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@PHDTHESIS{Hagiwara:1014675,
      author       = {Hagiwara, Kenta},
      title        = {{S}pin- and orbital-dependent band structure of
                      unconventional topological semimetals},
      volume       = {270},
      school       = {Univ. Duisburg-Essen},
      type         = {Dissertation},
      address      = {Jülich},
      publisher    = {Forschungszentrum Jülich GmbH Zentralbibliothek, Verlag},
      reportid     = {FZJ-2023-03380},
      isbn         = {978-3-95806-701-1},
      series       = {Schriften des Forschungszentrums Jülich Reihe
                      Schlüsseltechnologien / Key Technologies},
      pages        = {v, 115},
      year         = {2023},
      note         = {Dissertation, Univ. Duisburg-Essen, 2022},
      abstract     = {Topological semimetals host fermion quasiparticles with
                      band crossing points in their bulk electronic structures. In
                      Weyl semimetals, these crossing points are protected by
                      symmetry and topology, forming a Fermi arc at the surface,
                      which connects pairs of these points with opposite chiral
                      charges. Recently, unconventional topological semimetals
                      have emerged with strongly tilted Dirac cones, termed
                      type-II Dirac/Weyl semimetals. Additionally, higher
                      topological charges can be formed in structurally chiral
                      crystals, referred to as chiral topological semimetals. In
                      spite of the emergence of such new materials, the underlying
                      spin texture and its link to topological properties even in
                      conventional topological semimetals have still remained
                      elusive. In this thesis, we studied the type-II Dirac
                      semimetal NiTe2, the type-II Weyl semimetal MoTe2, and the
                      chiral topological semimetal CoSi. Here, when the symmetries
                      of the respective crystal structures are lower, a higher
                      topological charge can be formed. Inversion-symmetric NiTe2
                      leads to a degenerate topological charge C = 0, while broken
                      inversion symmetry in MoTe2 causes the splitting of
                      topological charges with C = ±1. Chiral structured CoSi is
                      characterized by C = ±2. By means of momentum microscopy
                      together with an imaging spin filter, we revealed spin- and
                      orbitaldependent electronic structures in connection with
                      symmetry and topology. For inversion-symmetric materials
                      like NiTe2, a spin polarization of bulk states is not
                      allowed. An observed “hidden” spin polarization of the
                      bulk Dirac cone, however, originates from the top Te atom of
                      a Te-Ni-Te trilayer. This can be understood in a concept
                      where the degenerate Dirac cone in NiTe2 is formed by a
                      superpositionof two Dirac cones with opposite spin
                      polarizations localized at the top and bottom Te atoms of
                      the trilayer. In particular, we found the same scenario for
                      NiTe2 and MoTe2: a pair of Weyl cones with opposite
                      chirality exhibits a reversed spin polarization. Depending
                      on the symmetry of the crystal structure, however, the cones
                      are degenerate in k space for inversion-symmetric NiTe2 and
                      separated for MoTe2 due to broken inversion symmetry. A
                      strong circular dichroism with reversed sign gives a
                      fingerprint of opposite chiral charges of the Weyl points in
                      MoTe2. The sensitivity of the circular dichroism to the
                      chirality of the system can be directly confirmed in the
                      case of CoSi, where the dichroism reverses its sign between
                      chiral crystals of the opposite structural handedness. The
                      circular dichroism further revealed a different orbital
                      texture of bands forming a higher-charge fermion in CoSi,
                      which is attributed to their topology. In this thesis, we
                      established a relationship between the spin and orbital
                      texture, topology, and symmetry. Beyond the three studied
                      materials, the results presented in this thesis
                      significantly contribute to the understanding of
                      unconventional topological semimetals, in general.},
      cin          = {PGI-6},
      cid          = {I:(DE-Juel1)PGI-6-20110106},
      pnm          = {5211 - Topological Matter (POF4-521)},
      pid          = {G:(DE-HGF)POF4-5211},
      typ          = {PUB:(DE-HGF)3 / PUB:(DE-HGF)11},
      doi          = {10.34734/FZJ-2023-03380},
      url          = {https://juser.fz-juelich.de/record/1014675},
}