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@PHDTHESIS{Mller:830200,
      author       = {Müller, Mathias Christian Thomas David},
      title        = {{S}pin-wave excitations and electron-magnonscattering in
                      elementary ferromagnets from $\textit{ab initio}4 many-body
                      perturbation theory},
      volume       = {146},
      school       = {RWTH Aachen},
      type         = {Dr.},
      address      = {Jülich},
      publisher    = {Forschungszentrum Jülich GmbH Zentralbibliothek Verlag},
      reportid     = {FZJ-2017-03774},
      isbn         = {978-3-95806-242-9},
      series       = {Schriften des Forschungszentrums Jülich. Reihe
                      Schlüsseltechnologien / Key Technologies},
      pages        = {VI, 174 S.},
      year         = {2017},
      note         = {RWTH Aachen, Diss., 2017},
      abstract     = {In this thesis, an $\textit{ab initio}$ theoretical
                      framework for the investigation of spin excitations and the
                      electron-magnon scattering is developed within many-body
                      perturbation theory and implemented in the full-potential
                      linearized augmented-plane-wave method. The spin
                      excitations, including single-particle Stoner excitations
                      and collective spin waves, are accessible through the
                      magnetic response function, which is obtained by the
                      solution of a Bethe-Salpeter equation employing four-point
                      functions. These four-point functions are represented in a
                      Wannier-function basis, which allows to exploit the
                      short-range behavior of the screened interaction in metallic
                      systems by truncating the matrices in real space. The spin
                      excitation spectrum of ferromagnetic materials contains an
                      acoustic magnon mode whose energy, in the absence of
                      spin-orbit coupling, vanishes in the long-wavelength limit
                      as a consequence of the spontaneously broken spin-rotation
                      symmetry in these materials according to the Goldstone
                      theorem. However, in numerical realizations of the magnetic
                      response function the acoustic magnon mode exhibits a small
                      but finite gap in the Goldstone-mode limit. We investigate
                      this violation of the Goldstone theorem and present
                      anapproach that implements the magnetic response function
                      employing the properly renormalized Green function instead
                      of the Kohn-Sham one. This much more expensive approach
                      shows a substantial reduction of the gap error. In addition,
                      we discuss a correction scheme motivated by the one-band
                      Hubbard model that cures the fundamental inconsistency of
                      using the Kohn-Sham Green function by adjusting the exchange
                      splitting. We present corrected magnon spectra for the
                      elementary ferromagnets iron, cobalt, and nickel. We then
                      employ the T-matrix approach for the description of the
                      electron-magnon interaction within the GT approximation,
                      which can be combined with the GW approximation without the
                      need of double-counting corrections. The multiple-scattering
                      T matrix is part of the four-point magnetic response
                      function and describes the correlated propagation of
                      electron-hole pairs with opposite spins from which the
                      collective spin excitations arise. We apply the GT
                      approximation to Fe, Co, and Ni and present renormalized
                      spectral functions. The GT approximation leads to a
                      pronounced spin-dependent lifetime broadening of the
                      quasiparticle states to the extent that the quasiparticle
                      character is virtually lost in certain energy regions. In
                      iron, the spectral functions exhibit an additional
                      quasiparticle peak indicating the emergence of a new
                      quasiparticle. We discuss the features of this quasiparticle
                      state that forms out of a superposition of single-particle
                      and magnon excitations. In addition, we find kink structures
                      in the quasiparticle dispersion of free-electron-like bands
                      of cobalt and nickel.},
      cin          = {PGI-1 / IAS-1 / JARA-FIT / JARA-HPC},
      cid          = {I:(DE-Juel1)PGI-1-20110106 / I:(DE-Juel1)IAS-1-20090406 /
                      $I:(DE-82)080009_20140620$ / $I:(DE-82)080012_20140620$},
      pnm          = {142 - Controlling Spin-Based Phenomena (POF3-142) / 143 -
                      Controlling Configuration-Based Phenomena (POF3-143)},
      pid          = {G:(DE-HGF)POF3-142 / G:(DE-HGF)POF3-143},
      typ          = {PUB:(DE-HGF)3 / PUB:(DE-HGF)11},
      url          = {https://juser.fz-juelich.de/record/830200},
}