Beyond Conventional Methods: Chemical Routes to Dope Topological Insulator Nanostructures and Two-Dimensional Materials Magnetically

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**Non-Technical Description**This award from the Condensed Matter Physics Program of the Division of Materials Research supports Yale University with a project to develop novel chemical doping methods for topological insulator nanostructures to alleviate current materials challenges facing the field. Topological insulators possess exotic conducting surface states that can be used as information carriers that do not generate wasted heat. Thus topological insulators can replace current copper interconnects, resulting in great reduction of energy consumption for the society. This research will bring the realization of topological insulators as alternative interconnects one step closer to reality. Additionally, the methods can be successfully applied to two-dimensional, layered semiconductors to create dilute magnetic semiconductors for much broader impact for the society. Dilute magnetic semiconductors are widely studied for spintronics applications. The work contributes to the training of skilled technical workforce and contains elements for new course development on nanomaterials. In addition, the project promotes the participation of underrepresented groups.**Technical Description**This award from the Condensed Matter Physics Program of the Division of Materials Research to Yale University supports a project to develop novel chemical methods to dope topological insulator nanomaterials with magnetic impurities, and to open a band gap in the topological surface states. Two chemical methods are investigated. The first method employs intercalation of magnetic atoms, ions, and molecules at the Van der Waals gap of layered topological insulators. The second method employs surface modification of topological insulator nanostructures with molecular spins. These methods exhibit significant advantages over conventional doping methods: 1) higher concentration of magnetic dopants, 2) no clustering of magnetic dopants, 3) spatial ordering of magnetic dopants into anti-ferromagnetism or ferromagnetism, and 4) broad applicability to other two-dimensional layered materials. Nanodevices will be fabricated to measure magnetotransport at low temperature to characterize the doping. The successful outcome of this research will lead to a materials platform in which fundamental condensed matter physics phenomena can be explored to advance knowledge in band gap in topological surface states, in topological magneto-electric effect, and quantum anomalous Hall effect. It is anticipated that the methodology developed in this project can be general. The research involves training undergraduate students to conduct research independently, developing new components for a nanotechnology course, and dissemination of knowledge through publications and conference presentations and outreach..