Magnetic Excitations in $\alpha$-RuCl$_{3}$

ORAL

Abstract

The layered material $\alpha$-RuCl$_{3}$ is composed of stacks of weakly coupled honeycomb lattices of octahedrally coordinated Ru$^{3+}$ ions. The Ru ion ground state has 5 d electrons in the low spin state, with spin-orbit coupling very strong compared to other terms in the single ion Hamiltonian. The material is therefore an excellent candidate for investigating possible Heisenberg-Kitaev physics. In addition, this compound is very amenable to investigation by neutron scattering to explore the magnetic ground state and excitations in detail. Here we discuss new time-of-flight inelastic neutron scattering data on $\alpha$-RuCl$_{3}$. A high energy excitation near 200 meV is identified as a transition from the single ion J=1/2 ground state to the J=3/2 excited state, yielding a direct measurement of the spin orbit coupling energy. Higher resolution measurements reveal two collective modes at much lower energy scales. The results are compared with the theoretical expectations for excitations in the Heisenberg - Kitaev model on a honeycomb lattice, and show that Kitaev interactions are important.

*Research at SNS supported by the DOE BES Scientific User Facilities Division

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Authors

  • Stephen Nagler

    • Quantum Condensed Matter Division, ORNL, USA
    • QCMD, Oak Ridge National Laboratory

  • Arnab Banerjee

    • QCMD, Oak Ridge National Laboratory

  • Craig Bridges

    • Chemical Sciences Division, ORNL, USA
    • CSD, Oak Ridge National Laboratory

  • Jiaqiang Yan

    • Material Sciences Division, ORNL, USA
    • MSTD, Oak Ridge National Laboratory
    • Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, USA

  • David Mandrus

    • Department of Physics, University of Tennessee, Knoxville, USA
    • Dep. of Mat. Sci. and Eng., U. Tennessee
    • Oak Ridge National Laboratory / Univ of Tennessee
    • Department of Materials Science \& Engineering, University of Tennessee, Knoxville

  • Matthew Stone

    • Quantum Condensed Matter Division, ORNL
    • Oak Ridge National Laboratory
    • Quantum Condensed Matter Division, ORNL, USA
    • QCMD, Oak Ridge National Laboratory
    • Oak Ridge National Lab

  • Adam Aczel

    • Quantum Condensed Matter Division, ORNL
    • Quantum Condensed Matter Division, ORNL, USA
    • QCMD, Oak Ridge National Laboratory
    • Oak Ridge National Laboratory
    • Quantum Condensed Matter Division, Oak Ridge National Laboratory

  • Ling Li

    • Dep. of Mat. Sci. and Eng., U.Tennessee

  • Yuen Yiu

    • Department of Physics, University of Tennessee, Knoxville, USA
    • Dep. of Physics, U. Tennessee

  • Mark Lumsden

    • Quantum Condensed Matter Division, ORNL, USA
    • QCMD, Oak Ridge National Laboratory
    • Oak Ridge National Lab

  • Johannes Knolle

    • Max-Planck-Institut, Dresden

  • Roderich Moessner

    • Max-Planck-Institut, Dresden
    • MPI-PKS Dresden
    • Max-Planck-Institut f\"ur Physik komplexer Systeme, Germany
    • MPIPKS
    • Max Planck Institute for the Physics of Complex Systems, Dresden, Germany

  • Alan Tennant

    • Neutron Sciences Directorate, ORNL, USA
    • NScD, Oak Ridge National Laboratory
    • Oak Ridge National Laboratory
    • Oak Ridge National Laboratory, Oak Ridge, TN, USA