Correlating and controlling local chemistry and electronic structure in quantum materials

Non-technical Abstract With Moore’s law beginning to push against the limits of quantum mechanics, new computing paradigms become more attractive, and these new approaches require novel materials and a trained workforce. One promising paradigm is to utilize the fact that electrons on the surface of a material often have behavior unachievable in the interior. The desired surface electronic behavior can be controlled by the types of atoms that are on the surface, and this surface composition can be inhomogeneous or variable. The project employs simultaneous measurements of surface atomic composition and surface electron motion to understand how to control desired surface electronic behavior via chemical composition. Broader impacts are achieved through outreach to the public about novel materials via social media and public lectures. Undergraduate and graduate students will be trained in materials physics and communication thereof via in-person and online tutorials and technical writing pedagogy. Technical Abstract This work assesses how characteristic surface states manifest amidst dynamic chemistry, electronic correlations, and real-space mesoscale phase separation. Bulk-boundary correspondence is a fundamental principle in topological materials including Weyl semimetals that establishes a connection between the bulk and surface electronic structure. The composition and morphology of the surface can markedly affect the surface electronic structure, and needs to be measured independently. In this project, the researchers are incorporating photoemissions measurements of local chemistry, periodic structure, and electronic structure into developing enhanced understanding and control of surface electronic states. This project uses bulk chemical substitution to push the Curie temperature to zero in magnetic Weyl semimetals. At these critical compositions, local chemical variation at the surface has an outsized role in driving topologically distinct surface electronic structures which can be tuned dynamically with ion migration. Multiple photoemission microscopies are coupled with automation, visualization, and correlation tools to connect surface chemistry, structure, and electronic structure in a closed loop. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.