  We report the low-temperature magneto-transport in the bulk-insulating single
crystal of topological insulator Sn doped Bi1.1Sb0.9Te2S. The Shubnikov-de Haas
oscillations appear with their reciprocal frequency proportional to cos/theta ,
demonstrating the dominant transport of topological surface states. While the
magnetic field is rotating in the sample surface, the planar Hall effect arises
with sizeable oscillations following a relation of cos/theta sin/theta . Its
amplitude reaches the maximum at the lowest temperature and drops to nearly
zero at the temperature higher than 100 K. All these evidences consolidate such
planar Hall oscillations as a new golden criterion on the topological surface
transport.
