bluuebunny/crossref_metadata_2025_split huggingface dataset:
Two‐Photon Spectroscopy of Excitons and Polaritons in Strained ZnTe
Authors: Fröhlich D. , Kubacki F. , Schlierkamp M. , Mayer H. , Rössler U. 
Published: July 2007

AbstractTwo‐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

AbstractIn 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

AbstractThe 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

AbstractUsing 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

AbstractThe 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.
Nonlinear Magnetic Response of the Highly Correlated Anderson Lattice
Authors: Rao T. Venkatappa , Reddy G. Gangadhar , Ramakanth A. 
Published: July 2007

AbstractThe 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

AbstractEPR 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

AbstractAn 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

AbstractA 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

AbstractEPR 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

AbstractCorrelated 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.
Energy Structure and Resonance Properties of Noncentral Ions in Icosahedral Environment
Authors: Roitsin A. B. 
Published: July 2007

AbstractThe 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

AbstractThe 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

AbstractSmS 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

AbstractExperimental 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

AbstractThe 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.
Effect of High Pressure on the Electrical Conductivity of TlInX2 (X = Se, Te) Layered Semiconductors
Authors: Rabinal M. K. , Titus S. S. K. , Asokan S. , Gopal E. S. R. , Godzaev M. O. , Mamedov N. T. 
Published: July 2007

AbstractThe dc electrical conductivity of TlInX2 (X = Se, Te) single crystals, parallel and perpendicular to the (001) c‐axis is studied under high quasi‐hydrostatic pressure up to 7.0 GPa, at room temperature. Conductivity measurements parallel to the c‐axis are carried out at high pressures and down to liquid nitrogen temperatures. These materials show continuous metallization under pressure. Both compounds have almost the same pressure coefficient of the electrical activation energy parallel to the c‐axis, d(ΔE∥)/dP = −2.9 × 10−10 eV/Pa, which results from the narrowing of the band gap under pressure. The results are discussed in the light of the band structure of these compounds.
Superconductors with a Superlattice of Voids
Authors: Rudko V. N. , Shevtsova O. N. 
Published: July 2007

AbstractThe problem of the interaction between the vortex lattice in superconductors with the void superlattice is investigated. It is shown that the effect of the void superlattice is strong enough and under conditions that can be easily realized, changes the symmetry of the latter. Then the minimum of free energy is reached for the vortex lattice whose unit cell before deformation in the vicinity of voids has the form of a parallelogram with, in general, unequal sides.
Magnetoresistance in NiFebCo/Cu/Co/Cu Multilayers
Authors: Miyazaki T. , Oikawa M. , Ishio S. 
Published: July 2007

AbstractMultilayer films of glass/[3 nm NiFeCo/dCuCu/3 nm Co]10, dCu = 0.5 to 24 nm are prepared by an electron beam evaporation method under a pressure of ≈ 1.3 × 10−4 Pa. The magnetoresistance for these multilayers is investigated in the temperature range between 4.2 and 300 K. The temperature dependence of magnetoresistance is discussed based on the model of thermal excitation of magnons and also the two‐current model.
Eletron‐Spin Dynamics in the Two‐Dimensional Compound [NH3(CH2)4NH3]MnCl4
Authors: Niang A. , Ablart G. , Pescia J. , Khechoubi E. M. , Chanh N. B. , Duplessix R. 
Published: July 2007

AbstractThe two‐dimensional (2D) system [NH3(CH2)4NH3]MnCl4 is investigated by means of electron spin resonance (ESR) at X‐band over the 40 to 300 K temperature range. The linewidth, the g‐factor, the spin‐lattice relaxation time T1, and their thermal and angular dependences are measured. The data are characteristic of a 2D compound. The angular dependence ΔH(θ) indicates, taking also into account the presence of a half‐field line, the diffusive character of the magnetization at long time. The observed thermal dependences are consistent with an antiferromagnetic order at 40 K. The experimental data are interpreted using the Bloembergen and Wang three‐reservoir model since a strong exchange interaction is present.
Magnetic Properties of the Amorphous Transverse Spin‐1 Ising Model
Authors: Benyoussef A. , Amraoui Y. El , Saber M. 
Published: July 2007

AbstractThe amorphization of the spin‐1 transverse Ising model on a square lattice is studied within the effective field theory. The total longitudinal and transverse magnetizations, and quadrupolar moments are obtained. A number of interesting phenomena is found in these quantities, due to the fluctuation of exchange interactions and the applied transverse field.
Time Dependence of Inelastic Mössbauer Scattering with Stepwise Phase Modulation
Authors: Haas M. , Realo E. , Jõgi J. 
Published: July 2007

AbstractThe theory of time dependence of inelastic Mössbauer scattering in the case of stepwise phase modulation of recoilless γ‐radiation is developed. In thin scatterer approximation the theory describes the conversion electron yield for different center shift and phase change values. Inhomogeneous broadening of resonant lines and a realistic law of source motion is taken into account. Experimentally the stepwise phase modulation of the 14.4 keV resonant radiation is performed by an x‐cut quartz piezotransducer to which a 57Co:Pd γ‐source is cemented. By using a resonance detector with thin 57FeAl‐alloy scatterers to detect conversion electrons, an acceptable time resolution (< 30 ns) is achieved. A good agreement between theory and experiments is obtained.
Resonance Trapping of Positrons in Solids
Authors: Dryzek J. 
Published: July 2007

AbstractBasing on the approach to the calculations of the positron trapping rate presented by Shirai and Takamura [1], an attempt is made to explain the prevacancy effects observed in positron annihilation measurements in real metals. The calculations are done for the point defect and for the dislocation, taking into account the thermal distribution of the positron energy and the thermal expansion of the crystal lattice. In spite of the thermal distribution of energy of thermalized positrons the resonance trapping of positrons can be responsible for prevacancy effects in metals and can help solve some problems in the study of positron annihilation.
Uniaxial Stress Dependence of the Ionic Conductivity of Some Alkali Halides
Authors: Barth M. , Mohler E. 
Published: July 2007

AbstractA sensitive method to measure ionic conductivity changes of uniaxially stressed crystals is described. The stress effect in the extrinsic regime of the conductivity of NaCl and LiF single crystals is used to determine the elastic dipole tensor of a migrating cation vacancy. The elastic dipole tensor is transformed to the double force tensor which gives insight into the jump path the ion takes and into the elastic displacements in the immediate neighbourhood of the jumping ion.
ESR Study of Deuterated Analogue of (BEDT‐TTF)4Hg3I8
Authors: Yudanova E. I. , Lyubovskaya R. N. , Hoffmann S. K. , Sekretarczyk G. , Graja A. 
Published: July 2007

AbstractElectron spin resonance g‐factor, linewidth, and spin susceptibility of single crystals of the fully deuterated bis(ethylenedithio)tetrathiafulvalene (D8‐(BEDT‐TTF)) based conductor with octaiodine‐ mercurate anion (Hg3I8)2‐ are found to show pronounced temperature dependences between 4 and 300 K. A first‐order phase transition of the type semiconductor‐semiconductor is observed at 258 K. Discussion of the ESR parameters and the nature of the phase transition is given.
Hamiltonian Dynamics of the Landau Model of Ferroelectric Liquid Crystals. I
Authors: Mundim K. C. , Pitanga P. , Filho A. Ribeiro 
Published: July 2007

AbstractA Hamiltonian treatment of the Landau theory of phase transitions is presented. This formulation is based on the analogy between the order parameter space and the ordinary coordinate space of a particle moving in two dimensions. As an application, ferroelectric smectic liquid crystals are considered.
Lattice Dynamics, Thermal Expansion, and Third‐Order Elastic Constants of Seminoble Metals
Authors: Barrera G. D. , Batana A. 
Published: July 2007

AbstractGeneral expressions to calculate the first, second‐, and third‐order coupling parameters considering a general interatomic model that includes both two‐ and three‐body uncoupled forces are given. These formulae are applied to deduce the analytic expressions of the pressure, the second‐(SOEC), and third‐order (TOEC) elastic constants and the dynamical matrix and its strain derivative for the case of metals with face‐centred cubic (f.c.c.) structure and considering two‐body interactions up to third neighbours and common nearest‐neighbour three‐body force ones. A scheme of parametrization is proposed and the four independent parameters of the model are estimated. Within this framework the lattice contribution to the dispersion curves, the TOEC's, and the Grüneisen function for Ni, Pd, and Pt are calculated and compared with the values obtained from experimental data. Also the microscopic information the model gives, particularly the importance of three‐body forces and the fulfilment of the Grüneisen rule is analyzed.
Bandgap Fluctuations in Compensated a‐Si : H (P, B) Films
Authors: Rath J. K. , Fuhs W. , Mell H. 
Published: July 2007

AbstractN‐type compensated films of a‐Si : H (P, B) and a‐Si : H (Li, B) are prepared by the glow discharge decompusition of SiH4. Doping is achieved from the gas phase by addition of PH3 and B2H6 or after film deposition by in‐diffusion of Li. The statistical shift of the Fermi level inferred from the temperature dependence of the dark conductivity is consistent with a pronounced minimum in the density of states distribution in the upper half of the mobility gap. This minimum apparently shifts towards midgap when the boron content of the films is increased. The optical absorption indicates a decrease of the bandgap and an increase of the Urbach‐tail parameter Et, with increasing boron content. Both the statistical shift and the changes in the optical absorption are explained in terms of an apparent broadening of the bandtails due to boron‐induced fluctuations of the bandgap.
Nonlinear Waves of Rayleigh Type
Authors: Adamashvili G. T. , Gapishvili N. G. , Ogiashvili Z. D. 
Published: July 2007

AbstractThe theory of self‐induced transparency for waves of Rayleigh type is applied to a system consisting of a solid layer on a solid surface which contains paramagnetic impurities. Explicit expressions for a soliton and breather are given. It is shown that the parameters of the nonlinear waves of Rayleigh type depend on the transverse structure of the field and are formed at any thickness of the film.
Internal Friction Related to Carriers in High‐ Tc Superconductors
Authors: Huang Y. N. , Wang Y. N. , Chen S. O. , Zhou H. L. , Zhang Q. M. , Shen H. M. , Yang Z. , Zhao Z. X. , Chao G. H. 
Published: July 2007

AbstractFor both BiSrCaCuO and TlBaCaCuO samples, internal frictions (Q−l) in the kHz range reveal a plateau (Qp−1) above Tc and drop rapidly below Tc with the turning points at Tc. This kind of anomaly cannot be observed for nonsuperconducting samples. Moreover, it is discovered that Qp−1 is nearly proportional to the Hall carrier density for Y(Pr)BaCuO with various Pr content. These results show that the drop of Q−1 below Tc is closely related to superconducting condensation. The mechanism of Qp−1 may be attributed to the carrier jump induced by the stress‐induced reorientation of the polaron‐like distortions around the carriers. Further, taking into account the smearing of the superconducting gap structure resulting from the recombination of quasi‐particles and modifying the BCS relative jump rate the calculated results of internal friction below Tc are in fairly good agreement with experimental data. The superconducting gap Δ and the damping rate Γ for both BiSrCaCuO and TlBaCaCuO have also been obtained, they are in accordance with those got by tunneling spectrum and NMR methods, etc.