Unusual Exchange Couplings and Intermediate Temperature Weyl State in ${\mathrm{Co}}_{3}{\mathrm{Sn}}_{2}{\mathrm{S}}_{2}$

Unusual Exchange Couplings and Intermediate Temperature Weyl State in ${Co}_{3} {Sn}_{2} S_{2}$

Qiang Zhang, Satoshi Okamoto, German D. Samolyuk, Matthew B. Stone, Alexander I. Kolesnikov, Rui Xue, Jiaqiang Yan, Michael A. McGuire, David Mandrus, and D. Alan Tennant

Phys. Rev. Lett. 127, 117201 – Published 7 September 2021

Abstract

Understanding magnetism and its possible correlations to topological properties has emerged to the forefront as a difficult topic in studying magnetic Weyl semimetals. ${Co}_{3} {Sn}_{2} S_{2}$ is a newly discovered magnetic Weyl semimetal with a kagome lattice of cobalt ions and has triggered intense interest for rich fantastic phenomena. Here, we report the magnetic exchange couplings of ${Co}_{3} {Sn}_{2} S_{2}$ using inelastic neutron scattering and two density functional theory (DFT) based methods: constrained magnetism and multiple-scattering Green’s function methods. ${Co}_{3} {Sn}_{2} S_{2}$ exhibits highly anisotropic magnon dispersions and linewidths below $T_{C}$ , and paramagnetic excitations above $T_{C}$ . The spin-wave spectra in the ferromagnetic ground state is well described by the dominant third-neighbor “across-hexagon” $J_{d}$ model. Our density functional theory calculations reveal that both the symmetry-allowed 120° antiferromagnetic orders support Weyl points in the intermediate temperature region, with distinct numbers and the locations of Weyl points. Our study highlights the important role ${Co}_{3} {Sn}_{2} S_{2}$ can play in advancing our understanding of kagome physics and exploring the interplay between magnetism and band topology.

Received 11 February 2021
Revised 17 June 2021
Accepted 16 July 2021

DOI:https://doi.org/10.1103/PhysRevLett.127.117201

Physics Subject Headings (PhySH)

Electronic structure Magnetic coupling

Weyl semimetal

Density functional theory Inelastic neutron scattering

Condensed Matter, Materials & Applied Physics

Authors & Affiliations

Qiang Zhang ^1,*, Satoshi Okamoto ^2,3,†, German D. Samolyuk², Matthew B. Stone ¹, Alexander I. Kolesnikov ¹, Rui Xue⁴, Jiaqiang Yan ², Michael A. McGuire^2,3, David Mandrus^5,2,4, and D. Alan Tennant ^2,6,3

¹Neutron Scattering Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, USA
²Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, USA
³Quantum Science Center, Oak Ridge, Tennessee 37831, USA
⁴Department of Physics & Astronomy, The University of Tennessee, Knoxville, Tennessee 37996, USA
⁵Department of Materials Science and Engineering, The University of Tennessee, Knoxville, Tennessee 37996, USA
⁶Shull Wollan Center, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, USA