Topological crossings in magnetic space groups

Non-symmorphic symmetry is known to enforce topological crossings in crystals. Using the elementary band irreducible representations non-trivial crossings in the form of hour-glass or accordian spectrum have been discovered in certain space groups. Here we extend such an analysis to a wider domain of magnetic space groups (MSGs). We show that the magnetic co-representations (coreps), which are derived from the non-magnetic irreducible representations, can be used to detect non-symmorphic symmetry enforced topological crossings in MSGs. We demonstrate this with two examples, where we find magnetic Weyl points and hour-glass dispersions. DFT band-structure calculation of corresponding magnetic materials confirms our findings. Furthermore, we compute the surface states and discuss other experimental consequences of the hourglass dispersion in magnetic materials.