bluuebunny/crossref_metadata_2025_split huggingface dataset:
Many‐phonon vibronic spectra of molecular crystals: II. Combination frequencies
Authors: Lalov I. J. 
Published: July 2007

AbstractVibronic spectra of molecular crystals with two phonons of different types (compound tones) are investigated in the weak coupling approximation. The foIIowing cases are considered: a) one of the phonons corresponds to a totally symmetrical vibration with linear vibronic coupling constant η2= 1; b) the purely electronic transition in the molecule is forbidden and one of the phonons corresponds t o a non‐totally symmetrical vibration; c) a two‐phonon vibronic spectrum with one totally symmetrical phonon and one non‐totally symmetrical phonon. In a) and b) the problem is reduced to a two‐particle problem with a known solution, while in c) the bands of the one‐particle states are found and the absorption taking into account the role of anharmonicity of intramolecular vibrations.
The influence of an electric field on the auger recombination in semiconductors
Authors: Gebranzig U. , Haug A. , Rosenthal W. 
Published: July 2007

AbstractAuger recombination in semiconductors is sometimes affected by an electric field. Proceeding from Bloch electrons in such a field the transition probability in this case is calculated. The result shows that electric fields of the order of 103 V/cm or 105 V/cm enhance the recombination probability in III−V‐compounds remarkably; the first value holds for low temperatures (T ≈ 10 K), the second one for high temperatures (T ≈ 300 K).
ESR study of the paramagnetic 10 centre in an α‐LiIO3 crystal
Authors: Martirosyan V. O. , Meilman M. L. , Marov I. N. , Shukov V. V. 
Published: July 2007

AbstractIn crystals of a polar phase of α‐LiIO3 an ESR spectrum at a frequency of v = 34.633 GHz and T = 290 °K is observed. The spectrum consists of two sextets. Each line of the sextet splits into a doublet and a multiplet. The spectrum is attributed to two centres of IO with an equivalent structure. It is shown that a 27‐electron centre, IO, is formed from 10 ions under γ‐irradiation. The charge compensation is based on the oxidation of Fe2+ present in crystals as an impurity. Experimental values of g‐tensor, hf splitting and shf splitting are determined. The values of spin‐Hamiltonian parameters and the mechanism of the centre formation and its location in the crystal are discussed.
Impurity‐induced transitions in differential spectroscopy
Authors: Mathieu H. , Camassel J. , Auvergne D. 
Published: July 2007

AbstractCareful investigation of differential spectra superimposed on interference phenomena permits one to obtain original information on impurity states localized in the gap. The piezomodulation technique used to obtain homogeneous modulation is a complementary test of luminescence experiments in identifying impurity states. Two examples of investigations on GaSb and ZnTe, are given.
Far‐infrared absorption of electron–hole drops in pure and doped germanium
Authors: Timusk T. , Silin A. 
Published: July 2007

AbstractElectron–hole drops in doped germanium are found to give an absorption at long wavelengths. A study of the neutral donor absorption, the near‐infrared luminescence, and the movement of electron–hole in a magnetic field gradient shows that in the doped materials the drops are very small and localized on the neutral donors.
Polarization dependence of indirect two‐photon transitions in AgCl
Authors: Popova M. N. , Pelant I. 
Published: July 2007

AbstractThe polarization dependence has been calculated for the allowed, indirect, phonon assisted two‐photon transitions L3 → Γ1 and Σ4 → Γ1 which are most important in the case of AgCl. The polarization dependence of the two‐photon absorption of ruby laser light in AgCl single crystals has been measured and found to belong to the Eg symmetry of the point group Oh. Comparison with the presented theory leads to the conclusion that the Σ4 → Γ1 transition with participation of the Σ1 phonon takes place.
Magneto‐optical investigations of the two‐dimensional ferromagnet (CH3NH3)2CuCl4
Authors: Arend H. , Schoenes J. , Wachter P. 
Published: July 2007

AbstractThe optical absorption of (CH3NH3)2CuCl4 has been investigated at 300 K in the spectral range between 0.2 and 40 μm and down to 4.2 K between the optical absorption edge and 2.5 μm. Absorption has also been measured with polarized light, parallel or perpendicular to the crystal axes or a magnetic field. In addition the magnetic linear dichroism and the Faraday rotation has been investigated in function of frequency, magnetic field strength and temperature, as well above as below TC = 8.9 K. From the Faraday rotation one can evaluate the magnetization for T < TC and the susceptibility for T > TC. The discussion is made in terms of critical exponents of the susceptibility. A cross‐over region could be determined above, but close to TC. The system changes from three dimensionality to two dimensional Ising. At higher temperatures only molecular field behavior is observed.
Effect of electric field on mixing of Frenkel excitons and charge transfer states of a linear molecular crystal
Authors: Petelenz P. , Zgierski M. Z. 
Published: July 2007

AbstractThe mixing between Frenkel excitons and charge‐transfer states of a linear molecular crystal in an electric field is investigated. The Merrifield model is adopted. It is shown that the electric field increases the above mentioned mixing, leading therefore to an increase of the light absorption with simultaneous creation of an electron–hole pair. It also can change slightly the position of the Frenkel exciton absorption line. Semiempirical calculations of anthracene dimers in an electric field show that this effect should be observable at electric fields with strengths higher than 106 V/cm, the direction of the field being along the long c‐axis of the anthracene crystal.
Modification of phonon distribution in degenerate semiconductors by high electric fields: Effect on transport coefficients
Authors: Sharma S. K. , Agarwal D. B. 
Published: July 2007

AbstractDrift mobility, Hall mobility, and Hall coefficient of a degenerate semiconductor at very low temperatures and high electric fields are calculated. Following Paranjape's approach the modified distribution of phonons are taken into account in the calculation of the transport coefficients for arbitrary degeneracy of simple model semiconductors. The electron scattering due to ionized impurities as well as due to acoustic phonons have been considered. The calculations show that the inclusion of the modified phonon distribution in the theory reduces the theoretical values of drift and Hall mobilities of degenerate semiconductors by a factor of two or more; its effect on Hall coefficients is to decrease the theoretical value slightly (20%).
Zone‐centered phonons in ternary compounds of chalcopyrite structure
Authors: Bettini M. 
Published: July 2007

AbstractA Keating model calculation of the zone‐centered phonons in ternary compounds of the chalcopyrite (ch) structure is presented. The calculations are restricted to phonons of the phosphor(P) ch‐family. The model describes reasonalby well the phonons of high energy. The spectra are determined preponderantly by the masses of the cations and the force constants between nearest neighbours. The influence of the force constants between second nearest neighbours and the effective charges is small. The dependence of the individual phonons upon changes in the model parameters is unravelled. The variation of the ir‐oscillator strength of the same mode in different compounds demonstrates the importance of changes in the eigenvectors. The force constants of the chalcopyrite (ch) bonds are compared to those of corresponding zincblende (zb) bonds and can be explained by changes in the bond length. The model calculations yield a symmetry assignment of the experimental spectra in CdSnP2 and ZnSnP2.
Theory of the absorption of electromagnetic radiation by hopping in n‐type Si and Ge considering all polarizations of acoustic phonons
Authors: Banaszkiewicz M. 
Published: July 2007

AbstractThe theory of the absorption of electromagnetic radiation by hopping in n‐type Si and Ge is investigated. Photon wavelengths from 100 to 800 μm for Si and from 500 μm to 2.5 cm for Ge are considered. Both longitudinal and transversal acoustic phonons are taken into account. It is shown that the absorption coefficient α(1) for absorption of a photon with emission of a phonon can be neglected in comparison with the coefficient α(0) describing the absorption of a photon without emission of a phonon. A new averaging method in the computations of α(0) is used. The agreement between the numerical results and the experimental data is good except of the region of short wavelengths.
Determination of the electron excitation spectrum in scandium and yttrium by means of characteristic energy loss measurements
Authors: Brousseau‐Lahaye B. , Colliex C. , Frandon J. , Gasgnier M. , Trebbia P. 
Published: July 2007

AbstractEnergy loss spectra of high energy electrons transmitted through thin foils of scandium and yttrium have been registered using two different experimental techniques. A detailed comparison of the results allows to distinguish between the spectra of metals, hydrides, and oxides and to calculate the optical constants in the pure metals. It is shown that the electron excitation spectra of these elements contain two main contributions in the energy range between 5 and 60 eV: collective excitations of the conduction electrons at 14 and 12 eV (plasmon peaks) and a strong absorption band due to the excitation of the inner 3p and 4p electrons between 30 and 50 eV. At higher energies, these spectra display well‐defined lines corresponding to the L2−3 edge in scandium and to the M4−5 and M2−3 edges in yttrium which are characteristic of the atom.
Recombination luminescence in alkali halides doped with divalent cations: (Vk + e)z‐type emission
Authors: Ikeya M. 
Published: July 2007

AbstractRecombination luminescence of alkali halides doped with divalent cations has been studied during X‐irradiation at several temperatures. Besides the emission bands from the excited states of the impurity, four types of additional bands were observed. These emission bands were tentatively assigned to (X2− + e) recombination perturbed by divalent cations on the basis of a model of (X2− + e) in which nearby cation orbitals are involved.
On the pressure dependence of the electrical conductivity of aluminium
Authors: Claesson A. , Larsson† R. 
Published: July 2007

AbstractThe electrical conductivity of metals depends on the shape of the Fermi surface. This surface for nearly‐free‐electron‐like substances like aluminium is spherical almost everywhere. However, the lattice structure gives rise to changes in curvature at the zone planes. The effect of hydrostatic pressure up to 100 kbar on the electrical conductivity of aluminium is investigated taking the detailed shape of the Fermi surface into account.
Investigation of the conduction band fermi surface in Bi2Se3 at high electron concentrations
Authors: Köhler H. , Fischer H. 
Published: July 2007

AbstractAn investigation is made of non‐parabolic terms in the ϵ(k) relation up to the order of [k4] at high electron densities up to 4 × 1019 cm−3. At low electron densities (<1018 cm−3) the Fermi surface is almost an ellipsoid of revolution with its symmetry axis along the trigonal kc axis. Besides, with increasing Fermi energies, a flattening of the Fermi surface in the direction of the kc axis was found, caused by [k4] or higher terms in the ϵ(k) relation. Furthermore the influence of trigonal warping of the Fermi surface was already observed at a concentration of 1.7 × 1018 cm−3 from Shubnikov‐de Haas effect. Here by means of the Shubnikov‐de Haas effect the extremal cross‐sectional areas of the Fermi surface were determined by application of stationary magnetic fields up to 15 T magnetic induction. The parameters of the assumed ϵ(k) model up to [k4] terms were fitted by numerical calculations of the extremal cross‐sectional areas of the Fermi surface perpendicular to arbitrary magnetic field directions and by comparison with the corresponding reciprocal Shubnikov‐de Haas periods.
Multiple s‐scattering in an ideal random medium. I. The coherent field in the low‐density limit
Authors: Lenk R. 
Published: July 2007

AbstractStarting from the multiple scattering hierarchy the low‐density solution for point‐like scatterers is constructed. A given scatterer interacts with itself via the medium consisting of all the other scatterers. All pair effects are neglected. A new and simple result has been found for the attenuation of the wave by elastic scattering. The damping mechanism in the total reflection regime represents an unsolved problem. The relation of the results obtained to the behaviour of ultracold neutrons is discussed.
On the hyperfine structure of the Mn2+ EPR line with g = 4.3 in chalcogenide glasses of some ternary systems
Authors: Lazukin V. N. , Chepeleva I. V. , Zhilinskaya E. A. , Chernov A. P. 
Published: July 2007

AbstractEPR of Mn2+ ions in glasses of ternary systems MAsSe (M = Cu, Zn, Ge, Ag, Hg, Tl, Pb, Bi), PGeSe, IAsX (X = S, Se, Te) of different compositions and in glassy As2Se3 are studied. The dependence of the Mn2+ EPR spectra on frequency, temperature, impurity concentration, and glass composition is observed. The complex HFS structure of the g = 4.3 line is explained by superposition of two sextets with a shift of the isotropic g‐factor of ≈︁0.08. The model of the Mn2+ incorporation into the glass network is proposed. A high regularity of Mn2+ surroundings is explained by a high degree of short range order in the glasses investigated.
Phase diagram for the conventional Hubbard model system
Authors: Röpke G. , Albani B. , Schiller W. 
Published: July 2007

AbstractFor the conventional Hubbard model system, the static magnetic susceptibility and the local magnetic moments are studied by means of the functional integral technique. Expanding functional integrals in the lattice space, the magnetic susceptibility, and the local moment are represented by graph series. Looking for the dependence of magnetic properties on the parameters of the model Hamiltonian, a phase diagram is obtained. The stability of the phases is considered. For special parameter values of the model system the phase diagram can be compared qualitatively with the diagram obtained experimentally for V2O3.
Diffusion drift paths in the core region of an edge dislocation
Authors: De Hosson J. Th. M. , Sleeswyk A. W. 
Published: July 2007

AbstractUsing the Johnson potential, the atomic configurations around perfect dislocations with 〈100〉Burgers vector in Ni and γ‐Fe were calculated using the relaxation procedure of Bullough and Perrin. Johnson's carbon–metal potential was used to calculate paths of maximum energy gain between octahedral sites. Four rows of sinks were found, in regions where the shear stress, the compressional and dilational stress predominate. Around each sink is a region draining into it. The binding energy of the C‐atom is strongest for the dilational sink: 0.21 and 0.11 eV for Ni and γ‐Fe, respectively. The imperfect 1/2 〈100〉 dislocation, which is a Frank partial, was also investigated for Ni. The binding energy of the C‐atom to the stacking fault sites is 0.74 eV (Suzuki effect).
The Lβ2valence band spectrum of niobium in the metal and in the α,β two‐phase region of the NbH system
Authors: Gilberg E. 
Published: July 2007

AbstractThe Lβ2valence band spectrum of niobium in the metal and in the α,β two‐phase region of the niobium‐hydrogen system was investigated using a high resolving bent crystal spectrograph with photoelectric registration. The spectrum was excited in fluorescence. The atomic ratio [H]/[Nb] varied between 0.45 and 0.70. The spectrum of the niobium metal has the shape of an asymmetric line with long tailing on the low energy side. In the NbH system a new emission band arises within the low energy tailing; in addition the line is slightly shifted towards higher energies. It is suggested that the new emission band is due to transitions from an energy band which is responsible for the NbH bonding.
On the theory of Hc2 anisotropy in cubic superconductors
Authors: Teichler H. 
Published: July 2007

AbstractThe anisotropy of the upper critical magnet field Hc2 of cubic type‐II superconductors with anisotropic Fermi surface and anisotropic attractive interaction is investigated. For a separable model interaction explicit results are given on the temperature and impurity dependence of the Hc2 anisotropy of impure metals in the „quasilocal”︁ regime and of clean metals for arbitrary temperatures below Tc. The clean‐limit results agree well with experimental data on Hc2 anisotropy of high‐purity Nb.
On the oscillator strength of F centers in alkali halides
Authors: Bosi L. , Fantola‐Lazzarini A. L. , Lazzarini E. , Ramaglia V. Marigliano , Tagliacozzo A. 
Published: July 2007

AbstractA radiochemical method, previously applied to NaCl, KCl, and KBr crystals has been used to determine the oscillator strength ƒ of F‐centers in RbCl. By extending theoretical calculations carried out by Smith and Spinolo, and by Iadonisi and Preziosi, estimates of ƒ for several alkali halides, including those previously mentioned, have been computed. The experimental results agree very closely with those obtained by Rauch and Heer and are in good accord with the theoretical estimates (the theoretical results are reported in brackets). ƒNaCl= 0.64 ± 0.02 (0.57); ƒKCl= 0.68 ± 0.02 (0.61); ƒKBr= 0.72 ± 0.02(0.57); ƒRbCl= 0.51 ± 0.05 (0.57). The experimental and theoretical results seemed to bear each other out and led to the conclusion that the ƒ values given in the literature, except those by Rauch and Heer, are overestimated.
The critical voltage effect in transmission electron microscopy. III. Influence of weak beams on degeneracy
Authors: Gevers R. , David M. , Serneels R. 
Published: July 2007

AbstractIn previous papers a theory of the critical voltage effect has been proposed based on a three‐beam treatment. The influence of further supplementary beams is considered using a general perturbation treatment. Two cases are considered: (i) the supplementary beams are all weak; (ii) there is a single non‐systematic strong perturbing beam. It is shown that the degeneracy may be retained, provided one changes in a proper way the illumination conditions, i.e. the accelerating voltage and possibly the crystal orientation. Perturbation calculus enables to obtain the shift of the critical voltage and of the excitation errors, as the sums of series in ascending powers of the Fourier coefficients (of the crystal potential) associated with the supplementary beams.
Model‐pseudopotential calculations of Grüneisen parameters, specific heat, and binding energy of sodium and potassium
Authors: Kushwaha S. S. , Rajput J. S. 
Published: July 2007

AbstractCalculations of the specific heat, Grüneisen parameter, binding energy, and compressibility of sodium and potassium are made using a two‐parameter model potential. The theoretical results are in qualitatively good agreement with available experimental results.
Hyperfine interactions in high‐silicate and quartz glasses
Authors: Cherenda N. G. , Shendrik A. V. , Yudin D. M. 
Published: July 2007

AbstractEPR measurements of HFS of nuclei 1H, 2D in spectra of quartz glasses and 29Si in spectra of high‐silicate glasses have been made and analysed. A stochastic model for the γ‐radiation‐induced paramagnetic centres are suggested. Calculations of the electronic structure of the unit AB4 have been carried out and a correlation diagram between the orbitals possible for tetrahedral (Td) and pyramidal (C3v) configurations has been obtained. This enables one to make comments on the EPR spectra of the units SiO43− and ROSiO32−.
A Quantum Spin Wave Theory for an Ising Ferromagnet in a Transverse Magnetic Field
Authors: Filatova L. D. , Tsukernik V. M. 
Published: July 2007

AbstractWith consideration of the Ising model a single‐axis ferromagnet is described to which a steady magnetic field is applied perpendicular to the anisotropy axis. The dispersion law for elementary excitations of such a system are derived in the extreme cases of weak and strong magnetic fields. It is shown that in the case of weak magnetic field an essential difference between quantum and classical results exists contrary to the case of strong magnetic field.
Ruby‐Laser‐Excited Delayed Fluorescence of Crystalline Tetracene. Combined Effects of Trap Saturation and Bimolecular Processes
Authors: Delannoy P. , Schott M. 
Published: July 2007

AbstractThe temporal decay of ruby‐laser‐excited delayed fluorescence of tetracene crystals is discussed. It is shown to be sensitive to minute amounts (≪ 1 ppm) of trapping centers, probably pentacene, whose lifetime may have been mistaken for the free triplet lifetime. General equations for the decay of the host delayed fluorescence in the presence of traps, trap saturation, and bimolecular processes, are given; their application to tetracene yields trap parameters and a lower limit of the free triplet lifetime, in the crystals studied. The two‐photon generation rate constant of singlets at 6943 Å is about 1.5 × 10−27cm s, a value comparable to those found in naphthalene and anthracene at corresponding energies.
The Effect of Uniaxial Stress on the Mutual Diffusion in the AgAu System
Authors: Gorskii V. V. , Dekhtyar M. I. , Yadekhtyar I. 
Published: July 2007

AbstractConsiderable decrease of the diffusion rate in the binary AgAu system was observed on applying pressure in the direction perpendicular to the contact zone. Making use of thermodynamic relations the above mentioned effect is shown to be connected with the increased degree of the localization of electrons near the atoms of each kind. A tentative explanation of this phenomenon is suggested.
The Generation of Individual Phonons and Photons under the Influence of Raman Paramagnetic Relaxation
Authors: Alekseev A. V. , Kopvillem U. Kh. 
Published: July 2007

AbstractThe relaxation of isolated spins in phonon‐photon fields is discussed using a two‐quantum incoherent relaxation process. It is shown that under the conditions of acoustic pumping the spins spontaneously generate photons and that electromagnetic pumping supports the phonon generation in the spontaneous regime in a controlled manner. Single quanta are urgently needed for testing the sensitivity of many quantum devices and masers and are also of interest for modelling the cosmic space. The processes discussed here may be applicable to the construction of two‐quantum masers and quantum counters.