Researchers at MIT and Harvard University have uncovered a "wonder material" that they claim can exhibit curious electronic properties.
Published in two papers in Nature, the team of physicians' discovery showed that graphene can be tuned to behave at two electrical extremes: as an insulator and superconductor, blocking electrons from flowing while also allowing an electrical current to stream through without resistance.
Since its discovery in 2004, scientists have found that graphene is made of a lacy, honeycomb-like sheet of carbon atoms, making it the thinnest material known to man. It's also very light and flexible while being hundreds of times stronger than steel, and more electrically conductive than copper.
While the research time have successful been able to synthesise graphene superconductors in the past by placing the material in contact with other superconducting metals, this time the researchers managed to find a way to make graphene superconduct on its own. This, they say, demonstrates that superconductivity can be an intrinsic quality in the purely carbon-based material.
This was made possible by the research team creating a "superlattice" of two graphene sheets stacked together, and that wasn't precisely on top of each other, but rotated a tiny amount to a "magic angle" of 1.1 degrees.
"As a result, the overlaying, hexagonal honeycomb pattern is offset slightly, creating a precise moiré configuration that is predicted to induce strange, ‘strongly correlated interactions' between the electrons in the graphene sheets," the report said.
"In any other stacked configuration, graphene prefers to remain distinct, interacting very little, electronically or otherwise, with its neighboring layers.
The team therefore found that when rotated at the magic angle, the two sheets of graphene exhibit nonconducting behavior. When the researchers then applied voltage, adding small amounts of electrons to the graphene superlattice, they found that, at a certain level, the electrons broke out of the initial insulating state and flowed without resistance, as if through a superconductor.
"We can now use graphene as a new platform for investigating unconventional superconductivity," said lead researcher on the team, Jarillo-Herrero.
"One can also imagine making a superconducting transistor out of graphene, which you can switch on and off, from superconducting to insulating. That opens many possibilities for quantum devices."
The researchers were eventually able to tune graphene to behave as an insulator or a superconductor, and any phase in between, exhibiting all these diverse properties in one single device.
This, the report said, is in contrast to other methods, in which scientists have had to grow and manipulate hundreds of individual crystals, each of which can be made to behave in just one electronic phase.
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