k-SPACE VIDEOS

Hard X-ray photoelectron diffraction of graphite (Ekin = 2572 to 7015 eV)

Source: O. Fedchenko, A. Winkelmann, K. Medjanik, S. Babenkov, D. Vasilyev, S. Chernov, C. Schlueter, A. Gloskovskii, Yu. Matveyev, W. Drube, B. Schönhense, H. J. Elmers and G. Schönhense, High-resolution hard-X-ray Photoelectron Diffraction in a Momentum Microscope - the Model Case of Graphite; New J. of Phys. 21, 113031 (2019)

  1. Sequence of hXPD diffractograms for photoelectrons from the carbon 1s core level of graphite for final-state energies between 2572 and 7015 eV (photon energies: 2.8 to 7.3 keV). Measurements (top) performed at beamline P22 of PETRA III at DESY (Hamburg). k-field of view 14 Å-1; width of central Kikuchi band |g110| =2π/1.228 Å=5.1166 Å-1: k-resolution 0.025 Å-1 (angular resolution 0.03°). Acquisition time 20 min. per energy. Calculation (bottom) employed the Bloch-wave approach to photoelectron diffraction with 3800 Fourier components (reciprocal lattice vectors) with 70 “strong reflections” selected for exact matrix diagonalization of the Schrödinger equation at each k-vector of observation. Inelastic mean free path 9 nm at all energies, Debye–Waller parameter B = 0.2 Å2.

 

Valence-band photoelectron diffraction using Soft X-rays at PETRA III, beamline P04

Source: G. Schönhense, K. Medjanik, S. Babenkov, D. Vasilyev, M. Ellguth, O. Fedchenko, S. Chernov, B. Schönhense and H.-J. Elmers, Momentum-Transfer Model of Valence-Band Photoelectron Diffraction, Comms. Phys. 3, 45 (2020)

  1. Momentum distribution (kx-ky) for Mo(110) as function of the binding energy at a photon energy of 1700 eV. The 3D data array I(EB,kx,ky) has been recorded at beamline P04 of PETRA III, DESY, Hamburg. Exposure time was ∼ 30 min. [link]

  1. Momentum kx versus binding energy EB as function of ky for Mo(110) at a photon energy of 1700 eV. The 3D data array I(EB,kx,ky) has been recorded at beamline P04 of PETRA III, DESY, Hamburg. Exposure time was ∼ 30 min [link]

  1. Momentum distribution (kx-ky) for Mo(110) as function of the binding energy
    (from EF until 6eV) at photon energies of 400 eV, 420 eV and 440 eV (from left to right).
    Some coincident core level signals are weakly visible at some energies. The 3D data arrays
    I(EB,kx,ky) have been recorded at beamline P04 of PETRA III, DESY, Hamburg. Exposure time
    was ∼ 20 min per energy. [link]

  1. Momentum kx versus binding energy EB as function of ky for Mo(110) at photon
    energies of 400 eV, 420 eV and 440 eV (from left to right). Some coincident core level signals
    are weakly 2 visible as sharp horizontal stripes. The 3D data arrays I(EB,kx,ky) have been
    recorded at beamline P04 of PETRA III, DESY, Hamburg. Exposure time was ∼ 20 min per
    energy. [link]

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  1. Momentum ky versus binding energy EB as function of kx for Mo(110) at photon
    energies of 400 eV, 420 eV and 440 eV (from left to right). Some coincident core level signals
    are weakly visible as sharp horizontal stripes. The 3D data arrays I(EB,kx,ky) have been
    recorded at beamline P04 of PETRA III, DESY, Hamburg. Exposure time was ∼ 20 min per
    energy. [link]

 

Result of space-charge correction algorithm in Fermi-surface imaging

Source: B. Schönhense, K. Medjanik, O. Fedchenko, S. Chernov, M. Ellguth, D. Vasilyev, A. Oelsner, J. Viefhaus, D. Kutnyakhov, W. Wurth, H. J. Elmers and G. Schönhense,  Multidimensional Photoemission Spectroscopy – the Space-Charge Limit, New J. of Physics 20, 033004 (2018)

Comparison of the tungsten Fermi surface as measured, with (left) and without (right) space-charge correction. There are prominent features (e.g. some of the isolated hole pockets at the N-points) missing in the uncorrected surface. More info here

Four-dimensional representation of the circular dichroism in the angular distribution (CDAD) in bulk photoemission in the soft X-ray range

Source: O. Fedchenko, K. Medjanik, S. Chernov, D. Kutnyakhov, M. Ellguth, A. Oelsner, B. Schönhense, T. Peixoto, P. Lutz, C.-H. Min, F. Reinert, S. Däster, Y. Acremann, J. Viefhaus, W. Wurth, J. Braun, J. Minár, H. Ebert, H. J. Elmers and G. Schönhense,  4D texture of circular dichroism in soft-x-ray photoemission from tungsten, New J. of Phys. 21, 013017 (2019)

  1. Spatial Visualization of the CDAD asymmetry in 4D (EB,k) parameter space. The time encodes the binding energy EB. Red and blue quantify positive and negative CDAD asymmetry.

  1. Spatial view of the Fermi surface, decorated with the CDAD asymmetry. Red and blue quantify positive and negative CDAD asymmetry.

  1. Spatial view of the energy isosurface at binding energy 1.5 eV, decorated with the CDAD asymmetry. Red and blue quantify positive and negative CDAD asymmetry.

  1. Spatial view of the energy isosurface at binding energy 2 eV, decorated with the CDAD asymmetry. Red and blue quantify positive and negative CDAD asymmetry.    

  1. kz momentum scan of the intensity of the Fermi surface (left) and corresponding CDAD asymmetry (right). Red and blue denote positive and negative CDAD asymmetry. The kz-coordinate is quantified in multiples of the reciprocal lattice vector G110.

  1. kz momentum scan of the intensity of the energy isosurface at binding energy 1.5 eV (left) and corresponding CDAD asymmetry (right). Red and blue denote positive and negative CDAD asymmetry. The kz-coordinate is quantified in multiples of the reciprocal lattice vector G110.

 

Measurement of the Fermi surface of Rhenium

Source: K. MedjanikS. V. BabenkovS. ChernovD. VasilyevB. SchönhenseC. SchlueterA. GloskovskiiY. MatveyevW. DrubeH. J. Elmers and G. Schönhense, Progress in HAXPES performance combining full-field k-imaging with time-of-flight recording, J. Synchrotron Rad. (2019). 261996-2012

 

  1. Fermi surface of Rhenium, measured using soft X-rays at beamline P04 of PETRA III at DESY, Hamburg. The corresponding 3D data arrays I(EB,kx,ky) have been recorded at 20 different photon energies. Exposure time was 30 min per energy.

  1. kz –scan of the Fermi surface of Rhenium, measured using soft X-rays at beamline P04 of PETRA III at DESY, Hamburg.

  1. Momentum ky versus binding energy EB (Gamma-M direction) as function of kx for Re (0001) at a photon energy of 731 eV. The corresponding 3D data arrays I(EB,kx,ky) have been recorded at beamline P04 of PETRA III, DESY, Hamburg. Exposure time was ∼ 30 min.

 

Spin- and momentum-resolved electronic structure analysis of Heusler compounds

Source: S. Chernov, C. Lidig, O. Fedchenko, K. Medjanik, S. Babenkov, D. Vasilyev, M. Jourdan, G. Schönhense and H. J. Elmers, Band structure tuning of Heusler compounds revisited: Spin- and momentum-resolved electronic structure analysis of compounds with different band filling, arXiv 1910.05205 (2019) and submitted

 

  1. Momentum distribution (kx-ky) of intensity (right) and spin polarization (left) as function of binding energy for the non-half-metallic ferromagnet Co2MnGa. Data recorded with linearly s-polarized excitation at a photon energy of 6.05 eV. Data have been recorded using an 80 MHz Ti:sapphire laser oscillator with two frequency-doubling stages. The two 3D data arrays with opposite magnetizations (up and down) are the raw data as measured in DLD2. The spin polarization (left panel) is derived voxel-by-voxel as P (EB,kx,ky) = [Iup(EB,kx,ky) - Idown(EB,kx,ky)] / S [Iup(EB,kx,ky) + Idown(EB,kx,ky)]; S is the Sherman function. Total exposure time was 20 min.

  1. Momentum – vs – binding energy section (kx -EB) of intensity (left) and spin polarization (right) as function of ky for the non-half-metallic ferromagnet Co2MnGa recorded with linearly s-polarized excitation at a photon energy of 6.05 eV. Total exposure time was 20 min.

  1. Momentum – vs – binding energy section (ky -EB) of intensity (left) and spin polarization (right) as function of kx for the non-half-metallic ferromagnet Co2MnGa recorded with linearly s-polarized excitation at a photon energy of 6.05 eV. Total exposure time was 20 min.

  1. Momentum distribution (kx-ky) of intensity (right) and spin polarization (left) as function of binding energy for the half-metallic ferromagnet Co2Fe0.4Mn0.6Si. Data are recorded with linearly s-polarized excitation at a photon energy of 6.05 eV. Two 3D data arrays with opposite magnetizations have been recorded. The intensity array is the sum of the two arrays. In order to enhance visibility of the band features the contrast is enhanced and the intensity is normalized by the brightest pixel in each energy slice. This exaggerates the intensity at the upper and lower end of the data array. Total exposure time was 20 min.