In 2018, physicists showed that something interesting happens when two sheets of the nanomaterial graphene are placed on top of each other. When one layer is rotated to a "magic angle" of around 1.1 degrees with respect to the other, the system becomes a superconductor—meaning it conducts electricity with zero resistance. Even more exciting, there was evidence that it was an unconventional form of superconductivity—a type that can happen at temperatures well above absolute zero, where most superconducting materials function.
Since the initial discovery, researchers have been working to understand this exotic state of matter. Now, a research team led by Brown University physicists has found a new way to precisely probe the nature of the superconducting state in magic-angle graphene. The technique enables researchers to manipulate the repulsive force between elections—the Coulomb interaction—in the system. In a study published in the journal Science, the researchers show that magic-angle superconductivity grows more robust when Coulomb interaction is reduced, an important piece of information in understanding how this superconductor works.
"This is the first time anyone has demonstrated that you can directly manipulate the strength of Coulomb interaction in a strongly correlated electronic system," said Jia Li, an assistant professor of physics at Brown and corresponding author of the research. "Superconductivity is driven by the interactions between electrons, so when we can manipulate that interaction, it tells us something really important about that system. In this case, demonstrating that weaker Coulomb interaction strengthens superconductivity provides an important new theoretical constraint on this system."
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