A three-peak structure for the critical relaxation function in the transverse Ising model

The dynamical properties of the transverse Ising model with an interaction of uniaxial dipolar nature are shown to exhibit a marked q-anisotropy in the critical region. For any wave vector q strictly non perpendicular to the z-axis the longitudinal relaxation shape function F_q^zz exhibits a three-peak structure and consequently a finite width of its central peak.     

Proposal of a new model for the modulated structure of α-uranium

The modulated structure of α-uranium is analysed in the framework of the theory of superspace groups. Arguments are given which lead to the (3 + 2)D superspace group Pmcm($\text{1}\text{2}$βγ) as the most probable one. The consequences for the structure are derived. The most important one is, that there are two independent atoms in the unit-cell, one with a displacement along b and c and the other with a displacement only along a. This model is quite different from that previously found, which has only one independent atom, and a modulation in all three directions.     

Multiplet structure of P-excitons in CuBr due to valence band degeneracy

The two-photon absorption spectrum of CuBr shows a fourfold energy splitting of the 2P- and 3P-excitons of the Z_1,2 series. The splitting results from d-like contributions to the kinetic energy of the hole (Γ_δ) which lead to a coupling between angular momentum and hole spin. The energy splitting allows to determine the spherical and cubic parameters μ and δ of the reduced exciton mass. The results are compared with corresponding values of an existing band structure calculation.     

Magnetic structure of the Nd5Ge3 compound

Neutron diffraction measurements of the Nd₅Ge₃ intermetallic compound with a hexagonal structure (space group P6₃/mcm) have been performed at temperatures of ～10 and 293 K. The basis functions of irreducible representations of the space group D _6h ³ (P6₃/mcm), which are calculated as a result of the symmetry analysis of possible magnetic structures with the wave vector k = μb ₁, are used to facilitate the search for a real model of the magnetic structure of the compound.     

Effects of band structure and matrix element on RKKY interaction

The effects of band structure and matrix elements on the RKKY interaction J(R) are separately investigated. When the Fermi surface has planes perpendicular to R, effects appear on the period of oscillation, the phase shift and the amplitude of J(R). The applicable region of the asymptotic form for large R and the validity of the free electron approximation are also examined. If there are no tangential planes perpendicular to R, it is found that: 1) when two interacting localized spins are on lattice points in the crystal, exponential damping appears even for the constant matrix element model and the matrix element effects introduce competing terms causing a sign change; 2) when one of the spins is at an interstitial position, the constant matrix model gives a weaker J(R) ∝ R^-2 damping, but the character of this term changes into the exponential damping by taking into account matrix elements.     

Probing the halo structure

Halo nuclei are characterized by outer nucleons that reside mostly in the classically forbidden region. The large average distance of halo nucleons suggests the decoupling of core and halo degrees of freedom. This is the basis for the few-body structure models developed in the past decade. Few-body models have been the most frequent tool when probing the halo structure. Coulomb dissociation, Knock-out or Transfer reactions have provided detailed structure information for exotic nuclei. Nowadays, the accumulating data impose severe tests for the few-body models. We discuss the achievements of these models as well as their limitations. To cite this article: F.M. Nunes, C. R. Physique 4 (2003).     

The harmonic force field and structure of chloryl fluoride

The microwave spectra of three isotopic species of chloryl fluoride, FClO₂, previously published by Parent and Gerry (J. Mol. Spectrosc., 49, 343–364 (1974)), have been refit to rotational constants and centrifugal distortion constants using Watson's Hamiltonian in both its A and S reductions. The quartic distortion constants have been combined with the vibrational data of Smith, Begun, and Fletcher (Spectrochim. Acta, 20, 1763–1770 (1964)) to calculate a refined harmonic force field. The rotational constants and force field have been used to calculate a zero-point average structure and an approximate equilibrium structure. Both the force field and structures are in essential agreement with those published earlier.     

Orbital and magnetic structure of two-dimensional ferromagnets with Jahn-Teller ions

The cooperative ordering of degenerate d-orbitals in two-dimensional ferromagnets of K₂CuF₄ type is considered by employing both the usual Jahn- Teller mechanism and the superexchange one. The orbital structure obtained differs from that usually assumed for K₂CuF₄; the latter is shown to be incompatible with the observed ferromagnetic ordering.     

A personal view of some issues involved in the structure of nuclei with large neutron excess

Large neutron excess poses new issues concerning the competition of deformation and pairing as well as changes in nuclear shell structure. To cite this article: I. Hamamoto, B.R. Mottelson, C. R. Physique 4 (2003).     

Band structure of platinum from angle resolved photoemission experiments

Angle-resolved and angle-dispersed ultraviolet photoelectron spectroscopy (ARUPS) has been used to determine the experimental band structure of platinum at various points along the ΓX, ΓKX and ΓL directions in the Brillouin zone. Various methods have been employed to obtain the E(k) points, among them absolute methods which determine the energy and the momentum independently without any assumption about the final state dispersion. The experimental points are compared with a self-consistent relativistic band structure calculation for energies below and above the Fermi energy. Good agreement between theory and experiment is found.     

Magnetic band structure in the valence band of CdSb

Starting from the band structure calculations of Yamada, we have undertaken to calculate in analytic form the Landau levels, de Haas-Shubnikov oscillation periods and effective masses in the valence band of CdSb. Because of the anomalous character of the E — k relation in the x-direction, it is necessaryto use different approximation methods for low and high hole energies; between the two is a region for which calculation is very difficult. Analytic forms have been obtained in both regimes, which should facilitate the calculation of magneto-transport properties and thus the determination of band parameters.     

Influence of the degenerate d level and of the Jahn-Teller effect on the manganite electronic structure calculated in the tight-binding approximation

E(k) dispersion curves for the charge carriers in the LaMnO₃-like perovskites were calculated for the basic types of canted antiferromagnetic ordering of the Mn sublattice in the framework of the tight-binding approximation. The E(k) spectrum of the antiferromagnetic structures was calculated for the first time taking into account the degeneracy of the Mn e _g level and the Jahn-Teller distortion of the cubic perovskite structure. This calculation involved diagonalization of the 8×8 Hamiltonian matrix. Analytical expressions for the E(k) function at separate points and symmetry lines of the Brillouin zone were derived. The calculations showed that the properties of the La_1?x Ca_xMnO₃ system do not have electron-hole symmetry.     

Reinvestigation of the quadrupole hyperfine structure in rotational spectra of 3-lodopropene

Quadrupole hyperfine structure of 3-iodopropene has been reinvestigated by the use of two methods, (1) Two-Level Approximation, and (2) Direct Solution of the Energy Matrix, to improve the discrepancies between the observed and calculated hyperfine spectra reported in a previous work (J. Mol. Spectrosc.66, 421–427 (1977)). Appreciable improvement can be found in the discrepancies between the observed and calculated spectra. By means of these two methods, the χ values of CH₂ICHCH₂ have been revised to be: |χ_ab| = 1160 MHz and χ_zz = ?1920 MHz, respectively.     

Dislocation structure of intermetallic Ti3Al subjected to high-temperature deformation

Transmission electron microscopy was used to examine the dislocation structure of intermetallic Ti₃Al subjected to deformation at tempertures T = 1073–1273 K. The microstructure of samples subjected to high-temperature deformation is established to contain mobile superdislocations of a and 2c + a types, and single dislocations with Burgers vector [0001] are also observed on the prismatic planes. Possible models of destruction of barriers associated with 2c + a superdislocations on the pyramidal planes are discussed using the results of computer simulations of the structure of a superdislocation core in in Ti₃Al.     

Antisymmetrized Molecular Dynamics: a new insight into the structure of nuclei

The AMD theory for nuclear structure is explained by showing its actual applications. First the formulation of AMD including various refined versions is briefly presented and its characteristics are discussed, putting a stress on its nature as an ab initio theory. Then we demonstrate fruitful applications to various structure problems in stable nuclei, in order to explicitly verify the ab initio nature of AMD, especially the ability to describe both mean-field-type structure and cluster structure. Finally, we show the results of applications of AMD to unstable nuclei, from which we see that AMD is powerful in elucidating and understanding various types of nuclear structure of unstable nuclei. To cite this article: Y. Kanada-En'yo et al., C. R. Physique 4 (2003).     

Vibration-rotation spectra of deuterated hypochlorous acid and the determination of the equilibrium structure

Vibration-rotation spectra of the three fundamental vibrations of D¹⁶O³⁵Cl have been measured at a resolution of 0.01 cm⁻¹ to determine vibration-rotation constants. From these results values for the equilibrium rotational constants have been established and used, in conjunction with the equilibrium rotational constants for H¹⁶O³⁵Cl (C. M. Deeley and I. M. Mills, J. Mol. Spectrosc. 114, 368–376 (1985)), to determine the equilibrium structure of hypochlorous acid.     

Fine structure of shallow donor lines in germanium induced by magnetic field

Photoconductivity spectra of Ge doped with Sb and P were investigated in a magnetic field (H) at the temperature T = 4.2K. Measurements were performed in the Voigt configuration (H ∥ [111]). Fine structure of lines connected with optical transitions from the ground to the excited states of shallow donors due to spin splitting of impurity energy states were observed.     

Current and constituent quarks: Their implications for resonance excitations polarized and unpolarized inelastic structure functions

The transformation between constituent and current quarks is discussed and applied to the calculation of matrix elements for nucleon to resonance transitions induced by arbitrary currents belonging to an octet. In particular, previous results on πN and γN transitions are subsumed while weak interactions (ΔQ = 0 or 1) and longitudinal photon induced transitions are discussed for the first time. The implications of a non-trivial Melosh transformation upon previous calculations in quark parton models of the non-diffractive component of the deep inelastic structure functions are discussed. The magnitudes of the unpolarized structure functions are found to be unchanged but for the polarized structure functions significant corrections to previous calculations are discovered. In particular it is found that it is not necessary that the polarization asymmetry A^γP be positive in the deep inelastic region. Our approach is valid for all Q², even for photoproduction, and is not restricted to deep inelastic scattering in contrast to earlier parton model calculations. The saturation of various current algebra sum rules is discussed.     

Location of direct transitions on the Λ line of the band structure of the noble metals using angle resolved photoelectron spectroscopy (ARUPS)

The triangulation method of angle-resolved photoemission for the absolute localization of direct transitions in k-space has been used on (110) and (111) faces in the ΓKLUX or (1$\text{1}$0) mirror plane in order to determine some points of the electronic bulk band structure of Cu, Ag and Au along the Λ line. It is found that the experimental points for the occupied bands and the unoccupied bands are in good agreement with recent ground state band structure calculations based on the local density functional theory.