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@PHDTHESIS{Leis:825284,
author = {Leis, Arthur},
othercontributors = {Voigtländer, Bert and Morgenstern, Markus},
title = {{N}anoscale four-point charge transport measurements in
topological insulator thin films},
school = {RWTH Aachen University},
type = {Dissertation},
address = {Aachen},
publisher = {RWTH Aachen University},
reportid = {RWTH-2021-08176},
pages = {1 Online-Ressource : Illustrationen},
year = {2021},
note = {Veröffentlicht auf dem Publikationsserver der RWTH Aachen
University; Dissertation, RWTH Aachen University, 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 SrTiO3
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 (Bi1-xSbx)2Te3, 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. While
a QSH phase is not observed in the investigated
(Bi0.16Sb0.84)2Te3 system, the demonstrated technique
provides a generic method for the detection of topological
phases in transport.},
cin = {134110 / 130000},
ddc = {530},
cid = {$I:(DE-82)134110_20140620$ / $I:(DE-82)130000_20140620$},
typ = {PUB:(DE-HGF)11},
doi = {10.18154/RWTH-2021-08176},
url = {https://publications.rwth-aachen.de/record/825284},
}
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