Twisting a monolayer and a bilayer sheet of graphene into a three-layer structure leads to new quantum mechanical states. — ScienceDaily

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Since the discovery of graphene more than 15 years ago, researchers have been in a global race to unlock its unique properties. Not only is graphene — a one-atom-thick sheet of carbon arranged in a hexagonal lattice — the strongest, thinnest material known to man, it is also an excellent conductor of heat and electricity.

Now, a team of researchers at Columbia University and the University of Washington has discovered that a variety of exotic electronic states, including a rare form of magnetism, can arise in a three-layer graphene structure.

The findings appear in an article published Oct. 12 in Nature Physics.

The work was inspired by recent studies of twisted monolayers or twisted bilayers of graphene, comprising either two or four total sheets. These materials were found to host an array of unusual electronic states driven by strong interactions between electrons.

“We wondered what would happen if we combined graphene monolayers and bilayers into a twisted three-layer system,” said Cory Dean, a professor of physics at Columbia University and one of the paper’s senior authors. “We found that varying the number of graphene layers endows these composite materials with some exciting new properties that had not been seen before.”

In addition to Dean, Assistant Professor Matthew Yankowitz and Professor Xiaodong Xu, both in the departments of physics and materials science and engineering at University of Washington, are senior authors on the work. Columbia graduate student Shaowen Chen, and University of Washington graduate student Minhao He are the paper’s co-lead authors.

To conduct their experiment, the researchers stacked a monolayer sheet of graphene onto a bilayer sheet and twisted them by about 1 degree. At temperatures a few degrees over absolute zero, the team observed an array of insulating states — which do not conduct electricity — driven by