a phase boundary, the system has characteristics similar to a spin glass. In the present paper, the PAM is treated in the infinite correlation limit and the magnetic properties are studied in the neighbourhood of the phase boundary. In particular the quantities that characterize nonlinearity, viz., the field dependent magnetization, the second‐order susceptibility, and the nonlinear response have been studied. It is found that in the present approximation the nonlinearity is reduced as compared with the weak correlation limit. However, the scaling relations which were examined earlier continue to be satisfied.
Influence of the Fine and Hyperfine Structure Terms on the Electron Paramagnetic Resonance Spectra of Polycrystalline Solids
Authors: Bissey J.‐Cl. , Lissayou J. , Beziade P. , Berger R. , Servant Y.
Published: July 2007

EPR spectra of polycrystalline compounds MnSO4 · (NH4)2SO4 · 6H2O, Gd2(SO4)3 · 8H2O, and NH4Fe(SO4)2 · 12H2O are recorded at X‐band and room temperature. For the first two compounds, good agreement with simulated spectra of Gaussian lineshape is found, and the numerical values of the fine (D) and hyperfine (A) structure constants are obtained by fitting with experimental spectra. For the last compound, the fine structure characteristic of the cubic term (a) is responsible for the “hyper‐Gaussian” shape of the EPR line.
Simulations of EPR Spectra in the Incommensurate Phase
Authors: Hrabański R.
Published: July 2007

An iterative least‐squares method for fitting experimental EPR spectra in the incommensurate phase to numerical multiparameter model spectra is outlined. The goal of this work is to provide a quantitative and reliable method for evaluating spectral simulation in the incommensurate phase and extracting the full information from experimental spectra. The Marquardt algorithm is used as a search procedure for adjusting the parameters that determine the simulated model spectra. An example relative to the EPR spectrum of Mn2+ in [Mg(H2O)6] SiF6, illustrates the application of the programme. Some simulations of EPR spectra in the multi‐soliton regime are also presented.
Study of Fourth‐Order Corrections to the Kinetic Energy for Metallic Surfaces
Authors: Martin‐García E. , Utreras‐Díaz C. A.
Published: July 2007

A study of the effect of fourth‐order gradient corrections to the kinetic energy functional Ts[n] on the ground state properties of metallic surfaces is presented. Two variational approximations are used; they are inspired by a method proposed by Levy et al. and show interesting properties. The exact numerical solution of the Euler equation is also obtained, and the relative merits of all the calculations are compared.
Electron Paramagnetic Resonance in MexC60 Fullerites for Me = K and Rb
Authors: Stankowski J. , Byszewski P. , Kempiński W. , Trybuła Z. , Żuk T.
Published: July 2007

EPR studies of superconducting fullerites MexC60 (Me = K and Rb) are performed for temperatures ranging from 4 to 300 K and compositions of x = 2 to 5. A paramagnetic center is an ion radical fullerene Ċ60 which may occur as a cation Ċ60+ or anion Ċ60y− of different valency. The EPR signal of Ċ60+ weakly depends on temperature whereas the signal of Ċ60y− in a Mex(Ċ60)y− complex is strongly dependent both on temperature and composition. A model of a paramagnetic center related to a wandering electron (hole) localized on the Ċ60 fullerene ball is presented.
Correlated Effective‐Field Treatment of the Blume‐Capel Model with Half‐Integer Spins
Authors: Kaneyoshi T. , Benyoussef A.
Published: July 2007

Correlated effective‐field theory and effective‐field theory with use of exact spin identities are applied to a study of the half‐integer spins, namely the Blume‐Capel model for spin‐3/2 and spin‐5/2. These methods are illustrated in a honeycomb lattice by investigating the phase diagram, the magnetization, the quadrupolar moment, and the correlated effective‐field parameter. The theory correctly accounts for many physical quantities and leads to results that are quite superior to those of previous works.
On an Anisotropy‐Grain Tensor
Authors: Maruszewski B.
Published: July 2007

The paper deals with a nonconventional description of a heterogeneous and anisotropic body. For this purpose the anisotropy‐grain tensor is introduced. The definition of that tensor is discussed on several examples as well as its evolution in time regarding it as an internal variable within thermodynamical nomenclature.
Energy Structure and Resonance Properties of Noncentral Ions in Icosahedral Environment
Authors: Roitsin A. B.
Published: July 2007

The group‐theoretical analysis of energy structure and transition rules is given for noncentral impurity ions in a crystal field of icosahedral symmetry. All possible ion displacements from the centres of icosehadron, pentagonal dodecahedron, and fullerene along the symmetry directions (toward the apexes, centres of faces and edges) are taken into account. Both the field‐free paraelectric resonance and paraelectric resonance in the presence of the external static electric field are considered. Accordingly, the transition rules between all possible pairs of irreducible representations of the icosehedral group and its subgroups are given.
Polaron Effects in the Protonic Conductor Hydrogen Uranyl Phosphate
Authors: Lupu D. , Grecu R. , Biriş A. R.
Published: July 2007

The isotope effects on the conductivity of hydrogen uranyl phosphate reveal ionic polaron effects in this solid protonic conductor, in agreement with the small polaron theory. An absorption band is observed at 0.67 eV, which can be correlated with the conduction mechanism consisting in both tunnelling and over‐barrier hopping processes.
A Modified Model for Lattice Vibrations in Sm0.75Y0.25S
Authors: Surendranath J. P. , Ilavarasi K. M. Sasintha , Ramachandran K.
Published: July 2007

SmS at a pressure of about 6 × 108 Pa undergoes a phase transition. A similar property is observed when Y is mixed with SmS (no external pressure applied) at an Y concentration of 0.25. Various models are available to work out the lattice dynamics of the mixed system SmYS and here a simple virtual crystal approximation is attempted and the results are compared with the experiments.
Continuous Phase Transitions and Orientational Ordering in Monolayers of Zwitterionic Amphiphilic Molecules at Fluid Interfaces
Authors: Katbamna P. , Dunne L. J. , Ford W. , Lavis D. A. , Southern B. W.
Published: July 2007

Experimental and theoretical evidence is presented which shows that orientational ordering of highly polar head groups in monolayers of amphiphilic molecules (zwitterionic 2 amino‐tetradecanoic acid) at fluid interfaces produces a smooth continuous phase transition. Hence this supports the view that models which interpret the sharp ‘kink’ point phase transitions exhibited by phospholipid monolayers at oil/water interfaces as being purely due to reorientation are deficient in important respects and suggests that the model which is most likely to be applicable to lipids of biological interest at oil/water interfaces is a blend of chain melting and collective molecular orientational ordering.
Analytical Expressions for XC Self‐Energies and Quasiparticle Shifts in Free‐Electron‐Like Materials
Authors: Bechstedt F.
Published: July 2007

The quasiparticle corrections to the energy bands for free‐electron‐like materials that result within the density‐functional local‐density approximation are discussed. Starting point is the exchange‐correlation self‐energy in GW approximation. The energy band structure is replaced by the empty‐lattice one but including an energy gap and free‐electron wave functions are applied. The screening in the system is described by generalizations of the electron‐gas dielectric function which account for energy gaps in the case of semiconductors and insulators and change over into the Lindhard function (or an approximate one) for completely free particles. Analytical expressions depending on electron density and dielectric constant of the material are obtained for XC self‐energies and quasiparticle shifts. The computed numbers are compared with results of more sophisticated GW calculations. An energy‐dependent extra potential is suggested that can lift the failure of the common local‐density approximation.