  We study surface plasmon polaritons on topological insulator-vacuum
interface. When the time-reversal symmetry is broken due to ferromagnetic
coupling, the surface states exhibit magneto-optical Kerr effect. This effect
gives rise to a novel transverse type surface plasmon polariton, besides the
longitudinal type. In specific, these two types contain three different
channels, corresponding to the pole of determinant of Fresnel reflection
matrix. All three channels of surface plasmon polaritons display tight
confinement, long lifetime and show strong light-matter coupling with a dipole
emitter.
