Pressure-induced topological phase transitions and strongly anisotropic magnetoresistance in bulk black phosphorus

We report the anisotropic magnetotransport measurement on a noncompound band semiconductor black phosphorus (BP) with magnetic field B up to 16 Tesla applied in both perpendicular and parallel to electric current I under hydrostatic pressures. The BP undergoes a topological Lifshitz transition from band semiconductor to a zero-gap Dirac semimetal state at a critical pressure Pc, characterized by a weak localization-weak antilocalization transition at low magnetic fields and the emergence of a nontrivial Berry phase of π detected by SdH magneto-oscillations in magnetoresistance curves. In the transition region, we observe a pressure-dependent negative MR only in the B∥I configuration. This negative longitudinal MR is attributed to the Adler-Bell-Jackiw anomaly (topological E·B term) in the presence of weak antilocalization corrections.