Spin-plasmons in topological insulator
  Collective plasmon excitations in a helical electron liquid on the surface of strong three-dimensional topological insulator are considered. The properties and internal structure of these excitations are studied. Due to spin-momentum locking in helical liquid on a surface of topological insulator, the collective excitations should manifest themselves as coupled charge- and spin-density waves. 
D. K. Efimkin, Yu. E. Lozovik, A. A. Sokolik
cond-mat.mes-hall