Ultra-thin flakes of bismuth display mysterious magnetic properties 鈥� which could help the soft, iridescent metal become a wonder material for making greener electronics.
鈥淔rankly, I鈥檓 still waking up at night because I wonder: what is at play here?鈥� says at McGill University in Montreal, Canada.
Researchers have suspected that very thin flakes of bismuth could have unusual physical properties, as other ultra-thin materials like carbon-based graphene do. But because bismuth is so soft, it is difficult to make it thin enough for these peculiar properties to emerge.
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Now, Gervais and his colleagues have developed a new technique to do this, which he likens to using a cheese grater. This enabled the researchers to make flakes of bismuth only 68 nanometres thick, less than a thousandth of the thickness of a piece of paper. They then exposed their flakes to a range of temperatures, from near absolute zero to room temperature, and to magnetic fields tens of thousands of times stronger than fridge magnets.
Across that range of conditions 鈥� from very cold and extremely magnetic to fairly standard 鈥� the bismuth always exhibited one particular electromagnetic behaviour. Namely, when the researchers connected wires to it, a type of electrical current called the 鈥渁nomalous Hall effect鈥� always flowed.
at the University of Salerno in Italy says that the new experiment features a fundamental measurement with a 鈥渧ery, very surprising鈥� result because known properties of bismuth suggest that it just shouldn鈥檛 have an anomalous Hall effect.
Because the effect happens even at room temperature, ultra-thin bismuth may be useful for developing electronic devices, says Ortix. The metal is also less toxic than many similar materials, he says.
Gervais says that he was shocked to see the anomalous Hall effect persist even when his team exposed the samples to extremely strong magnetic fields at the National High Magnetic Field Laboratory in Florida. When increasing these fields didn鈥檛 affect the current, he bet his colleagues that increasing the temperature would do the trick 鈥� but he lost.
鈥淚 can鈥檛 point to one theory that would explain this, only some bits and pieces of a potential explanation,鈥� he says. One possibility may be that the way bismuth鈥檚 atoms are arranged constrains the energies and motion of their electrons according to a set of mathematical rules called topology. But the details of that explanation remain unclear.
Journal reference:
Physical Review Letters,
