# Magnetic structure and excitations of the topological semimetal YbMnBi$_2$

## TL;DR

This study uses neutron scattering to analyze the magnetic structure and excitations of YbMnBi$_2$, revealing antiferromagnetic order and excluding Weyl node formation via time-reversal symmetry breaking in the bulk.

## Contribution

It provides the first detailed magnetic structure and excitation spectrum of YbMnBi$_2$, demonstrating that Weyl nodes are not formed through bulk time-reversal symmetry breaking.

## Key findings

- YbMnBi$_2$ exhibits C-type antiferromagnetic order below 290 K.
- Magnon spectrum matches models used for CaMnBi$_2$.
- Weyl nodes are excluded in the bulk due to magnetic structure.

## Abstract

We investigated the magnetic structure and dynamics of YbMnBi$_2$, 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 $T_{\rm N} = 290$ K, and determine that the spins point along the $c$-axis to within about $3^\circ$. The observed magnon spectrum can be described very well by the same effective spin Hamiltonian as was used previously to model the magnon spectrum of CaMnBi$_2$. Our results show conclusively that the creation of Weyl nodes in YbMnBi$_2$ by the time-reversal-symmetry breaking mechanism can be excluded in the bulk.