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@PHDTHESIS{Leis:903223,
      author       = {Leis, Arthur},
      title        = {{N}anoscale four-point charge transport measurements in
                      topological insulator thin films},
      volume       = {70},
      school       = {RWTH Aachen},
      type         = {Dissertation},
      address      = {Jülich},
      publisher    = {Forschungszentrum Jülich GmbH Zentralbibliothek, Verlag},
      reportid     = {FZJ-2021-04930},
      isbn         = {978-3-95806-580-2},
      series       = {Schriften des Forschungszentrums Jülich. Reihe Information
                      / Information},
      pages        = {ix, 153 S.},
      year         = {2021},
      note         = {RWTH Aachen, Diss., 2021},
      abstract     = {Topological insulator (TI) materials, with their exotic
                      electronic properties, cause a growing interest in modern
                      solid state physics as promising systems for novel
                      applications. This work presents the measurement and the
                      analysis of characteristic transport properties of
                      topological insulator films on the nanometer scale. The use
                      of a multi-tip scanning tunneling microscope (STM) allows
                      for position-dependent electrical measurements on the
                      surface of the samples. For this purpose, the high degree of
                      versatility of the individual tips is exploited to realize
                      resistance measurements in dedicated configurations, even at
                      the nanoscale. Chapter 2 presents an introduction into the
                      operation principle of the instrument and the
                      position-dependent four-point measurement technique. The
                      fundamental relation between the measured resistance and the
                      conductivity of the underlying system is derived.
                      Furthermore, the outlined technique and its experimental
                      capabilities are demonstrated on the example of a
                      SrTiO$_{3}$ sample, which allows to comprehend the influence
                      of dimensionality on the resistance. In chapter 3, a more
                      sophisticated method of tip positioning based on overlaps of
                      STM scans is presented. Using this method, it is possible to
                      realize four-point measurement configurations on the
                      nanoscale with considerable spatial precision. Chapter 4
                      provides an introduction into the material class of
                      topological insulators, focusing on the origin of the
                      associated characteristic properties. In chapters 5 – 7,
                      nanoscale four-point resistance measurements on thin films
                      of the strong topological insulator
                      (Bi$_{1-x}$Sb$_{x}$)$_{2}$Te$_{3}$, enabled by the
                      demonstrated positioning technique, are presented. Chapter 5
                      is focused on the electrical detection of the intrinsic spin
                      polarization of the surface states of a TI. For this
                      purpose, a ferromagnetic STM tip is used to extract the
                      spin-dependent electrochemical potential of carriers during
                      charge transport. Chapters 6 and 7 are dedicated to the
                      topological phase transition of a 3D TI thin film into a
                      quantum spin Hall (QSH) insulator system with reduced film
                      thickness. In chapter 6, the necessary condition for such a
                      phase transition, namely the interaction of the topological
                      surface states on the two interfaces of the thin film, is
                      studied by means of charge transport. Chapter 7 presents a
                      measurement scheme for helical edge states, which are the
                      sufficient condition for the formation of a QSH phase.
                      [...]},
      cin          = {PGI-3},
      cid          = {I:(DE-Juel1)PGI-3-20110106},
      pnm          = {5213 - Quantum Nanoscience (POF4-521)},
      pid          = {G:(DE-HGF)POF4-5213},
      typ          = {PUB:(DE-HGF)3 / PUB:(DE-HGF)11},
      urn          = {urn:nbn:de:0001-2021122115},
      url          = {https://juser.fz-juelich.de/record/903223},
}