Jackiw-Rebbi magnons

We theoretically study the elementary excitations of a magnetic topological insulator. These excitations combine aspects of Jackiw-Rebbi bound states and magnon modes. Specifically, we consider the delocalized excitations of a quantum ferromagnet in contact with a 2D Dirac electron system. The local magnetization gaps the electron system, leading to bound states at magnetic domain walls (Jackiw-Rebbi modes). The delocalized (magnon) excitations of this system thus inherit a charge from the delocalized Jackiw-Rebbi bound states. We show that these composite excitations (Jackiw-Rebbi magnons) can be probed experimentally through the characteristic chiral current distribution and through unique characteristics of the longitudinal and transverse spin susceptibilities.