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1. Ziegler, Johannes. Quantum transport in HgTe topological insulator nanostructures.

Degree: PhD, Physik, 2019, Universität Regensburg

In this thesis, a number of transport effects in topological insulator nanostructures are investigated. A novel wet-chemical etching approach enabled the fabrication of high-quality nanostructures from strained HgTe thin films and CdTe/HgTe quantum wells and the investigations of topological boundary states in HgTe-based 2D and 3D topological insulators. Measurements of Hall bars, Aharonov-Bohm rings, antidots superlattices, and nanowires were carried out at dilution refrigerator temperatures. The properties of topological surface states were studied in high-mobility, wet-etched macroscopic Hall bars in large magnetic fields. Distinct Landau levels from bulk holes, topological surface states, and bulk electrons were observed. The high mobilities in wet-etched devices brought coexisting Landau levels from bulk holes and topological surface states to light. In the nanostructures, a number of mesoscopic effects were investigated. The Aharonov-Bohm effect was studied for low and high magnetic fields in a 3D topological insulator ring structure, where the surface states wrap around a torus-shaped insulating bulk. In 2D antidot superlattices in HgTe quantum wells, commensurable oscillations and the interference of quantum spin Hall edge channels was probed. Topological nanowires were probed in in- and out-of-plane magnetic fields, with regard to Aharonov-Bohm conductance oscillations and the quantum Hall effect. Furthermore, the subband-structure of quasi-ballistic topological nanowires was probed via subband-induced oscillations. The topological nature of the surface states could be conclusively proven with the help of a quantitative model. The model is justified by theoretical simulations, which give further insight into the properties of the coherent surface states.

In dieser Arbeit wird eine Reihe von Transporteffekten in topologischen Isolator-Nanostrukturen untersucht. Ein nasschemischer Ätzprozess ermöglicht die Herstellung hochwertiger Nanostrukturen aus verspannten HgTe und CdTe/HgTe-Quantentrögen, sowie die Untersuchung topologischer Oberflächenzuständen in HgTe-basierten 2D- und 3D topologischen Isolatoren. Messungen an Hall-Bars, Aharonov-Bohm-Ringen, Antidot-Übergittern und Nanodrähten wurden in einem Verdünnungskryostat durchgeführt. Die Eigenschaften topologischer Oberflächenzustände wurden in hochbeweglichen, nassgeätzten makroskopischen Hallstäben in großen Magnetfeldern untersucht. Es wurden deutliche Landauniveaus von volumenartigen Lochzuständen, topologischen Oberflächenzuständen und volumenartigen Elektronenzuständen beobachtet. Die hohe Beweglichkeit in nassgeätzten Strukturen brachte überlappende Landauniveaus von lochartigen Volumenzuständen und topologischen Oberflächenzuständen ans Licht. In den Nanostrukturen wurde eine Reihe von mesoskopischen Effekten untersucht. Der Aharonov-Bohm-Effekt wurde für niedrige und hohe Magnetfelder in einer 3D-topologischen Isolatorringstruktur untersucht, bei der die Oberflächenzustände um ein isolierendes, torusförmiges Volumen. In 2D…

Advisors/Committee Members: Weiss, Dieter (advisor).

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APA (6th Edition):

Ziegler, J. (2019). Quantum transport in HgTe topological insulator nanostructures. (Doctoral Dissertation). Universität Regensburg. Retrieved from https://epub.uni-regensburg.de/38428

Chicago Manual of Style (16th Edition):

Ziegler, Johannes. “Quantum transport in HgTe topological insulator nanostructures.” 2019. Doctoral Dissertation, Universität Regensburg. Accessed March 20, 2019. https://epub.uni-regensburg.de/38428.

MLA Handbook (7th Edition):

Ziegler, Johannes. “Quantum transport in HgTe topological insulator nanostructures.” 2019. Web. 20 Mar 2019.

Vancouver:

Ziegler J. Quantum transport in HgTe topological insulator nanostructures. [Internet] [Doctoral dissertation]. Universität Regensburg; 2019. [cited 2019 Mar 20]. Available from: https://epub.uni-regensburg.de/38428.

Council of Science Editors:

Ziegler J. Quantum transport in HgTe topological insulator nanostructures. [Doctoral Dissertation]. Universität Regensburg; 2019. Available from: https://epub.uni-regensburg.de/38428

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