original version of this story appeared in Quanta Magazinee.
In 2024, superconductivity (current flow with zero resistance) was discovered in three different materials. Two examples extend the textbook understanding of phenomena. The third shreds it completely. “This is a very unusual form of superconductivity, and many people would say it’s impossible,” said Ashvin Vishwanath, a physicist at Harvard University who was not involved in the discovery.
Superconductivity has fascinated physicists since Dutch scientist Heike Kamerling Onnes first witnessed the disappearance of electrical resistance in 1911. There is a complete mystery as to how that happens. This phenomenon requires electrons to pair up to carry an electric current. Electrons repel each other, but how can they bond?
And then there are technological expectations. Already, superconductivity has enabled the development of MRI machines and powerful particle colliders. If physicists can fully understand when and how this phenomenon occurs, they may be able to design wires that superconduct electricity under everyday conditions, not just at low temperatures as they currently do. World-changing technologies such as lossless power grids and magnetic levitation vehicles may follow.
A flurry of recent discoveries complicates the mystery of superconductivity while also increasing optimism. “Superconductivity appears to be ubiquitous in materials,” said Matthew Jankowitz, a physicist at the University of Washington.
These discoveries stem from recent revolutions in materials science. All three new examples of superconductivity occur in devices assembled from flat sheets of atoms. These materials exhibit unprecedented flexibility. Physicists can switch them between conducting, insulating, and more exotic behavior with the push of a button. This is a modern form of alchemy that accelerates the search for superconductivity.
It now appears that a variety of causes are increasingly likely to cause this phenomenon. Just as birds, bees, and dragonflies all use different wing structures to fly, matter appears to combine electrons in different ways. While researchers debate exactly what is going on in the various two-dimensional materials in question, the growing zoo of superconductors could help us understand this fascinating phenomenon more universally. I hope it will be like that.
electron pairing
The case of Kamerling-Onnes observations (and superconductivity seen in other cryogenic metals) was finally solved in 1957. John Bardeen, Leon Cooper, and John Robert Schriefer discovered that more happens at lower temperatures because the nervous atomic lattices of materials quiet down. A delicate effect is conveyed. The electrons gently tug on the protons in the lattice, pulling them inward and creating an excess positive charge. That variant, known as a phonon, pulls in a second electron, forming a “Cooper pair.” Cooper pairs can bring everything together into a coherent quantum entity in a way that a single election cannot. The resulting quantum soup slides frictionlessly between the atoms of the material, which would normally impede the flow of electricity.
Bardeen, Cooper, and Schriefer’s phonon-based theory of superconductivity won them the Nobel Prize in Physics in 1972. But it turns out that’s not all. In the 1980s, physicists discovered that copper-filled crystals called cuprates could become superconducting at high temperatures, and the shaking of the atoms could wash away phonons. Other similar examples followed.
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