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@PHDTHESIS{Heber:625263,
      author       = {Heber, Michael},
      othercontributors = {Rossnagel, Kai and Kärtner, Franz},
      title        = {{S}tudies on ultrafast dynamics in correlated electron
                      systems with time- and angle-resolved photoemission
                      spectroscopy},
      school       = {University of Hamburg},
      type         = {Dissertation},
      address      = {Hamburg},
      reportid     = {PUBDB-2025-01079},
      pages        = {102},
      year         = {2024},
      note         = {Dissertation, University of Hamburg, 2024},
      abstract     = {Angle-resolved photoemission spectroscopy (ARPES) is a
                      potent technique for studying the electronic band structure
                      of condensed matter. The use of the pump-probe technique
                      extends ARPES into the time domain, allowing the electron
                      dynamics to be observed on an ultrafast timescale. High
                      harmonic generation (HHG) sources and free electron lasers
                      (FELs) generate extreme ultraviolet (EUV) or X-ray pulses
                      that have a temporal width of 100 fs or less. HHG converts
                      optical or infrared laser radiation into the EUV, whereas in
                      the FEL, relativistic electrons emit coherent synchrotron
                      radiation in an alternating magnetic field. The FEL FLASH
                      (Free electron LASer Hamburg) is a high-repetition-rate FEL
                      that extends the photon energy into the soft X-ray range.
                      Electron spectrometers with high detection efficiency are
                      essential because the repetition rate of the pump and probe
                      source frequently constrains time-resolved (tr-)ARPES
                      measurements. Therefore, time-of-flight photoelectron
                      spectrometers with a 3D detection scheme are best suited for
                      this purpose. The tr-ARPES setups, the wide-angle
                      photoelectron spectrometer WESPE and the momentum microscope
                      HEXTOF, are based on the time-of-flight technique and
                      designed for the plane grating beamline PG2 at FLASH. In
                      this thesis I present the time resolved studies on three
                      different quantum materials.Frequently, the momentum
                      microscope is also paired with a HHG source. In the first
                      scientific application of this thesis, a sample of pristine
                      graphene on iridium(111) is investigated to evaluate the
                      potential of this laboratory-based experimental setup. The
                      results demonstrate a sub-100 fs time resolution and a field
                      of view larger than the first Brillouin zone. The
                      multispectral nature of the HHG spectrum enables measurement
                      of kz-dependent ARPES signal which were used to reconstruct
                      a tomogram of the Fermi surface of iridium.The Dirac cone is
                      not a unique feature of Graphene. It also appears as a
                      characteristic feature of the surface state of topological
                      insulators, which were investigated in the second experiment
                      chapter. Despite being insulating in the bulk, topological
                      insulators possess an intriguing conducting topological
                      state at the surface. The topological insulator bismuth
                      selenide (Bi2Se3) was investigated using the HEXTOF setup.
                      Tr-ARPES data was obtained for the topological surface
                      state, and tr-XPS data was obtained for the Bi 4d and Se 3d
                      core levels. Our study aimed to explore the electron
                      dynamics at high pump fluences within the topological
                      surface state, as well as to examine the robustness of the
                      state itself. Even at fluences that result in surface
                      ablation, our experiments have demonstrated that the
                      topological surface state remains intact, and its dynamics
                      maintain their characteristics.The last scientific case in
                      this thesis deals with a heavy fermionic system, where 4f
                      and 5f electrons interact with conduction band electrons,
                      forming quasi-particles in the band structure. Thulium
                      selenide (TmSe) is a heavy fermionic system with mixed
                      valence character on the Tm site. The Tm 4f electrons
                      hybridize with the electrons in the conduction band,
                      resulting in the formation of a heavy fermion multiplet in
                      the PES spectra near the Fermi level. When TmSe is doped
                      with tellurium, the lattice expands, causing a transition
                      from the mixed valence state to a predominantly divalent
                      state. The dynamics of the 3H6 multiplet peak shows a
                      dependence on the Te concentration. In the mixed valence
                      state, a delayed long-lasting dynamic is observed.This
                      thesis not only demonstrates how versatile and powerful
                      tr-ARPES is for the study of condensed/quantum matter in
                      general, but also explicitly shows that recent developments
                      in momentum microscope instrumentation can satisfy a wide
                      range of needs, paving the way to a “one fits
                      all”-design which includes besides time and angle also
                      spin resolution.},
      cin          = {U HH / DOOR ; HAS-User / $XFEL_E2_SXP$},
      cid          = {$I:(DE-H253)U_HH-20120814$ / I:(DE-H253)HAS-User-20120731 /
                      $I:(DE-H253)XFEL_E2_SXP-20240106$},
      pnm          = {6G2 - FLASH (DESY) (POF4-6G2) / 6G3 - PETRA III (DESY)
                      (POF4-6G3) / PHGS, VH-GS-500 - PIER Helmholtz Graduate
                      School $(2015_IFV-VH-GS-500)$},
      pid          = {G:(DE-HGF)POF4-6G2 / G:(DE-HGF)POF4-6G3 /
                      $G:(DE-HGF)2015_IFV-VH-GS-500$},
      experiment   = {EXP:(DE-H253)F-PG2-20150101 / EXP:(DE-H253)P-P04-20150101},
      typ          = {PUB:(DE-HGF)11},
      urn          = {urn:nbn:de:gbv:18-ediss-122082},
      doi          = {10.3204/PUBDB-2025-01079},
      url          = {https://bib-pubdb1.desy.de/record/625263},
}