Fractional Excitation Induced Giant Phonon Anomalies in the Proximate Kitaev Quantum Spin Liquid a-RuCl3

ORAL

Abstract

The Kitaev quantum spin liquid epitomizes an entangled topological state, for which two flavors of fractionalized low-energy excitations are predicted: the itinerant Majorana fermion and the Z2 gauge flux. Detection of these excitations remains challenging, because of their fractional quantum numbers and non-locality. It was proposed recently that fingerprints of fractional excitations are encoded in the phonon spectra of Kitaev quantum spin liquids through a novel fractional-excitation-phonon coupling. Here, we uncover this effect in a-RuCl3 using inelastic X-ray scattering with meV resolution. At high temperature, we discover interlaced optical phonons intercepting a transverse acoustic phonon between 3 and 7 meV. Upon decreasing temperature, the optical phonons display a large intensity enhancement near the Kitaev energy, JK~8 meV, that coincides with a giant acoustic phonon softening near the Z2 gauge flux energy scale. This fractional excitation induced giant phonon anomalies uncover the key ingredient of the quantum thermal Hall effect in a-RuCl3 and demonstrates a proof-of-principle method to detect fractional excitations in topological quantum materials.

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Presenters

  • Haoxiang Li

    • Physics, University of Colorado Boulder
    • Oak Ridge National Laboratory
    • Materials Science and Technology Division, Oak Ridge National Laboratory

Authors

  • Haoxiang Li

    • Physics, University of Colorado Boulder
    • Oak Ridge National Laboratory
    • Materials Science and Technology Division, Oak Ridge National Laboratory

  • Tiantian Zhang

    • Department of Physics, Tokyo Institute of Technology
    • Beijing National Laboratory for Condensed Matter Physics, and Institute of Physics, Chinese Academy of Sciences
    • Tokyo Inst of Tech - Tokyo

  • Ayman Said

    • Advanced Photon Source, Argonne National Laboratory
    • Argonne National Laboratory
    • APS, Argonne National Laboratory

  • Gilberto F L Fabbris

    • Argonne National Laboratory
    • Advanced Photon Source, Argonne National Laboratory

  • Daniel Mazzone

    • Brookhaven National Laboratory
    • Condensed Matter Physics and Materials Science Department, Brookhaven National Laboratory

  • Jiaqiang Yan

    • Materials Science and Technology Division, Oak Ridge National Lab
    • Oak Ridge National Laboratory
    • University of Tennessee
    • Oak Ridge National Lab
    • Materials Science and Technology Division, Oak Ridge National Laboratory
    • Materials Science and Technology, Oak Ridge National Laboratory
    • Oak Ridge National Laboratory, Materials Science and Technology Division

  • David George Mandrus

    • Materials Science and Technology Division, Oak Ridge National Labratory
    • Materials Science and Engineering, University of Tennessee
    • Department of Materials Science and Engineering, University of Tennessee
    • University of Tennessee
    • Department of Materials Science and Engineering, University of Tennessee Knoxville
    • Department of Materials Science & Engineering, University of Tennessee, Knoxville, Tennessee 37996, USA
    • Oakridge National Laboratory
    • Materials Science and Engineering, University of Tennessee, Knoxville
    • Oak Ridge National Laboratory
    • University of Tennessee - Knoxville
    • Materials Science and Technology Division, Oak Ridge National Laboratory
    • Department of Physics, University of Tennessee Knoxville
    • Materials Science and Technology, Oak Ridge National Laboratory
    • Oak Ridge National Laboratory, Materials Science and Technology Division
    • Department of Materials Science, The University of Tennessee
    • University of Tennessee, Knoxville

  • Gabor Halasz

    • Materials Science and Technology Division, Oak Ridge National Laboratory
    • Oak Ridge National Lab
    • Oak Ridge National Laboratory

  • Satoshi Okamoto

    • Oak Ridge National Lab
    • Materials Science and Technology Division, Oak Ridge National Laboratory
    • Oak Ridge National Laboratory

  • Shuichi Murakami

    • Department of Physics, Tokyo Institute of Technology
    • Physics, Tokyo Institute of Technology
    • Tokyo Inst of Tech - Tokyo

  • Mark Dean

    • Brookhaven National Laboratory
    • Condensed Matter Physics and Materials Science Department, Brookhaven National Laboratory

  • Ho Nyung Lee

    • Oak Ridge National Lab
    • Oak Ridge National Laboratory
    • Materials Science and Technology Division, Oak Ridge National Laboratory

  • Hu Miao

    • Oak Ridge National Laboratory, USA
    • Brookhaven National Laboratory
    • Oak Ridge National Laboratory
    • Materials Science and Technology Division, Oak Ridge National Laboratory