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Sökning: WFRF:(Weinelt M)

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1.
  • Aaltonen, T., et al. (författare)
  • Combination of Tevatron Searches for the Standard Model Higgs Boson in the W+W- Decay Mode
  • 2010
  • Ingår i: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 104:6, s. 061802-
  • Tidskriftsartikel (refereegranskat)abstract
    • We combine searches by the CDF and D0 Collaborations for a Higgs boson decaying to W+W-. The data correspond to an integrated total luminosity of 4.8 (CDF) and 5.4 (D0) fb(-1) of p (p) over bar collisions at root s = 1.96 TeV at the Fermilab Tevatron collider. No excess is observed above background expectation, and resulting limits on Higgs boson production exclude a standard model Higgs boson in the mass range 162-166 GeV at the 95% C.L.
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2.
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3.
  • Frietsch, B., et al. (författare)
  • Disparate ultrafast dynamics of itinerant and localized magnetic moments in gadolinium metal
  • 2015
  • Ingår i: Nature Communications. - : Springer Science and Business Media LLC. - 2041-1723. ; 6
  • Tidskriftsartikel (refereegranskat)abstract
    • The Heisenberg-Dirac intra-atomic exchange coupling is responsible for the formation of the atomic spin moment and thus the strongest interaction in magnetism. Therefore, it is generally assumed that intra-atomic exchange leads to a quasi-instantaneous aligning process in the magnetic moment dynamics of spins in separate, on-site atomic orbitals. Following ultrashort optical excitation of gadolinium metal, we concurrently record in photoemission the 4f magnetic linear dichroism and 5d exchange splitting. Their dynamics differ by one order of magnitude, with decay constants of 14 versus 0.8 ps, respectively. Spin dynamics simulations based on an orbital-resolved Heisenberg Hamiltonian combined with first-principles calculations explain the particular dynamics of 5d and 4f spin moments well, and corroborate that the 5d exchange splitting traces closely the 5d spin-moment dynamics. Thus gadolinium shows disparate dynamics of the localized 4f and the itinerant 5d spin moments, demonstrating a breakdown of their intra-atomic exchange alignment on a picosecond timescale.
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4.
  • Frietsch, B., et al. (författare)
  • The role of ultrafast magnon generation in the magnetization dynamics of rare-earth metals
  • 2020
  • Ingår i: Science Advances. - : American Association for the Advancement of Science. - 2375-2548. ; 6:39
  • Tidskriftsartikel (refereegranskat)abstract
    • Ultrafast demagnetization of rare-earth metals is distinct from that of 3d ferromagnets, as rare-earth magnetism is dominated by localized 4f electrons that cannot be directly excited by an optical laser pulse. Their demagnetization must involve excitation of magnons, driven either through exchange coupling between the 5d6s-itinerant and 4f-localized electrons or by coupling of 4f spins to lattice excitations. Here, we disentangle the ultrafast dynamics of 5d6s and 4f magnetic moments in terbium metal by time-resolved photoemission spectroscopy. We show that the demagnetization time of the Tb 4f magnetic moments of 400 fs is set by 4f spin-lattice coupling. This is experimentally evidenced by a comparison to ferromagnetic gadolinium and supported by orbital-resolved spin dynamics simulations. Our findings establish coupling of the 4f spins to the lattice via the orbital momentum as an essential mechanism driving magnetization dynamics via ultrafast magnon generation in technically relevant materials with strong magnetic anisotropy.
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5.
  • Öström, Henrik, et al. (författare)
  • Ethylene on Cu(110) and Ni(110) : Electronic structure and bonding derived from x-ray spectroscopy and theory
  • 2004
  • Ingår i: Surface Science. - : Elsevier. - 0039-6028. ; 559:2-3, s. 85-93
  • Tidskriftsartikel (refereegranskat)abstract
    • The bonding of ethylene to Cu(1 1 0) and Ni(1 1 0) is analyzed in detail using symmetry-resolved X-ray absorption (XAS) and emission (XES) spectroscopies in conjunction with density functional theory (DFT) calculations of geometric structure and spectra. XES, which probes the occupied valence states, reveals the formation of bonding and non-bonding orbitals of π-3d as well as π*-3d character. Additional mixing of σ and π states indicates rehybridization upon adsorption. The anti-bonding π-3d and π*-3d combinations are unoccupied and seen in XAS. A lower intensity of the π* transition for Ni is evidence of larger π* occupancy upon bonding. The position of the σ* shape-resonance indicates a 0.02 Å longer C–C bond on Ni than on Cu, in good agreement with the DFT structure optimizations. The XE spectra are well-reproduced both by specific spectrum calculations based on cluster models and by the carbon p-density of states calculated using periodic boundary conditions. The contribution of both π and π* levels to the new, surface-induced occupied states close to the Fermi-level lends support to the traditional Dewar–Chatt–Duncanson picture of the bonding. Theoretical charge-density difference plots support an alternative view of ethylene bonding in terms of the specific involvement of the excited molecular triplet state. Based on the variation in XE intensities the main difference between ethylene bonding to Cu and Ni is found to be an about two times larger occupancy of the π* orbital upon chemisorption on the transition metal, which comes along with C–C bond elongation and stronger σ–π rehybridization.
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6.
  • Hasselstrom, J, et al. (författare)
  • Ammonia adsorbed on Cu(110): An angle resolved x-ray spectroscopic and ab initio study
  • 1999
  • Ingår i: JOURNAL OF CHEMICAL PHYSICS. - : AMER INST PHYSICS. - 0021-9606. ; 110:10, s. 4880-4890
  • Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
    • We present a study of a monolayer of ammonia (NH3) adsorbed on Cu(110) using core level spectroscopies in combination with ab initio calculations based on density functional theory. In particular, x-ray emission spectroscopy has been applied, providing an
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7.
  • Hasselstrom, J, et al. (författare)
  • The adsorption structure of glycine adsorbed on Cu(110); comparison with formate and acetate/Cu(110)
  • 1998
  • Ingår i: SURFACE SCIENCE. - : ELSEVIER SCIENCE BV. - 0039-6028. ; 407:1-3, s. 221-236
  • Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
    • The molecular orientation of an ordered monolayer of glycine adsorbed on Cu(110) has been studied using X-ray Photoelectron Spectroscopy (XPS), Near Edge X-ray Absorption Fine Structure (NEXAFS), X-ray Photoelectron Diffraction (XPD), Low-Energy Electron
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8.
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9.
  • Karis, O., et al. (författare)
  • Observation of short- and long-range hybridization of a buried Cu monolayer in Ni
  • 2000
  • Ingår i: Physical Review B Condensed Matter. - 0163-1829 .- 1095-3795. ; 62:24, s. R16239-R16242
  • Tidskriftsartikel (refereegranskat)abstract
    • The electronic structure of a Cu monolayer buried in Ni fcc(100) is studied by means of x-ray emission and absorption spectroscopies in combination with first principles calculations. The local character of the x-ray probes allows us to investigate changes in the chemical interaction for these ultrathin film systems. In comparison to bulk Cu, the occupied d states of a buried Cu monolayer, as mapped in the x-ray emission spectrum, remain mostly unaltered. The absorption spectrum on the other hand shows that the empty states of the buried Cu monolayer are modified, and instead resemble the unoccupied electronic density of bulk Ni. These findings agree well with our first principle electronic structure calculations and the results are interpreted in terms of short- and long-range hybridization.
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10.
  • Karis, O, et al. (författare)
  • One-step and two-step description of deexcitation processes in weakly interacting systems
  • 1996
  • Ingår i: PHYSICAL REVIEW LETTERS. - : AMER INST PHYSICS. ; 76:8, s. 1380-1383
  • Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
    • The origin of one- and two-step behavior of core-hole decay processes is identified in connection with high resolution autoionization spectra for Ar/Pt(111). The spectra simultaneously show features of the two types (resonant Raman vs Auger-like behavior)
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11.
  • Karis, O, et al. (författare)
  • Probing surface states of Cu/Ni thin films using x-ray absorption spectroscopy
  • 2001
  • Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 63:11
  • Tidskriftsartikel (refereegranskat)abstract
    • Surface and interface properties of Cu thin films (1–4 monolayers) deposited on Ni(100) have been extracted by means of x-ray absorption spectroscopy and analyzed in combination with ab initio density-functional calculations. An unoccupied Cu surface state is identified in an x-ray absorption spectra and studied as a function of film thickness. Experimental data is supported by calculations of the layer-resolved density of states and the results from this combined theoretical-experimental effort show that the surface state is almost entirely located on the atomic layer closest to the vacuum. Our results also indicate strong hybridization between unoccupied states at the Cu/Ni interface boundary.
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12.
  • Karis, O, et al. (författare)
  • The bonding of simple carboxylic acids on Cu(110)
  • 2000
  • Ingår i: JOURNAL OF CHEMICAL PHYSICS. - : AMER INST PHYSICS. - 0021-9606. ; 112:18, s. 8146-8155
  • Tidskriftsartikel (refereegranskat)abstract
    • We present a study of the bonding of formate (HCOO) and acetate (CH3COO) chemisorbed on Cu(110) using core level spectroscopies in combination with theoretical calculations. For the first time, we apply x-ray emission spectroscopy (XES) to these systems.
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13.
  • Magnuson, M., et al. (författare)
  • Angular-dependent resonant-photoemission processes at the 2p thresholds in nickel metal
  • 1999
  • Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 60:4, s. 2436-2440
  • Tidskriftsartikel (refereegranskat)abstract
    • Angle-resolved valence-band resonant-photoemission of nickel metal has been measured close to the 2p core-level thresholds with synchrotron radiation. The well-known 6-eV correlation satellite has an intensity enhancement of about two orders of magnitude at resonance. The angular dependence of the photoemission intensity has been studied as function of photon energy and provides unambiguous evidence for interference effects all the way up to the resonance maximum. The observation of different angular asymmetries, β, for the valence band and the satellite is discussed in connection to the origin of the resonant-photoemission process and the character of the satellite.
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14.
  • Magnuson, Martin, 1965-, et al. (författare)
  • Coherent and Incoherent Processes in resonant Photoemission
  • 1997
  • Ingår i: Advanced Light Source. - California, USA : Ernest Orlando Lawrence Berkeley National Laboratory, University of California Berkeley. ; 65:2, s. 159-167
  • Bokkapitel (populärvet., debatt m.m.)
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16.
  • Martensson, N, et al. (författare)
  • Coherent and incoherent processes in resonant photoemission
  • 1997
  • Ingår i: APPLIED PHYSICS A-MATERIALS SCIENCE & PROCESSING. - 0947-8396. ; 65:2, s. 159-167
  • Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
    • The basis for resonant photoemission is discussed in connection with data for a physisorption system, Ar/Pt(111) and a 3d transition metal, Ni(100). For Ar/Pt(111) the quasi-localized character of the intermediate state leads to two types of features in t
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17.
  • Nilsson, A, et al. (författare)
  • Local probing of the surface chemical bond using X-ray emission spectroscopy
  • 1997
  • Ingår i: APPLIED PHYSICS A-MATERIALS SCIENCE & PROCESSING. - : SPRINGER VERLAG. - 0947-8396. ; 65:2, s. 147-154
  • Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
    • X-ray emission spectroscopy applied to adsorbate systems is shown to reveal new details of the chemical bond formed at surfaces. An atom and symmetry projected view of the bonding orbitals is obtained. We will present recent studies of N-2 and CO on Ni(10
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18.
  • Nyberg, M, et al. (författare)
  • The electronic structure and surface chemistry of glycine adsorbed on Cu(110)
  • 2000
  • Ingår i: JOURNAL OF CHEMICAL PHYSICS. - : AMER INST PHYSICS. - 0021-9606. ; 112:12, s. 5420-5427
  • Tidskriftsartikel (refereegranskat)abstract
    • We present a combined density functional theory and x-ray emission spectroscopy study of the bonding and chemistry of glycine (NH2CH2COOH) chemisorbed on Cu(110). The amino acid deprotonates upon adsorption. The adsorbate exhibits a rich surface chemistry
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19.
  • Triguero, L., et al. (författare)
  • Direct experimental measurement of donation/back-donation in unsaturated hydrocarbon bonding to metals
  • 2000
  • Ingår i: Journal of the American Chemical Society. - : American Chemical Society (ACS). - 0002-7863 .- 1520-5126. ; 122:49, s. 12310-12316
  • Tidskriftsartikel (refereegranskat)abstract
    • Using resonant and off-resonant X-ray emission spectroscopy, in combination with ground-state density functional calculations, we examine the electronic structure of chemisarbed ethylene and benzene on thr Cu(110) surface to investigate the suitability of the donation/back-donation bonding model given by Dewar(1) and Chart and Duncanson(2) (DCD) for the interaction of unsaturated hydrocarbons with metal surfaces. We give an experimental verification of the DCD model and find donation/back-donation to be twice as large for ethylene as for benzene. In particular, the degree of sigma-pi mixing (rehybridization) is found to correspond to the amount of donation/back-donation, which is put in relation to the aromatic and nonaromatic pi characters of benzene and ethylene, respectively.
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20.
  • Weinelt, M, et al. (författare)
  • Electronic structure of benzene on Ni(100) and Cu(110): An x-ray-spectroscopy study
  • 1998
  • Ingår i: PHYSICAL REVIEW B-CONDENSED MATTER. - : AMERICAN PHYSICAL SOC. - 0163-1829. ; 58:11, s. 7351-7360
  • Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
    • The valence electronic structure of benzene chemisorbed on Ni(100) and Cu(110) has been studied using angle-dependent x-ray emission and x-ray absorption spectroscopy. These techniques allow us to resolve the benzene p contributions involved in the chemic
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21.
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22.
  • Weinelt, M., et al. (författare)
  • Resonant Photoemission at the 2p Edges of Ni: Resonant Raman and Interference Effects
  • 1997
  • Ingår i: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 78:5, s. 967-970
  • Tidskriftsartikel (refereegranskat)abstract
    • Unambiguous evidence for resonant photoemission in Ni is presented. Interference effects are identified at the 2p edges for the valence band and the 6 eV satellite. A rapid transition from a resonant Raman to an Auger-like regime shows that the core-excited states above threshold are not localized enough to significantly enhance the photoemission intensity, implying a large fraction of incoherent intensity. The results indicate that the appearance of interference effects does not require strong localization of the intermediate state.
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23.
  • Weinelt, M, et al. (författare)
  • Resonant photoemission at the 2p edges of Ni: Resonant Raman and interference effects
  • 1997
  • Ingår i: PHYSICAL REVIEW LETTERS. - 0031-9007. ; 78:5, s. 967-970
  • Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
    • Unambiguous evidence for resonant photoemission in Ni is presented. Interference effects are identified at the 2p edges for the valence band and the 6 eV satellite. A rapid transition from a resonant Raman to an Auger-like regime shows that the core-excit
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24.
  • Andres, Beatrice, et al. (författare)
  • Strong momentum-dependent electron-magnon renormalization of a surface resonance on iron
  • 2022
  • Ingår i: Applied Physics Letters. - : American Institute of Physics (AIP). - 0003-6951 .- 1077-3118. ; 120:20
  • Tidskriftsartikel (refereegranskat)abstract
    • The coupling of electrons to spin excitations and the generation of magnons is essential for spin mixing in the ultrafast magnetization dynamics of 3d ferromagnets. Although magnon energies are generally much larger than phonon energies, until now their electronic band renormalization effect in 3d ferromagnets suggests a significantly weaker quasiparticle interaction. Using spin- and angle-resolved photoemission, we show an extraordinarily strong renormalization leading to two-branch splitting of an iron surface resonance at ~& nbsp;200 meV. Its strong magnetic linear dichroism unveils the magnetic nature and momentum dependence of the energy renormalization. By determining the frequency- and momentum-dependent self-energy due to generic electron-boson interaction to compute the resultant electron spectral function, we suggest that the surface-state splitting can be described by strong coupling to an optical spin wave in an iron thin film.& nbsp;& nbsp;Published under an exclusive license by AIP Publishing.
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25.
  • Karis, O, et al. (författare)
  • Observation of short- and long-range hybridization of a buried Cu monolayer in Ni
  • 2000
  • Ingår i: PHYSICAL REVIEW B. - 0163-1829. ; 62:24, s. R16239-R16242
  • Tidskriftsartikel (refereegranskat)abstract
    • The electronic structure of a Cu monolayer buried in Ni fcc(100) is studied by means of x-ray emission and absorption spectroscopies in combination with first principles calculations. The local character of the x-ray probes allows us to investigate change
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26.
  • Liu, Bo, et al. (författare)
  • Signature of magnon polarons in electron relaxation on terbium revealed by comparison with gadolinium
  • 2021
  • Ingår i: Physical Review B. - : American Physical Society. - 2469-9950 .- 2469-9969. ; 104:2
  • Tidskriftsartikel (refereegranskat)abstract
    • Magnons and phonons are elementary excitations of spin and lattice systems that can form a hybrid quasi-particle in the presence of strong magnetoelastic coupling. Here we use spin-, angle-, and energy-resolved photoemission spectroscopy to show that magnon-phonon hybridization plays an important role for the relaxation of the electron surface-state in Tb, opening both majority and minority spin channels in electron-phonon scattering. This is attributed to the strong 4f spin-orbit coupling, as evidenced by a comparison of the lifetime broadening in the occupied surface states of Gd and Tb. Both ferromagnetic metals have a comparable valence electronic structure, but the magnetocrystalline anisotropy is much stronger in Tb as compared to Gd. Consequently, in Gd electron-phonon and electron-magnon scatterings lead to spin-dependent photohole relaxation rates. Unlike in Gd, the lifetime broadening of the occupied surface state in Tb is only weakly spin dependent and the mass enhancement parameter lambda is twice the spin-averaged value of Gd. This difference in phase space is explained by the intimate coupling of phonons and magnons to form magnon polarons, which opens both minority and majority spin bands as decay channels.
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27.
  • Nilsson, A, et al. (författare)
  • An atom-specific look at the surface chemical bond
  • 1997
  • Ingår i: PHYSICAL REVIEW LETTERS. - : AMER INST PHYSICS. - 0031-9007. ; 78:14, s. 2847-2850
  • Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
    • High resolution x-ray emission spectroscopy is shown to reveal unprecedented details of the chemical bond formed between a molecule and a transition metal surface. An atom and symmetry projected view of the bonding orbitals is obtained. We find that all o
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28.
  • Thielemann-Kühn, Nele, et al. (författare)
  • Optical control of 4f orbital state in rare-earth metals
  • 2024
  • Ingår i: Science Advances. - : American Association for the Advancement of Science (AAAS). - 2375-2548. ; 10:16
  • Tidskriftsartikel (refereegranskat)abstract
    • A change of orbital state alters the coupling between ions and their surroundings drastically. Orbital excitations are hence key to understand and control interaction of ions. Rare-earth elements with strong magneto-crystalline anisotropy (MCA) are important ingredients for magnetic devices. Thus, control of their localized 4f magnetic moments and anisotropy is one major challenge in ultrafast spin physics. With time-resolved x-ray absorption and resonant inelastic scattering experiments, we show for Tb metal that 4f-electronic excitations out of the ground-state multiplet occur after optical pumping. These excitations are driven by inelastic 5d-4f-electron scattering, altering the 4f-orbital state and consequently the MCA with important implications for magnetization dynamics in 4f-metals and more general for the excitation of localized electronic states in correlated materials.
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29.
  • Triguero, L, et al. (författare)
  • Direct experimental measurement of donation/back-donation in unsaturated hydrocarbon bonding to metals
  • 2000
  • Ingår i: JOURNAL OF THE AMERICAN CHEMICAL SOCIETY. - : AMER CHEMICAL SOC. - 0002-7863. ; 122:49, s. 12310-12316 Language: English
  • Tidskriftsartikel (refereegranskat)abstract
    • Using resonant and off-resonant X-ray emission spectroscopy, in combination with ground-state density functional calculations, we examine the electronic structure of chemisarbed ethylene and benzene on thr Cu(110) surface to investigate the suitability of
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