Properties of topological semimetals and altermagnetic materials using electronic structure calculations
Date
2025
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Publisher
University of Delaware
Abstract
Quantum materials have emerged as promising candidates for the latest technological advancements. Among the key areas of focus are topological materials and unconventional magnetic materials. This thesis explores the potential for understanding and controlling the electronic and magnetic properties of these materials. ☐ In the initial section of the thesis, we provide an overview of fundamental concepts of topology in materials science and introduce a recently identified phase of collinear magnetism known as altermagnetism. We also present representative material classes, including rare-earth monopnictide (RE-V) as an example of topological materials and antiferromagnetic materials possessing the rutile structural motif, exemplified by ruthenium dioxides RuO$_2$, with an emphasis on its debated magnetic properties, as an example of altermagnets. This is followed by a brief description of the theoretical methodology employed in our simulations, specifically the Density Functional Theory. ☐ The main content of the thesis begins with semimetallic RE-V compounds, where we demonstrate that their electronic structures can be tuned via structural perturbations such as strain and dimensionality reduction. This is achieved by utilizing a detailed understanding of their electronic structures, especially those near the Fermi level. Interestingly, we also show that these perturbations can ultimately modify their band topology, opening new possibilities for controlling their use in electronics and spintronics. ☐ Subsequently, we shift our focus to altermagnets, a novel class of collinear magnetic materials where the unique arrangement of non-magnetic ligands around magnetic entities contributes to their distinctive spin-group symmetry. This symmetry enables anisotropic exchange interactions, thereby inducing spin-splitting along specific high-symmetry momentum directions in the Brillouin zone despite the absence of net magnetization. RuO2 in its rutile structure serves as a candidate for such behavior. Recent experiments, however, have challenged earlier conclusions about its magnetic structure, raising questions about the origin of magnetism in the material. Interestingly, we demonstrate that spontaneous surface magnetization, as a possible contribution to the magnetic property of RuO2, can develop on the (110) surface of the material due to the breaking of local symmetry at the surface, leading to spin-polarization effects. The significance of this surface magnetization as a relevant source of magnetism and its role as a potential explanation for conflicting experimental results are discussed.
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Keywords
Altermagnets, Electronic structure calculations, Quantum materials, Rare-earth monopnictides, Ruthenium dioxides, Topological materials