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

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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