title: Nanoscale β-nuclear magnetic resonance depth imaging of topological insulators.
abstract: Considerable evidence suggests that variations in the properties of topological insulators (TIs) at the nanoscale and at interfaces can strongly affect the physics of topological materials. Therefore, a detailed understanding of surface states and interface coupling is crucial to the search for and applications of new topological phases of matter. Currently, no methods can provide depth profiling near surfaces or at interfaces of topologically inequivalent materials. Such a method could advance the study of interactions. Herein, we present a noninvasive depth-profiling technique based on β-detected NMR (β-NMR) spectroscopy of radioactive (8)Li(+) ions that can provide "one-dimensional imaging" in films of fixed thickness and generates nanoscale views of the electronic wavefunctions and magnetic order at topological surfaces and interfaces. By mapping the (8)Li nuclear resonance near the surface and 10-nm deep into the bulk of pure and Cr-doped bismuth antimony telluride films, we provide signatures related to the TI properties and their topological nontrivial characteristics that affect the electron-nuclear hyperfine field, the metallic shift, and magnetic order. These nanoscale variations in β-NMR parameters reflect the unconventional properties of the topological materials under study, and understanding the role of heterogeneities is expected to lead to the discovery of novel phenomena involving quantum materials.
authors.affiliation: Department of Chemistry and Biochemistry, University of California, Los Angeles, CA 90095;
authors.forename: Dimitrios
authors.initials: D
authors.lastname: Koumoulis
authors.affiliation: TRI University Meson Facility (TRIUMF), Vancouver, BC, Canada V6T 2A3;
authors.forename: Gerald D
authors.initials: GD
authors.lastname: Morris
authors.affiliation: Department of Electrical Engineering, University of California, Los Angeles, CA 90095;
authors.forename: Liang
authors.initials: L
authors.lastname: He
authors.affiliation: Department of Electrical Engineering, University of California, Los Angeles, CA 90095;
authors.forename: Xufeng
authors.initials: X
authors.lastname: Kou
authors.affiliation: Department of Chemistry and Biochemistry, University of California, Los Angeles, CA 90095;
authors.forename: Danny
authors.initials: D
authors.lastname: King
authors.affiliation: Department of Physics & Astronomy, University of British Columbia, Vancouver, BC,Canada V6T 1Z1;
authors.forename: Dong
authors.initials: D
authors.lastname: Wang
authors.affiliation: TRI University Meson Facility (TRIUMF), Vancouver, BC, Canada V6T 2A3; Department of Physics & Astronomy, University of British Columbia, Vancouver, BC,Canada V6T 1Z1;
authors.forename: Masrur D
authors.initials: MD
authors.lastname: Hossain
authors.affiliation: Department of Electrical Engineering, University of California, Los Angeles, CA 90095;
authors.forename: Kang L
authors.initials: KL
authors.lastname: Wang
authors.affiliation: Department of Physics, University of Texas at Austin, Austin, TX 78712;
authors.forename: Gregory A
authors.initials: GA
authors.lastname: Fiete
authors.affiliation: Department of Chemistry, Northwestern University, Evanston, IL 60208;
authors.forename: Mercouri G
authors.initials: MG
authors.lastname: Kanatzidis
authors.affiliation: Department of Chemistry and Biochemistry, University of California, Los Angeles, CA 90095; California NanoSystems Institute, University of California, Los Angeles, CA 90095 louis.bouchard@gmail.com.
authors.forename: Louis-S
authors.initials: LS
authors.lastname: Bouchard
keywords: condensed matter physics; depth profiling; nanoscale physics; nuclear magnetic resonance; topological insulator