Graphene is an incredible material. It is just one atom thick, yet is 200 times stronger than steel. It’s a lattice of carbon atoms and can conduct electricity. Under the right conditions, it’s a superconductor, so that electrical flow encounters no resistance.
We have only known about graphene’s superconductivity since 2018. Two layers of graphene were placed on top of each other. They were not perfectly overlayed, they had a little twist of 1.1 degrees. The layers were cooled to just slightly above absolute zero, and voila! Superconductive graphene.
As reported in Science, the new work added an extra layer of graphene. Superconductivity in this graphene sandwich is achieved at a slightly different twist angle (averaging 1.56 degrees), but up to a higher temperature – although still only a few degrees above absolute zero. The finding is interesting in itself, as we are learning more about graphene. However, it has wider implications. It allows researchers to study superconductivity in a completely new way.
The three-layer graphene superconductor is sensitive to an externally applied electric field. By adjusting the strength of that field, the researchers can control the level of superconductivity of the system. Researchers now have a tunable way to study superconductivity.
"Superconductivity in twisted graphene provides physicists with an experimentally controllable and theoretically accessible model system where they can play with the system's properties to decode the secrets of high temperature superconductivity," said one of the paper's co-lead authors, postdoctoral researcher at Harvard University Andrew Zimmerman, in a statement.
"It enabled us to observe the superconductor in a new dimension and provided us with important clues about the mechanism that's driving the superconductivity," added the study's other lead author Zeyu Hao, a PhD student also at Harvard.
The holy grail of superconductivity is creating a material that is superconducting at room conditions. Last year, the first material superconducting at room temperature was announced, but it has few complications. It was just a small amount of material, and to become a superconductor it had to be squeezed between two diamonds at a pressure of 2.5 million atmospheres. This really doesn’t scream "wonder-material that will change our lives".
The new tri-layer graphene has shown evidence that its superconductivity is driven by strong interaction between electrons. This mechanism is believed to be very important in creating stable, high-temperature superconductors, but they are not fully understood. This system could provide crucial insight into the theory of superconductivity.
"The more we understand, the better we have chance to increase the superconducting transition temperatures," said Kim.