Anomalous negative longitudinal magnetoresistance and violation of Ohm's law deep in the topological insulating regime in Bi[Formula: see text] Sb[Formula: see text]

Bi[Formula: see text] Sb[Formula: see text] is a topological insulator (TI) for [Formula: see text] –0.20. Close to the Topological phase transition at [Formula: see text] , 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 [Formula: see text] ). We report the unexpected discovery of Chiral anomaly-like features in the whole range ([Formula: see text] ) 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 [Formula: see text] . Surprisingly, the strongest Weyl phase is found at [Formula: see text] with a non-saturating negative LMR much larger than observed for [Formula: see text] . The negative LMR vanishes rapidly with increasing angle between B and I. Additionally, non-linear I–V is found for [Formula: see text] indicating a violation of Ohm’s law. This unexpected observation of a strong Weyl state in the whole TI regime in Bi[Formula: see text] Sb[Formula: see text] points to a gap in our understanding of the detailed crystal and electronic structure evolution in this alloy system.