Charge neutral fermions and quantum oscillations in a topological Kondo insulator YbB12

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