Published in

American Institute of Physics, Journal of Vacuum Science and Technology A, 2(40), 2022

DOI: 10.1116/6.0001500

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Spin- and time-resolved photoelectron spectroscopy and diffraction studies using time-of-flight momentum microscopes

Journal article published in 2022 by Gerd Schönhense, Hans-Joachim Elmers ORCID
This paper was not found in any repository, but could be made available legally by the author.
This paper was not found in any repository, but could be made available legally by the author.

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Abstract

Momentum microscopy (MM) is a novel way of performing angle-resolved photoelectron spectroscopy (ARPES). Combined with time-of-flight (ToF) energy recording, its high degree of parallelization is advantageous for photon-hungry experiments like ARPES at x-ray energies, spin-resolved and time-resolved ARPES. This article introduces the technique of ToF-MM and illustrates its performance by selected examples obtained in different spectral ranges. In a multidimensional view of the photoemission process, spectral density function ρ(k,EB), spin polarization P(k,EB), and related quantities of circular dichroism in the angular distribution (CDAD) are part of the “complete experiment,” a concept adopted from atomic photoemission. We show examples of spin-resolved valence-band mapping in the UV and VUV, and the soft- and hard-x-ray range. Spin mapping of the Heusler compounds such as Co2MnGa and Co2Fe0.4Mn0.6Si at hν = 6 eV proves that the second compound is a half-metallic ferromagnet. Analysis of the Tamm state on Re(0001) using VUV-excitation reveals a Rashba-type spin texture. Bulk band structure including Fermi surface, Fermi-velocity distribution vF(k,EF), full CDAD texture, and spin signature of W(110) have been derived via tomographic mapping with soft x-rays. Hard x rays enable accessing large k||-regions so that the final-state sphere crosses many Brillouin zones in k-space with different kz’s. At hν = 5.3 keV, this fast 4D mapping mode (at a fixed hν) revealed the temperature dependence of the Fermi surface of the Kondo system YbRh2Si2. Probing the true bulk spin polarization of Fe3O4 at hν = 5 keV proved its half-metallic nature. The emerging method of ToF-MM with fs x-ray pulses from free-electron lasers enables simultaneous valence, core-level, and photoelectron diffraction measurements in the ultrafast regime.