EXAFS Study on Local Structure of Iron Crystal by the Use of Asymmetrical Monochromator and PSPC

The EXAFS spectroscopy equipment constructed from an asymmetrical cut flat monochromator and PSPC is applied to the structural determination of pure α-iron which has small difference (0.038nm) in the first and second nearest neighbour distance. The efficiency of the curve fitting method for the two shell model of known structure material (α-iron) is discussed, in addition to describing the details of the experimental procedure of our new type of spectrometer and of the EXAFS data analysis

Band gap of essentially fourfold-coordinated amorphous diamond synthesized from C60 fullerene

The band gap and density of state for a form of amorphous diamond synthesized from C60 fullerene by shock compression were measured by electron energy-loss spectroscopy in this study. The dielectric functions of the material were derived from the loss function obtained from its spectrum by Kramers-Kronig transformation. The imaginary part of the dielectric function, ɛ2, showed that the magnitude of the gap was up to 4.5 eV, somewhat smaller than that of crystalline diamond, which is 5.5 eV, but larger than those of any other amorphous material reported before. The excitation of interband transition was observed only at the Γ point, not at the X and L points. The density of state around the gap was rather broad. The radial distribution function analysis made previously revealed that the carbon atoms of the material were tetrahedrally coordinated; furthermore, these tetrahedra were arranged in the same manner as that of crystalline diamond within the region of unit cell size. The characteristic electronic properties of the amorphous diamond measured were consistently attributable to the unique atomic configuration of the material. The band gap and density of state were discussed in relation to the fraction of fourfold coordination, the density, and the short-range structure, comparing with other amorphous carbon materials

Resonant Inelastic X-ray Scattering Studies of Elementary Excitations

In the past decade, Resonant Inelastic X-ray Scattering (RIXS) has made remarkable progress as a spectroscopic technique. This is a direct result of the availability of high-brilliance synchrotron X-ray radiation sources and of advanced photon detection instrumentation. The technique's unique capability to probe elementary excitations in complex materials by measuring their energy-, momentum-, and polarization-dependence has brought RIXS to the forefront of experimental photon science. We review both the experimental and theoretical RIXS investigations of the past decade, focusing on those determining the low-energy charge, spin, orbital and lattice excitations of solids. We present the fundamentals of RIXS as an experimental method and then review the theoretical state of affairs, its recent developments and discuss the different (approximate) methods to compute the dynamical RIXS response. The last decade's body of experimental RIXS data and its interpretation is surveyed, with an emphasis on RIXS studies of correlated electron systems, especially transition metal compounds. Finally, we discuss the promise that RIXS holds for the near future, particularly in view of the advent of x-ray laser photon sources.Comment: Review, 67 pages, 44 figure

Theory of Orbital Ordering, Fluctuation and Resonant X-ray Scattering in Manganites

A theory of resonant x-ray scattering in perovskite manganites is developed by applying the group theory to the correlation functions of the pseudospin operators for the orbital degree of freedom. It is shown that static and dynamical informations of the orbital state are directly obtained from the elastic, diffuse and inelastic scatterings due to the tensor character of the scattering factor. We propose that the interaction and its anisotropy between orbitals are directly identified by the intensity contour of the diffuse scattering in the momentum space.Comment: 4 pages, 1 figur

Sharper and Simpler Nonlinear Interpolants for Program Verification

Interpolation of jointly infeasible predicates plays important roles in various program verification techniques such as invariant synthesis and CEGAR. Intrigued by the recent result by Dai et al.\ that combines real algebraic geometry and SDP optimization in synthesis of polynomial interpolants, the current paper contributes its enhancement that yields sharper and simpler interpolants. The enhancement is made possible by: theoretical observations in real algebraic geometry; and our continued fraction-based algorithm that rounds off (potentially erroneous) numerical solutions of SDP solvers. Experiment results support our tool's effectiveness; we also demonstrate the benefit of sharp and simple interpolants in program verification examples

Dynamics of metallic stripes in cuprates

We study the dynamics of metallic vertical stripes in cuprates within the three-band Hubbard model based on a recently developed time dependent Gutzwiller approximation. As doping increases the optical conductivity shows transfer of spectral weight from the charge transfer band towards i) an incoherent band centered at 1.3eV, {ii} a Drude peak, mainly due to motion along the stripe, {iii} a low energy collective mode which softens with doping and merges with ii} at optimum doping in good agreement with experiment. The softening is related to the quasidegeneracy between Cu centered and O centered mean-field stripe solutions close to optimal doping.Comment: 4 pages, 5 figures, corrections to Fig.

Development of genomic simple sequence repeat markers for yam

Yam ( Dioscorea spp.) is a major staple crop widely cultivated for its starchy tubers. To date, very few marker resources are publicly avail - able as tools for genetic and genomic studies of this economically important crop. In this study, 90 simple sequence repeat (SSR) markers were developed from an enriched genomic library of yellow Guinea yam ( D. cayenensis Lam.). Cross- amplification revealed that 85 (94.4%) and 51 (56.7%) of these SSRs could be successfully transferred to the two major cultivated species of D. rotundata Poir. and D. alata L., respec - tively. Polymorphisms in 30 markers selected on the basis of reliability and reproducibility of DNA bands were evaluated using a panel of 12 D. cayenensis , 48 D. rotundata , and 48 D. alata accessions. Accordingly, number of alleles per locus ranged from 2 to 8 in D. cayenensis (mean = 3.9), 3 to 30 in D. rotundata (mean = 13.9), and 2 to 22 in D. alata (mean = 12.1). The average observed and expected heterozygosi - ties were 0.156 and 0.634 ( D. cayenensis ), 0.326 and 0.853 ( D. rotundata ), and 0.247 and 0.836 ( D. alata ), respectively. Clustering based on six SSRs that were polymorphic in at least four of the five cultivated Dioscorea species studied, including D. cayenensis , D. rotundata , D. alata , D. dumetorum (Kunth) Pax., and D. bulbifera L., detected groups consistent with the phyloge - netic relationships of the species except for D. dumetorum . These new SSR markers are invalu - able resources for applications such as genetic diversity analysis and marker-assisted breedingYam ( Dioscorea spp.) is a major staple crop widely cultivated for its starchy tubers. To date, very few marker resources are publicly avail - able as tools for genetic and genomic studies of this economically important crop. In this study, 90 simple sequence repeat (SSR) markers were developed from an enriched genomic library of yellow Guinea yam ( D. cayenensis Lam.). Cross- amplification revealed that 85 (94.4%) and 51 (56.7%) of these SSRs could be successfully transferred to the two major cultivated species of D. rotundata Poir. and D. alata L., respec - tively. Polymorphisms in 30 markers selected on the basis of reliability and reproducibility of DNA bands were evaluated using a panel of 12 D. cayenensis , 48 D. rotundata , and 48 D. alata accessions. Accordingly, number of alleles per locus ranged from 2 to 8 in D. cayenensis (mean = 3.9), 3 to 30 in D. rotundata (mean = 13.9), and 2 to 22 in D. alata (mean = 12.1). The average observed and expected heterozygosi - ties were 0.156 and 0.634 ( D. cayenensis ), 0.326 and 0.853 ( D. rotundata ), and 0.247 and 0.836 ( D. alata ), respectively. Clustering based on six SSRs that were polymorphic in at least four of the five cultivated Dioscorea species studied, including D. cayenensis , D. rotundata , D. alata , D. dumetorum (Kunth) Pax., and D. bulbifera L., detected groups consistent with the phyloge - netic relationships of the species except for D. dumetorum . These new SSR markers are invalu - able resources for applications such as genetic diversity analysis and marker-assisted breedin

Resonant X-ray Scattering in Manganites - Study of Orbital Degree of Freedom -

Orbital degree of freedom of electrons and its interplay with spin, charge and lattice degrees of freedom are one of the central issues in colossal magnetoresistive manganites. The orbital degree of freedom has until recently remained hidden, since it does not couple directly to most of experimental probes. Development of synchrotron light sources has changed the situation; by the resonant x-ray scattering (RXS) technique the orbital ordering has successfully been observed . In this article, we review progress in the recent studies of RXS in manganites. We start with a detailed review of the RXS experiments applied to the orbital ordered manganites and other correlated electron systems. We derive the scattering cross section of RXS where the tensor character of the atomic scattering factor (ASF) with respect to the x-ray polarization is stressed. Microscopic mechanisms of the anisotropic tensor character of ASF is introduced and numerical results of ASF and the scattering intensity are presented. The azimuthal angle scan is a unique experimental method to identify RXS from the orbital degree of freedom. A theory of the azimuthal angle and polarization dependence of the RXS intensity is presented. The theoretical results show good agreement with the experiments in manganites. Apart from the microscopic description of ASF, a theoretical framework of RXS to relate directly to the 3d orbital is presented. The scattering cross section is represented by the correlation function of the pseudo-spin operator for the orbital degree of freedom. A theory is extended to the resonant inelastic x-ray scattering and methods to observe excitations of the orbital degree of freedom are proposed.Comment: 47 pages, 24 figures, submitted to Rep. Prog. Phy

Intersubband spin-density excitations in quantum wells with Rashba spin splitting

In inversion-asymmetric semiconductors, spin-orbit coupling induces a k-dependent spin splitting of valence and conduction bands, which is a well-known cause for spin decoherence in bulk and heterostructures. Manipulating nonequilibrium spin coherence in device applications thus requires understanding how valence and conduction band spin splitting affects carrier spin dynamics. This paper studies the relevance of this decoherence mechanism for collective intersubband spin-density excitations (SDEs) in quantum wells. A density-functional formalism for the linear spin-density matrix response is presented that describes SDEs in the conduction band of quantum wells with subbands that may be non-parabolic and spin-split due to bulk or structural inversion asymmetry (Rashba effect). As an example, we consider a 40 nm GaAs/AlGaAs quantum well, including Rashba spin splitting of the conduction subbands. We find a coupling and wavevector-dependent splitting of the longitudinal and transverse SDEs. However, decoherence of the SDEs is not determined by subband spin splitting, due to collective effects arising from dynamical exchange and correlation.Comment: 10 pages, 4 figure