bluuebunny/crossref_metadata_2025_split huggingface dataset:
Phenomenological description of dynamics in a diluted anisotropic heisenberg paramagnet at high temperatures
Authors: Tahir‐Kheli R. A. , Kawasaki K. 
Published: July 2007

AbstractA recent work on space and time dependent spin correlation function for a diluted isotropic Heisenberg paramagnet at infinite temperature is generalized in two important directions: firstly, now also lattices are considered which, admit nearest neighbour triangles, e.g. f.c.c. lattice, and, secondly, now the exchange interaction is allowed to be uni‐axially Anisotropic. The latter generalization necessitates the consideration of two different types of spin‐correlations: longitudinal and transverse. As limiting cases, the longitudinal correlation is examined for XY model and the transverse spin correlation for the Ising model. Between these limits, correlations are computed for J0/J+ = 2 and 0.5, for several concentrations, and the results are compared with those for the isotropic case, i.e. J0/J+ = 1.
Extra‐atomic relaxation and X‐ray spectra of narrow‐band metals. I. Formalism
Authors: Grebennikov V. I. , Babanov Yu. A. , Sokolov O. B. 
Published: July 2007

AbstractFor narrow band metals the distortions of the form of X‐ray and X‐ray photoelectron spectra are investigated under the influence of the vacancy on the inner level. A calculation method over the whole energy interval of the distoring influence of the hole field is proposed and realized numerically. The site formalism is developed to describe the X‐ray spectra. Equations are obtained in the energetic representation which allow to effect a numerical analysis.
Conduction electron spin resonance due to exchange and spin‐orbit scatterings by silute impurities in superconductors
Authors: Tsallis C. 
Published: July 2007

AbstractA simple theory is developed to calculate the transverse relaxation time, T2, of the spin of the conduction electrons in a slightly dirty superconductor. Two scattering mechanisms are considered: exchange interaction between the conduction electron spin and the impurity spin (for magnetic impurities only), and spin‐orbit interaction of the conduction electron around the impurity (for all kinds of impurities). As in Maki's Green‐function theory, a sudden increase (decrease) of T with respect to its value in the normal state, for the exchange (spin‐orbit) mechanism is obtained immediately below the critical temperature T0 which separates the normal and superconducting states. For vanishing temperature, T vanishes in both the cases. The asymptotic behaviours for T → T0 and T→0 are calculated. In the spin‐orbit case, T goes to zero, for T→0, surprisingly slowly. In order to exhibit the great sensitivity of T2 on the density of electronic states, it is re‐calculated, for both mechanisms, using an heuristic density of states which is physically reasonable but different from the BCS one. The height and width of the density of states modify not only the proportionality coefficients of T vs. T, but even the exponents in the limit T→0.
The model hamiltonian and some properties of magnetic resonance of triplet excitons. II. Kubo‐tomita approximation
Authors: Berim G. O. , Kessel A. R. 
Published: July 2007

AbstractThe temperature effects of the electron paramagnetic resonance (EPR) spectrum of triplet excitons described earlier by the exchange Hamiltonian are considered on the basis of the Kubo‐Tomita theory of exchange narrowing of EPR lines. It is shown that the proposed model qualitatively explains both the temperature behaviour of the lineshift and the linewidth of the fine‐structure components of the EPR spectrum and the non‐existence of hyperfine structure over the whole temperature range.
On the electric field dependence of the conductivity of holes in Si at low temperatures. II. The influence of the variation of steady‐state hole density with electric field on the conductivity
Authors: von Borzeszkowsei J. , Scholz J. 
Published: July 2007

AbstractMeasurements of the electric field dependence of the hole conductivity of Si with various doping levels and orientations are performed at 20.3 and 27.1 K. A description of the essential characteristics of the experimental results is achieved within the frame of a theoretical model. In this model, the field dependence of the hole mobility (taking into account non‐parabolicity of the valence band and non‐equipartition of acoustic phonon energy in the distribution function as well as in the momentum relaxation time) and the field dependence of the hole concentration (based on Lax′ cascade theory) are combined. Comparison of experimental and numerical results gives the relation between the participation of optical phonons in the hole capture process on shallow acceptors and the transition from super‐ to sublinear current‐voltage characteristics in high‐purity p‐Si at low temperatures and at electric field strengths below the breakdown range.
Giant spin splitting induced by exchange interactions in Hg1−kMnkTe mixed crystals
Authors: Bastard G. , Rigaux C. , Mycielski A. 
Published: July 2007

AbstractT6 → T8, magnetoabsorption spectra of semimetallic Hg1−kMnkTe alloys (k ≦ 2%) provide evidence of striking modifications in the “spin” states of the T8 Landau levels, in particular a drastic increase of the electronic Lande factor is observed. These anomalous spin effects are interpreted as the manifestation of the exchange interactions between the mobile electrons and the d electrons localized on the Mn atoms. The exchange integral for T8 levels is estimated.
Calibration of the isomer shift for 119Sn
Authors: Antončík E. 
Published: July 2007

AbstractThe isomer shift calibration constant for 119Sn is determined using the calculated electron contact densities for α‐tin and for an isolated tin atom in the solid rare‐gas matrix. The theoretical value of 8R/R = 0.92 × 104 thus estimated is compared with the experimental values.
On the binding energy of wannier excitons in strong anisotropic crystals
Authors: Gerlach B. 
Published: July 2007

AbstractThe strong anisotropic limit of the discrete energy‐values of excitons in uniaxial crystals is calculated. It is shown that all states of a given quantum number m of the z‐component of angular momentum approach the same limit – 4/(2 ∣m∣ + 1)2. First corrections to this value are discussed in terms of the anisotropy constant A  ε⟂μ⟂/ε∥︁μ∥︁ They come out to be at most of order A1/3 for m  0 and A1/2 for m ≠ 0.
Effect of hydrostatic pressure on the vibrational properties and the structure of SrWO4 and PbMoO4
Authors: Ganguly B. N. , Nicol M. 
Published: July 2007

AbstractRaman spectra of SrW04 are measured up to 35 kbar at 300 K. At (21 ± 2) kbar the doubly‐degenerate Eg modes are observed to split which indicates a structural transformation to a lower symmetry. The high pressure Raman spectra are similar to spectra of the structure of ZnW04. Raman spectra of PbMoO4 are also measured up to 35 kbar at both 300 and 80 K, but no evidence of a structural change is observed. The pressure dependence of the phonon spectra suggests the presence of harmonic phonon‐phonon interaction in this system. The possible origins of the different high pressure form of the scheelites are discussed on the basis of lattice phonon‐phonon interaction.
Electrical and magnetic properties of two crystallographic forms of (DEPE)2+(TCNQ)
Authors: Ashwell G. J. , Eley D. D. , Willis M. R. , Woodward J. 
Published: July 2007

Abstract1,2‐di(N‐ethyl‐4‐pyridinium)ethylene2+ (7,7,8,8‐tetracyanoquinodimethane) crystallises in two forms: a metallic form (DEPE)2+(TCNQ) I and a semiconducting form (DEPE)2t(TCNQ) II. On cooling from room temperature to 30 mK the electrical conductivity of I increases monotonic‐ally such that σ30mk/σRT=3.7. The thermoelectric power, in the temperature range studied, and the paramagnetic susceptibility of I, in the range of 60 to 300 K, are nearly independent of temperature, indicative of metallic behaviour. The magnetic susceptibility of II, however, exhibits singlet‐triplet behaviour with a singlet‐triplet separation of 0.029 eV. The electrical conductivity and thermoelectric power are similarly activated. The electrical and magnetic properties of both forms are discussed.
Conduction electron spin resonance in aluminium at 20.98 and 9.27 GHz
Authors: Sambles J. R. , Sharp‐Dent G. , Cousins J. E. , Stesmans A. , Witters J. 
Published: July 2007

AbstractThe linewidths of the conduction electron spin resonances from high purity aluminium foils and films are measured at frequencies of 9.27 and 20.98 GHz using reflection spectrometers. An attempt is made to fit a breakdown of motional narrowing model to the data. It is found that such a model cannot satisfactorily explain the dependence of the linewidths on frequency, temperature, and sample thickness. Likewise a model based on many‐body effects, although explaining some of the features of the results, does not fit all the data. It is possible that a contribution to the impurity induced linewidth which is frequency dependent would provide a better fit and it is concluded that to fully interpret the data a more complex theory is necessary.
Dispersion of cyclotron waves in metals and observability of many‐body effects
Authors: Saermark K. , Lebech J. 
Published: July 2007

AbstractExperimental results on the dispersion of cyclotron waves of the extraordinary and the ordinary type are analyzed in order to examine whether or not numerical estimates for some of the Landau An coefficients can be deduced. The analysis includes results on silver and potassium and the conclusion drawn is that no such estimate can be given. On the contrary, the experimental results are in good agreement with dispersion curves calculated on the basis of a finite value of Ωτ. The behaviour of the dispersion relations in the vicinity of thc Azbel‐Kaner rosonances is examined in the limit ωτ → CO.
The double resonance in two‐phonon Raman scattering
Authors: Abdumalikov A. A. , Klochikhin A. A. 
Published: July 2007

AbstractThe two‐LO‐phonon and one‐LO plus one‐TO‐phonon Raman scattering cross‐sections are calculated in a two‐band model. Double resonance is taken into account. It is shown that the cross‐section maxima are disposed at incident light frequencies of ω = ϵg + 2ΩLO and at ω = ϵg + ΩLO ΩTOfor the 2LO and LO + TO cross‐sections. The cross‐sections decrease with increasing |ϵg – ω| with different laws below and above the band gap ϵg. The cross‐sections above the band gap are strongly dependent functions of the damping constant of the electron system. The results of the numerical calculation are compared with experimental data.
Lo‐phonon‐assisted two‐photon absorption of the first excited state of the biexciton in CuCl
Authors: Ekardt W. , Sheboul M. I. 
Published: July 2007

AbstractLO‐phonon‐assisted two‐photon absorption of the first excited level of the excitonic molecule in CuCl is considered on the basis of the previously derived symmetry properties of this state. A giant cross‐section for this process is predicted mainly due to the “resonant” intermediate state Γ 1/5 of the single exciton. The process under consideration overcomes the difficulties of pure two‐photon absorption (TPA) of p‐type envelope states of the excitonic molecule as stated by Hanamura.
Plasmon‐enhanced sound amplification in piezoelectric semiconductors under a strong magnetic field
Authors: Lima C. A. S. , Miranda L. C. M. 
Published: July 2007

AbstractThe effect is considered of a strong dc magnetic field upon the contribution to sound amplification in piezoelectric semiconductors arising from the energy conversion mechanism “plasmon + + carrier → phonon + carrier”. An explicit expression is derived for the amplification coefficient. It is shown that under suitable conditions such contribution largely differs from that in the absence of a magnetic field both in the strength of the effect and in the angular distribution of the emitted phonons. A physical interpretation of the results is presented.
Galvanomagnetic effects and alloy scattering in n‐type Pb1–xSnxTe at low temperatures
Authors: Takita K. , Thanh Truong Dinh , Tanaka S. 
Published: July 2007

AbstractGalvanomagnetic effects are investigated in n‐type Pb1‐‐‐xSnxTe with comparatively low carrier concentration (1.4 × 1017 to 3.5 × 1018 cm―3) grown from the melt. From the analysis of the longitudinal and transverse magnetoresistances and Hall coefficient at low temperatures together with the Shubnikov‐de Haas data, it is found that the scattering is very much isotropic in spite of the large anisotropy of the effective mass. Further analysis of the scattering relaxation time, τ, indicates that the alloy scattering is dominant at low tmperatures. The matrix elements of the alloy scattering potential at the band edges are deduced; Uc(Pb‐Sn) = 8.2 × 10―35 erg cm3 and Uv(Pb‐Sn) ≈ 3Uc(Pb‐Sn). These values are close to those estimated from the pseudopotential theory of alloy scattering after Harrison.
The formation energies of a vacancy and a divacancy and the binding energy of a divacancy in simple metals
Authors: Takai O. , Yamamoto R. , Doyama M. 
Published: July 2007

AbstractThe formation energies of a vacancy and a divacancy and the binding energy of a divacancy in simple metals are formulated up to third‐order terms on the basis of the Lloyd‐Sholl theory. The calculations are performed using the Harrison approach under the condition of constant volume and lattice distortions are neglected.
Investigation of plasma effects in bismuth‐antimony alloys in the submillimeter wave range
Authors: Herrmann R. , Goy P. 
Published: July 2007

AbstractThe microwave absorption in the submillimeter range is investigated in semimetallic bismuthantimony alloys, Bi(1–x)Sbx (x = 0.0275, 0.050). The objects of measurement are hybrid resonances, the dielectric anomaly, and the plasma cyclotron resonance. In the alloy, Bi0.95Sb0.05 the electron‐hole hybrid resonance is found to be a quadratic function of the frequency. In the frequency range 136 to 587 GHz the resonance shift is more than 50%.
E–e Jahn‐Teller system: Optical response studies
Authors: Rueff M. , Sigmund E. 
Published: July 2007

AbstractThe E‐e Jahn‐Teller system is considered. An exact Fourier transformation of the optical response, as calculated by an operator method, is given. The absorption functions depend on the coupling strength and on temperature. Their behaviour is discussed. Comparisons are made with other theoretical investigations.
Superexchange field and intense magnetic field dependences of the Faraday rotation induced by the electric dipole transitions in YIG
Authors: Guillot M. , Le Gall M. 
Published: July 2007

AbstractThe influence of the superexchange field on the Faraday rotation induced in YIG at 1.15 μm wavelength by electric dipole transitions is analyzed in both the octahedral and tetrahedral sites where the contributions of the strong allowed transitions and the weak “forbidden” transitions are determined. It is shown that the temperature evolution of the magneto‐optical coefficients associated with the electric dipole transitions, as deduced from experiments on YIG, is well described by an effective field model which uses the superexchange and the applied magnetic fields. From this model it is shown also that under high (≈ 105 Oe) and intense (> 106 Oe) magnetic fields, Ha, the total Faraday rotation depends on Ha, firstly through the direct influence of the field on the sublattice magnetization and secondly through the magnetic field dependence of the “electric” magneto‐optical coefficients in the a and d sites.
The electron states associated with the core region of the 60° dislocation in silicon
Authors: Alstrup I. , Marklund S. 
Published: July 2007

AbstractA geometrical arrangement of silicon atoms corresponding to a cylinder of infinite length with a 60° dislocation core along the axis is constructed using linear elasticity theory. The one‐electron energy bands of this cylinder are studied using extended Hückel theory with parameters optimized to give best fit to the absolute bulk energy bands of finite silicon crystals. Electron states localized at the atoms in the dislocation core have a profound dangling bond character and form a band in the bandgap with a width of about 0.7 eV.
Anisotropy of lattice vibrations of layered compounds
Authors: van der Valk H. J. L. , Haas C. 
Published: July 2007

AbstractThe polarizable ion model is used to explain the observed anisotropy of the lattice vibrations of layered compounds with the Cd(OH)2 or CdCl2 structure. The electronic polarizabilities of the ions, the Szigeti effective charge, and the contribution of the short‐range forces to the frequencies of the optical modes are deduced from optical data for the lattice vibrations of PbI2, CdI2, SnS2, and SnSe2. From the analysis it is found that the contribution of the short‐range forces is rather isotropic. The large anisotropy of the optical modes is caused mainly by static dipoles of the anions induced by local electric fields. For the semiconductors SnS2 and SnSe2 the reduction of the ionic charges and static dipoles is larger than for the more ionic compounds PbI2 and CdI2.
The pseudopotential method and the problem of ordering in alloys. III. Intermetallic compounds LiAl, LiTl, and NaTl
Authors: Makhnovetskii A. B. , Krasko G. L. 
Published: July 2007

AbstractA method, developed in previous papers is applied to the a priori analysis of the thermodynamical stability of the crystal structures of the compounds LiAl, TiTl, and NaTl. Allowing for only pairwise interaction (second order of the pseudopotential perturbation theory), it is found that the structure B‐2 (of CsCl type) is the most stable one for LiAl and LiTl, while in NaTl a spinodal decomposition must arise. Inclusion of multi‐ion interaction, using some higher‐order terms of the Brillouin‐Wigner perturbation theory results in a stabilization of the B‐32 structure in NaTl and LiAl while in LiTl the B‐2 structure is left stable. The structures obtained are experimentally observed. The thermodynamical evolution of the structures is also discussed.
Analysis of lattice thermal conductivity of solid argon at low temperatures
Authors: Gupta I. J. , Trikha S. K. 
Published: July 2007

AbstractAn attempt is made to analyse the lattice thermal conductivity of solid argon at low temperatures, using Holland's model. The dispersion relation q = C sin―1 (ω/ωmax), for transverse phonons, is used to determine vg/v2p in the conductivity integrals. A fairly good agreement is obtained between the calculated and the experimental results of Clayton and Batchelder, in the temperature range 1.5 to 20 K. The dislocation density and the average grain size of the polycrystalline specimen are determined to be 2.5 × 1011 m―2 and 0.05 mm, respectively.
Fluctuations of Order Parameter and Anharmonic Interaction in the Vibronic Model of Ferroelectrics
Authors: Mailyan G. L. , Plakida N. M. 
Published: July 2007

AbstractThe free energy for the vibronic model of a ferroelectric is calculated taking into account the fluctuations of the order parameter (soft phonons) defined by the electron‐phonon and anharmonic interactions. As a result, a considerable lowering of the phase transition temperature Tc in comparison to its mean field value is obtained. Both the anharmonic and electron‐phonon interactions define this reduction of Tc, the latter being more important for narrow‐gap ferroelectrics.
Pseudocubic Angular Dependence of the M = −1/2 to +1/2 EPR Transitions for Ions with S = 3/2 by Small Distortions of the Cubic Crystal Field
Authors: Gehlhoff W. 
Published: July 2007

AbstractThe line positions of the EPR transitions — determined by the generalized spin Hamiltonian ℋ︁ = gβBS + ∫β{S Bx + S By + S Bz − 1/5 (SB) [3S(S + 1) − 1]} for cubic symmetry and S = 3/2 — are calculated to the second order of perturbation theory taking into account small rhombic distortions of the crystal field. In the case of the transition M = −1/2 ⟷ +1/2 — frequently the only one experimentally observed — it is shown that under certain conditions such distortions of the crystal field apparently cause the same cubic angular dependence as the term ∫βS3B does. Therefore, the parameters f and g determined from the experiment may contain contributions of non‐cubic fields. These contributions, which can be determined by measuring at two microwave frequencies, are calculated for four different systems of the rhombic principal axes.
The Dielectric Relaxation of Impurity—Vacancy Complexes in KI Doped with Cl+ Anions
Authors: Zílio S. C. , De Souza M. 
Published: July 2007

AbstractUsing the ITC technique the dielectric relaxation of KI doped with divalent ions and small amounts of Cl− or Br− anions is studied. New low temperature ITC peaks are found at temperatures as low as 120 K. Also a strong effect is found in the aggregation kinetics of the divalent ions. A model for the trapping of the divalent ions by the Cl− or Br− anions is proposed.
Random One‐Dimensional Classical Magnet
Authors: Krzemiński S. 
Published: July 2007

AbstractFor the thermodynamic quantities (specific heat, spin‐spin correlation functions, magnetic susceptibility) of an impure one‐dimensional system of classical spins of arbitrary dimensionality with arbitrary, isotropic nearest‐neighbour interactions rigorous expressions are found in the thermodynamic limits. The quenched approximation is considered for both, site and bond impurity models. The present theory is an extension of Liu and Joseph's work for the pure case.
The Influence of Lattice Vibrations on the Parametric Resonance in Hydrogen‐Bonded Ferroelectrics by Means of Parallel Electric Microwave Pumping
Authors: Stamenković S. , Stojanović S. D. , Žakula R. B. 
Published: July 2007

AbstractThe pseudospin–phonon formalism is used to describe the influence of lattice vibrations on the occurrence of a parametric resonance in the hydrogen‐bonded ferroelectrics. The theoretical results obtained show that such a resonance is considerably stabilized by the strong coupling between protons and heavy ions.
Concentration Dependence of Exchange Field in Dilute Metals
Authors: Khalyullin G. G. 
Published: July 2007

AbstractThe dependence of the exchange field on the paramagnetic impurity concentration in dilute metals is investigated. The consideration of the difference in the occupation probability of sites at different coordination spheres results in a variety of concentration dependences of the exchange field instead of a linear dependence. The concrete type of this dependence is determined by the conduction electron density. Numerical calculations are made of the paramagnetic Curie temperature change with dilution for a simple cubic crystal.
Dynamical Properties of NO Impurity Molecules in Alkali Halides. II. Vibrational Spectra
Authors: Rebane L. A. , Zavt G. S. , Haller K. E. 
Published: July 2007

AbstractThe first‐order Raman scattering induced by the NO molecule in KI and RbCl is measured. The spectral features are compared with those observed in the ultraviolet and infrared spectra. The spectral properties are interpreted within the models which take into account the librational motion of the molecule. The force constants connecting the molecule with its neighbours are found to possess high anisotropy. The main spectral features are explained as the result of the modification of the local densities of states and as the manifestations of librational motion.
Fermi Liquid Effects in Ferromagnetic Metals
Authors: Carneiro G. M. , Pereira P. R. Rodrigues 
Published: July 2007

AbstractMicroscopic Fermi‐liquid theory is used together with the s–f or s–d exchange model to discuss Fermi‐liquid effects in ferromagnetic metals at zero temperature. The contribution from exchange of virtual magnons to the quasiparticle scattering amplitude and the Landau quasiparticle inter‐action are calculated in the Migdal approximation. It is shown that exchange of magnons lead to strong forward electron–electron scattering. It is found that the quasiparticle effective mass and the spin susceptibility of the conduction electrons are strongly enhanced, whereas their compressibility is unaffected by electron–magnon interactions.