The original version of this story appeared in Quanta Magazinee.
In 2024, superconductivity – the flow of electrical current without resistance – was discovered in three distinct materials. Two examples expand the classical understanding of the phenomenon. The third completely destroys it. “This is an extremely unusual form of superconductivity that many people would have said was not possible,” said Ashvin Vishwanathphysicist at Harvard University who was not involved in the discoveries.
Since 1911, when Dutch scientist Heike Kamerlingh Onnes first saw electrical resistance disappear, superconductivity has captivated physicists. There is a pure mystery about how this happens: the phenomenon requires electrons, which carry electric current, to come together. Electrons repel each other, so how can they come together?
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 this phenomenon occurs, they might be able to design a wire that superconducts electricity under everyday conditions rather than exclusively at low temperatures, as is currently the case. World-changing technologies – lossless power grids, magnetic levitation vehicles – could follow.
The recent wave of discoveries has both deepened the mystery of superconductivity and increased optimism. “It seems that in materials, superconductivity is everywhere,” said Matthew Yankowitzphysicist at the University of Washington.
The findings stem from a recent revolution in materials science: The three new cases of superconductivity come from devices assembled from flat sheets of atoms. These materials display 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 energized the hunt for superconductivity.
It now seems increasingly likely that various causes could be behind this phenomenon. Just as birds, bees, and dragonflies all fly using different wing structures, materials appear to associate electrons in different ways. Although researchers debate what exactly is happening in the various two-dimensional materials in question, they anticipate that the growing superconductor zoo will help them gain a more universal view of this alluring phenomenon.
Electron pairing
The case of the Kamerlingh Onnes observations (and of superconductivity observed in other extremely cold metals) was finally resolved in 1957. John Bardeen, Leon Cooper and John Robert Schrieffer Understood that at low temperatures, the unstable atomic lattice of a material calms down, allowing more delicate effects to be achieved. The electrons gently pull on the protons in the lattice, pulling them inward to create excess positive charge. This deformation, known as a phonon, can then attract a second electron, forming a “Cooper pair”. Cooper pairs can all come together into a coherent quantum entity, unlike isolated elections. The resulting quantum soup slides frictionlessly between the material’s atoms, which normally impede electrical flow.
Bardeen, Cooper and Schrieffer’s theory of phonon-based superconductivity earned them the Nobel Prize in Physics in 1972. But it turned out that this was not enough. In the 1980s, physicists discovered that copper-filled crystals, called cuprates, could be superconductors at higher temperatures, where atomic vibrations suppressed phonons. Other similar examples followed.
