Science, Physics, Research, Graphite and Superconduction

"Jarillo-Herrero and his collaborators found that graphene, a two-dimensional layer of carbon atoms with a honeycomb-like lattice, can behave at two electrical extremes when rotated at a certain angle: as an insulator, in which electrons are completely blocked from flowing; and as a superconductor, in which electrical current can stream through without resistance. This discovery led to the development of 'twistronics'", which Physics World reporter Hamish Johnston called 'a new and very promising technique for adjusting the electronic properties of graphene'."
MIT News

“Until last year, graphene was slowly becoming out of fashion."
"There was good theoretical motivation to see what would happen [experimenting with graphite]." 
"When we saw superconductivity, all hell broke loose. Then we realized this was a very big thing."
Pablo Jarillo-Herrero, physicist, Massachusetts Institute of Technology

Pablo Jarillo-Herrero (right), an associate professor of physics at MIT, was honored with Physics World's Breakthrough of the Year for his group's discovery of “magic-angle” graphene, a “promising technique for adjusting the electronic properties of graphene.” Graduate student Yuan Cao (left) was a lead researcher in the work.  Photo: Melanie Gonick/MIT

"He’s the guy [Dr.Pablo Jarillo-Herrero] who’s done this the best. Somehow they [Dr.Jarillo-Herrero and his laboratory collaborators] have the magic touch."
"There’s a lot of things that could happen, and which one does happen depends on a lot of experimental details."
"We’re just beginning to understand and map out that space. But the hope is that there will be something there that isn’t seen in any other system."
Andrea Young, physics professor, University of California, Santa Barbara

Take the commonplace writing instrument like a pencil with its graphite/clay 'lead' so commonly used and seldom thought deeply about -- for as a rude and reliable tool it is simply taken for granted. Not, however, the graphite portion of its constituents. Fifteen years ago a discovery was made that a single sheet of one-atom thick layer of carbon atoms in a honeycomb pattern represents a newfound physics wonder. Called graphene, the ultrathin carbon is 200 times stronger than steel, though it is flexible and lighter than paper.

And it was found to be a conductor of heat and electrical current. Soon scientists figured out whatever seemed most usefully interesting about this element and set further investigation into its properties and potentials aside. Until last year, when physicists at the Massachusetts Institute of Technology made the discovery that by stacking two sheets of the material twisted at a slight angle between them produced most peculiar phenomena. And this discovery produced a new field of scientific enquiry: twistronics.

A device containing an unusual form of carbon: two one-atom-thick sheets pressed together with the lattice of one rotated slightly. Experiments by Dmitri Efetov and his colleagues show that this material can exhibit different electronic properties, including superconductivity.  Credit...ICFO – The Institute of Photonic Sciences

 A detailed explanation of the material's potential was published in Nature in late October, detailing the material now known as magic-angle twisted bilayer graphene. By tweaking graphene's temperature, magnetic field and the number of electrons able to move freely, the international team of scientists showed how the material morphed, becoming a superconductor with the capacity to convey electrical current without encountering resistance. Minus those alterations, electrical current failed to flow and the material acted as an insulator.

It is now anticipated that with the use of twistronics researchers will be enabled to advantage the superconductivity and any other material properties to engineer novel electronics for computers. Besides which there may be potential applications in other areas to produce hitherto unimagined properties. Two layers of graphene, perfectly aligned would have the same results as a single sheet of graphene. By twisting one of the layers slightly against another, rotational misalignment produces a repeating pattern affecting their atomic structure.

Dmitri Efetov and Xiaobo Lu .Credit. Institute of Photonic Sciences

Leaving electrons to readily move between the two sheets where their lattices line up while in places where the sheets were misaligned, the flow would become more difficult. Dr.Jarillo-Herrero and his research team made the discovery that by using one layer of graphene torn into two pieces they produced two flakes with aligned lattices. In the process, one of the graphene flakes becomes rotated by around 1.3 degrees, pressed down on the other; that discovery induced other scientists to work with that formula to produce their own discoveries.

Dmitri K.Efetov, a physicist at the Institute of Photonic Sciences and the Barcelona Institute of Science and Technology in Spain, along with colleagues, confirmed Dr.Jarillo-Herrero's findings, and at the same time discovered that employing more permutations of temperature, magnetic field and electron density  turned graphene into a superconductor. In addition to which they found graphene could exhibit an unusual kind of magnetism related to the electron movement, not the intrinsic magnetism of atoms similar to materials like iron.

Experimenting with materials on which to place the graphene on, and utilizing other configurations could conceivably yield varying results since the electronic behaviour of the material may depend on the very material graphene is placed upon. "I think this is just the beginning", Harvard  University physicist Philip Kim remarked, as scientists have started looking at three layers of graphene and an entire range of other two-dimensional materials.

Stack and Twist  Graphene is an atom-thin sheet of carbon atoms arranged in a hexagonal pattern. Stacking two sheets and twisting one by the “magic angle” of 1.1 degrees yields a superconductive material with other strange properties. The New York Times