摘要:

After a short discussion of all conventional core level spectroscopies within the single particle model, the effects of the coupling of the core and valence wave function on the x-ray emission spectral shapes is discussed. It will be shown that these so-called multiplet effects strongly affect all x-ray emission spectra taken around the metal 2p resonances. In case of 1s resonances, valence band x-ray emission is not affected, but the spectral shapes of 1s2p and 1s3p x-ray emission can only be sensibly described with the inclusion of multiplets. A special example is the resonant excitation into the pre-edge region, which gives rise to a quadrupole resonance. ©2000 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1303828

出版商:AIP    

年代:1900

数据来源: AIP

摘要:

Theoretical investigation is made for the polarization dependence of resonant X-ray emission spectroscopy (RXES) ofTiO2.InTi&hthinsp;2p→3d→2p&hthinsp;RXES,a dramatic resonant enhancement of a 13 eV inelastic peak is predicted withTiO6cluster model, when the incident photon energy is tuned to a satellite of theTi&hthinsp;2p&hthinsp;XAS.A strong polarization dependence of this RXES is shown in the calculation, and confirmed by recent experimental observations. These results suggest strongly that the satellite of theTi&hthinsp;2p&hthinsp;XASoriginates from the excitation to the anti-bonding state between theTi&hthinsp;3dandO&hthinsp;2pstates due to the covalency hybridization, i.e., it is the charge transfer satellite. ©2000 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1303829

出版商:AIP    

年代:1900

数据来源: AIP

摘要:

Resonant scattering experiments at the iron K edge of the (002) and (006) forbidden reflections in magnetite are shown and discussed. The energy dependence of the intensity of these reflections, their dependence on the azimuthal angle and the polarization analysis are given. Experiments have been performed at room temperature and at low temperatures, below the Verwey transition. An identical behavior has been observed at high and at low temperatures, showing that the same kind of local anisotropy is present in the two phases. This experiment demonstrates the absence of either charge fluctuation between octahedral atoms in the metallic phase, or charge ordering in the insulating phase. ©2000 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1303830

出版商:AIP    

年代:1900

数据来源: AIP

摘要:

The experimental evidence for orbital ordering (OO) inLaMnO3is critically reexamined in the light of realistic calculations based on finite difference method (FDM) for the resonant x-ray scattered intensity at a forbidden reflection. After some introduction on the way of calculation, it is shown that the main contribution to the scattered intensity is not due to orbital ordering but to the Jahn-Teller distortion. It is concluded that the dipole resonant x-ray diffraction at the Mn K-edge is not a suitable technique for thedirectobservation of the orbital ordering in the considered compounds. A short glance on theFe3O4compound is also given demonstrating a mixed dipolar-quadrupolar contribution in the anomalous signal. ©2000 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1303831

出版商:AIP    

年代:1900

数据来源: AIP

摘要:

We reexamine the ground state properties of the Antiferromagnetic Insulating Phase ofV2O3in the light of the recent experimental observations by L. Paolasini &etal; [1] based on Resonant X-ray Scattering at the V K-edge and non-resonant magnetic scattering. We propose a model capable of reconciling their finding that the V atoms are in anS=1state with the concomitant evidence of an Orbital Ordering of the magnetic electrons. Realistic calculations for the response function of the non-magnetic resonant scattering based on the3dcharge distribution suggested by the model show an amazingly good agreement with the energy and azimuthal scans presented in ref. [1] Its relevance to the physics of the low-temperature (150 K) metal-insulator transition is also briefly discussed in the light of the inelastic neutron scattering data. ©2000 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1303832

出版商:AIP    

年代:1900

数据来源: AIP

摘要:

Quantum Monte-Carlo calculations for the ground state are well established, and a few work exists already on excited states. For the purpose of band structure investigations with angle resolved photoemission further development with respect to excitation and transport is still necessary on a Monte-Carlo basis to take full advantage of its many-body capacity and to generalize the one-step model of photoemission. As a surface sensitive technique the method has especially to address to surface systems. ©2000 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1303833

出版商:AIP    

年代:1900

数据来源: AIP

摘要:

Here we report use of angle resolved photoemission (ARPES) in the angle scanning mode to explore the Fermi surface topology of the highTcsuperconductors. We have measured momentum distribution of the spectral weight at the Fermi level ofBi2Sr2CaCu2O8±&dgr;&hthinsp;(Bi2212)superconductor. The measurements were made in two different experimental geometry to take care of the polarization dependence of the transition probability (matrix element effects). We find an asymmetric suppression of spectral weight around (&pgr;, 0) that is a direct indication of coupling of the itinerant carriers with an incommensurate charge density wave (ICDW) or with an ‘orbital wave,’ i.e., stripes, with a wave vectorq(0.4&pgr;,0.4&pgr;).©2000 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1303834

出版商:AIP    

年代:1900

数据来源: AIP

摘要:

Ab initiocalculations of excited state properties of solids have become feasible with a steady increase in computing power. A suitable method for studying excited-state properties of extended systems is the Green function method which requires knowledge of the self-energy operator. A simple and fruitfull approximation to the self-energy beyond the Hartree-Fock approximation that takes into account screening is theGWapproximation (GWA). It has been found to be successful in describing quasiparticle energies in a wide range of systems. Despite its success, there are some theoretical difficulties. The GWA has been found to be inadequate for describing satellite structures and self-consistentGWcalculations tend to worsen the good agreement with experiment. Recent development beyond the GWA to improve the satellite description as well as the self-consistency issue will be discussed. As an application of the GWA we considerYH3.Metal hydrides show a reversible metal-insulator transition in the visible range, making them attractive for optical switch. Density-functional calculations give incorrectly a metallic state unless we assume a complicated structure butGWcalculations suggests thatYH3is a normal insulator. ©2000 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1303835

出版商:AIP    

年代:1900

数据来源: AIP

摘要:

Through an example of recent experimental evidence of spin-charge separation in one dimensional correlated electron systems.Sr2CuO3andSrCuO2,the seemingly natural concept of a ‘hole’ being a single particle is re-considered. It is argued that a hole as a particle should be an exception rather than the norm, contrary to one’s usual perception. This implies that strange phenomena such as spin-charge separation in correlated systems may not be as strange as one may think. ©2000 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1303836

出版商:AIP    

年代:1900

数据来源: AIP

摘要:

All theories of x-ray based spectroscopies are based fundamentally on quantum electrodynamics (QED), which fully describes the interaction between the electromagnetic field and matter. Since there is no exact solution for the many-body QED Hamiltonian, approximations specific for each particular spectroscopy have been developed separately. Thus for Extended X-ray Absorption Fine Structure (EXAFS) a the scattering potential is well approximated by a superposition of individual atomic electron densities. However this can be a bad approximation near absorption edges, where effects of charge transfer and non spherical potentials can be important. In an attempt to develop a general treatment of x-ray spectroscopies, we have developed an all electron, relativistic, self-consistent real space Green’s function (RSGF) code FEFF8, for multiple-scattering calculations of x-ray absorption, emission, diffraction, etc. Simultaneous, auxiliary calculations of the projected density of states (DOS) are also carried out, which permit an interpretation of the spectra in terms of electronic structure. An illustrative example for Cu anomalous x-ray scattering is also presented, which emphasizes the importance of self-consistency for calculations and interpretation of near-edge data. ©2000 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1303837

出版商:AIP    

年代:1900

数据来源: AIP