bluuebunny/crossref_metadata_2025_split huggingface dataset:
Angular dispersion of the internal phonon modes in ferroelectric sodium nitrite
Authors: Castellucci E. , Schettino V. 
Published: July 2007

AbstractThe angular dispersion of the frequencies of the internal modes in ferroelectric sodium nitrite are determined by measuring the Raman spectra with observation of phonon propagating in the ab, ac and bc crystallographic planes. Using the exciton model and a resonant dipole–dipole interaction mechanism the angular dispersion is calculated resulting in good agreement with the experiment. The k dispersion curves are also calculated for points along the [100], [010], and [001] directions.
Nuclear flip‐flop transitions induced by paramagnetic impurities
Authors: Sabirov K. Kh. 
Published: July 2007

AbstractThe general formulas for the nuclear flip‐flop transition probability induced by paramagnetic impurities are given based on the correlation function of the electronic subsystem. The calculation does not deal with the exact electronic spin fluctuation mechanism. The expressions for the spin‐diffusion coefficients associated with the modulation of the nuclear dipole–dipole interactions and indirect nuclear–nuclear interactions are derived.
Modulation of Mössbauer radiation by coherent ultrasonic excitation in crystals
Authors: Mketchyan A. R. , Arutyunyan G. A. , Arakelyan A. R. , Gabrielyan R. G. 
Published: July 2007

AbstractFor the first time experimental observations are made of the oscillation in the intensity of the unshifted line and in the intensities of the US satellites when the γ‐resonance radiation is modulated by the coherent US excitation. It is stated that the coherent US can be excited in the investigated sample if the US amplitude is transmitted homogeneously from the generator to the sample. A special sample‐unit is described which provides a homogeneous transmission, and it is shown hat the lifetime of the US phonons is not substantial and does not affect the oscillation of the absorption line intensities.
Equilibrium vacancy concentration measurements on tin single crystals
Authors: Balzer R. , Sigvaldason H. 
Published: July 2007

AbstractSimultaneous length and lattice parameter change measurements are performed on tetragonal tin single crystals in a‐ and c‐direction from room temperature to melting temperature. Length and lattice parameter change measurements agree within experimental error for all temperatures. From this it can be concluded that the maximum vacancy concentration is less than 3 × 10−5, which is the maximum experimental uncertainty. Using the energy of formation E = 0.50 eV from other experiments an upper limit for the entropy of formation of s/k = 1.1 is calculated.
The influence of two‐particle states (excitons) on the dielectric function of the electron—hole plasma
Authors: Röpke G. , Der R. 
Published: July 2007

AbstractImprovements of the RPA‐dielectric function of a plasma are investigated using the framework of Green's‐function technique which are of importance especially if bound states (excitons) are formed. It is shown that beyond the contribution of free carriers to the dielectric function a contribution due to the polarizability of the bound states arises.
The electro‐absorption edge spectra of 2H‐MoS2
Authors: Murray R. , Evans B. L. 
Published: July 2007

AbstractMeasurements are described of the effects of applied electric fields on the delocalised exciton spectra which comprise the direct absorption edge in 2H‐MoS2 (77 K). The field‐modulated transmission spectrum is predominantly due to thermal modulation of the illuminated crystal, but when this is reduced, field ionisation of the exciton states is observed at predicted field strengths.
Theory of Inelastic Reflection of Particles by Rayleigh Waves
Authors: van Trong Nguyen 
Published: July 2007

AbstractA quantum mechanical theory of particle reflection by Rayleigh waves is presented. The semiinfinite target is considered as a continuous elastic medium and its interaction with incident particles is treated as fluctuations of the boundary surface on which the particle wave function must vanish. The cross section is found to be expressed in terms of the correlation function for surface displacements of reflecting medium. The spectral distribution of correlation function is then related with the medium response function, in spirit of the fluctuation–dissipation theorem. That response function is obtained in the framework of the elastic theory. It is suggested that the spectral distribution of fluctuations shows the presence of Rayleigh waves.
Surface Waves in Low‐Dimensional Crystals
Authors: Chebotarev L. V. 
Published: July 2007

AbstractThe acoustic surface waves are investigated propagating along the free boundary of highly anisotropic crystals having layer‐ or chain‐structure. It is shown that due to the anomalous smallness of some of the elasticity moduli very slow surface waves can exist in such crystals penetrating deeply into the bulk of the crystal.
Theory of Exciton Migration in a Critical Region
Authors: Gaididei Yu. B. , Trofimov A. S. 
Published: July 2007

AbstractThe migration of exciton excitations in a crystal undergoing a second‐order phase transition is considered using the density matrix theory. Near the phase transition temperatures in a crystal appear large‐scale fluctuations of the order parameter at which, as shown, an exciton may be scattered additionally. An anomalous temperature dependence of the exciton diffusion coefficient in the critical region is predicted.
The Lattice Dynamics of Quantum Crystals of F.C.C. 4He
Authors: Kushwaha M. S. , Kushwaha S. S. 
Published: July 2007

AbstractThe lattice dynamics of solid helium in the f.c.c. phase is investigated using an unpaired elastic force model (EFM). The potential energy of the crystal is assumed to be made up of two parts: (1) the potential energy, giving rise to the central (pair‐wise) forces and 2. that one, giving rise to the unpaired forces. The model parameters are calculated using five experimental phonon frequencies. The frequency spectruy calculated at all the irreducible points of the first Brillouin zone is further used to compute the phonon density of states, lattice heat capacities, and Debye characteristic temperatures. The use of the model parameters is also made to predict the experimentally unavailable elastic constants in the f.c.c. phase. The theoretical results for the phonon frequencies along [100], [110], and [111] symmetry directions compare well with recent available experimental data.
Electronic States of the Dilute Transiation Metal–Simple Metal Alloy According to the Resonant Model Potential Method
Authors: Dagens L. 
Published: July 2007

AbstractThe transition metal–simple metal alloy problem is formulated in the framework of the resonant model potential theory. It is reduced to a formally equivalent problem involving a tight‐bindinglike Hamiltonian, with non‐hermitian and energy dependent matrix elements. The s–d hybridization potential is exactly described by this non‐hermiticity. The Friedel‐Anderson virtual bound state (VBS) is recovered in the dilute limit. The theory is then applied to the 3d‐transition impurities in aluminium and the results are compared with observed values of the VBS widths.
Drift Diffusion in Grain Boundaries under the Influence of Stress Fileds
Authors: Trinkaus H. 
Published: July 2007

AbstractThe diffusive‐elastic coupling between a misfitting inhomogeneity in a grain boundary and the related stress field is analysed within a continuum approach. The scaling behaviour of the basic equations allows some general conclusions on the time dependence of various processes like the spreading of an inhomogeneity, the diffusional creep and the growth of grain‐boundary voids. The coupled Green's functions for the spreading of an inhomogeneity and the related stress field over an infinite plane grain boundary are derived. They show that in the early stage the width of such an inhomogeneity develops in time as t1/3 (grain‐boundary diffusion), in the late stage as t1/2 (volume diffusion). Possible applications to the quantitative treatment of creep and void growth are indicated.
Effects of Surface Spin Waves and Surface Anisotropy in Magnetic Thin Films at Finite Temperatures
Authors: Levy Diep‐The‐Hung, J. C. S. , Nagai O. 
Published: July 2007

AbstractThe validity of the Green function theory developed by Haubenreisser et al. for ferromagnetic thin films (TF) is investigated. Their method, although to rough for the calculation of magnetization spatial distribution, is found useful for the calculation of critical temperature. By using their method, the effect of surface spin wave modes on the critical temperature is analyzed of both ferro‐ and antiferromagnetic TF. The film thickness dependence and the surface anisotropy dependence of the critical temperature are presented. The condition of the appearance of the so‐called “hard surface” and “pinned spin wave” is discussed. The effect of temperature in ferro‐ and antiferromagnetic resonance is also studied.
The Scattering of γ‐Rays in the Regime of Double Resonance
Authors: Bashkirov Sh. Sh. , Belyanin A. L. , Sadykov E. K. 
Published: July 2007

AbstractThe resonance scattering of γ‐quanta is considered theoretically when a radiofrequency field of large intensity with a frequency equal to hyperfine splitting is imposed on the scatterer. The spectra of scattered radiation and the dependence of the line intensities on rf field amplitude are derived. The accordance between experimental results obtained earlier and the obtained results is outlined.
Electro‐Optic Effects Due to the Stark Splitting of Energy Bands
Authors: Enderlein R. , Renner P. , Scheele M. 
Published: July 2007

AbstractThe effect of the electric field induced interband coupling on the electronic structure and optical properties of cubic materials is investigated theoretically. The three independent coefficients of the quadratic electro‐optic effect are expressed by band structure parameters in the case of the E0, E0 + Δ0 transition of diamond type crystals and of the blue and violet exciton series in Cu2O. In the latter case relations between the band parameters of Cu2O are obtained from a comparison with experimental results.
Excitonic Molecule Transitions in ZnO
Authors: Hvam J. M. 
Published: July 2007

AbstractBy means of excitation spectroscopy, the M‐band emission in ZnO is identified to be mainly due to decay of excitonic molecules (EM) into longitudinal B excitons and upper B polaritons. The latter process is easily stimulated and gives rise to a band (M2) of positive optical gain. Formation of EM by two‐photon resonance absorption and by induced absorption is observed in excitation spectra as well as directly in transmission. From the experiments the EM energy is deduced to EM = 6.740 eV.
Measurement of the Cyclotron Masses in n‐Conducting BiSb under High Hydrostatic Pressure
Authors: Krüger H. , Herrmann R. , Fellmuth B. , Kraak W. 
Published: July 2007

AbstractFor a series of n‐type Bi1−xSbx samples (0.08 < x < 0.14), the pressure dependence of the small cyclotron mass mC1c (B | C1) and of the anisotropy m3c/mC1c (B ⊥ C2) is determined up to the gap‐less state (p = pc). At low pressure values the small mass decreases proportionally to the pressure, thereafter reaching a constant value depending on the charge carrier concentration, which leads to a reduction of the anisotropy of the cyclotron masses. The results, when discussed with regard to galvanomagnetic measurements, present problems in their interpretation by means of the known models.
Magnetic Excitations in Amorphous Ferromagnets
Authors: Continentino M. A. , Rivier N. 
Published: July 2007

AbstractThe propagation of magnetic excitations in amorphous ferromagnets is studied from the point of view of the theory of random frequency modulation. It is shown that the spin waves in the hydrodynamic limit are well described by perturbation theory while the roton‐like magnetic excitations with wave vector about the peak in the structure factor are not. A criterion of validity of perturbation theory is found which is identical to a narrowing condition in magnetic resonance.
Magnetoreflectance of exciton‐polaritons in cubic II–VI compounds. I. Comparison of the magnetic field behaviour of excitons and polaritons
Authors: Uihlein Ch. , Feierabend S. 
Published: July 2007

AbstractUp to now the magnetic field behaviour of heavy and light excitons of the II‐VI compounds is discussed in the limiting cases of large and small exchange interaction Δexch with respect to the magnitude of the Zeeman terms HZee. In this paper it is shown that the effective g‐value, which is obtained from the rigid shift of the reflectance minimum, agrees with the excitonic g‐value of the limiting case Δexch ≫ HZee even in the opposite limiting case Δexch = 0. This results from the fact that heavy and light excitons are mixed within the relevant polariton states in the same way as in the limiting case of large exchange interaction. The considerable consequences for the determination of gc, χ, and Δexch are not realised in former publications.
The observation of optical transitions from valence band states in CuInTe2
Authors: Thwaites M. J. , Tomlinson R. D. , Hampshire M. J. 
Published: July 2007

AbstractSome features of the valence band structure of the chalcopyrite semiconductor CuInTe2, are established using an electroreflectance technique. The results are related to the current theoretical model for the valence band of the I–III–VI2 group of compounds.
Raman and infrared spectra in organic layer crystals of squaric acid
Authors: Nakashima S. , Aziza A. , le Postollec M. , Balkanski M. 
Published: July 2007

AbstractThe Raman spectra of squaric acid and its deuterated derivative are measured for temperatures from 77 to 450 K covering both ordered and disordered phases. Infrared absorption spectra are investigated for thin films of the single crystals and compared with the Raman spectra. It is found that the vibrational Davydov splitting due to the interlayer interaction is large for the external modes, while it is small for the internal modes of the squarie molecule. This behavior is explained by the model that the interlayer interaction acts between the hydrogen bonds of adjacent layers and is localized in the region near the hydrogen bonds. The temperature dependence of the frequencies and the linewidths is discussed in relation to the phase transition mechanism.
Treatment of the electron–hole droplet nucleation in the Fokker‐Planck approximation
Authors: Koch S. W. , Haug H. 
Published: July 2007

AbstractThe master equation which governs the nucleation of electron–hole drops in highly excited semiconductors is approximated by a Fokker‐Planck equation which determines the distribution function of the cluster size. From the Fokker‐Planck equation a closed set of equations for the exciton concentration and for different moments of the droplet distribution function is constructed. These equations are solved numerically for various generation rates. Using an eigenvalue analysis of the Fokker‐Planck equation, the time‐development of the full droplet distribution function is found from the time‐dependent moments.
Chemisorption of ordered atomic layers on a model transition metal
Authors: Masuda Kin‐Ichi 
Published: July 2007

AbstractThe effect of chemisorption of ordered atomic layers with p(1 × 1), p(2 × 1), c(2 × 2), p(2 × 2), p(4 × 1), and c(4 × 2) structures on the (001) surface of a tight‐binding (model transition) metal is investigated within the Newns‐Anderson model using the Hartree‐Fock Green's function formalism and the phase shift technique. The self‐consistent adatom charge q, the heat of adsorption ΔE, and the change in the electronic density of states during chemisorption are calculated for the two binding sites (on‐site and centered fourfold‐site). Particular attention is paid to the H/W(001) system and the results are compared with the available experimental results. It is shown that the long‐range order and adsorption geometry of the overlayers are of great importance for the electronic properties of the chemisorbed systems.
Resonance interaction of electronic two‐level states and short‐wave phonon radiation in ruby
Authors: Pauli G. , Renk K. F. , Klimke G. , Kreuzer H. J. 
Published: July 2007

AbstractThe resonance interaction of 874 GHz phonons with the electronic (Ē, 2Ā)‐two‐level‐states in optically pumped ruby is studied. In a resonance volume containing the two‐level states phonon pulses are generated by optical pumping. The occupation number of these phonons is determined and also their escape time from the resonance volume for a large range of concentrations of two‐level states. A simple diffusion model for the phonon propagation in the resonance volume cannot explain the results. It is suggested that the resonant electron–phonon interaction is dominated by a process of spectral and spatial phonon diffusion.
Very‐low‐frequency inelastic light scattering in non‐crystalline films of alkaline‐earth halides
Authors: Harbach F. 
Published: July 2007

AbstractThe Raman scattering of non‐crystalline films of SrCl2, BaCl2, and BaFCl contains a strong “central peak” with a half‐width of about 40 cm−1 at 100 K. It can be explained as a superposition of a Lorentzian line centered at the laser frequency and a Debye‐like density of states. A structural correlation range 2σ ≈︁ 3 Å is deduced from the deviation of the experimental data points from this theoretical model above 36 cm−1.
Multimode jahn‐teller effect for an E‐Term with strong vibronic coupling II. Band shapes of the infrared and raman spectra
Authors: Polinger V. Z. , Bersuker G. I. 
Published: July 2007

AbstractInfrared and Raman spectra for a Jahn‐Teller (JT) impurity in the E state strongly coupled with crystalline vibrations, as well as vibronic reduction, are investigated. The spectra are shown to represent a superposition of the delta‐like zero‐phonon lines, corresponding to transitions between the rotational levels of the system, with their multiphonon side bands, the latter manifesting the special JT local and resonant states in the crystal density of states, revealed earlier.
Electronic band structure of pseudodirect chalcopyrite semiconductors I. CdSiP2 and ZnSiP2
Authors: Cordts W. , Monecke J. , Heinrich A. 
Published: July 2007

AbstractThe band structure of the chalcopyrite semiconductor CdSiP2 is calculated using the empirical pseudopotential method applied successfully already in the case of ZnSiP2. The band structure is in good agreement with recent experimental data, especially with the inverse crystal field splitting found by Shileika et al. The influence of the three contributions to the deviation of the chalcopyrite structure from a cubic one (antisymmetric cation potential, tetragonal compression and distortion of the anion sublattice) on the band structure and the optical transition energies is investigated in detail for both ZnSiP2 and CdSiP2.
Identification of the absorption bands in KI:Pb2+ crystals
Authors: Tsuboi T. 
Published: July 2007

AbstractAbsorption and magnetic circular dichroism spectra of KI:Pb2+ single crystals are investigated at temperatures from 80 to 375 K, which are compared with the spectra of KBr:Pb2+. The absorption spectra of KI:Pb2+ at 80 K show five bands centred at 348.0, 290, 273.1, 252.3, and 225 nm, which are assigned to the so‐called A, B, C, D′, and D bands, respectively. The D″ and D bands are attributed to the electron transfer from I− to Pb2+ in a PbI4−6 complex ion.
Symmetry properties of the energy bands of Cd3As2 type crystals
Authors: Dowgiałło‐plenkiewicz B. , Plenkiewicz P. 
Published: July 2007

AbstractSome symmetry properties of the C space group and the resulting details of energy bands of the Cd3As2 type crystals are reported. The single and spinor representations with the T‐R degeneracies included and the compatibility relations are presented. The spinor SCPW for the A‐axis and two symmetry points Γ and Z are constructed. The selection rules for direct and indirect optical transitions are calculated.
Excitation spectroscopy of the I2 bound exciton and the excitonic molecule in CdS II. Relation between I2‐line and EM‐lines
Authors: Puls J. , Rückmann I. , Voigt J. 
Published: July 2007

AbstractUsing a narrow band dye laser the creation of EM's in CdS via TPA is demonstrated in the transmission spectra. Knowing the excited states of the I2 bound exciton from Part I the connection between TPA and EM emission lines and the relation between the excitation spectra of the I2 bound exciton and the EM are investigated. The creation of a cold EM gas under resonant two‐photon excitation is firstly found in CdS and the intrinsic nature of the M‐lines is shown.
Scattering mechanisms of electrons in ZnSe crystals with high mobility
Authors: Emelyanenko O. V. , Ivanova G. N. , Lagunova T. S. , Nedeoglo D. D. , Shmelev G. M. , Simashkevich A. V. 
Published: July 2007

AbstractIn low‐ohmic n‐type ZnSe crystals with the room temperature specific resistance of (3 to 5) Ω cm and electron concentration from 3 × 1015 to 2 × 1016 cm−3 Hall‐effect, electrical conductivity, and charge carrier mobility is investigated in the temperature interval from 10 to 300 K. The basic parameters of the samples are determined. It is found from the experimental data that the mobility is higher than the theoretical value in the investigated temperature range. It is argued that in the region of ionized impurity scattering this descrepancy between theory and experiment is due to the inadequacy of known scattering based on the Born approximation, as for ZnSe this approximation is valid at T > 140 K, where the phonon scattering is predominant. To square the theory with the experiment in the phonon scattering region a polaron effect is taken into account, which manifests itself in renormalization of the carrier effective mass as well as in alteration of the mobility temperature dependence due to the effect of screening of the interaction with polar vibrations. The theoretical consideration of this question is given which allows to bring the theory and the experiment to a satisfactory correspondence.
Metal—Insulator Transition in Boron Carbide
Authors: Werheit H. , de Groot K. 
Published: July 2007

AbstractThe electrical conductivity and the thermoelectric power of boron carbide are investigated in the temperature range from 80 to 700 K on samples of compositions between B12.94C2.06 and B10.59C4.41. While the extrinsic thermal activation of free carriers dominates the electronic transport at high temperatures, at low temperatures a metal—insulator transition occurs depending on the C content. Lower C contents than B12C3 cause variable‐range hopping (In σ ∼ T−1/4) whereas higher contents lead to impurity‐band conduction. The overlap of two impurity bands (possibly Hubbard bands) attributed to the carbon in boron carbide is assumed.
Luminescence des centres associés Bi3+‐Na+ et Bi3+‐Li+ dans le phosphore CaS
Authors: Asano S. , Yamashita N. 
Published: July 2007

AbstractEmission and excitation spectra of CaS:Bi3+; Na+ and CaS:Bi3+; Li+ phosphors are measured at 6, 80, and 300 K. Seven excitation bands originating from the associated centers Bi3+‐Na+ and Bi3+‐Li+ are observed in addition to those of a single Bi3+ center. The energy matrices of the associated center is calculated theoretically on the basis of the localized electron model. The energy parameters appearing in the energy matrices are determined so that the positions of observed and calculated excitation bands may coincide with each other.
Raman Scattering of Cadmium Chlorate Single Crystal
Authors: Campelo L. C. , Filho J. Mendes , Mello F. E. A. , Vargas H. 
Published: July 2007

AbstractA low temperature Raman survey of cadmium chlorate single crystal is presented. An assignment is made of all the optical phonons. The internal and external modes are separated out. The observed chlorate ion internal mode frequencies are seen to agree closely with the values obtained for other metal chlorates.