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Exploring Topology in Epitaxial Thin Films of Topological Magnets

Cheng, Shuyu
http://orcid.org/0000-0002-4784-4142
http://rave.ohiolink.edu/etdc/view?acc_num=osu171222181554275

Abstract Details

2024, Doctor of Philosophy, Ohio State University, Physics.
The concept of “topology” provides a new merit for categorizing materials based on the properties that are not changed under continuous transforms. The introduction of this concept into condensed matter physics has led to the prediction and realization of many exotic quantum states in both momentum space and real space. In momentum space, two topologically distinct insulating states are expected to have a well-defined boundary where a metallic state emerges. In terms of material selection, the kagome lattice inherently manifests Dirac cones and flat bands, which becomes topologically nontrivial in the presence of spin-orbit coupling. In real space, the concept of topology can be used to classify different distributions of order parameters, and the ones with nonzero winding numbers are expected to be more stable since they are topologically protected. The magnetic skyrmions, as prototypical spin textures with a winding number of ±1, are of particular interest for next-generation memory and logic devices. This thesis aims to demonstrate that the nontrivial topology can be realized in thin films via epitaxial growth, where molecular beam epitaxy (MBE) plays a crucial role in controlling the sample structure at the atomic scale. Using MBE, we have synthesized thin films of kagome materials with different magnetic orderings: ferromagnetic Fe3Sn2 (Chapter 3), paramagnetic CoSn (Chapter 4). and ferrimagnetic RMn6Sn6 (Chapter 5), and the magnetic properties of these materials are studied using a combination of the magneto-optical Kerr effect (MOKE) and the superconducting quantum interference device (SQUID) magnetometer. In CoSn, we have directly observed topologically non-trivial flat bands using synchrotron-based angle-resolved photoemission spectroscopy (ARPES). We have also established a quantitative connection between the band structures and the transport properties of CoSn by a semiclassical transport theory. In Chapter 6, we show that the real-space topology can also be manipulated via thin film synthesis. The magnetic properties of [Pt/Co/Cu]N multilayers can be vastly tuned by varying the sample structures, and magnetic skyrmions are observed in those samples with zero-field multidomain states. Finally, in Chapter 7, we will discuss the time- and angle-resolved photoemission spectroscopy at the National Extreme Ultrafast Science (NeXUS) facility, which will become a formidable machine for investigating and manipulating the band topology.
Roland Kawakami (Advisor)
Louis DiMauro (Committee Member)
Jay Gupta (Committee Member)
Yuanming Lu (Committee Member)
267 p.
Condensed Matter Physics; Physics
topological material; magnetic skyrmion; molecular beam epitaxy (MBE); angle-resolved photoemission spectroscopy (ARPES)

Recommended Citations

Citations

  • Cheng, S. (2024). Exploring Topology in Epitaxial Thin Films of Topological Magnets [Doctoral dissertation, Ohio State University]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=osu171222181554275

    APA Style (7th edition)

  • Cheng, Shuyu. Exploring Topology in Epitaxial Thin Films of Topological Magnets. 2024. Ohio State University, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=osu171222181554275.

    MLA Style (8th edition)

  • Cheng, Shuyu. "Exploring Topology in Epitaxial Thin Films of Topological Magnets." Doctoral dissertation, Ohio State University, 2024. http://rave.ohiolink.edu/etdc/view?acc_num=osu171222181554275

    Chicago Manual of Style (17th edition)

osu171222181554275
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© 2024, all rights reserved.
This open access ETD is published by The Ohio State University and OhioLINK.