Abstract
We study the topological properties of magnon excitations in three-dimensional antiferromagnets, where the ground state configuration is invariant under time reversal followed by space inversion ( symmetry). We prove that Dirac points and nodal lines, the former being the limiting case of the latter, are the generic forms of symmetry-protected band crossings between magnon branches. As a concrete example, we study a Heisenberg spin model for a “spin-web” compound, , and show the presence of the magnon Dirac points assuming a collinear magnetic structure. Upon turning on symmetry-allowed Dzyaloshinsky-Moriya interactions, which introduce a small noncollinearity in the ground state configuration, we find that the Dirac points expand into nodal lines with nontrivial -topological charge, a new type of nodal line not predicted in any materials so far.
- Received 29 March 2017
DOI:https://doi.org/10.1103/PhysRevLett.119.247202
© 2017 American Physical Society