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@PHDTHESIS{Gehlmann:849597,
      author       = {Gehlmann, Mathias},
      title        = {{T}he electronic structure of transition metal
                      dichalcogenides investigated by angle-resolved photoemission
                      spectroscopy},
      volume       = {170},
      school       = {Universität Duisburg},
      type         = {Dr.},
      address      = {Jülich},
      publisher    = {Forschungszentrum Jülich GmbH Zentralbibliothek, Verlag},
      reportid     = {FZJ-2018-03776},
      isbn         = {978-3-95806-324-2},
      series       = {Schriften des Forschungszentrums Jülich. Reihe
                      Schlüsseltechnologien / Key Technologies},
      pages        = {II, 108, 1-XVIII S.},
      year         = {2018},
      note         = {Universität Duisburg, Diss., 2018},
      abstract     = {Van der Waals (vdW) materials offer a perspective to
                      revolutionize basically every facet of nowadays technology
                      with a new generation of atomically thin devices. Transition
                      metal dichalcogenides (TMDCs) are a family of vdW crystals,
                      that includes several semiconducting materials with band
                      gaps within the optical range. This makes them ideal for
                      numerous applications such as transistors, optical sensors,
                      solar cells, and LEDs. In this study we focuses on two
                      members of the TMDC family: molybdenum disufide (MoS$_{2}$)
                      and rhenium disulfide (ReS$_{2}$). Using a combination of
                      angle-resolved photoemission spectroscopy (APRES) with
                      density functional theory (DFT), we provide a thorough
                      analysis of the electronic band structure of these two
                      exceptional materials. In monolayers of MoS$_{2}$ the
                      combination of broken inversion symmetry with the heavy
                      element molybdenum leads to a large spin-splitting of
                      distinct valleys within its electronic structure. Therefore,
                      MoS$_{2}$ combines the essential ingredients for socalled
                      $\textit{spintronics}$ and $\textit{valleytronics}$. It was
                      generally believed that these fascinating features are
                      forbidden in MoS$_{2}$ bulk crystals due to their
                      centrosymmetric space group. This study demonstrates that
                      the strong confinement of the valleys within the vdW layers
                      leads to a recently discovered type of $\textit{hidden
                      spin-polarization}$, which results in quasi two-dimensional,
                      highly spin-polarized states in this centrosymmetricbulk
                      crystal. Furthermore, we present the first ARPES study of
                      ReS$_{2}$ bulk, monolayer, and bilayer crystals. Recent
                      literature reported indications for a total confinement of
                      the bulk electronic structure within the plains of the vdW
                      layers. Our study comes to the opposite conclusion. Based on
                      the observation of a considerable out-of-plane dispersion in
                      the ARPES experiments, as well as in the band structure
                      calculations, we show that valence electrons are
                      significantly delocalized across the vdW gap. In addition,
                      we identify the valence band maximum of bulk, monolayer, and
                      bilayer ReS$_{2}$ experimentally. The combination of ARPES
                      and band structure calculations shows that ReS$_{2}$
                      undergoes a transition from a direct band gap in the bulk
                      and bilayer to an indirect gap in the monolayer.},
      cin          = {PGI-6},
      cid          = {I:(DE-Juel1)PGI-6-20110106},
      pnm          = {899 - ohne Topic (POF3-899)},
      pid          = {G:(DE-HGF)POF3-899},
      typ          = {PUB:(DE-HGF)3 / PUB:(DE-HGF)11},
      url          = {https://juser.fz-juelich.de/record/849597},
}