The original version of this story appeared in Quanta Magazinee.
In 2024, superconductivity—the flow of electric current with zero resistance—was discovered in three different materials. Two cases stretch the textbook’s understanding of the phenomenon. The third tears it completely apart. “It’s an extremely unusual form of superconductivity that many people would have said is not possible,” said Ashvin Vishwanath, a physicist at Harvard University who was not involved in the discoveries.
Ever since 1911, when Dutch scientist Heike Kamerlingh Onnes first saw electrical resistance disappear, superconductivity has captivated physicists. There is the sheer mystery of how it happens: the phenomenon requires electrons, which carry electric current, to pair up. Electrons repel each other, so how can they unite?
Then there is the technological promise: superconductivity has already enabled the development of MRI machines and powerful particle colliders. If physicists could fully understand how and when the phenomenon occurs, they might be able to engineer a wire that superconducts electricity under everyday conditions rather than only at low temperatures, as is currently the case. World-changing technologies – lossless power grids, magnetically levitating vehicles – may follow.
The latest wave of discoveries has both heightened the mystery of superconductivity and increased optimism. “It seems to be, in materials, that superconductivity is everywhere,” said Matthew Yankowitz, a physicist at the University of Washington.
The discoveries stem from a recent revolution in materials science: All three new cases of superconductivity occur in devices assembled from flat sheets of atoms. These materials show unprecedented flexibility; at the touch of a button, physicists can switch them between conducting, insulating and more exotic behaviors—a modern form of alchemy that has supercharged the pursuit of superconductivity.
It now seems more and more likely that various causes may give rise to the phenomenon. Just as birds, bees and dragonflies all fly with different wing structures, materials appear to pair electrons together in different ways. Although researchers debate exactly what happens in the various two-dimensional materials involved, they expect the growing zoo of superconductors to help them achieve a more universal view of the alluring phenomenon.
Pairing of electrons
The case for Kamerlingh Onnes’s observations (and superconductivity seen in other extremely cold metals) was finally broken in 1957. John Bardeen, Leon Cooper and John Robert Schrieffer found that at low temperatures a material’s jittery atomic lattice becomes still, so more delicate effects come through. Electrons gently tug at protons in the lattice, pulling them inward to create an excess of positive charge. This deformation, known as a phonon, can then pull in another electron to form a “Cooper pair.” Cooper pairs can all come together into a coherent quantum entity in a way that solitary choices cannot. The resulting quantum soup slides frictionlessly between the material’s atoms, which normally inhibit electrical flow.
Bardeen, Cooper and Schrieffer’s theory of phonon-based superconductivity won them the Nobel Prize in Physics in 1972. But that turned out not to be the whole story. In the 1980s, physicists found that copper-filled crystals called cuprates could superconduct at higher temperatures, where atomic jiggles wash out phonons. Other similar examples followed.