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Topological and Edge Transport in Two-Dimensional Electron Systems.

Record Type:	Language materials, manuscript : Monograph/item
Title/Author:	Topological and Edge Transport in Two-Dimensional Electron Systems./
Author:	Andersen, Molly Patricia.
Description:	1 online resource (227 pages)
Notes:	Source: Dissertations Abstracts International, Volume: 85-06, Section: A.
Contained By:	Dissertations Abstracts International85-06A.
Subject:	Phase transitions. -
Online resource:	click for full text (PQDT)
ISBN:	9798381020557

Topological and Edge Transport in Two-Dimensional Electron Systems.
Andersen, Molly Patricia.

Topological and Edge Transport in Two-Dimensional Electron Systems. - 1 online resource (227 pages)

Source: Dissertations Abstracts International, Volume: 85-06, Section: A.

Thesis (Ph.D.)--Stanford University, 2023.

Includes bibliographical references

The bulk insulator (Bi, Sb)2Te3(BST) hosts a spin-momentum-locked Dirac cone of electronic states at its two-dimensional surface. This state arises to mediate the topological phase transition that occurs at the surface of this topologically nontrivial material. As such, it is topologically protected against disorder. Introducing magnetism breaks time reversal symmetry at the Dirac point and allows for observation of the quantum anomalous Hall effect, a unique phenomenon characterized by chiral transport, dissipationless longitudinal conduction, and quantized Hall conduction.In Chapter 3, I explore the quantum anomalous Hall effect (QAHE) in Cr-doped BST (Cr-BST). After establishing the basic phenomenology of the QAHE, I illustrate immediately relevant use cases of the QAHE in resistance and current metrology. Next, careful potential profile measurements allow investigation of current flow in the QAHE, where we find evidence that current flows through the bulk of a thin film and not along the one-dimensional edges as has been historically assumed.Although the electronic states in BST and Cr-BST boast remarkably robust topological protection, the materials themselves are relatively disordered and fragile under normal micro- and nano-fabrication processing conditions. In Chapter 4, I review the different types of defects in these materials and their impact on band structures and transport. I additionally demonstrate that electron beam lithography with high (30+ kV) accelerating voltages can damage BST and Cr-BST in an unacceptable manner, but electron beam lithography with a 10 kV accelerating voltage does not result in the same damage.Dissipationless devices with inherent nonreciprocal transport are of great interest in the cryogenic microwave devices community for potential applications in quantum information architectures. In Chapter 5 I discuss efforts to better-understand high frequency transport in Cr-BST with an eye towards high-frequency circulators or gyrators. I begin with quasi-dc measurements of a Hall bar under microwave irradiation, where I identify frequency-dependent dissipative transport, and then proceed to discuss the design and fabrication of high-impedance microwave resonators.Proximitization of a topological insulator by a superconductor is a promising platform for realization of Majorana fermions in a condensed matter platform. In Chapter 6, I discuss materials characterization and electronic transport measurements in Josephson junctions with topological insulator weak links, where the superconducting contact is enabled by a self-formed superconductor. Measurements provide some evidence that Majorana bound states are indeed formed. Additionally inspired by some of these topological Josephson junction measurements, I discuss the design of a Josephson junction with a bilayer graphene weak link. Here, a tunable supercurrent distribution should allow for a controllable asymmetric Josephson e↵ect whereby the critical current magnitude depends on the sign of the current.Finally, in Chapter 7 I discuss measurements of a disordered thin film of MnBi2Te4, a new topological insulator with a rich magnetic phase diagram. Although I did not observe obvious signatures of clean, topologically-determined transport, I did identify universal conductance fluctuations across the entire magnetic phase diagram of MnBi2Te4. Analysis of these universal conductance fluctuations reveals a sensitivity to reconfiguration in the magnetic domain structure of MnBi2Te4, providing a possible transport-based probe of magnetic disorder.

Electronic reproduction.
Ann Arbor, Mich. :
ProQuest,
2024

Mode of access: World Wide Web

ISBN: 9798381020557Subjects--Topical Terms:

1464712
Phase transitions.
Index Terms--Genre/Form:

554714
Electronic books.

Topological and Edge Transport in Two-Dimensional Electron Systems.
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500 $a Source: Dissertations Abstracts International, Volume: 85-06, Section: A.
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502 $a Thesis (Ph.D.)--Stanford University, 2023.
504 $a Includes bibliographical references
520 $a The bulk insulator (Bi, Sb)2Te3(BST) hosts a spin-momentum-locked Dirac cone of electronic states at its two-dimensional surface. This state arises to mediate the topological phase transition that occurs at the surface of this topologically nontrivial material. As such, it is topologically protected against disorder. Introducing magnetism breaks time reversal symmetry at the Dirac point and allows for observation of the quantum anomalous Hall effect, a unique phenomenon characterized by chiral transport, dissipationless longitudinal conduction, and quantized Hall conduction.In Chapter 3, I explore the quantum anomalous Hall effect (QAHE) in Cr-doped BST (Cr-BST). After establishing the basic phenomenology of the QAHE, I illustrate immediately relevant use cases of the QAHE in resistance and current metrology. Next, careful potential profile measurements allow investigation of current flow in the QAHE, where we find evidence that current flows through the bulk of a thin film and not along the one-dimensional edges as has been historically assumed.Although the electronic states in BST and Cr-BST boast remarkably robust topological protection, the materials themselves are relatively disordered and fragile under normal micro- and nano-fabrication processing conditions. In Chapter 4, I review the different types of defects in these materials and their impact on band structures and transport. I additionally demonstrate that electron beam lithography with high (30+ kV) accelerating voltages can damage BST and Cr-BST in an unacceptable manner, but electron beam lithography with a 10 kV accelerating voltage does not result in the same damage.Dissipationless devices with inherent nonreciprocal transport are of great interest in the cryogenic microwave devices community for potential applications in quantum information architectures. In Chapter 5 I discuss efforts to better-understand high frequency transport in Cr-BST with an eye towards high-frequency circulators or gyrators. I begin with quasi-dc measurements of a Hall bar under microwave irradiation, where I identify frequency-dependent dissipative transport, and then proceed to discuss the design and fabrication of high-impedance microwave resonators.Proximitization of a topological insulator by a superconductor is a promising platform for realization of Majorana fermions in a condensed matter platform. In Chapter 6, I discuss materials characterization and electronic transport measurements in Josephson junctions with topological insulator weak links, where the superconducting contact is enabled by a self-formed superconductor. Measurements provide some evidence that Majorana bound states are indeed formed. Additionally inspired by some of these topological Josephson junction measurements, I discuss the design of a Josephson junction with a bilayer graphene weak link. Here, a tunable supercurrent distribution should allow for a controllable asymmetric Josephson e↵ect whereby the critical current magnitude depends on the sign of the current.Finally, in Chapter 7 I discuss measurements of a disordered thin film of MnBi2Te4, a new topological insulator with a rich magnetic phase diagram. Although I did not observe obvious signatures of clean, topologically-determined transport, I did identify universal conductance fluctuations across the entire magnetic phase diagram of MnBi2Te4. Analysis of these universal conductance fluctuations reveals a sensitivity to reconfiguration in the magnetic domain structure of MnBi2Te4, providing a possible transport-based probe of magnetic disorder.
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538 $a Mode of access: World Wide Web
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650 4 $a Materials science. $3 557839
650 4 $a Graphene. $3 886892
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