Nature’s 10-Ten people who mattered this year
Yuan Cao’s teenage years were hardly typical. By age 18, he had already graduated from high school, completed an undergraduate degree at the University of Science and Technology of China in Hefei, and travelled to the United States to begin his PhD. He hasn’t slowed down since: this year, aged just 21, Cao had two papers published on strange behaviour in atom-thick layers of carbon that have spurred a new field of physics. Cao admits that his situation is unusual, but says he isn’t special. After all, he did spend a full four years at university: “I just skipped some of the boring stuff in middle school.”
Pablo Jarillo-Herrero’s group at the Massachusetts Institute of Technology (MIT) in Cambridge was already layering and rotating sheets of carbon at different angles when Cao joined the lab in 2014. Cao’s job was to investigate what happened in two-layer stacks when one graphene sheet was twisted only slightly with respect to the other, which one theory predicted would radically change the material’s behaviour.
Many physicists were sceptical about the idea. But when Cao set out to create the subtly twisted stacks, he spotted something strange. Exposed to a small electric field and cooled to 1.7 degrees above absolute zero, the graphene — which ordinarily conducts electricity — became an insulator (Y. Cao et al. Nature 556, 80–84; 2018). That by itself was surprising. “We knew already that it would have a big impact on the community,” says Cao. But the best was yet to come: with a slight tweak to the field, the twisted sheets became a superconductor, in which electricity flowed without resistance (Y. Cao et al. Nature 556, 43–50; 2018). Seeing the effect in a second sample convinced the team that it was real.