bluuebunny/crossref_metadata_2025_split huggingface dataset:
Temperature Dependence of the Interface Polaron in Polar Crystals
Authors: Xiao Jing‐Lin , Sun Bao‐Quan , Xiao Wei 
Published: July 2007

AbstractThere 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

AbstractIn 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

AbstractThe 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

AbstractThe 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

AbstractA 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

AbstractThe 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

AbstractThe 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

AbstractWithin 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

AbstractThe 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

AbstractUsing 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.
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

AbstractFeynman 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

AbstractHall 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

AbstractLes 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

AbstractThe 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

AbstractThe 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

AbstractThe 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

AbstractA 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

AbstractHelicon 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

AbstractInfrared 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

AbstractA 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

AbstractCharge 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

AbstractVarying 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

AbstractThe 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

AbstractA 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

AbstractThis 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

AbstractThe 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

AbstractThe 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.