Oscillatory angular dependence of the magnetoresistance in a topological insulator Bi1-xSbx

The angular-dependent magnetoresistance and the Shubnikov-de Haas oscillations are studied in a topological insulator Bi0.91Sb0.09, where the two-dimensional (2D) surface states coexist with a three-dimensional (3D) bulk Fermi surface (FS). Two distinct types of oscillatory phenomena are discovered in the angular dependence: The one observed at lower fields is shown to originate from the surface state, which resides on the (2 (11) over bar) plane, giving a distinct way to distinguish the 2D surface state from the 3D FS. The other one, which becomes prominent at higher fields, probably comes from the (111) plane and is obviously of unknown origin, pointing to peculiar physics in transport properties of topological insulators.