Just a year ago, scientists presented results that seemed almost too good to be true: Carbon sheets only a single atom thick, called graphene, took on a pair of important physical properties when they were twisted at just the right "magic" angle relative to one another. If the atmosphere this month at the world's largest physics conference was any indication, twisted graphene has now spawned an entirely new field of physics research. The result has drawn interest from physicists around the world who hope to understand the strange phenomena locked into the carbon sheets.
Last year, a team of physicists led by graduate student Yuan Cao made a discovery as close to shocking as science can get. They stacked a pair of graphene sheets on top of one another, cooled the system down to near absolute zero, and twisted one of the sheets to a 1.1-degree angle relative to the other. They added a voltage, and the system became a kind of insulator such that the interactions between the particles themselves prevent electrons from moving. When they added more electrons, the system became a superconductor, a kind of system in which electrical charge can move without resistance.
"It was amazing," Jarillo-Herrero said. "We thought it was too good to be true... We were so doubtful at first that we wondered if we should spend more time on it, but when we saw the results, we were blown away."
The results have since been replicated by several teams, and a year after the discovery, physicists are researching the material in droves. Albeit, there's still plenty that physicists don't understand about the origin of the superconductivity and the nature of the insulating states. But why has this system taken off? Jarillo-Herrero explained that it combines already-flourishing fields of physics, including those that study graphene and other two-dimensional materials, topological properties, super-cold matter, and unusual electronic behaviors that come about from the way electrons are distributed in certain materials. On top of that, stacked graphene sheets are controllable and accessible in a way that other materials aren't, given that they are relatively easy to produce. And the ability to switch between various effects with just a twist, a voltage, and some electrons allows a higher level of control than other materials.
Even as physicists are buzzing with excitement, it will probably be decades before you see twisted bilayer graphene in your smartphone or any consumer device, though obviously that's hard to predict.
