Anomalous Hall Effect induced by extremely low field in ultra pure ZrTe₅

ZrTe₅ has gathered interest in recent years due to its non-trivial topology. In monolayer form, it is predicted to be a quantum spin hall insulator. In bulk, it is predicted to reside extremely close to a phase transition between a strong and weak topological insulator, with a 3D Dirac semimetal state at the boundary between these two phases. We report detailed measurements of the anomalous hall effect (AHE) in ultra-pure, high mobility bulk ZrTe₅. We find the hall resistance saturates at an extremely low magnetic field ( B << 1T ), and remains at the saturation value for fields up to 32T. This AHE is present despite no evidence of magnetism in ZrTe₅. We investigate the AHE effect in ZrTe5 as a function of temperature, magnetic field angle, strain, and doping, and discuss the origins of this effect.