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@PHDTHESIS{Johnsen:860526,
author = {Johnsen, Tjorven},
othercontributors = {Morgenstern, Markus and Libisch, Florian},
title = {{I}nterplay of quantum {H}all edge states in graphene with
the tip-induced quantum dot and graphene sample fabrication
techniques for advanced scanning tunneling microscopy},
school = {RWTH Aachen University},
type = {Dissertation},
address = {Aachen},
publisher = {RWTH Aachen University},
reportid = {RWTH-2022-11449},
pages = {1 Online-Ressource : Illustrationen, Diagramme},
year = {2022},
note = {Veröffentlicht auf dem Publikationsserver der RWTH Aachen
University 2023; Dissertation, RWTH Aachen University, 2022},
abstract = {The quantum Hall effect (QHE) is in large portion
rationalized by the edge channel (EC) picture in which the
charge transport takes place in stripe like channels along
the edge of the sample. For the adequate parameters, ECs can
run along a pn interface instead of the physical edge of the
sample. Using such a gate-defined pn interface in graphene,
compressible stripes that combined with incompressible
stripes constitute the ECs are studied within this thesis by
scanning tunneling microscopy (STM) and spectroscopy (STS).
To this end, the Landau level (LL) features are investigated
a tan interface of different filling factors for varying
gate voltages. Charging lines (CLs) emerging in the
measurements reveal that a tip-induced quantum dot (QD)
develops below the STM tip. Poisson simulations of the
experimental setting involving the tip, the graphene layer,
and the electrostatic interface are conducted with the
purpose to disentangle the contributions of tip and
interface on the ECs. Together with tight binding (TB)
calculations on the basis of the Poisson simulations, all
experimental features are well understood establishing a
useful method for the investigation of ECs. Flat plateaus of
constant LL energy and about 40nm width close to the pn
interface indicate electrostatic reconstruction of the ECs
into compressible and incompressible stripes due to
screening. Besides branches of LL features evolve at the pn
interface interconnecting neighbouring LLs. Their
explanation depends on the choice of sample and back gate
voltage. If a QD is below the tip, its position with respect
to the tip gets shifted at the pn interface whereby states
at a different position within the QD are probed by the tip.
These states are at different orbital energies within the
QD. Their successive measurement leads to the observed LL
branches. If in contrast no QD exits below the tip, the wave
function of the compressible stripe is directly probed. Its
position and width are influenced by the tip but without
altering the structure of the wave function significantly.
This enables to map the wave function of compressible
stripes of several LLs for a specific choice of parameters.
Likely, the structure of the compressible stripe wave
function also reflects a lateral shift of the two sublattice
components at the interface. Furthermore, various processes
to fabricate graphene samples for combined electrical
transport and STM investigations are described. Two of them
are novelly conceived and integrate a graphite back gate
into the sample structure. A third process employs a
standard dry stacking technique followed by evaporating
contacts through a shadow mask. A sample prepared by this
method is characterized both by STM and transport
measurements displaying interaction induced symmetry
breaking of the LLs and the fractional 1/3 quantum Hall
state yet only in transport. A different sample prepared by
one of the novel methods has little improved quality and a
similar outcome of symmetry broken states in transport
measurements. Linking the STM experiments and sample
fabrication processes, two procedures to locate a STM tip on
a micron-sized graphene sample are presented and both
successfully carried out. The first one relies on the
optical alignment of tip and sample by means of a long
distance microscope. In the second procedure the spatially
varying and externally tunable electrostatic force between
tip and sample measured by a tuning fork sensor guides the
tip to the sample.},
cin = {132310 / 130000},
ddc = {530},
cid = {$I:(DE-82)132310_20140620$ / $I:(DE-82)130000_20140620$},
typ = {PUB:(DE-HGF)11},
doi = {10.18154/RWTH-2022-11449},
url = {https://publications.rwth-aachen.de/record/860526},
}
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