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Proc Natl Acad Sci U S A. 2018 Aug 21;115(34):8558-8562. doi: 10.1073/pnas.1806910115. Epub 2018 Aug 6.

Evidence for a conducting surface ground state in high-quality single crystalline FeSi.

Author information

1
Materials Science and Engineering Program, University of California, San Diego, La Jolla, CA 92093.
2
Center for Advanced Nanoscience, University of California, San Diego, La Jolla, CA 92093.
3
Department of Physics, University of California, San Diego, La Jolla, CA 92093.
4
Department of Chemistry, Louisiana State University, Baton Rouge, LA 70803.
5
Department of NanoEngineering, University of California, San Diego, La Jolla, CA 92093.
6
Materials Science and Engineering Program, University of California, San Diego, La Jolla, CA 92093; mbmaple@ucsd.edu.

Abstract

We report anomalous physical properties of high-quality single-crystalline FeSi over a wide temperature range of 1.8-400 K. The electrical resistivity ρ(T) can be described by activated behavior with an energy gap Δ = 57 meV between 150 and 67 K, below which the estimated energy gap is significantly smaller. The magneto-resistivity and Hall coefficient change sign in the vicinity of 67 K, suggesting a change of dominant charge carriers. At ∼19 K, ρ(T) undergoes a cross-over from semiconducting to metallic behavior which is very robust against external magnetic fields. The low-temperature metallic conductivity depends strongly on the width/thickness of the sample. In addition, no indication of a bulk-phase transition or onset of magnetic order is found down to 2 K from specific heat and magnetic susceptibility measurements. The measurements are consistent with one another and point to complex electronic transport behavior that apparently involves a conducting surface state in FeSi at low temperatures, suggesting the possibility that FeSi is a 3D topological insulator.

KEYWORDS:

FeSi; metal-semiconductor transition; surface conductivity; topological insulator

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