Topologically nontrivial magnons at an interface of two kagome ferromagnets

Magnon band structures of topological magnon insulators exhibit a nontrivial topology due to the Dzyaloshinskii-Moriya interaction, which manifests itself by topologically protected edge magnons. Bringing two topological magnon insulators into contact can lead to nontrivial unidirectional magnons located at their common interface. We study theoretically interfaces of semi-infinite kagome ferromagnets in various topological phases, with a focus on the formation and the confinement of nontrivial interface magnons. We analyze generic magnon dispersions with respect to the number of band gaps and the respective winding numbers. Eventually, we prove that interfaces of topologically identical phases can host nontrivial interface magnons as well.