bluuebunny/crossref_metadata_2025_split huggingface dataset:
Volume Plasma Faraday Effect in n‐Type GaAs
Authors: Rheinländer B. 
Published: July 2007

AbstractThe infrared Faraday rotation of transmitted light is measured on highly Sn‐doped, n‐type GaAs epitaxial layers in the spectral region of the plasma resonance at temperatures of 300 and 130 K. The experimental results are explained applying the Drude theory. The statistical effect of the energy distribution of the electrons in the band is taken into consideration. The damping influence on the rotation is discussed in detail. The availability of the plasma rotation method for the determination of volume properties of epitaxial layers is pointed out.
Impurity Scattering in n‐Ge in Quantizing Magnetic Fields
Authors: Babich V. M. , Baranskii P. I. , Demidenko L. S. , Ilchishin V. A. , Korolyuk L. S. , Samoilovich A. G. 
Published: July 2007

AbstractThe magnetic field dependence of the magnetoresistance in nondegenerate n‐Ge is experimentally and theoretically investigated. The conductivity component connected with the impurity scattering (σ) is selected. Its magnetic field dependence in quantizing magnetic field is in accordance with theory.
Bound Exciton–Neutral Acceptor Complex in ZnTe
Authors: Wardzyński W. , Pataj K. 
Published: July 2007

AbstractThe splitting of I1 (2.3758 eV) and I2 (2.3590 eV) lines observed in luminescence at liquid helium temperature due to uniaxial stress is investigated. The I1 line splits into three components, all of them allowed for both polarizations. The I2 line splits into two components, one allowed for ℰ⟂p and the second allowed for both polarizations. The I1 and I2 lines are interpreted as due to radiative annihilation of excitons bound to neutral acceptor and donor, respectively.
Reaction Field Approximation for Heisenberg Paramagnets and the Magnetic Specific Heat
Authors: Scherer C. , Aveline I. 
Published: July 2007

AbstractThe concept of “reaction field” introduced by Onsager is applied to the case of a Heisenberg system in the paramagnetic phase. The procedure to obtain the static q‐dependent susceptibility and pair correlation functions is reviewed and extended to calculate the magnetic specific heat. The result of this calculation is compared with experiment.
Plasmon–Phonon‐Coupled Mode Sideband of Excitons
Authors: Ueba H. , Ichimura S. 
Published: July 2007

AbstractThe plasmon–LO‐phonon coupled mode sidebands of the exciton absorption spectra are investigated by means of the dielectric function formalism. Exciton‐coupled mode field coupling strength is calculated against the free carrier concentration, 1016 to 1018 cm−3. At any concentrations it is found that the coupling strength is very small. A possibility of the observation of this sideband is discussed.
Elastic Quasi‐Isotropy Normal to the Basal Plane in the Hexagonal System
Authors: Kirchner H. O. K. , Bluemel K. H. 
Published: July 2007

AbstractWithin the framework of the integral theory of anisotropic elasticity the Green tensor for point forces and the prelogarithmic tensor for dislocation energies are derived for the direction normal to the basal plane of a hexagonal crystal. They can be written in closed form and no numerical integration is necessary. The stress and displacement fields of a dislocation running in that direction are derived. Since a hexagonal crystal is transversely iso‐tropic in the basal plane, the most important dislocation interaction problem in a hexagonal crystal, the interaction between a glide dislocation in the basal plane and a dislocation tree normal to it, can be treated with the same ease as in isotropy.
Triplet Exciton Decay Processes in Crystalline Tetracene
Authors: Arden W. , Kotant M. , Peter L. M. 
Published: July 2007

AbstractThe decay of triplet excitons in crystalline tetracene is investigated. The monomolecular decay is characterised by a rate constant βt ≈ 5 × 103 s−1 and the bimolecular annihilation of triplet excitons is characterised by a rate constant γtt ≈ 2 × 10−11 cm3 s−1. The interaction between mobile triplet excitons and trapped holes is characterised by a rate constant γth ≈ 1 × 10−11 cm3 s−1. These values differ by two orders of magnitude from previous estimates. Some possible reasons for this are discussed.
X‐Ray Scattering from Crystals with Intracellular Disorder
Authors: de Almeida A. M. Ozorio , Ellis S. Caticha 
Published: July 2007

AbstractX‐Ray scattering from disordered crystals has been the subject of numerous investigations. In this paper an analysis made of the distribution of intensity scattered by crystals with static and dynamic disorder inside each cell resembles a general treatment for fluids. It is shown that only a two‐particle probability distribution function is needed in the theoretical treatment to account for correlated motions of the atoms. This is in contrast with the simpler case of independent motions described by a single‐particle probability distribution, which leads to a generalized Debye‐Waller factor. As an outcome of this approach it is demonstrated that static and dynamic disorder effects on the scattered intensity are indistinguishable for the infinite crystal. On the contrary, very small crystals would be expected to show differences in both cases. Finally the results are applied to the phase transition of NaN02.
Formal Results on the Susceptibility of Dilute Alloys. I. Green's Function Approach
Authors: Bisch P. M. , Gomes A. A. 
Published: July 2007

AbstractThe susceptibility of conduction electrons of dilute alloys is discussed including both electron–electron interactions and one‐electron impurity potentials. Adopting a two band model (s–d bands) a formal result is obtained for the partial susceptibilities, using the Green's function formalism and the Hartree‐Fock approximation. This solution is given in terms of a power series involving the Coulomb interaction and impurity parameters. An approximation is proposed, corresponding to a maximum exchange enhancement, for summing the power series, and an effective Coulomb scattering is obtained (for the fluctuations in the host) mediating the impurity scattering process.
Electron Nuclear Double Resonance of Mn2+ in SrF2
Authors: Falin M. L. , Meiklyar V. P. , Ulanov V. A. , Zaripov M. M. 
Published: July 2007

AbstractThe superhyperfine interaction (SHFI) of Mn2+ with four nearest coordination spheres of F− environment in SrF2 crystal is studied by means of electron nuclear double resonance (ENDOR). The SHFI constants are determined. The covalency parameters in the [MnF8]6−complex are determined for the fluorite type crystals.
Magnetism in S = 3/2 Models Magnetization Jumps and Reorientations, Heat Magnetization, and Trieritical Points
Authors: Sivardiére J. 
Published: July 2007

AbstractWe have studied in the molecular field approximation the statistical mechanical properties of a S = 3/2 ferromagnetic Hamiltonian with single‐ion uniaxial and biaxial anisotropy, anisotropic exchange, and a magnetic field. The phase diagrams exhibit various features such as: trieritical points and lines, magnetization jumps and reorientations, and heat magnetization.
Free‐to‐Bound Transitions in Lithium‐Doped Zinc Telluride
Authors: El Akkad F. 
Published: July 2007

AbstractThe two no‐phonon emission lines at 2.336 eV ± 4 meV (A) and 2.362 eV ± 8 meV (B) characteristic of Li‐doped ZnTe at 4.2 K are studied as a function of temperature (4.2 < T < 300 K) and of impurity concentration (5 × 1016 to 5 × 1018cm−3). It is found that the energy of the B transition decreases linearly with the pone; 1/3 of the donor concentration. It is shown that this law is expected theoretically for free‐to‐bound transitions in a compensated p‐type semiconductor when the screening length is determined by the concentration of ionized impurities (Debye and Conwell model). The effect of doping on the temperature dependence of the intensity can be explained in terms of the previously proposed interpretation: conduction band‐to‐acceptor transition for the A‐line and donor‐to‐valence band transition for the B‐line.
Calculation of Hot Electron Mobility and Electron Temperature in n‐Type InSb under the Assumption of Maxwellian Distribution
Authors: Komissarov V. S. 
Published: July 2007

AbstractFormulae with matrix elements regarding screened polar optical (PO), deformation acoustic (DA), and impurity (I) scattering, nonparabolicity, and s‐p interaction of the conduction band for nondegenerate and degenerate cases are used for the calculation of the mean energy 〈ϵ〉 of hot electrons in n‐type InSb semiconductors. The distribution function (DF) taken as an unexpended diplaced one, due to the lower values of Te, results in an electron‐gas “cooling” in nondegenerate n‐type InSb below To = 80 K, as well as in a reduction of the electron mobility in comparison with the calculated one for expanded DF. Taking into account the interaction of C‐ and V‐zones limits the runaway of electrons. A strong increase of the electric field increases the mean energy of carriers, being more effective for high‐resistance specimens due to the increase of the frequency of inter‐electron collisions. The mean energy of carriers calculated is compared with data of experiments performed in a wide range of electron concentrations.
Spatial and Spectral Spin Diffusion in Dilute Spin Systems
Authors: Vugmeister B. E. 
Published: July 2007

AbstractThe character of spatial and spectral spin diffusion Processes in disordered spin systems is studied. The analysis is based on averaging of the rate equations, valid for fixed spin positions, over different particle configurations. New Expressions for the spatial and spectral diffusion constants are derived and compared with earlier theories.
Evidence for a Partial F.C.C.—H.C.P. Phase Transition in Solid Neon from Raman Scattering
Authors: Schuberth E. , Creuzburg M. , Müller‐Lierheim W. 
Published: July 2007

AbstractRaman spectra from crystalline neon are investigated that show a sharp peak at 25.2 cm−1 identified as first order. Its energy is very close to that of the TA phonon at the L‐point of the f.c.c. Brillouin zone. A first‐order Raman effect is expected for the h.c.p. structure with the Raman‐active TO phonon almost degenerate with the TA phonon at the L‐point. From the haracteristic temperature dependence of the intensity of the peak, from its sharpness, and from its energetic position a partial phase transition at 10.5 K is deduced.
Green's Function Approach for High‐Temperature Ferromagnetic Systems in the Presence of Uniaxial Anisotropy
Authors: Kumar V. , Sharma K. C. 
Published: July 2007

AbstractThe effect of uniaxial anisotropy on the transition temperature for a ferromagnetic spinone system is investigated using the double time Green's function technique. The calculations are carried out up to the second order in the exchange coupling and exactly in the anisotropy term. The localized and the static correlations used in the formulation are calculated selfconsistently. The calculation is compared with corresponding results for an ordered system, which predicts an effective reduction in Tc with anisotropy in high temperature crystalline magnetic systems.
k‐q Functions and the Landau Theory of Second‐Order Phase Transitions
Authors: Litvin D. B. 
Published: July 2007

AbstractThe use of k‐q functions is introduced into the Landau theory of second order phase transitions. The expansion of an arbitrary density function in a crystal is given in terms of basis functions of irreducible representations of a space group which are linear combinations of k‐q functions. This leads to a new condition on the irreducible representations which can be associated with second order phase transitions.
Piezoresistance of Uniaxially Deformed n‐Si
Authors: Mitin V. V. , Tolpygo E. I. 
Published: July 2007

AbstractPiezoresistance of nondegenerate n‐Si is calculated for the case when the directions of the current and compression axis coincide with the 〈100〉 axis. Low temperatures are considered (T<100 K), when electrons are scattered by acoustic phonons, ionized impurities, and electrons of its own and other valleys. The piezoresistance is shown to depend not only on the impurity concentration but also on the scattering intensity of the electrons of one valley by those of the other valleys. The latter may be determined by comparing the experimental and theoretical deformation resistance dependences under the conditions when the acoustic scattering is inessential due to low temperatures or high doping levels.
Surface Plasmon and Polariton Dispersion at Rough Boundaries
Authors: Kröger E. , Kretschmann E. 
Published: July 2007

AbstractThe influence of surface roughness on electromagnetic surface modes is investigated theoretically. A frequency or wave vector shift is found and a damping of the modes depending on the autocorrelation of the surface roughness. This could be described by an explicit analytic expression. There is good agreement with experimental results on sinus‐odially modulated silver surfaces.
Optical and Electrical Spectroscopy of Zinc Oxide Crystals Simultaneously Doped with Copper and Donors
Authors: Muller G. 
Published: July 2007

AbstractIn Cu‐doped ZnO crystals the Fermi level is varied by additional donor doping (In or H) in the energy range 0 to 250 meV below the bottom of the conduction band. The results of optical absorption and electrical conductivity measurements carried out in these crystals can be explained by using the model in which Cu acts as an acceptor with an energy spacing of ECA = 190 meV from the bottom of the conduction band. Moreover oscillator strengths of inner transitions of the Cu2+‐ion are presented.
Determination of Optical Constants: Au
Authors: Jungk G. , Gründler R. 
Published: July 2007

AbstractThe dielectric function ε = ε1 + iε2, of Au films is measured at room temperature in the spectral range 1.6 ≦ E ≦ 4.6 eV with an ellipsometric null method. Numerical consideration of the free‐electron like part allows the computation of the interband dielectric function and its energy derivatives above 2 eV. The mathematical lineshape analysis of the derivative spectra of εl and ε2 leads to critical points at 2.54 ± 0.02, 3.28 ± 0.01, 3.64 ± 0.01, and roughly 4.5 eV of M0, M2, M1, and M2 type, respectively, and a rough estimate of the relative oscillator strengths.
Exciton Band Width versus Peak Shift in NH4Br in Phases II and III as Measured by Thermoreflectance
Authors: Rieflin E. , Stühmer G. , Schwab E. 
Published: July 2007

AbstractExperiments on the temperature dependent band widths in comparison to peak energies of the low energy exciton doublet of NH4Br are performed between room temperature and liquid nitrogen temperature. The band width is established as a linear function of the peak shift following the order parameter in phase III as pointed out earlier. The discussion includes this underlying temperature dependence of the peak energies.
A Generalization of the Sondheimer‐Wilson Formula for the Averaged Density Matrix and Magnetic Susceptibility of Conduction Electrons in a Model of Disordered Semiconductors
Authors: Bezák V. , Banský J. 
Published: July 2007

AbstractA model of disordered non‐degenerate semiconductors is investigated in which the bands are randomly undulated. A compact formula is derived for the averaged canonical density matrix of the conduction electrons in the presence of a magnetic field. A generalization of the formula of Sondheimer and Wilson is thus achieved. The magnetic susceptibility due to the conduction electrons is calculated. The enhancement of the diamagnetism with increasing disorder is discussed and interpreted as a consequence of the increase in the average density of the conduction electrons.
Surface Specifie Heat of Isotropic Solids
Authors: Grechko L. G. , Falko G. L. , Fedorchenko A. M. 
Published: July 2007

AbstractThe correlation functions of thermal fluctuations in a semi‐infinite isotropic elastic solid are obtained and the contribution of the surface to the specific heat is evaluated on the basis of the fluctuation‐dissipation theorem. The calculated specific heat coincides better with the experiments than the results of previous papers. The theory presented may be generalized for solids of complicated geometry and symmetry.
Band Structure Changes in Interealates of Niobium Diselenide
Authors: Birks A. R. , Hind S. P. , Lee P. M. 
Published: July 2007

AbstractThe KKR method has been used to calculate the energy bands in both pure NbSe2 and a simple model of its intercalates. The results show a complicated dependence of the upper valence band states on changes in the lattice parameter and charge transfer. These effects are estimated on the basis of data from optical and NMR measurements. Changes in the density of states afford an explanation of the changes in superconducting transition temperature as observed experimentally.
Two‐Photon Absorption of Anisotropic Excitons in β‐AgI
Authors: Dinges R. , Fröuhlich D. , Uihlein Ch. 
Published: July 2007

AbstractExciton fine structure is measured in hexagonal AgI by two‐photon absorption. A detailed assignment of the different P‐exciton states is possible using the appropriate polarization configurations. The experimental results can be explained quantitatively taking into account anisotropy as the only perturbation on the hydrogenic series. Using an effective mass Hamiltonian for degenerate valence bands it is shown that the Hd‐contributions to the hole kinetic energy are responsible for the mass anisotropy of the A and B series. An expression for the two‐photon transition probability in a three‐band model using the abovementioned Hamiltonian is derived.
Influence of Phonon Damping on the Electrical Resistivity of Open Electron‐Phonon Model Systems
Authors: Röpke G. , Christoph V. , Vojta G. 
Published: July 2007

AbstractA direct calculation of the electrical resistivity of an electron‐phonon system is made by means of the force‐force correlation function method. The coupling of the system considered to a bath is essential for the correct physical and mathematical formulation of the theory. It is assumed that the conduction electrons interact with the longitudinal phonons (only normal processes are taken into account). The interaction of the longitudinal phonons with the bath is given by a relaxation term with a wave‐vector dependent relaxation time. The corrections to the electrical resistivity caused by the finite coupling strength between phonons and bath are derived in lowest order and discussed; they are connected with the phonon drag.
Lattice Vibrations of V2O5. Determination of TO and LO Frequencies from Infrared Reflection and Transmission
Authors: Clauws P. , Vennik J. 
Published: July 2007

AbstractThe reflectance of V2O5, single crystals is measured between 20 and 2000 cm−1. Eleven resonances are observed: six with E ∥ a, two with E ∥ b, and three with E ∥ c. Values of ϵ0 are obtained separately from thin crystal channel spectra: ϵ0 = 37.2 with E ∥ a and 20.1 with E ∥ c. The reflectance data are analysed by Kramers‐Kronig integration, classical dispersion analysis, and four‐parameter dispersion analysis, all three methods yielding comparable results. Additional transmission measurements of thin single crystals and powders are performed. For the thin single crystal, absorption peaks at 982 and 1038 cm−1 are observed which are assigned to direct absorption of a TO and a LO vibration.
Thermomagnetie Properties of n‐Type and p‐Type HgTe
Authors: Jędrzejczak A. , Dietl T. 
Published: July 2007

AbstractThe electric conductivity, Hall coefficient, thermoelectric power, longitudinal and transverse Nernst‐Ettingshausen effects are measured between 100 and 300 K on heavily doped n‐type and p‐type HgTe samples. The temperature coefficient of the band gap, d|Eo|/dT = −5 × 10−4 eV K−1, is obtained by fitting the electronic effective‐mass data with a band model based upon the full Kane theory with higher‐band corrections. The phonon‐drag contribution to the thermoelectric power of p‐type samples is observed. The heavy‐hole effective mass m*/m0 = 0.45 ± 0.04 and one of the deformation potential constants, a = (2.7 ± 0.3) eV, are determined.
The Model Hamiltonian and Some Properties of Magnetic Resonance of Triplet Excitons. I. Non‐Localized Exciton Approximation
Authors: Berim G. O. , Kessel A. R. 
Published: July 2007

AbstractA theoretical investigation is made of the magnetic resonance of triplet excitons (TE) inchains of molecules, each of them containing two paramagnetic spins S = 1/2 coupled by a strong exchange interaction (I) and by exchange (K ≪ I) with spins of neighbouring molecules. A Hamiltonian describing the appearance and interaction of unlocalized TE is proposed. The zone structure and wave functions of single‐exciton and bi‐exciton states are defined. It is shown that the considered model describes well the effects in electron paramagnetic resonance (EPR) spectrum which do not depend on temperature (nonexistence of hyperfine structure and of fine structure, caused by inequivalent positions of the molecules in the crystal). Qualitative estimations of the temperature behaviour of the EPR lines are made from the analysis of the bi‐excitonic states.
An Analytically Tractable Structure Model for Disordered Systems. II. Complicated Structures and Application to Amorphous Selenium
Authors: Unger H.‐J. 
Published: July 2007

AbstractA previously proposed structure model is generalized to the case of a complicated structure where the corresponding crystalline unit cell contains more than one atom. An analytical expression for the radial distribution function is obtained depending on two adjustable parameters. The model is applicable for the description of amorphous structures containing a significant fraction of larger distorted clusters. Numerical calculations are performed for amorphous selenium. A comparison with the experiment shows that the monoclinic form predominates over the trigonal form in a‐Se.
Mobility of holes in p‐InSb crystals
Authors: Filipchenko A. S. , Bolshakov L. P. 
Published: July 2007

AbstractResults are given of an investigation of the temperature and concentration dependences of the Hall mobility of holes in p‐InSb crystals. The theoretical foundation of the results obtained is based on a strict account of the real structure of the valence band in indium antimonide crystals. It is shown that the experimentally obtained dependences of the Hall mobility of holes on concentration and temperature in p‐InSb crystals are well explained if one assumes that the holes are scattered by acoustical phonons and ionized impurities. The scattering of holes on optical phonons in the investigated interval of concentrations and temperatures can be neglected.
Roth's method and moment conservation of the spectral weight function for the neutral Hubbard model
Authors: Heiner E. 
Published: July 2007

AbstractThe method of Roth for the calculation of a (2 × 2 ) Green's function matrix is equivalent to the moment technique for the spectral weight function up to the fourth order. The method can be extended in order to derive a set of orthogonalized operators. With this method a selfconsistent calculation of the single‐particle Green's function and all important correlation functions of nearest neighbour sites is possible for the neutral Hubbard model. The results agree for a sc lattice in the strong correlation region at arbitrary temperatures with those of Shiba and Pincus for finite Hubbard systems. An antiferromagnetic coupling of neighboured lattice sites is increasing with a decrease of the temperature, a metalinsulator transition does not exist in this two‐pole approximation.
Derivation and calculation of a sequence of lower‐bound results for lattice thermal conductivity
Authors: Srivastava G. P. 
Published: July 2007

AbstractBetter variational lower bounds are derived as approximate solutions of a linearized Boltzmann equation for phonons. The role of the off‐diagonal part of the linearized phonon collision operator is considered in the frame of B displaced Planck distribution for phonons. A result derived here can be expressed in terms of the Debye term and the Ziman‐limit conductivity result‐showing that the Debye term is the “zeroth approximation” of that variational lower bound.