Anisotropic and strong negative magnetoresistance in the three-dimensional topological insulator Bi2Se3

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.