Coherent Topological Transport on the Surface of Bi$_2$Se$_3$

ORAL

Abstract

We report weak anti-localization (WAL) measurements in gate-tuned, bulk insulating Bi$_2$Se$_3$ thin crystals with thicknesses varying between 5 and 17 nm. The gate-voltage dependent WAL behavior shows systematic variation as a function of crystal thickness. For the thickest samples, we observe two decoupled surfaces exhibiting perfect WAL as expected for the symplectic class. As the films are made thinner, we observe a gate-voltage tuned crossover from two decoupled surfaces to a single coherently coupled 2D system exhibiting WAL. The observed crossover is governed by competition between the phase coherence time and inter-surface tunneling time associated with the hybridization gap. In contrast to classical transport in which the signature of the hybridization gap appears only in the ultrathin limit ($\le $ 3nm), phase coherent transport is extraordinarily sensitive to sub-meV coupling between top and bottom topological surfaces, and the surfaces of a TI film may be coherently coupled even for thicknesses as large as 12 nm. On further thinning, the WAL behavior is suppressed altogether at small carrier density, which we associate with the opening of a sizable gap on order the Fermi energy and destruction of topological protection.

*The authors acknowledge support from Center for Nanophysics and Advanced Materials (CNAM).

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Authors

  • Dohun Kim

    • Department of Physics, University of Maryland

  • Paul Syers

    • University of Maryland
    • Department of Physics, University of Maryland

  • Nicholas Butch

    • Lawrence Livermore National Laboratory
    • Physical and Life Sciences Directorate, Lawrence Livermore National Laboratory
    • Condensed Matter and Materials Division, Lawrence Livermore National Laboratory

  • Johnpierre Paglione

    • Center for Nanophysics and Advanced Materials, Department of Physics, University of Maryland-College Park
    • Ceter for Nanophysics and Advanced Materials, Department of Physics, University of Maryland, College Park, MD 20742
    • University of Maryland
    • Department of Physics, University of Maryland
    • Center for Nanophysics and Advanced Materials, Department of Physics, University of Maryland, College Park, MD 20742
    • Center for Nanophysics and Advanced Materials, Dept. of Physics, University of Maryland, College Park

  • Michael Fuhrer

    • Department of Physics, University of Maryland
    • University of Maryland
    • CNAM-UMD
    • Center for Nanophysics and Advanced Materials, University of Maryland, College Park, MD 20742-4111, USA
    • Center for Nanophysics and Advanced Materials University of Maryland, College Park
    • Center for Nanophysics and Advanced Materials, University of Maryland, College Park