Insights into The Role of Disorder in Topological Semimetals

As a result of their bandstructures, three-dimensional topological semimetals (TSMs) exhibit phenomena that are of potential interest for device applications, including ultra-high electron mobility, broadband optical absorption, linear magnetoresistance and the chiral anomaly. These behaviors have largely been studied in bulk crystals, but thin films will be required for devices. Given that disorder, in the form of defects, impurities and interfaces, will inevitably be present in thin films, it is important to understand the role they play on the behavior of TSMs. In this talk, I will discuss our use of epitaxy to intentionally vary specific forms of disorder and thereby generate new insights into property-disorder relationships. Our studies, mostly performed in Cd₃As₂ grown by molecular beam epitaxy, suggest that point defects modestly affect electron mobility but can substantially influence magnetoresistance. Impurities also offer important control knobs for controlling the Fermi level, either as extrinsic dopants or through indirect influence on the balance of point defects. Finally, I will discuss challenges and outstanding questions that the TSM field must address to effectively implement these materials into device applications.