Temperature-independent anomalous Hall effect and magnetic field angular dependence in thin bismuth electronic devices

A requirement to observe the anomalous Hall effect (AHE) in an electronic system is for it to break time-reversal symmetry, such as for example in materials that are ferromagnetic. In this work, making use of a newly-developed mechanical exfoliation technique, we have fabricated thin electronic devices in diamagnetic bismuth and performed electronic transport experiments over a wide range of temperatures and magnetic fields. In a 68 nm thick bismuth device, we unequivocally observe an AHE that surprisingly was observed to be entirely temperature independent from 15 mK to 300 K temperatures. In addition, the longitudinal resistance was observed to be entirely featureless, i.e., exhibited no quantum oscillations or magnetoresistance for magnetic fields up to ± 30 T. These observations suggest there could be a hidden mechanism responsible for time-reversal symmetry breaking in bismuth and this could be of fundamental importance considering recent compelling evidence for bismuth to be a higher-order topological insulator.