Superconductors, materials that carry electricity without resistance, can be divided into two broad groups depending on how they react to a magnetic field--or so physicists thought. New experiments show that one well-studied superconductor actually belongs to both groups at the same time. "If the experiment is true, this would add a whole new class of superconductors," says Egor Babaev, a theorist at the University of Massachusetts, Amherst.