Anomalous negative longitudinal magnetoresistance and violation of Ohm's law deep in the topological insulating regime in Bi $$_{1-x}$$ 1 - x Sb $$_x$$ x

Abstract

Abstract Bi $$_{1-x}$$ 1 - x Sb $$_x$$ x is a topological insulator (TI) for $$x \approx 0.03$$ x ≈ 0.03 –0.20. Close to the Topological phase transition at $$x = 0.03$$ x = 0.03 , a magnetic field induced Weyl semi-metal (WSM) state is stabilized due to the splitting of the Dirac cone into two Weyl cones of opposite chirality. A signature of the Weyl state is the observation of a Chiral anomaly [negative longitudinal magnetoresistance (LMR)] and a violation of the Ohm’s law (non-linear $$I{-}V$$ I - V ). We report the unexpected discovery of Chiral anomaly-like features in the whole range ( $$x = 0.032, 0.072, 0.16$$ x = 0.032 , 0.072 , 0.16 ) of the TI state. This points to a field induced WSM state in an extended x range and not just near the topological transition at $$x = 0.03$$ x = 0.03 . Surprisingly, the strongest Weyl phase is found at $$x = 0.16$$ x = 0.16 with a non-saturating negative LMR much larger than observed for $$x = 0.03$$ x = 0.03 . The negative LMR vanishes rapidly with increasing angle between B and I. Additionally, non-linear I–V is found for $$x = 0.16$$ x = 0.16 indicating a violation of Ohm’s law. This unexpected observation of a strong Weyl state in the whole TI regime in Bi $$_{1-x}$$ 1 - x Sb $$_x$$ x points to a gap in our understanding of the detailed crystal and electronic structure evolution in this alloy system.