Highly Dispersive Scattering from Defects in Noncollinear Magnets

We demonstrate that pointlike defects in noncollinear magnets give rise to a highly dispersive structure in the magnon scattering, violating a standard paradigm of its momentum independence. For a single impurity spin coupled to a prototypical noncollinear antiferromagnet, we find that the resolvent is dominated by a distinct dispersive structure with its momentum dependence set by the magnon dispersion and shifted by the ordering vector. This feature is a consequence of umklapp scattering off the impurity-induced spin texture, which arises due to the noncollinear ground state of the host system. Detailed results for the staggered and uniform magnetization of this texture as well as the T matrix from numerical linear spin-wave theory are presented.