X-ray fluorescence spectra of metals excited below threshold

X-ray scattering spectra of Cu and Ni metals have been measured using monochromatic synchrotron radiation tuned from far above to more than 10 eV below threshold. Energy conservation in the scattering process is found to be sufficient to explain the modulation of the spectral shape, neglecting momentum conservation and channel interference. At excitation energies close to and above threshold, the emission spectra map the occupied local partial density of states. For the sub-threshold excitations, the high-energy flank of the inelastic scattering exhibits a Raman-type linear dispersion, and an asymmetric low energy tail develops. For excitation far below threshold the emission spectra are proportional to a convolution of the occupied and unoccuppied local partial densities of states.Comment: 10 pages, 3 figures, http://link.aps.org/doi/10.1103/PhysRevB.68.04511

State dependent fluorescence yields through the core valence Coulomb exchange parameter

Total and partial fluorescence yield PFY L edge x ray absorption spectra differ from the transmission x ray absorption spectra XAS through state dependent fluorescence yield across the XAS. For 3d1 to 3d9 in octahedral symmetry we apply simulations of PFY and XAS and show how the atomic 2p3d Coulomb exchange parameter Gpd governs the differences in the L3 L2 L3 branching ratio between PFY and XAS. Gpd orders the XAS final states following Hund s rules creating a strong state dependent fluorescence decay strength variation across the XAS leading to the differences between PFY and XA

Laser pump X ray probe experiments with electrons ejected from a Cu 111 target space charge acceleration

A comprehensive investigation of the emission characteristics for electrons induced by X rays of a few hundred eV at grazing incidence angles on an atomically clean Cu 111 sample during laser excitation is presented. Electron energy spectra due to intense infrared laser irradiation are investigated at the BESSY II slicing facility. Furthermore, the influence of the corresponding high degree of target excitation high peak current of photoemission on the properties of Auger and photoelectrons liberated by a probe X ray beam is investigated in time resolved pump and probe measurements. Strong electron energy shifts have been found and assigned to space charge acceleration. The variation of the shift with laser power and electron energy is investigated and discussed on the basis of experimental as well as new theoretical result

Time and Angle Resolved Time of Flight Electron Spectroscopy for Functional Materials Science

Electron spectroscopy with the unprecedented transmission of angle resolved time of flight detection, in combination with pulsed X ray sources, brings new impetus to functional materials science. We showcase recent developments towards chemical sensitivity from electron spectroscopy for chemical analysis and structural information from photoelectron diffraction using the phase transition properties of 1T TaS2. Our development platform is the SurfaceDynamics instrument located at the Femtoslicing facility at BESSY II, where femtosecond and picosecond X ray pulses can be generated and extracted. The scientific potential is put into perspective to the current rapidly developing pulsed X ray source capabilities from Lasers and Free Electron Laser

Thresholding of the Elliott Yafet spin flip scattering in multi sublattice magnets by the respective exchange energies

How different microscopic mechanisms of ultrafast spin dynamics coexist and interplay is not only relevant for the development of spintronics but also for the thorough description of physical systems out of equilibrium. In pure crystalline ferromagnets, one of the main microscopic mechanism of spin relaxation is the electron phonon el ph driven spin flip, or Elliott Yafet, scattering. Unexpectedly, recent experiments with ferro and ferrimagnetic alloys have shown different dynamics for the different sublattices. These distinct sublattice dynamics are contradictory to the Elliott Yafet scenario. In order to rationalize this discrepancy, it has been proposed that the intra and intersublattice exchange interaction energies must be considered in the microscopic demagnetization mechanism, too. Here, using a temperature dependent x ray emission spectroscopy XES method, we address experimentally the element specific el ph angular momentum transfer rates, responsible for the spin flips in the respective sub lattices of Fe20Ni80, Fe50Ni50 and pure nickel single crystals. We establish how the deduced rate evolution with the temperature is linked to the exchange coupling constants reported for different alloy stoichiometries and how sublattice exchange energies threshold the related el ph spin flip channels. Thus, these results evidence that the Elliott Yafet spin flip scattering, thresholded by sublattice exchange energies, is the relevant microscopic process to describe sublattice dynamics in alloys and elemental magnetic system

The degree of electron itinerancy and shell closing in the core ionized state of transition metals probed by Auger photoelectron coincidence spectroscopy

Auger photoelectron coincidence spectroscopy APECS has been used to examine the electron correlation and itinerance effects in transition metals Cu, Ni and Co. It is shown that the LVV Auger, in coincidence with 2p photoelectrons, spectra can be represented using atomic multiplet positions if the 3d shell is localized atomic like and with a self convoluted valence band for band like itinerant materials as explained using the Cini Sawatzky model. For transition metals, the 3d band changes from band like to localized with increasing atomic number, with the possibility of a mixed behavior. Our result shows that the LVV spectra of Cu can be represented by atomic multiplet calculations, those of Co resemble the self convolution of the valence band and those of Ni are a mixture of both, consistent with the Cini Sawatzky mode

Resonant Auger spectroscopy at the L2,3 shake-up thresholds as a probe of electron correlation effects in nickel

The excitation energy dependence of the three-hole satellites in the L3-M4,5M4,5 and L2-M4,5M4,5 Auger spectra of nickel metal has been measured using synchrotron radiation. The satellite behavior in the non-radiative emission spectra at the L3 and L2 thresholds is compared and the influence of the Coster-Kronig channel explored. The three-hole satellite intensity at the L3 Auger emission line reveals a peak structure at 5 eV above the L3 threshold attributed to resonant processes at the 2p53d9 shake-up threshold. This is discussed in connection with the 6-eV feature in the x-ray absorption spectrum.Comment: 8 pages, 4 figures; http://prb.aps.org/abstract/PRB/v58/i7/p3677_