Doctoral Dissertations

Keywords and Phrases

Josephson Junction; Magnetic Topological Insulators; Quantum materials; Superconducting Nanowires; Topological Insulators

Abstract

Quantum materials play a pivotal role in the advancement of next-generation technology. Superconducting quantum computing, dissipationless spintronics, or valleytronics offer promising ways forward beyond traditional chip miniaturization. Josephson Junctions (JJs) have already revolutionized quantum information and high precision detectors. Quantum systems, however, are either hard to control, produce, and/or maintain. This calls for a better understanding of microscopic properties and tuning of these quantum states.

In this work, we experimentally investigated growth methods to control the electric and magnetic properties of Topological Insulator (TI) Sb2Te3 through Cr-doping. Our results demonstrate the onset of a Magnetic Topological Insulator (MTI) and have successfully tuned Fermi level toward the Dirac gap. This positions our material as a candidate for the Quantum Anomalous Hall Effect. We also developed a novel growth method to easily produce high quality superconducting TaS2 nanowires to explore superconductivity in dimensionally constrained systems, with applications in confinement-driven quantum phenomena.

Additionally, we computationally studied Al/AlOx/Al JJs to investigate their microscopic behavior in the presence of hydrogen defects, leading to noise and degradation of coherence in JJs. We find an uneven distribution of O-H defects in the junction that understanding could give insight into refining experimental growth. We also report and quantify the formation of aluminum suboxides in the transition between the bulk Al and AlOx layers that give rise to H bond transformation on 10-200fs time scales

Advisor(s)

Hor, Yew San
Medvedeva, Julia E.

Committee Member(s)

Yamilov, Alexey
Choudhury, Amitava
Waddill, George Daniel

Department(s)

Physics

Degree Name

Ph. D. in Physics

Publisher

Missouri University of Science and Technology

Publication Date

Summer 2025

Journal article titles appearing in thesis/dissertation

Paper I, found on pages 41-55. This paper will be submitted to arXiv with the title “Anomalous Hall Effect in n-type Cr-doped Sb2Te3 Topological Insulator” with Ali Sarikhani, Jacob Cook, Qiu Sheng, Sheng Lee, Laleh Avazpour, Jack Crewse, William Fahrenholtz, Guang Bian, and Yew San Hor.

Paper II, found on pages 56-70. This paper has been submitted to Applied Physics Letters under the title “Enhanced Superconductivity and Vortex Dynamics in One-Dimensional TaS2 Nanowires” with Visakha Hor, Clarissa Wisner, Eric Bohannan, and Yew San Hor.

Paper III, found on pages 71-85 with supplement Pages 86-111. This paper will be submitted to Physical Review Letters under the title “Suboxide formation and structural voids in hydrogenated Al/AlOx/Al Josephson junction’ with Julia e. Medvedeva.

Pagination

xi, 123 pages

Note about bibliography

Includes_bibliographical_references_(pages 118-122)

Rights

© 2025 Mathew Pollard , All Rights Reserved

Document Type

Dissertation - Open Access

File Type

text

Language

English

Thesis Number

T 12543

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Included in

Physics Commons

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