  Whether the surface states in SmB6 are topological is still a critical issue
in the field of topological Kondo insulators. In the magneto-transport study of
single crystalline SmB6 microribbons, we have revealed a positive planar Hall
effect (PHE), the amplitude of which increases dramatically with decreasing
temperatures but saturates below 5 K. This positive PHE is ascribed to the
surface states of SmB6 and expected to arise from the anisotropy in lifting the
topological protection from back-scattering by the in-plane magnetic field,
thus suggesting the topological nature of surface states in SmB6. On the
contrary, a negative PHE is observed for the bulk states at high temperatures,
which is almost three orders of magnitudes weaker than the surface-induced
positive PHE.
