Anisotropic and strong negative magnetoresistance in the three-dimensional topological insulator Bi 2 Se 3

We report on high-field angle-dependent magnetotransport measurements on epitaxial thin films of Bi2Se3, a three-dimensional topological insulator. At low temperature, we observe quantum oscillations that demonstrate the simultaneous presence of bulk and surface carriers. The magnetoresistance of Bi2Se3 is found to be highly anisotropic. In the presence of a parallel electric and magnetic field, we observe a strong negative longitudinal magnetoresistance that has been considered as a smoking gun for the presence of chiral fermions in a certain class of semimetals due to the so-called axial anomaly. Its observation in a three-dimensional topological insulator implies that the axial anomaly may be in fact a far more generic phenomenon than originally thought.