Helical Edge Transport in Millimeter-Scale Thin Films of Na<sub>3</sub>Bi.
basic_science · Level V
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- Record sourced from PubMed, PMID 32841034.
- Also identified by DOI 10.1021/acs.nanolett.0c01649.
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Abstract
A two-dimensional topological insulator (2DTI) has an insulating bulk and helical edges robust to nonmagnetic backscattering. While ballistic transport has been demonstrated in micron-scale 2DTIs, larger samples show significant backscattering and a nearly temperature-independent resistance of unclear origin. Spin polarization has been measured, however the degree of helicity is difficult to quantify. Here, we study 2DTI few-layer Na<sub>3</sub>Bi on insulating Al<sub>2</sub>O<sub>3</sub>. A nonlocal conductance measurement demonstrates edge conductance in the topological regime with an edge mean free path ∼100 nm. A perpendicular magnetic field suppresses spin-flip scattering in the helical edges, resulting in a giant negative magnetoresistance (GNMR) up to 80% at 0.9 T. Comparison to theory indicates >96% of scattering is helical spin scattering significantly exceeding the maximum (67%) expected for a nonhelical metal. GNMR, coupled with nonlocal measurements, thus provides an unambiguous experimental signature of helical edges that we expect to be generically useful in understanding 2DTIs.