Atomic to wafer-scale imaging and control of two-dimensional quantum materials
- Two-dimensional quantum materials have emerged as a class of growing interest for their potential in technological applications and as platforms for exploring new physics. Access and control of atomic- scale features of these materials is critical to understanding their behavior at device and wafer scales. Scanning tunneling microscopy and spectroscopy (STM/STS) provide powerful tools to both locally measure and locally control the electronic properties of these materials. This thesis explores the connection between atomic-scale features, including those locally manipulated by STM, and wafer- scale characteristics of two distinct two-dimensional electronic systems. First, we demonstrate that the Cu(111) surface state under wafer-scale hBN is homogeneous in energy and spectral weight over nanometer length scales and across atomic terraces. In contrast, a new spectral feature, not seen on bare Cu(111), varies with atomic registry and shares the spatial periodicity of the hBN/Cu(111) moir ́e pattern. This demonstrates that, for some 2D electron systems, an hBN overlayer can act as a protective yet remarkably transparent window on fragile low-energy electronic structure below. The second system I will discuss is magnetically active manganese atoms in molybdenum disulfide (Mn-MoS2), a system which theory has suggested could behave as a two-dimensional dilute magnetic semiconductor, with implications for spintronics applications and novel ground states. Local gating with the STM tip allows for identification and control of the charge and magnetic state of individual Mn atoms, enabling an understanding of bulk paramagnetic behavior observed with Kerr rotation experiments over centimeter-size samples. These experiments show that single Mn atoms in MoS2 function as active unscreened magnetic moments in the monolayer, and can be harnessed for spin physics applications and science. The third material, sodium cobaltate, hosts a half-metallic surface state. Using a superconducting STM tip, superconductivity can be introduced into the surface state via the proximity effect, producing interesting point contact spectroscopy features including a zero-bias peak suggestive of a Majorana mode. By comparison with models of chiral p-wave superconductivity it is shown that it is likely that the superconductivity induced into this surface state is topologically non-trivial. Lastly, a characterization of the surface and subsurface defects on cleaved Weyl semi-metal tungsten ditelluride is performed. It is shown that defects in this material affect the electronic structure at the Fermi level over several nanometers, and that even subsurface defects not visible iv in topography of the surface act as scattering centers for the surface electrons. This has important implications for the study of superconductivity induced into the topological surface state of this material.
|Type of resource
|electronic resource; remote; computer; online resource
|1 online resource.
|Zerger, Caleb Zamora
|Degree committee member
|Stanford University, School of Humanities and Sciences
|Stanford University, Department of Applied Physics
|Statement of responsibility
|Caleb Zamora Zerger.
|Submitted to the Department of Applied Physics.
|Thesis Ph.D. Stanford University 2023.
- © 2023 by Caleb Zamora Zerger
- This work is licensed under a Creative Commons Attribution Non Commercial 3.0 Unported license (CC BY-NC).
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