Home > Publications database > Electrical anisotropy and shear-resistant topology in the quasi one-dimensional van-der-Waals material α-Bi$_{4}$Br$_{4}$ > print

001     1048443
005     20251125202202.0
024 7 _ |a 10.18154/RWTH-2025-06556
|2 doi
037 _ _ |a FZJ-2025-04649
041 _ _ |a English
100 1 _ |a Hofmann, Jonathan Karl
|0 P:(DE-Juel1)192445
|b 0
|u fzj
245 _ _ |a Electrical anisotropy and shear-resistant topology in the quasi one-dimensional van-der-Waals material α-Bi$_{4}$Br$_{4}$
|f - 2025-03-10
260 _ _ |c 2025
|b RWTH Aachen University
300 _ _ |a pages 1 Online-Ressource : Illustrationen
336 7 _ |a Output Types/Dissertation
|2 DataCite
336 7 _ |a DISSERTATION
|2 ORCID
336 7 _ |a PHDTHESIS
|2 BibTeX
336 7 _ |a Thesis
|0 2
|2 EndNote
336 7 _ |a Dissertation / PhD Thesis
|b phd
|m phd
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|s 1764067691_23058
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336 7 _ |a doctoralThesis
|2 DRIVER
502 _ _ |a Dissertation, RWTH Aachen, 2025
|c RWTH Aachen
|b Dissertation
|d 2025
520 _ _ |a The quasi-one-dimensional van-der-Waals material α-Bi4Br4 crystallizes in a monoclinic crystal structure consisting of covalently bonded Bi4Br4 chains parallel to the lattice vector b. The van-der-Waals interaction connects these chains to form 2D layers. These layers are then stacked in c-direction. α-Bi4Br4 features AB stacking. In contrast to well-known van-der-Waals materials such as WTe2 or MoS2, α-Bi4Br4 features two van-der-Waals gaps. A monolayer of α-Bi4Br4 is a quantum spin Hall insulator. α-Bi4Br4 bulk crystals readily cleaves to expose the (001) surface. Furthermore, flakes of α-Bi4Br4 showing the same surface can be prepared by mechanical exfoliation. Electrical transport measurements are preformed using a four-tip scanning tunnelling microscope (STM) to investigate the anisotropy of the resistivity of α-Bi4Br4. A four-tip STM integrates four individual STMs into a tight unit, to enable transport measurements on surfaces. The piezo drives of the individual STMs allow flexible tip configurations to be set up as needed for a transport measurement. Furthermore, a four-tip STM still can image the surface by scanning a single tip and perform scanning tunnelling microscopy. Due to the small resistances measured here, the exact calibration of the voltage measurement in the four-tip STM became a major issue for the measurement. This calibration is therefore addressed in chapter 3. Chapter 5 presents a modified surface structure of the α-Bi4Br4(001) surface. Atomically resolved STM images show that the parallel Bi4Br4 chains exhibit a mutual shift different from the one expected for this surface. Density functional theory calculations by Mingqian Zheng and Jin-Jian Zhou indicate that a monolayer of this new structure is also a quantum spin Hall insulator. The modified structure arises due to shear stress which is able to shift the parallel chains with respect to each other because neighbouring chains are only connected by weak van-der-Waals forces. Two different methods to disentangle the resistivity tensor ρ of α-Bi4Br4 are implemented: In chapter 6, the in-plane anisotropy is first measured on the (001) surface of a bulk α-Bi4Br4 crystal. For this, two measurements of the resistance in a square tip configuration are used. Then, the value of resistivity in b-direction is determined using a distance-dependent measurement on a thin flake. Assuming that the influence of the off-diagonal element of the resistivity tensor can be neglected, an in-plane anisotropy of A= ρ_{a} / ρ_{b} = 6.4(5) is obtained at room temperature. Furthermore, the anisotropy normal to the ab plane is found to be A_{z} = ρ_{z} / ρ_{b} = 1300. Thus, the resistivity in b-direction, parallel to the chains, is the smallest, as expected from the crystal structure. At 77 K, A = 5.0(3) and A_{z} = 6500 were measured. Chapter 7 demonstrates an alternative approach to disentangle the three elements on the main diagonal of the resistivity tensor ρ when the off-diagonal element is neglected. Here, the tips are positioned in the corners of a large, rectangular flake. The anisotropy can then be obtained by the Bierwagen-Simon method. While it is possible to demonstrate the disentanglement of the three components of the resistivity tensor, the in-plane anisotropy A measured with the second method was substantially smaller than the result obtained before. The origin of this discrepancy is traced back to imperfections of the flake.
536 _ _ |a 5213 - Quantum Nanoscience (POF4-521)
|0 G:(DE-HGF)POF4-5213
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|f POF IV
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588 _ _ |a Dataset connected to DataCite
650 _ 7 |a Hochschulschrift
|2 Other
650 _ 7 |a Rastertunnelmikroskopie ; scanning tunneling microscopy ; Vierspitzen-Rastertunnelmikroskopie ; four-tip scanning tunneling microscopy ; Ladungstransport ; charge transport ; topologische Isolatoren ; topological insulators ; quasi-one-dimensional crystals ; quasi-eindimensionale Kristalle ; higher-order topological insulators ; Anisotropie ; anisotropy ; Resistivitätstensor ; resistivity tensor
|2 Other
700 1 _ |a Voigtländer, Bert
|0 P:(DE-Juel1)128794
|b 1
|e Supervisor
|u fzj
700 1 _ |a Morgenstern, Markus
|0 P:(DE-HGF)0
|b 2
|e Supervisor
773 _ _ |a 10.18154/RWTH-2025-06556
856 4 _ |u https://publications.rwth-aachen.de/record/1015733
909 C O |o oai:juser.fz-juelich.de:1048443
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914 1 _ |y 2025
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980 _ _ |a phd
980 _ _ |a VDB
980 _ _ |a I:(DE-Juel1)PGI-3-20110106
980 _ _ |a UNRESTRICTED

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