Investigating the ferromagnetism-induced surface gap formation and effects of optical excitations in Cr-doped topological insulators (TIs)

ORAL

Abstract

Despite the exciting observation of the quantum anomalous Hall effect (QAHE) in Cr-doped (BixSb1-x)2Te3 compounds, the microscopic origin of ferromagnetism (FM) and the temperature (T) evolution of the anomalous Hall (AH) resistance in these magnetic TIs remain poorly understood. We perform scanning tunneling spectroscopic and electrical transport studies on MBE-grown magnetic TIs, including uniformly 10% Cr-doped (BixSb1-x)2Te3 and bilayer systems consisting of a layer of pure (BixSb1-x)2Te3 on top of a 10% Cr-doped (BixSb1-x)2Te3 layer. In the STS studies on the bilayer system, a surface gap Δ opens up at TC2D ~ 180 K, much higher than the bulk Curie temperature TC3D ~ 35 K determined from the onset of AHE. The spatial distribution of Δ is largely homogeneous, and Δ increases with decreasing T, reaching Δ = (59±7) meV at 147K. Additionally, longitudinal (Rxx) and AH (Rxy) resistance are measured both with and without light. An increase in Rxy and decrease in Rxx is observed in the bilayer system under circularly polarized (CP) light (wavelengths λ =1600 ~ 1700 nm). In contrast, both Rxx and Rxy are suppressed under CP light for uniformly Cr-doped (BixSb1-x)2Te3. The physical implications of these findings will be discussed.

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Presenters

  • Adrian Llanos

    Department of Materials Science, California Institute of Technology

Authors

  • Adrian Llanos

    Department of Materials Science, California Institute of Technology

  • Chien-Chang Chen

    Physics, Caltech, Pasadena, CA 91125, USA, Department of Physics, California Institute of Technology

  • Marcus Teague

    Physics, California Institute of Technology, Physics, Caltech, Department of Physics, California Institute of Technology

  • Peng Zhang

    Department of Electrical Engineering, University of California, Los Angeles, Electrical and Computer Engineering Department, University of California, Los Angeles

  • Lei Pan

    Electrical Engineering, University of California, Los Angeles, University of California, Los Angeles, University of California Los Angeles, Department of Electrical Engineering, University of California, Los Angeles, Electrical and Computer Engineering Department, University of California, Los Angeles

  • Koichi Murata

    Department of Electrical Engineering, University of California, Los Angeles

  • Kang Wang

    University of California, Los Angeles, Electrical and Computer Engineering, University of California, Los Angeles, Department of Electrical Engineering, University of California, Los Angeles

  • Nai-Chang Yeh

    Physics, California Institute of Technology, Physics, Caltech, Dept. of Physics, Caltech, Physics, Caltech, Pasadena, CA 91125, USA, Department of Physics, California Institute of Technology