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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.

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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