Physicists discover new property of graphene: magnetism

A team of Stanford University physicists has observed a form of magnetism - predicted but never seen - that is generated when two networks of graphite honeycomb are stacked and carefully rotated at a special angle.

The authors of the scientific paper, published July 25 in the journal Science, suggest that magnetism, called orbital ferromagnetism, may be useful for certain applications, particularly in quantum computing.

“We were not focusing our attention on magnetism. We have discovered what may be the most exciting discovery of my career through partial and completely accidental exploration, ”research leader David Goldhaber-Gordon said in a statement.

"Our discovery shows that the most interesting things often come as a surprise," he added, quoted by EuropaPress.

The researchers made the discovery while trying to reproduce another discovery. In early 2018, MIT's Pablo Jarillo-Herrero group announced that it had obtained a two-sheet stack of subtly misaligned carbon atoms (twisted two-layer graphene) to conduct unresisted electricity, a property known as superconductivity.

At the time, the discovery was a striking confirmation of a nearly decade-long prediction that graphene sheets rotated at a very particular angle should replicate interesting phenomena. And it seems to be true.

When stacked and twisted, graphene forms a superstructure with an interference or moire pattern. "It's like when we play two musical sounds with slightly different frequencies," said Goldhaber-Gordon. “As a result, we will get a beat that is related to the difference between the frequencies of the two sounds. This is similar to what you get by stacking two trusses on top of each other and twisting them so that they are not perfectly aligned, ”he continued.

The superstructure formed when graphene rotated at 1.1 degrees causes the normally varying energy states of electrons in the material to collapse, creating what physicists call the flat band where the speed at which electrons move falls. to almost zero.

After this deceleration, the movements of any electron become highly dependent on the electrons in its vicinity. These interactions are at the center of many exotic quantum states of matter.