Topological spin-plasma waves

The surface of a topological insulator hosts Dirac electronic states with the spin-momentum locking, which constrains spin orientation perpendicular to electron momentum. As result, collective plasma excitations in interacting liquid manifest themselves as coupled charge- and spin-waves. Here we demonstrate that presence component enables effective coupling between waves at interfaces insulating magnet. Moreover, helical nature locking textures provides phase winding makes spectrum hybridized spin-plasma modes be topologically nontrivial. We also show such lead large thermal Hall response.