For the reason that discovery of graphene greater than 15 years in the past, researchers have been in a worldwide race to unlock its distinctive properties. Not solely is graphene — a one-atom-thick sheet of carbon organized in a hexagonal lattice — the strongest, thinnest materials recognized to man, it’s also a wonderful conductor of warmth and electrical energy.
Now, a workforce of researchers at Columbia College and the College of Washington has found that quite a lot of unique digital states, together with a uncommon type of magnetism, can come up in a three-layer graphene construction.
The findings seem in an article printed Oct. 12 in Nature Physics.
The work was impressed by latest research of twisted monolayers or twisted bilayers of graphene, comprising both two or 4 whole sheets. These supplies have been discovered to host an array of bizarre digital states pushed by sturdy interactions between electrons.
“We puzzled what would occur if we mixed graphene monolayers and bilayers right into a twisted three-layer system,” mentioned Cory Dean, a professor of physics at Columbia College and one of many paper’s senior authors. “We discovered that various the variety of graphene layers endows these composite supplies with some thrilling new properties that had not been seen earlier than.”
Along with Dean, Assistant Professor Matthew Yankowitz and Professor Xiaodong Xu, each within the departments of physics and supplies science and engineering at College of Washington, are senior authors on the work. Columbia graduate scholar Shaowen Chen, and College of Washington graduate scholar 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 diploma. At temperatures just a few levels over absolute zero, the workforce noticed an array of insulating states — which don’t conduct electrical energy — pushed by sturdy interactions between electrons. In addition they discovered that these states may very well be managed by making use of an electrical discipline throughout the graphene sheets.
“We discovered that the course of an utilized electrical discipline issues lots,” mentioned Yankowitz, who can also be a former postdoctoral researcher in Dean’s group.
When the researchers pointed the electrical discipline towards the monolayer graphene sheet, the system resembled twisted bilayer graphene. However once they flipped the course of the electrical discipline and pointed it towards the bilayer graphene sheet, it mimicked twisted double bilayer graphene — the four-layer construction.
The workforce additionally found new magnetic states within the system. Not like standard magnets, that are pushed by a quantum mechanical property of electrons known as “spin,” a collective swirling movement of the electrons within the workforce’s three-layer construction underlies the magnetism, they noticed.
This type of magnetism was found not too long ago by different researchers in numerous buildings of graphene resting on crystals of boron nitride. The workforce has now demonstrated that it can be noticed in an easier system constructed solely with graphene.
“Pure carbon shouldn’t be magnetic,” mentioned Yankowitz. “Remarkably, we will engineer this property by arranging our three graphene sheets at simply the best twist angles.”
Along with the magnetism, the examine uncovered indicators of topology within the construction. Akin to tying several types of knots in a rope, the topological properties of the fabric could result in new types of info storage, which “could also be a platform for quantum computation or new forms of energy-efficient information storage functions,” Xu mentioned.
For now, they’re engaged on experiments to additional perceive the basic properties of the brand new states they found on this platform. “That is actually only the start,” mentioned Yankowitz.