Magnonic analogs of topological Dirac semimetals

In electronic topological Dirac semimetals (DSMs) the conduction and valence bands touch at discrete points in the Brillouin zone and formDirac cones. They are robust against spin–orbit interaction (SOI) and protected by crystal symmetries. They can be driven to different topological phases by breaking the symmetries. In the low-temperature quantummagnetic systems themagnon dispersions have similar band structures as the electron dispersions, butwith positive definite energies. In these magnetic systems SOImanifests in the formof theDzyaloshinskii–Moriya interaction (DMI). In this communication, we identify two types ofmagnonic DSMs in quasi-two-dimensional quantum magnets. Thefirst type is a consequence of topological phase transition between trivial and topological magnon insulators and the second type is intrinsic and protected by crystal symmetries. They are robust against DMI and can be driven to a topologicalmagnon phase by breaking the symmetries. They can bemanipulated by an externalmagnetic field and accessible by the bulk sensitive inelastic neutron scattering experiments.