Anti-chiral spin order, its soft modes, and their hybridization with phonons in the topological semimetal Mn<sub>3</sub>Ge.

 · Invited

Abstract

We report the magnetic structure and spin excitations of Mn3Ge, a breathing kagome antiferromagnet with transport anomalies attributed to Weyl nodes. Using polarized neutron diffraction, we show the magnetic order is a k = 0 co-planar state belonging to a Γ9 irreducible representation, which can be described as a perfect 120° anti-chiral structure with a moment of 2.2(1)μB/Mn, superimposed with weak collinear ferromagnetism. Inelastic neutron scattering shows three collective Q = 0 excitations at Δ1= 2.9(6) meV, Δ2 = 14.6(3), and Δ3 = 17.5(3) meV. A field theory of Q ≈ 0 spin waves in triangular antiferromagnets with a 120° spin structure was used to classify these modes. The in-plane mode (α) is gapless, Δ1 is the gap to a doublet of out-of-plane spin excitations (βx,βy), and Δ2, Δ3 result from hybridization of optical phonons with magnetic excitations. While a phenomenological spin Hamiltonian including exchange interactions, Dzyaloshinskii-Moriyainteractions, and single ion crystal field terms can describe aspects of the Mn-based magnetism, spin wave damping (Γ = 25(8) meV) and the extended range of magnetic interactions indicate itinerant magnetism consistent with the transport anomalies.

*This work was supported as part of the Institute for Quantum Matter, an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Basic Energy Sciences under Award No.DE-SC001933. J.G. acknowledges support from the NSERC Postdoctoral Fellowship Program. C.B. was supported by the Gordon and Betty Moore Foundation through the EPIQS program GBMF-4532. This work is also partially supported by CREST (JPMJCR18T3), Japan Science and Technology Agency (JST), by Grants-in-Aids for Scientific Research on Innovative Areas (15H05882 and 15H05883) from the Ministry of Education, Culture, Sports, Science, and Technology of Japan, by Grants-in-Aid for Scientific Research(19H00650), and by New Energy and Industrial Technology Development Organization.

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Presenters

  • Jonathan Gaudet

    • Department of Physics and Astronomy and Institute for Quantum Matter, The Johns Hopkins University
    • Johns Hopkins University
    • Department of Physics and Astronomy and Institute for Quantum Matter, Johns Hopkins University, Baltimore, Maryland 21218, USA

Authors

  • Jonathan Gaudet

    • Department of Physics and Astronomy and Institute for Quantum Matter, The Johns Hopkins University
    • Johns Hopkins University
    • Department of Physics and Astronomy and Institute for Quantum Matter, Johns Hopkins University, Baltimore, Maryland 21218, USA

  • Youzhe Chen

    • Johns Hopkins University

  • Sayak Dasgupta

    • Johns Hopkins University

  • Guy G Marcus

    • Institute for Quantum Matter and Department of Physics and Astronomy, Johns Hopkins University
    • Johns Hopkins University

  • Jiao Lin

    • Neutron Scattering Division, Oak Ridge National Laboratory

  • Taishi Chen

    • Univ of Tokyo
    • Institute for Solid State physics, University of Tokyo

  • Takahiro Tomita

    • Institute for Solid State physics, University of Tokyo

  • Muhammad Ikhlas

    • Institute for Solid State Physics, University of Tokyo
    • Institute for Solid State physics, University of Tokyo
    • University of Tokyo

  • Yang Zhao

    • NIST Center for Neutron Research,, National Institute of Standards and Technology
    • NIST Center for Neutron Research, National Institute of Standards and Technology
    • National Institute of Standard and Technology
    • Center for Neutron Research, National Institute of Standards and Technology
    • National Institute of Standards and Technology

  • Wangchun C Chen

    • NIST Center for Neutron Research, National Institute of Standards and Technology

  • Matthew Brandon Stone

    • Oak Ridge National Lab
    • Oak Ridge national lab
    • Quantum Condensed Matter Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831, USA
    • Neutron Scattering Division, Oak Ridge National Laboratory
    • Oak Ridge National Laboratory
    • Oakridge National Laboratory

  • Oleg Tchernyshyov

    • Johns Hopkins University
    • Institute for Quantum Matter and Department of Physics and Astronomy, Johns Hopkins University

  • Satoru Nakatsuji

    • Department of Physics and ISSP, University of Tokyo
    • Department of Physics, the University of Tokyo
    • Univ of Tokyo
    • Institute for Solid State Physics, University of Tokyo
    • The Institute for Solid State physics, The Univeristy of Tokyo
    • The Institute for Solid State Physics, The University of Tokyo
    • Institute for Solid State physics, University of Tokyo

  • Collin Leslie Broholm

    • Johns Hopkins University
    • Department of Physics and Astronomy and Institute for Quantum Matter, The Johns Hopkins University
    • Department of Physics and Astronomy and Institute for Quantum Matter, Johns Hopkins University, Baltimore, Maryland 21218, USA
    • Institute for Quantum Matter and Department of Physics and Astronomy, Johns Hopkins University
    • Physics, The Johns Hopkins University