The quantum anomalous Hall effect : uses in electrical metrology and understanding residual dissipation
- When a company manufactures and sells a resistor, they typically aim to traceably link its resistance value to a quantum Hall (QH) effect measurement. When a thin semiconductor is cooled to a low enough temperature and exposed to a large enough magnetic field, it exhibits zero longitudinal resistance and quantized Hall (transverse) resistance. This quantized resistance is a topological phenomenon, insensitive to sample details, and since 1990 has been used to define the ohm. Magnetic topological insulators exhibit the same resistance properties, but at zero magnetic field — this is the quantum anomalous Hall (QAH) effect. QAH materials offer significant advantages as possible replacements for QH resistance standards. Eliminating the need for large magnetic fields not only allows simplifying measurement infrastructure, but also allows a quantum resistance standard to be directly integrated with a Josephson voltage standard to produce a quantum current standard. However, all measurements of the QAH effect to date have observed non-zero longitudinal resistance despite quantization of the Hall resistance to h/e^2 (where h is Planck's constant and e the electron charge) being confirmed to within one part per billion. This residual dissipation is strongly temperature-dependent, lowering the temperature at which the QAH effect is well-quantized and thus limiting industrial applications. This dissertation will focus on our efforts to understand and find metrological applications for the QAH state of the canonical magnetic topological insulator — Cr-doped (Bi,Sb)2Te3. The nature of non-equilibrium dissipationless current flow in this system will be explored by comparing the measured potential profile in a QAH Hall bar to numerical simulations of the Poisson equation. Separately, residual dissipation will be studied by decoupling edge and bulk contributions using an annular geometry known as the Corbino disk. We will also show that despite their limitations, these materials are already useful within the field of electrical metrology. We will discuss how metrological measurements of resistance are made and highlight the construction of a novel quantum current sensor based on a single-cryostat combination of a QAH resistor with a programmable Josephson voltage standard.
|Type of resource
|electronic resource; remote; computer; online resource
|1 online resource.
|Rodenbach, Linsey Kathryn
|Degree committee member
|Degree committee member
|Stanford University, School of Humanities and Sciences
|Stanford University, Department of Physics
|Statement of responsibility
|Linsey K. Rodenbach.
|Submitted to the Department of Physics.
|Thesis Ph.D. Stanford University 2023.
- © 2023 by Linsey Kathryn Rodenbach
- This work is licensed under a Creative Commons Attribution Non Commercial 3.0 Unported license (CC BY-NC).
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