Magnetic structure and excitations of the topological semimetal YbMnBi2

We investigated the magnetic structure and dynamics of YbMnBi₂, with elastic and inelastic neutron scattering, to shed light on the topological nature of the charge carriers in the antiferromagnetic phase. We confirm C -type antiferromagnetic ordering of the Mn spins below T_N=290 K and determine that the spins point along the c axis to within about 3^∘. The observed magnon spectrum can be described very well by the same effective spin Hamiltonian that was used previously to model the magnon spectrum of CaMnBi₂. Our results show conclusively that the creation of Weyl nodes in YbMnBi₂ by the time-reversal symmetry-breaking mechanism can be excluded in the bulk.