Charge neutral fermions and quantum oscillations in a topological Kondo insulator YbB<sub>12</sub>

ORAL

Abstract

Recent observations of quantum oscillations (QOs) in transport and thermodynamic parameters at high magnetic fields in a Kondo insulator YbB12 have been a big surprise since it seems to host a Fermi surface, which is a defining character of a metal. In this talk, I will present low-temperature heat-transport measurements to discuss low energy excitations in the ground state of YbB12. At zero field, despite the resistivity ρxx being far larger than that of conventional metals, a sizeable T-linear dependent term in the thermal conductivity in the zero-temperature limit, κ0xx/T is clearly resolved, leading to a spectacular violation of the Wiedemann-Franz law: the Lorenz ratio L = κxxρxx/T is 104-105 times larger than that expected in conventional metals. These data indicate that YbB12 is a charge insulator but a thermal metal, suggesting the presence of itinerant neutral fermions. Remarkably, more insulating crystals with larger activation energies exhibit larger amplitudes of the resistive QOs as well as a larger κ0xx/T, in stark contrast to conventional metals. Moreover, we find that these fermions couple to magnetic field, despite their charge neutrality. Our findings expose novel gapless and highly itinerant, charge-neutral quasi-particles in this unconventional quantum state.

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Presenters

  • Yuki Sato

    • Physics, Kyoto University
    • Department of Physics, Kyoto University
    • Kyoto University

Authors

  • Yuki Sato

    • Physics, Kyoto University
    • Department of Physics, Kyoto University
    • Kyoto University

  • Ziji Xiang

    • Physics, University of Michigan
    • Department of Physics, University of Michigan
    • University of Michigan

  • Yuichi Kasahara

    • Department of Physics, Kyoto University
    • Physics, Kyoto University
    • Kyoto University

  • Tomoya Taniguchi

    • Physics, Kyoto University
    • Department of Physics, Kyoto University

  • Shigeru Kasahara

    • Physics, Kyoto University
    • Dept of Physics, Kyoto Univ.
    • Kyoto University
    • Department of Physics, Kyoto University

  • Lu Chen

    • Physics, University of Michigan
    • Department of Physics, University of Michigan
    • University of Michigan

  • Tomoya Asaba

    • Physics, University of Michigan
    • MPA-CMMS, Los Alamos National Laboratory
    • Department of Physics, University of Michigan
    • University of Michigan
    • Los Alamos National Laboratory

  • Colin Tinsman

    • Physics, University of Michigan
    • Department of Physics, University of Michigan
    • University of Michigan

  • Hinako Murayama

    • Physics, Kyoto University
    • Department of Physics, Kyoto University
    • Kyoto University

  • Ohei Tanaka

    • Advanced Materials Science, University of Tokyo
    • Department of Advanced Materials Science, University of Tokyo

  • Yuta Mizukami

    • University of Tokyo
    • Univ of Tokyo-Kashiwanoha
    • Advanced Materials Science, University of Tokyo
    • Department of Advanced Materials Science, University of Tokyo

  • Takasada Shibauchi

    • University of Tokyo
    • Univ of Tokyo-Kashiwanoha
    • Advanced Materials Science, University of Tokyo
    • Department of Advanced Materials Science, University of Tokyo
    • Department of Advanced Material Science, University of Tokyo
    • Dept. Adv. Mat. Sci., Univ. Tokyo
    • Tokyo University

  • Fumitoshi Iga

    • Science, Ibaraki University
    • College of Science, Ibaraki University

  • John Singleton

    • National High Magnetic Field Laboratory, Los Alamos National Laboratory
    • MPA-MAG, Los Alamos National Laboratory
    • National High Magnetic Field Laboratory, Los Alamos National Laboratory, Los Alamos, NM 87545
    • Los Alamos National Laboratory
    • NHMFL, Los Alamos National Labs
    • NHMFL, Los Alamos National Laboratory
    • Los Alamos, National High Magnetic Field Laboratory
    • NHMFL, Los Alamos Natl Lab
    • Los Alamos Natl Lab

  • Lu Li

    • University of Michigan
    • Physics, University of Michigan
    • Department of Physics, University of Michigan

  • Yuji Matsuda

    • Physics, Kyoto University
    • Department of Physics, Kyoto University
    • Dept of Physics, Kyoto Univ.
    • Kyoto University