bluuebunny/crossref_metadata_2025_split huggingface dataset:
Resonant secondary radiation in polar semiconductors
Authors: Ivchenko E. L. , Lang I. G. , Pavlov S. T. 
Published: July 2007

AbstractA theory of secondary radiation in semiconductors is presented. The general expression for the differential cross‐section is derived which in the corresponding limiting cases describes off‐resonant light scattering and luminescence and is valid in resonance conditions. The theory developed is applied to the analysis of two‐phonon resonant Raman scattering by longitudinal optical phonons. It is shown that in this case the secondary radiation contains an additional contribution arising from quantum interference, comparable with the main contribution. The additional contribution may lead to a peculiarity of the radiation angular distribution in the backscattering direction.
On the theory of photon‐induced DC hopping conductivity in disordered semiconductors
Authors: Keiper R. , Schuchardt R. 
Published: July 2007

AbstractBased on the Kubo formalism a detailed discussion of the static hopping transport is given for the case that the electron transitions between localized gap states are caused by intense illumination of the specimen. The statistical correlations of the excited hopping system taking into account by means of the percolation theory, the resulting conductivities in the low‐frequency and highfrequency limits are analyzed with respect to their spectral dependences and their orders of magnitude in relation to Mott's phonon‐induced variable range hopping. Apart from its purely theoretical interest this new mechanism of photoconduction should also deserve experimental interest, in particular, because of the possibility of a frequency‐controlled „reading”︁ of the electronic density of states within the mobility gap.
On the mass dependence of the energy factor ΔK of the isotope effect for impurity diffusion in copper
Authors: Eckseler H. , Herzig Ch. 
Published: July 2007

AbstractUsing diffusion and isotope effect measurements of Au and Co in Cu a lower limit of the correlation factor of impurity diffusion as well as the corresponding limits of the kinetic energy factor ΔK are calculated from Manning's jump frequency model of vacancies near impurity atoms. The results show that a variation in impurity mass by a factor of three does not change ΔK for impurity diffusion significantly. For Au and Co in Cu ΔK is found to be about the same as for self‐diffusion in copper. This result allows to estimate the jump frequency ratios and the corresponding vacancy flow factors.
On the tight binding eigenvalues of finite S.C. and F.C.C. crystallites with (100) surfaces
Authors: Bílek O. , Kadura P. 
Published: July 2007

AbstractThe properties of small crystallities more or less deviate from those of infinite periodic crystals. An investigation is made of the size and habit dependence of one‐electron states of small crystallites in the Hückel approximation. Analytic formulae for s‐quasi‐bana electronic levels of finite s.c. and f.c.c. crystallites with (100) surfaces are presented. The symmtery classification of the levels for the f.c.c. crystallites possessing C4v point symmetry is also given.
Influence of mass defect disorder on resonance Raman scattering
Authors: Kleinert P. , Bechstedt F. 
Published: July 2007

AbstractA theory is developed for the influence of mass defect disorder on the one‐phonon Raman scattering. By using a Green's function formalism the scattering cross‐section is calculated in the case of mass defect disorder which influences the phonon subsystem only. An explicit expression for the scattering spectrum is given for monatomic and diatomic materials. The impurities substituted in the host crystal cause the occurrence of shifted frequencies in the scattering spectrum and the modification of the intrinsic Raman lines. The dependence of the scattering spectrum on the concentration and the mass of the impurities as well as the frequency of the incident light is studied.
On the existence of a spin‐glass state in an ising alloy model with mixed nearest‐neighbour exchange interactions
Authors: Medvedev M. V. , Rumyantsev E. L. 
Published: July 2007

AbstractThe possibility is investigated of a spin‐glass state as the ground state of a binary Ising magnet AB which is characterized (in the nearest neighbour approximation) by the competitive exchange interactions: IAA > 0; IAB > 0; IBB > 0. It is shown that due to increase of the antiferromagnetic component B concentration c in an intermediate concentration region either a spin‐glass state occurs or the first‐order phase transition from a random ferromagnetic state into a random antiferromagnetic one occurs depending upon exchange parameter ratios and crystal lattice type.
On the decay of the luminescence emission of Pb2+ centres in alkali halide crystals
Authors: Mǎrculescu L. , Vlahovici N. , Velula T. 
Published: July 2007

AbstractSome experimental results concerning the decay times of the luminescence emission of Pb2+ centres in KCl and NaCl crystals are reported and discussed in order to clarify the origin of the two emissions excitable in the A absorption band. The experimental features support the luminescent Pb2+ centre model implying a resonant energy transfer.
Delayed fluorescence excitation spectra in doped anthracene crystals
Authors: Graber N. , Zschokke‐Gränacher I. 
Published: July 2007

AbstractThe triplet excitation spectrum of the delayed fluorescence is measured in anthracene crystals doped with tetracene. It is shown that below 150 K the quantum yield ratio of delyed host and guest fluorescence depends on the wavelength of the exciting light within the triplet absorption. This effect is attributed to direct excitation of traps below 150 K. Although these traps are not connected with the teracene guest their influence on the triplet excitation spectrum of the anthracene host can be observed only in doped anthracene where the delayed host fluorescence intensity is sufficiently quenched by the guest.
EPR of lithium in mechanically affected silicon
Authors: Höhne M. 
Published: July 2007

AbstractAn intense narrow EPR spectrum is observed at 20 and 1.5 K in lithium doped silicon, which has been mechanically affected. The spectrum exhibits an angular dependent, only partly resolved structure. The spectra at the different temperatures can be explained by assuming lithium donors in rhombic strain fields of intermediate strengths. A Dyson effect yields the line shape at 1.5 K.
Isotropic ferromagnets with biquadratic interactions
Authors: Chaddha G. 
Published: July 2007

AbstractA spin‐one Heisenberg ferromagnet with biquadratic exchange is investigated, using Green's function technique in the Callen decoupling approximation. Assuming that the transition from the dipolar or quadrupolar state to the disordered phase is of second order, the transition temperature is found to decrease with the biquadratic exchange parameter α for 0 ≦ α ≦ 1 and increase for α > 1. The results for 0 ≦ α ≦ 1 are found to be significantly different from the earlier results in RPA and in Anderson‐Callen decoupling approximation.
Channel model in isotropic exchange theory (III)
Authors: Eremin M. V. , Rakitin Yu. V. 
Published: July 2007

AbstractThe exchange channel model developed earlier is applied to interpret the data on exchange interactions in ion pairs containing ions in excited states. The model is shown to give a satisfactory description of the available experimental data on doping pairs in perovskite‐type crystals provided the resonance excitation transfer effects are taken into account. The relationships based on the exchange channel model are used to calculate the superexchange contribution to the spectroscopic splitting parameter, 10Dq.
Nonrandom strain in „crushed”︁ silicon. EPR of thermally excited lithium donors
Authors: Höhne M. 
Published: July 2007

AbstractSi:Li single crystals with „crushed”︁ surface layers are investigated by EPR. Measurements at 1.5 K show that these layers, which contain in the outer part also the dangling bond centre with g = 2.0055, nearly preserve their crystalline order, but exhibit strains preferentially perpendicular to the surface. At 20 K thermal population of higher strain‐split levels feigns equal probability of all strain directions. A dynamical averaging process is discussed.
The OCN− vibrational spectrum and the phase transitions in KCNxKCl1−x single crystals
Authors: Castro J. C. , de Souza M. 
Published: July 2007

AbstractThe OCN− bending mode and Fermi resonances are studied in pure KCN and in mixed KCNxKCl1−x crystals. The two phase transitions in these salts are followed as a function of the Cl− concentration. By the application of uniaxial stress in the mixed crystals almost single domain regions are formed that allow to verify that the CN− and OCN− alignment in the orthorhombic phase is along the (110) direction. These single domain regions keep their alignment without applied stress by temperatures below the cubic orthorhombic phase transition. No change in dichroism is found in cooling the crystal to very low temperatures.
Pressure dependence of the electrical conductivity in 2H‐MoS2 and 2H‐WSe2
Authors: El‐Mahalawy S. H. , Evans B. L. 
Published: July 2007

AbstractThe electrical conductivity of synthetic crystals of n‐type MoS2 and p‐type WSe2 over the range 300 to 870 K are measured at pressures up to 30 kbar. The derived values for the pressure‐dependent activation energies are assessed in terms of existing energy band models.
Two‐photon resonant Raman scattering via biexcitons
Authors: Phach Vu Duy , Bivas A. , Hönerlage B. , Grun J. B. 
Published: July 2007

AbstractTwo‐photon resonant Raman scattering processes are studied in different scattering configurations in CuCl. Observation of Raman lines from the front face of the crystal (backward scattering) yields new information on the energy of the transverse T5 exciton and on the biexciton damping. In transmission (forward scattering), two new emission lines can be identified as due to the Raman effect. They show a strong angular dependence because of the polariton nature of the particles involved. Their characteristic features contradict an interpretation in terms of Bose‐Einstein condensed biexcitons.
Investigation of the simultaneous absorption of three CO2‐laser photons by tellurium
Authors: Pöhler M. , Staupendahl G. 
Published: July 2007

AbstractThe selection rule of the simultaneous absorption of three CO2‐laser photons (ThPA) by tellurium is experimentally determined by a two‐beam method. These experiments yield a new proof for the existence of a strong ThPA in Te. At Δ = 10.8 μm the ThPA absorption rates C⊥ ≈︁ 5 × × 102 cm3/W3 s and C∥ ≈︁ 8 cm3/W3 s are estimated. For the first time a three‐photon spectroscopy of the absorption band of Te (E ⊥ c) is reported. The absorption edge shows a distinct exciton peak. Finally, measurements of the intensity‐dependent transmission (E ⊥ c) of Te under various conditions demonstrate the considerable ThPA reduction at wavelengths ⪆ 11 μm.
Force‐correlation function method applied to the electrical resistivity of many‐band metals
Authors: Christoph V. , Schiller W. 
Published: July 2007

AbstractThe method of calculating the electrical resistivity by force–force correlation functions is generalized to many‐band metals. For two‐band metals a formula is derived from which the electrical resistivity R can be calculated by means of a simple perturbation treatment. For the phonon assisted s‐d scattering the temperature dependence of R is calculated for the case that the d‐electrons do not remain in thermal equilibrium. The two‐current formula for the electrical resistivity of ferromagnetic metals and alloys is derived.
Electrical conductivity in the strong‐coupling non‐half‐filled band Hubbard model
Authors: Ihle D. 
Published: July 2007

AbstractThe chemical potential μ and the electrical dc conductivity σ in the one‐dimensional Hubbard model in the strong‐coupling region U≫t (U intra‐atomic Coulomb energy, –t nearest‐neighbour hopping integral) are calculated as functions of temperature and electron density n. In the non‐half‐filled band case n ≠ 1 the Bari‐Kaplan approximation lim (σ/t2) is shown to yield an un magnified image physical singularity in the dc conductivity at T = 0 which is connected with the discontinuity of the zero‐temperature chemical potential at n = 1. An improved calculation for n ≠ 1 going beyond the Bari‐Kaplan approximation (i.e. taking into account the band terms in μ and σ/t2) yields a finite zero‐temperature conductivity which is proportional to the first power in t. For small deviations from the half‐filled band case the conductivity as a function of increasing temperature subsequently shows a metal‐like behaviour, a semiconductor‐like behaviour, and a repeated decrease at high temperatures.
On the nature of E1‐transitions in germanium
Authors: Humlíček J. 
Published: July 2007

AbstractThe E1 optical structure of Ge is studied by unmodulated, first‐derivative, and low‐field electroreflectance spectra. An extensive investigation of heavily doped samples shows only minor changes of their electron structure for impurity concentrations up to 6 × 1019 cm−3. As the freecarrier plasma screens the electron–hole interaction, exciton effects are reduced owing to the doping. While the exciton interaction is found to modify the electroreflectance lineshapes, its role is not essential in unmodulated and first‐derivative ones. The lineshape analysis of the room temperature spectra shows that the E1‐structure is not well described by a simple parabolic critical point of the joint density of states, except for the low‐field electroreflectance, which is fitted satisfactorily by a two‐dimensional minimum (substituting a rather complex band structure with at least one M1 saddle point).
Bandstruktur von bis(catena‐poly(methylarsen))
Authors: Tyutyulkov N. N. , Petkov J. I. , Schuster P. 
Published: July 2007

AbstractEs wird gezeigt, daß die Energielücke in BCPMA durch die Delokalisation der 4p‐Elektronen der As‐Atome bestimmt wird. Die Energielücke hat nur Korrelationscharakter. Es werden die beiden Formen von BCPMA – mit und ohne Alternation der As–As‐Bindungen in der Polymerkette untersucht. Es wird die Annahme eines strukturellen Peierls‐Übergangs in BCPMA gemacht.
Spontaneous parametric scattering of light in ammonium bioxalate monohydrate
Authors: Georgiev G. M. , Nikolov J. S. 
Published: July 2007

AbstractSpectra of spontaneous parametric scattering of light are obtained for the first time in the biaxial crystal ammonium bioxalate monohydrate ((NH4)2C2O4 · H2O). Some peculiarities of the spectra, such as asymmetry, intensity fall, and others are explained. Three zones of many‐particle states are discovered. The dispersion of the polariton wave vectors px(v) and pz(v) are determined in the range 900 to 6500 cm−1. By analyzing the Stokes lines in the spectrum of the spontaneous parametric crystal scattering some vibrations of Bx and Bz symmetry are identified for the first time.
Statistical mechanics of impurity states I. General treatment
Authors: Foglio M. E. 
Published: July 2007

AbstractCreation and annihilation operators that replace one ion in a crystal by an impurity in one of a set of states are defined. To use statistical mechanics with these operators, an ensemble that is close to the grand canonical ensemble is introduced. From the model Hamiltonian (given at a fixed value of the volume per crystal site) and the empirical knowledge of the pressure, most of the thermodynamic quantities are derived. A simple example is worked out in detail.
First‐order raman scattering of CsF doped with F centres
Authors: Lefrant S. , Buisson J. P. , Ghomi M. , Taurel L. 
Published: July 2007

AbstractFirst‐order Raman spectra of CsF (F centres) studied in resonance with the F band (610 and 640 nm) at T = 10 K are described. The acoustic (43, 48, and 76 cm−1) and optical (135 and 137 cm−1) modes are due to electron‐phonon interactions involving the displacements of the first and second shells of the F centre neighbouring ions, respectively. The interpretation of the spectra needs to consider the breaking of the “usual” selection rules due to the spin‐orbit coupling in the first I4− orbital state of the F centre via the electron interactions with the Γ, Γ, and Γ phonons.
Binding‐energy calculations for multiple bound excitons
Authors: Wünsche H.‐J. , Henneberger K. , Khartsiev V. E. 
Published: July 2007

AbstractThe Hohenberg‐Kohn‐Sham density‐functional formalism is used to describe multiple bound exciton complexes (MBE's) in indirect semiconductors. Correlation effects are considered in localdensity approximation (LDA) using an interpolation formula concerning the correlation energy of the non‐neutral homogeneous electron‐hole plasma. Adopting an isotropic model band structure for silicon (me = 0.2588m0, mlh = mhh = 0.2375m0) the localization energies of complexes D0Xm are found to be 2.9 meV (BE), 5.6 meV (m = 2), 6.1 meV (m = 3), and 7.8 meV (m = 4). The high stability of these complexes is due to the degeneracies of band edges enabling to occupy the lowest orbital with 12 (4) electrons (holes) without violating the Pauli principle. As a consequence, adding of one exciton doesn't lead to an remarkable enlargement but to an increasing particle density of the complex and, thus, a correspondingly strong enhancement of correlation effects is produced.
Determination of the effective g‐value of electrons in n‐type InSb by spin‐flip Raman scattering and electric‐dipole‐excited electron spin resonance
Authors: Appold G. , Pascher H. , Ebert R. , Steigenberger U. , von Ortenberg M. 
Published: July 2007

AbstractThe effective g‐value of n‐InSb is determined in magnetic fields up to 65 kG by spin‐flip Raman gain measurements and by electric‐dipole‐excited electron spin resonance. Results are shown for a non‐degenerate n‐InSb sample (8 × 1013 cm−3) and a sample with the electron gas being in a degenerate regime (1.35 × 1015 cm−3). The g‐value of the degenerate sample decreases monotonously from 51 at B = 0 to 41 at B = 60 kG. With the non‐degenerate sample two g‐values are found. They are interpreted as associated with shallow donor states, which have different binding energies for the spin‐up and the spin‐down states. For magnetic fields smaller than 28 kG the two donor state g‐values are smaller than the conduction band g‐value, which is measured in the higher doped sample. For magnetic fields above 28 kG, however, the conduction band g‐value becomes smaller than the larger donor state value.
Experimental phonon frequencies of RbBr at 80, 290, and 370 K
Authors: Nilsson G. G. , Karlsson U. , Raunio G. 
Published: July 2007

AbstractPhonon frequencies in RbBr are determined at the three temperatures 80, 290, and 370 K in the symmetry directions, Δ, Σ, and A using neutron inelastic scattering. The experimental frequency shifts obtained are compared to theoretical mode Grüneisen parameters calculated by Jex.
Phonon conductivity of InSb and GaAs
Authors: Al‐Edani M. C. , Dubey K. S. 
Published: July 2007

AbstractThe new expression for the three‐phonon scattering relaxation rate τ = (BN + BUe−θ/αT) × × g(w) Tm proposed by Dubey and Misho is used to calculate the lattice thermal conductivity of InSb and GaAs in the entire temperature range 2 to 300 K and 2 to 800 K, respectively and very good agreement is obtained between experimental and calculated values of the phonon conductivity of both the samples, InSb and GaAs, in the entire temperature range investigated. The reduced contribution due to transverse and longitudinal phonons are also studied by calculating the separate contribution due to each mode of phonons. The percentage contributions of three‐phonon normal and three‐phonon umklapp processes are studied. A comparative study of present results with the results obtained by previous workers is also made for both of the samples.
Electromagnetic waves in inhomogeneous semiconductors with non‐equilibrium carriers
Authors: Dykman I. M. , Tomchuk P. M. 
Published: July 2007

AbstractIn the presence of a heating field of carriers, F, the propagation of an electromagnetic wave in an extrinsic semiconductor with periodically distributed impurity centres, according to the law N(z) = = N0 + N1 cos z/L, is considered. At a wave vector k, of the wave inside the semiconductor, near to the condition of the Bragg resonance (k≈︁1/2L), the reflection |R0|2 and the transmission |D0|2 coefficients essentially differ from their values in a homogeneous semiconductor even at a small modulation of the impurity concentration (N1≪N0). The electric field F essentially influences the values of |R0|2 and |D0|2. With an increase of the field F, when k⪅1/2L a substantial bleaching of the material occurs. The reflection coefficient sharply decreases with the field, reaches a maximum value, and then asymptotically approaches to the value |R0|lim2, characteristic for the homogeneous semiconductor. When k⪅1/2L, |R0|2 monotonically decreases with the field down to its limiting value |R0|. As the wave vector k deviates from the resonance value, the above peculiarities become less pronounced.
Instability of the OPW Method in Relation to the Error in Core Eigenvalues
Authors: Reser B. I. , Dyakin V. V. 
Published: July 2007

AbstractThe influence of error in core eigenvalues on valence and conduction eigenvalues calculated by the OPW method is investigated. The general consideration is illustrated by a calculation of a silicon crystal. It is shown that due to the tendency of the determinant of the non‐orthogonality matrix to zero, a small error in core eigenvalues may cause large changes in the valence and conduction eigenvalues. Suggestions are given on how to reduce the influence of this drawback of the OPW method on the energy band calculations.
Theory of Free Carrier Absorption in Mixed Semiconductors with Composition Fluctuations
Authors: Kurowska A. 
Published: July 2007

AbstractA theory of intraband absorption is derived for the cases of a degenerate and a nondegenerate electron gas in mixed semiconductors with composition fluctuations. In those materials both the band edge and the effective mass are position‐dependent. It is found that for low electron concentration (Ne ≈ 1015 cm−3) absorption coefficients due to composition fluctuations (chemical disorder) and due to ionized impurities are of the same order.
Optical Spectra and Band Structure of As2Se3
Authors: Althaus H. L. , Weiser G. , Nagel S. 
Published: July 2007

AbstractThe optical properties of the layer material As2Se3 at low temperature are presented in the energy range between 1 and 9 eV for polarization of light parallel to the three crystal axes including the stacking direction of the layers. The results are compared with a band structure calculated by means of a semi‐empirical tight‐binding model. It turns out that in As2Se3 no lone‐pair bands exist like for instance in Se. In particular there is no gap between bonding and non bonding p states. The direct gap occurs at the point Γ. Some of the upper valence bands near Γ show considerable splitting due to interlayer interaction. Nevertheless selection rules and the dependence of the optical spectra on the polarization of light are essentially determined by the symmetry of the single layer.
Theoretical and Experimental Investigation of the Electronic Structure of the B2‐Compound FeAl
Authors: Ziesche P. , Wonn H. , Müller Ch. , Nemoshkalenko V. V. , Krivitskii V. P. 
Published: July 2007

AbstractThe band structure and the density of states of the ordered B2‐type intermetallic compound FeAl are calculated with a simplified KKR method. The crystal potential is obtained by the Mattheiss construction, which involves a charge transfer from the Al atoms to the Fe atoms. The self‐consistency of the assumed configuration 3d74s1 for the Fe atoms is discussed. The obtained results are contrasted to the results of Okochi. The soft X‐ray emission spectra Fe M2,3 and Al L2,3 are measured. The comparison of the theoretical results with these and other experimental data shows a reasonable agreement.