bluuebunny/crossref_metadata_2025_split huggingface dataset:
Dielectric function in HgSe at 2, 95, and 300 K
Authors: Manabe A. , Nougchi H. , Mitsuishi A. 
Published: July 2007

AbstractReflectivity spectra of n‐HgSe with various carrier concentrations are measured in the spectral region 20 to 500 cm−1. Their main features are well explained by the theoretical dielectric function which is constructed as a sum of Γ8–Γ8 interband, intraband, and phonon contributions and is calculated using the available values of band parameters in the full Kane theory. The effect of the interband contribution on the plasmon–LO phonon coupling and on the frequency of LO phonon is discussed. Possible origins for the discrepancy between experimental and calculated spectra are also discussed.
Quasiparticle, charge, and energy conservation in weak‐coupling superconductors
Authors: Mathews W. N. 
Published: July 2007

AbstractThe conservation of quasiparticles, electric charge, and energy in weak‐coupling superconductors is discussed and correlated with the interpretation of the quasiparticles as particle and hole excitations. The formulation employed is that of the Bogolyubov‐de Gennes equations. In the absence of spin‐dependent interactions these equations are written in the form of a time‐dependent Schrödinger equation with a two‐component wave function and a two‐by‐two matrix Hamiltonian. Accordingly, the desired conservation laws are discussed on much the same basis as in ordinary quantum theory. The generalization to permit nonlocal quasiparticle and pair potentials and spin‐dependent interactions is briefly presented.
An estimate of the pressure dependence of the dielectric constant in alkali halides
Authors: Varotsos P. A. 
Published: July 2007

AbstractThe determination of the pressure dependence of the static dielectric constant, ϵS, from the Szigeti relations, demands the knowledge of the volume dependence of the Szigeti charge e*, which unfortunately is unknown. By using the classical Lorentz‐Lorenz relation and connecting the ionic polarizability to the bulk modulus a simple relation for dϵS/dP is derived; although it gives the correct order of magnitude, the calculated values exceed the experimental ones by a factor 1.2 to 2. This difference is possibly due to the increase of e* with pressure. A simple relation for the Gruneisen constant of the transverse optical mode is also given.
Resistivity and thermo‐electric power of monovalent, divalent, and trivalent liquid metals
Authors: Sinha N. N. , Srivastava P. L. 
Published: July 2007

AbstractElectrical resistivity and thermo‐electric power of monovalent (Li, Na, K, Rb, Cs), divalent (Zn, Cd), and trivalent (In, Tl, Al) liquid metals are studied using the corrected parameters of the Shaw model. The results show improvement over those obtained without the parametric correction. Effect of various forms of exchange and correlation correction on the properties is also investigated.
Thermoluminescence of irradiated RbCl and RbCl:Sn crystals
Authors: Sastry S. B. , Balasubramanyam K. 
Published: July 2007

AbstractThe thermoluminescence (TL) and emission of coloured RbCl and RbCl:Sn crystals are studied in the temperature range 300 to 560 K. The glow peaks responsible for F centres and tin centres in different valence states are identified using optical bleaching studies. The glow peaks are analysed using total curve fitting method and the kinetic parameters are determinet. In moderately γ‐irradiated tin‐ doped RbCl crystals, the TL emission bands observed at 4.0, 3.6, and 2.2 eV are attributed to Sn0, Sn+, and Sn− centers, respectively. A comprehensive energy level diagram depicting the various TL processes in these undoped and tin‐ doped RbCl crystals is proposed.
Optical constants of n‐ and p‐type GaAs between 2.5 and 3.5 eV
Authors: Vigil E. , Rodríguez J. A. , Alvarez R. Pérez 
Published: July 2007

AbstractThe normal incidence reflectance for n‐ and p‐type GaAs is measured at room temperature in the spectral range from 1.2 to 3.8 eV. Using Kramers‐Kronig analysis, the values of the refractive index and absorption coefficient for n‐ and p‐type GaAs are determined from the reflectance data in the spectral range from 2.5 to 3.5 eV. The results obtained show that the optical‐constant spectra depend on impurity concentration in the spectral range investigated.
Fast electron scattering in metals with the excitation of a core electron
Authors: Zhivopistsev F. A. , Hernández F. C. 
Published: July 2007

AbstractFast electron scattering in thin metallic films is discussed, considering the excitation of a core electron. The first plasmon satellite is incorporated using Langreth's model, but assuming a dispersion law quadratic with the wave vector. An expression is obtained for the transition rate. Numerical results are shown for Li, with a discussion of spectral structure for different values of the scattering angle.
Optical absorption of off‐centre Cu+ in CsBr
Authors: Rambabu B. , Ramasastry C. , Chowdari B. V. R. 
Published: July 2007

AbstractOptical absorption studies of Cu+ in CsBr are made in the temperature range 300 to 10 K. Nine absorption bands at 6.15, 5.99, 5.80, 5.64, 5.44, 5.33, 5.09, 4.95, and 4.87 eV could be resolved at liquid helium temperature. Their intensities are temperature independent. The observed spectrum is in agreement with the calculated spectrum, if the Cu+ ion replaces a Cs+ ion and gets displaced along the 〈111〉 direction. The crystal field at Cu+ ion is predominently cubic (δc = —0.45 eV) with a trigonal component (δt = —0.055 eV) superposed on it.
Spin glass transition. A dynamical instability
Authors: Deutges D. , Freudenhammer A. , Heber G. 
Published: July 2007

AbstractThe instability of a spin glass phase against an external magnetic field is discussed on the basis of a Landau‐type theory of phase transition with two order parameters. There are two different critical magnetic fields, both approaching zero for T → TSG; the principal meaning of these critical fields is considered. The free energy F(H, T) develops different branches as a function of H and T with bifurcations typical for non‐equilibrium phase transitions (or dynamical instabilities).
Electronic structure of FeNi alloys studied by means of X‐ray photoelectron spectroscopy. I. Valence bands
Authors: Berndt K. , Marx U. , Brümmer O. 
Published: July 2007

AbstractXPS spectra of FeNi alloys are measured. Using the spectroscopic, thermodynamic, and magnetic moment data so far available a consistent model of density of states for the FeNi alloys is proposed. This model is based on the band theory of ferromagnetism and some known properties of the electronic band structure of the first series transition metals. The measured XPS valence band spectra can be explained by means of the model DOS neglecting the influence of the transition probabilities. The CPA calculations so far available for FeNi do not fit the spectra satisfactorily. The model assumes the d‐bands to penetrate each other. The up‐spin bands are shifted against the down‐spin bands by a rigid exchange splitting corresponding to the measured atomic magneton number in the alloy. The model neglects the spin–orbit coupling which would couple states of opposite spin but this influence should be small.
Surface impedance investigations of superconducting niobium
Authors: Rothkirch L. , Herrmann R. , Dwelk H. , Preppernau U. 
Published: July 2007

AbstractMeasurements of the surface resistance derivative dR/dH in dependence on magnetic field strength H are presented as observed at pure superconducting niobium single crystals. At crystals not annealed after preparation procedure the measured impedance spectra do not represent the phase transitions appearing at critical fields indicating thus the existence of surface layers with properties different from the bulk of pure niobium. At annealed crystals the critical magnetic field strengths are marked as characteristic discontinuities in the spectra. The spectra observed at recently annealed crystals being in Meissner state can be interpreted by means of magnetic surface states.
UPS measurements of CO chemisorbed and condensed on Rh (111) using synchrotron radiation
Authors: Braun W. , Neumann M. , Iwan M. , Koch E. E. 
Published: July 2007

AbstractThe photoemission data of the clean Rh(111) surface are strongly dependent upon photon energy in the range 15 to 27.5 eV. Three different chemisorption levels are distinguished for CO chemisorbed on Rh(111) by exploiting the dependence of photoionization cross sections upon photon energy. Exciton–electron and electron–electron scattering dominate the intensity variations of the spectra of CO condensed on Rh(111). The origin of the observed energy level shifts of CO in the three different phases, gas, condensed and chemisorbed, are discussed in terms of relaxation, bonding, and chemical shifts.
Evidence of non‐linear behaviour of soft modes in crystals with KDP structure
Authors: Scarparo M. A. F. , Katiyar R. S. , Srivastava R. , Porto S. P. S. 
Published: July 2007

AbstractThe low‐frequency B2 Raman spectra of KDP, RDP, RDA, and D‐RDA are measured as a function of temperature. The low‐frequency data are fitted to the response function of two coupled harmonic oscillators and of two coupled lattice oscillators. The results show that the overdamped proton tunneling mode softens with temperature as the transition temperature Tc is approached. However, the results show that very near Tc, the soft mode attains a hard‐core frequency. In view of these results the various models proposed in literature to explain the phase transition in these crystals are critically examined. The nature of the coupling between the two modes is also discussed.
Acoustic phonon scattering by electron–hole droplets in Ge. II. Total scattering rate and anisotropy of scattering, as reflected in the shape of a droplet cloud
Authors: Markiewicz R. S. 
Published: July 2007

AbstractThe pair‐phonon scattering rate is calculated for carriers inside an electron–hole drop in Ge. The calculation includes effects due to screening, electron mass anisotropy, and sound velocity anisotropy. The net scattering time is shorter by about a factor of two than found in previous calculations. A very similar integral occurs in calculating the force of the ‘phonon wind’ on the cloud of droplets. Using a simple model, this integral can explain the anisotropic shape of the cloud observed experimentally by Greenstein and Wolfe. The calculation accounts for both the broad lobes observed along 〈111〉 axes and the sharp flares along 〈100〉 axes (the latter due to a focusing of the phonons in Ge).
Infrared Studies of Al Complexes in Zinc Sulphide
Authors: Król A. , Kozielski M. J. , Nazarewicz W. 
Published: July 2007

AbstractInfrared absorption is studied in zinc sulphide doped with the following impurities: a) Al and Cu, b) Al and Ag, c) Al and Au. Al is introduced during crystal growth and Cu, Ag, and Au by saturation diffusion. The ZnS samples with two dopants have the zincblende structure with a low density of stacking faults. In the spectral range 360 to 650 cm−1 a number of absorption bands are observed that could be ascribed to the localized vibrational modes of unassociated Al and Al in complexes with Cu, Ag or Au. On the basis of symmetry considerations the following defect models are suggested: AlZn, AlZn–CuZn, AlZn–AuZn and AlZn–AgS or AlZn–Agi (where i denotes interstitial location). The results obtained with ZnS are compared with published data for CdTe and ZnSe.
Tunnel measurements on Nb single crystals
Authors: Schöneich B. , Elefant D. , Otschik P. , Schumann J. 
Published: July 2007

AbstractIn order to investigate the mechanism of superconductivity in transition metals, tunnel measurements on niobium single crystals annealed in ultrahigh vacuum are carried out. The residual resistivity ratio of the single crystals is r0 ≧ 20 000. The tunnel junctions yielding most information have the structure NbIAg. The insulator is produced by thermal oxidation of niobium. The value of the energy gap is Δ0 = (1.50 ± 0.05) meV. The interpretation of dU/dI and d2U/dI2 characteristics yields the electron‐phonon coupling constant Λ = 0.62 and the Coulomb pseudopotential μ* = 0.002. From tunnel curves values about the thickness and height of the tunnel barrier are estimated. The normal‐conducting properties of the tunnel junctions are discussed.
Quantitative determination of the valley splitting in n‐type inverted silicon (100) MOSFET surfaces
Authors: Köhler H. , Roos M. 
Published: July 2007

AbstractShubnikov‐de Haas oscillations including an abrupt phase shift of the extrema position at a critical magnetic field are reproduced by computer simulation allowing a quantitative evaluation of the spin and valley splittings Δs and Δv with a high accuracy. Varying the gate voltage and tilt angle of a sample in the magnetic field data are obtained over a wide field range. The computer simulation also permits to check the assumptions about the magnetic field dependence of the energy width and the shape of the broadened levels in quantizing magnetic and electric fields. The results obtained for Δs and Δv both depend on the history of even the same sample.
Electron spin resonance absorption spectrum of divalent manganese in single crystal calcite
Authors: Marshall S. A. , Marshall T. , Zager S. A. , Zimmerman D. N. 
Published: July 2007

AbstractThe electron spin resonance absorption spectrum of divalent manganese in single crystal calcite is reinvestigated at X‐band wavelength. Electron‐nucleus double resonance absorption spectroscopy is used to assist in the analysis of the hyperfine structure spectrum. Best fit spectral parameters obtained at T = 4.2 K are listed.
Resonant magneto‐Raman scattering in polar semiconductors
Authors: Sampaio A. J. C. , Luzzi R. 
Published: July 2007

AbstractResonant Raman scattering of LO phonons in a magnetic field is studied. Direct gap, small effective mass, n‐doped semiconductors are considered in conditions in which the laser and the scattered frequencies are of the order and larger than the harmonics of the cyclotron frequency. In these resonant and near resonant conditions the lifetime of the intermediate states gives important contribution to the scattered intensity. A calculation is presented of the scattering cross‐section for the magneto‐Raman scattering by LO phonons which includes the electron‐phonon interaction contribution to the electron lifetimes. Numerical application to InSb is done.
The electronic spectra and parametric instabilities in charge‐ordered crystals with intraband electron attraction
Authors: Ionov S. P. , Manakova L. A. , Zemskov B. G. 
Published: July 2007

AbstractAn analysis of the electron properties of the charge‐ordered systems with the intraband attraction is given. Two models of these systems are assumed 1) an intraband attraction takes part in the formation both the charge ordering and pair correlation of the superconductive type; 2) only the interband interactions are responsible for the formation of the charge ordering. For these models the coexistence of the charge ordering and pair correlation problem is considered. The interaction parameter regions in which the coexistence occurs are found. The low‐lying collective excitation energies are calculated for the charge‐ordered state both, with pair correlation and without. The possible types of parametric instabilities of the charge ordered state are obtained.
Extended Hückel molecular orbital calculation of defects in LiH cluster crystals
Authors: Ikeya M. , Schwan L. O. 
Published: July 2007

AbstractAn LCAO‐matrix method (extended Hückel MO) is applied for the calculation of the intrinsic and defect properties of LiH crystals. The ionic clusters of Li+ and H− involving 8, 27, and 64 ions are considered as well as the atomic clusters of Li0 and H0. Defect properties of negative and positive ion vacancies, interstitials H− (H) and H0(H), and substitutional H0 at the anion and cation sites (H and H) are discussed from the result of the calculation taking the experimental results into account.
Linear optical response of highly excited semiconductors electron–hole liquid in CdS
Authors: Müller G. O. , Weber H. H. , Höricke I. 
Published: July 2007

AbstractA thorough investigation of highly excited direct gap semiconductors requires determination of optical constants within the duration of the nanosecond excitation period. A simultaneous recording of reflection and transmission (and probing) spectra is possible by virtue of the multiple track mode of PAR's OMA. Interfacing to a computer and use of classical optics allow for an on‐line absolute calibration. The absolute values of absorption and refraction spectra of highly excited CdS are indicative of an electron–hole liquid with a chemical potential of about 2.537 eV and a density of about 3 × 1018 cm−3.
Collective vibrations of protons in compounds of the KH2PO4‐type the cluster approximation
Authors: Stasyuk I. V. , Levitskii R. R. , Korinevskii N. A. 
Published: July 2007

AbstractThe dynamics of the proton system of KH2PO4‐type compounds is considered in the cluster approximation taking into account their real structure. The equation for the excitation spectrum is obtained. For the particular case of the four‐sublattice de Gennes model the conclusion is made that the excitation spectrum contains the pseudo‐soft mode. It is shown also, that for KH2PO4 model the mentioned conclusion is correct.
Force–force correlation function approach to the electrical resistivity of disordered transition metal alloys
Authors: Goedsche F. , Richter R. , Vojta G. 
Published: July 2007

AbstractThe method of the force‐force correlation functions is used to derive, beyond the weak scattering approximation, a tractable approximative formula for the electrical resistivity of disordered binary alloys. The starting point is a one‐particle expression for the resistivity formulated in terms of the total scattering operator T. The local approximation is introduced by replacing the T operator by the atomic t matrices in order to treat transition metal alloys described by muffin‐tin single‐particle Hamiltonians. Short‐range multiple‐scattering corrections to the local approximation are evaluated using a non‐selfconsistent single‐site average‐t‐matrix approximation. Explicit results are given and discussed for the resistivity of a one‐dimensional muffin‐tin model for transition‐metal‐like alloys with resonant states.
Scattering of X‐rays near the K absorption edge I. Fluorescence and resonant Raman scattering in transition metals
Authors: Suortti P. 
Published: July 2007

AbstractFormulas for the resonant cross section of X‐rays are rederived emphasizing the similarity of the resonant Raman scattering (RRS) to the fluorescence, and are given in terms of the oscillator strengths and radiative widths. In both processes only a fraction results in radiation, and for the RRS this is termed the RRS yield, wRRS, in analogy with the fluorescence yield, wK. Measurements are made in the symmetrical reflection geometry from totally absorbing samples. The fluorescence yield is measured CuKα as exciting radiation for Ti, V, Cr, Mn, and Fe, the results being 0.237, 0.265, 0.291, 0.325, 0.356, respectively. The absolute cross section of the (1s, 2p) contribution to the RRS is measured for Cr, Mn, Fe, Ni, and Cu at energies 42 to 940 eV below the K absorption edge. The RRS yields are 0.404, 0.426, 0.422, 0.415 (0.460 in another measurement), and 0.473 (0.468), respectively. Also evidence is found for the existence of the (1s, 3p) contribution to the RRS.
The charge on dislocations in alkali halides for the case of a saturated region
Authors: Mejía C. Ruíz , Araiza L. Cota , Broder F. , Mijangos R. R. 
Published: July 2007

AbstractThe case of a charged dislocation with a saturated region is considered, allowing for the discrete nature of charges and defects on the core of the dislocation. The potential due to the charged dislocation is obtained by combining the results of Kliewer and Koehler with those of Whitworth. The method used in this case to determine the charge on the dislocation, is the same as that of Whitworth.
Short‐range magnetic order in a spin glass with nearest‐neighbour random exchange bonds
Authors: Medvedev M. V. 
Published: July 2007

AbstractIn the molecular field approximation it is shown that in a spin glass with nearest‐neighbour random exchange bonds of different signs (IA > 0 and IB < 0) the ferromagnetic short‐range order will appear below the transition temperature from the paramagnetic state, if the concentration c of antiferromagnetic bonds IB is less than a concentration c★, and the antiferromagnetic short‐range one will appear, if c is more than c★. The Edwards‐Anderson spin‐glass state, in which the short‐range magnetic order is completely absent, is realized only at the concentration c★ that corresponds to zero paramagnetic Curie point.
Observation of infrared active and silent modes in cubic crystals by hyper‐Raman scattering
Authors: Vogt H. , Neumann G. 
Published: July 2007

AbstractHyper‐Raman spectra of CsI, CsBr, RbI, and SrTiO3 are measured at room temperature. All optical phonons at the I′‐point of the Brillouin zone can be detected including the longitudinal modes and one silent mode. The results obtained for SrTiO3 are compared with data due to other experimental techniques. Superiority of hyper‐Raman speetroscopy in determining frequencies and linewidths is demonstrated.
Propagation of electromagnetic waves in a direction perpendicular to the magnetic field in semiconductive BiSb alloys I. B ⊥ C3 ∥ k
Authors: Stegmann R. , Oelgart G. , Herrmann R. 
Published: July 2007

AbstractThe propagation of electromagnetic waves is detected in semiconductive Bi1−xSbx alloys in a direction perpendicular to the magnetic field at helium temperatures and in a frequency range between 36 and 140 GHz. For lacking spatial dispersion and for arbitrary orientations of the magnetic field the wave propagation takes place within the trigonal plane. In both, the quasiclassical limiting case and the ultra‐quantum state, it is found that the experimentally and theoretically determined values of wave dispersion are in mutual agreement. The measurements permit statements to be made about the cyclotron masses and it is possible to obtain a spin splitting parameter of G2 = 0.9.
Acceptor photoionization and light‐to‐heavy hole absorption in Cd1−xMnxTe
Authors: Wojtal R. , Golnik A. , Gaj J. A. 
Published: July 2007

AbstractThe observed temperature‐dependent absorption spectrum in the wavelength region 2.2 to 12.5 μm in Cd1−xMnxTe mixed crystals can be explained as originating from acceptor photoionization and light‐to‐heavy hole band transitions. The application of simple models to experimental data for two compositions allows to determine the ionization energy of the acceptor level EI = 0.17 eV and the heavy‐to‐light hole mass ratio m/m = 4.
Scattering of X‐rays near the K absorption edge II. Dispersion factors f′ and f″
Authors: Suortti P. 
Published: July 2007

AbstractThe dispersion factors of the X‐ray scattering amplitude, f′ and f″ are studied in the dipole approximation where they are independent of the scattering angle. The imaginary part is proportional to the absorption coefficient, and below the Kedge the observedf″K is in a close agreement with the value calculated from the resonant Raman cross‐section. The real part is calculated from the tabulated absorption coefficients in a number of cases where comparison with direct determinations of f′ can be made. The agreement is good, particularly when extensive data near the edge are available, while recent theoretical values are consistently low. Calculated values of f′ are tabulated for transition elements at several commonly used X‐ray wavelengths.