Bismuth Breaks the Rules: Mysterious Magnetic Effect Stays Unchanged Across Extreme Temperatures

Published March 10, 2025

(a) Micro-trench exfoliation technique. (b) Hall response and schematic of the bismuth device.

Our ability to observe new physics sometimes depends on the thinnest of margins and in the case of MagLab users from McGill University, that margin is roughly 68nm. Using an innovative “cheese grater” technique to produce ultra-thin (68nm) flakes of elemental bismuth they found that the flakes displayed a temperature independent version of the anomalous hall effect that is not present in the bulk material. This discovery prompts a number of questions as to what governs the behavior of electrons in elemental bismuth.

What is the finding

Researchers created ultra-thin bismuth films, about 68 nanometers thick — thinner than a thousandth of a human hair — using a unique method similar to a cheese grater to shave off thin flakes. When exposed to a magnetic field, the electrical resistance in the bismuth showed an unusual behavior (called the anomalous Hall effect), which remained the same from near absolute zero to room temperature. (see Fig. 1(b)).

Why is this important?

The anomalous Hall effect shouldn’t happen in bismuth because of its magnetic properties, making this discovery unexpected. Even more puzzling is that the effect stays the same across a huge temperature range, from near absolute zero to room temperature—something never seen before. This suggests that the effect is intrinsic to bismuth and not caused by magnetic impurities. Looking ahead, bismuth could be a valuable material for exploring quantum versions of this effect and for developing biocompatible electronics, thanks to its low toxicity.

Who did the research?

Oulin Yu¹, F. Boivin¹, A. Silberztein¹, and G. Gervais¹

¹Department of Physics, McGill University, Montréal, H3A 2T8, Canada

Why did they need the MagLab?

This discovery was made on a resistive 31 Tesla magnet equipped with a variable temperature insert at the MagLab’s DC Field Facility. The specialized magnet system was of fundamental importance to the discovery of temperature independence since no magnet with this field and temperature range is available at the researchers’ home laboratory.