The exponential localization of Wannier functions in two or three dimensions is proven for all insulators that display time-reversal symmetry, settling a long-standing conjecture. Our proof relies on the equivalence between existence analytic quasi-Bloch and nullity Chern numbers (or Hall current) system under consideration. same implies cannot exponentially localized functions. An explicit condition reality identified.

A detailed account of the dependence X-ray absorption spectra (XAS) on polarisation and light beam directions is given. Anisotropic XAS measured single crystals, layered compounds, polymers oriented powders are tabulated. The cross section by non-magnetic samples derived, including electric dipole quadrupole contributions. Orders magnitude found for magnetic dipole-octupole terms. Using a spherical tensor expansion section, simple analytical formulae given angular contributions to all...

We outline a many-body description of the photoemission and photoabsorption processes that incorporates multichannel treatment atomic dynamical excitations into framework multiple-scattering (MS) theory. This generalization is most natural one, in internal structure constituents physical system under study taken account by introduction an interchannel t matrix fixes probability amplitude particular excitation (channel) degrees freedom atom photoelectron impinging on it. For rest MS theory...

Angular-dependent core hole screening effects have been found in the cobalt $K$-edge x-ray absorption spectrum of ${\text{LiCoO}}_{2}$, using high-resolution data and parameter-free general gradient approximation plus $U$ calculations. The $\text{Co}\text{ }1s$ on absorber causes strong local attraction. nearest-neighbors induces a 2 eV shift density states with respect to on-site $1s\text{\ensuremath{-}}3d$ transitions, as detected }K$ pre-edge spectrum. Our functional theory calculations...

Magnetic circular x-ray dichroism (MCXD) studies at ${\mathit{L}}_{2,3}$ absorption edges in intermediate-valence (IV) compounds ${\mathrm{CeFe}}_{2}$, Ce(${\mathrm{Fe}}_{0.8}$${\mathrm{Co}}_{0.2}$${)}_{2}$, ${\mathrm{CeCo}}_{5}$, ${\mathrm{Ce}}_{2}$${\mathrm{Co}}_{17}$, and trivalent 4${\mathit{f}}^{1}$ systems (${\mathrm{CeRu}}_{2}$${\mathrm{Ge}}_{2}$, ${\mathrm{Ce}}_{3}$${\mathrm{Al}}_{11}$, CePd, ${\mathrm{CeFe}}_{2}$${\mathrm{H}}_{3.8}$) the Ce are presented. The comparison with...

An implementation of the multiple-scattering approach to x-ray magnetic circular dichroism (XMCD) in K-edge absorption spectroscopy is presented. The convergence problems due cluster size and relativistic corrections are solved using an expansion Dirac Green function for complex energies up second order 1/$c$. Fermi energy dealt with via a plane integration. Numerical methods used obtain semi-relativistic whole explained. We present calculation at bcc-iron including core hole effect. A good...

Pre-edge features in x-ray absorption spectroscopy contain key information about the lowest excited states and thus on most interesting physical properties of system. In transition-metal oxides they are particularly structured but extracting parameters by comparison with a calculation is not easy due to several computational challenges. By combining core-hole attraction correlation effects first-principles approach, we calculate $\text{Ni}\text{ }K$-edge spectra NiO. We obtain striking...

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTFull Multiple Scattering and Crystal Field Multiplet Calculations Performed on the Spin Transition FeII(phen)2(NCS)2 Complex at Iron K L2,3 X-ray Absorption EdgesV. Briois, Ch. Cartier dit Moulin, Ph. Sainctavit, Brouder, A.-M. FlankCite this: J. Am. Chem. Soc. 1995, 117, 3, 1019–1026Publication Date (Print):January 1, 1995Publication History Published online1 May 2002Published inissue 1 January...

We produce the first experimental evidence of x-ray natural circular dichroism (XNCD) in a uniaxial gyrotropic crystal α-LiIO3 that is known to crystallize with space group P63 and exhibit very strong nonlinear susceptibility. For sake simplicity, optical axis was set colinear direction exciting beam order get rid undesirable birefringence linear effects. The nicely structured XNCD spectra recorded at LI, LII, LIII edges iodine are assigned electric dipole–electric quadrupole (E1.E2)...

Multiple-scattering theory is generalized to take into account the effects of spin-orbit interaction and spin polarization photoelectron that are at origin magnetic x-ray circular dichroism (MXD) effect observed in x-ray-absorption spectra where final state delocalized. The basic framework this treatment nonrelativistic relativistic corrections considered as perturbations. multiple-scattering approach sheds light on various aspects MXD spectra: relation between ${\mathit{L}}_{\mathrm{II}}$-...

In this paper we present an experimental investigation of the magnetic properties metallic multilayers (here Nd-Fe) by x-ray dichroism (MXD). The absorption cross sections have been measured, using a dispersive optics, on both ${\mathit{L}}_{\mathrm{II}}$ edge Nd and K Fe in several Nd-Fe (\ensuremath{\Lambda}\ensuremath{\approxeq}40--100 \AA{}), for temperatures ranging from 77 to 300 K. We will show that intensity can be roughly correlated ordered moments either or Fe, thus MXD allows...

The wavefront set provides a precise description of the singularities distribution. Because its ability to control product distributions, was key element recent progress in renormalized quantum field theory curved spacetime, gravity, discussion time machines or energy inequalitites. However, is somewhat subtle concept whose standard definition not easy grasp. This paper step by introduction set, with examples and motivation. Many different definitions new interpretations are presented. Some...

The local arrangement of atoms surrounding a substitutional ${\mathrm{Cr}}^{3+}$ and ${\mathrm{Fe}}^{3+}$ ion in $\ensuremath{\alpha}$-${\mathrm{Al}}_{2}{\mathrm{O}}_{3}:$ (ruby) $\ensuremath{\alpha}$-${\mathrm{Al}}_{2}{\mathrm{O}}_{3}:(\mathrm{F}\mathrm{e}\ensuremath{-}\mathrm{T}\mathrm{i})$ (blue sapphire) has been studied experimentally using natural x-ray linear dichroism absorption at the Cr Fe K edge. isotropic dichroic signals have recorded single crystals reliable method applied to...

For the first time, commonly unaccessible local electronic structure parameters of Fe2+ and Fe3+ in minerals are derived from calculation pre-edge features X-ray absorption spectra at Fe K edge. The Ligand Field Multiplet approach is used to calculate eigenstates ions absolute intensities electric-quadrupole dipole transitions involved pre-edge. tetrahedral symmetry, a new model for p-d hybridization developed. degree admixture between 3d 4p levels (crystal field, bond covalency) obtained.

We report the first experimental detection of x-ray magnetochiral dichroism in magnetoelectric ${\mathrm{Cr}}_{2}{\mathrm{O}}_{3}$. This dichroism, which does not require any polarized beam, is related to time-reversal odd part optical activity tensor dominated by electric dipole-electric quadrupole $E1E2$ interference terms. The experiments were carried out using either a single crystal or powdered pellet required grow antiferromagnetic domain annealing. new element (edge) specific...

Magnetic circular x-ray dichroism experiments at the ${\mathit{M}}_{4,5}$ absorption edges of cerium in intermetallic compounds CeCuSi, ${\mathrm{CeRh}}_{3}$${\mathrm{B}}_{2}$, and ${\mathrm{CeFe}}_{2}$ are reported. By applying general sum rules, it is shown that these able to yield both magnitude direction 4f magnetic moment on Ce. An estimation orbital contribution those moments given. Our demonstrate existence a Ce confirm extreme sensitivity degree localization electrons. This...

Magnetic X-ray dichroism (MXD) experiments have been performed on several REFe2 Laves phases compounds (RE: Ce, Gd, Lu), both at the K edge of iron and LIII edges rare-earth elements. In all large spin-dependent absorption effects are observed, below Curie temperatures, rare earth. case CeFe2 MXD signal observed Ce follows same temperature dependence as bulk magnetization confirms that an ordered magnetic moment develops sites in this mixed-valence compound. A special attention is given to...

The angular dependence (x-ray linear dichroism) of the $\text{Cr}\text{ }K$ pre-edge in ${\text{MgAl}}_{2}{\text{O}}_{4}:{\text{Cr}}^{3+}$ spinel is measured by means x-ray absorption near-edge structure spectroscopy and compared to calculations based on density functional theory (DFT) ligand field multiplet (LFM) theory. We also present an efficient method, symmetry considerations, compute dichroism cubic crystal starting from a single substitutional site. DFT shows that electric dipole...

After a review of temperature-dependent experimental x-ray absorption near-edge structure (XANES) and related theoretical developments, we present the Al K-edge XANES spectra corundum beryl for temperature ranging from 300K to 930K. These results provide first evidence role thermal fluctuation in at especially pre-edge region. The study is carried out by polarized measurements single crystals. For any orientation sample with respect beam, peak grows shifts lower energy temperature. In...

The influence of atomic vibrations on x-ray absorption near edge structure (XANES) is calculated by assuming that vibrational energies are small with respect to the instrumental resolution. resulting expression shows that, at K-edge, enable electric dipole transitions 3s and 3d final states. theory applied K-edge Al in Al2O3 corundum Ti TiO2 rutile compared experiment. At sizeable towards states obtained, leading a clear improvement agreement experimental spectra. explain temperature...