New Superconductive Materials Have Just Been Discovered

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In 2024, superconductivity—the flow of electric current with zero resistance—was discovered in three distinct materials. Two instances stretch the textbook understanding of the phenomenon. The third shreds it completely. “It’s an extremely unusual form of superconductivity that a lot of 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 the Dutch scientist Heike Kamerlingh Onnes first saw electrical resistance vanish, superconductivity has captivated physicists. There’s the pure mystery of how it happens: The phenomenon requires electrons, which carry electrical current, to pair up. Electrons repel each other, so how can they be united?

Then there’s the technological promise: Already, superconductivity has enabled the development of MRI machines and powerful particle colliders. If physicists could fully understand how and when the phenomenon arises, perhaps they could engineer a wire that superconducts electricity under everyday conditions rather than exclusively at low temperatures, as is currently the case. World-altering technologies—lossless power grids, magnetically levitating vehicles—might follow.

The recent spate of discoveries has both compounded the mystery of superconductivity and heightened the 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 instances of superconductivity arise in 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 supercharged the hunt for superconductivity.

It now seems increasingly likely that diverse causes can give rise to the phenomenon. Just as birds, bees and dragonflies all fly using different wing structures, materials seem to pair electrons together in different ways. Even as researchers debate exactly what’s happening in the various two-dimensional materials in question, they anticipate that the growing zoo of superconductors will help them achieve a more universal view of the alluring phenomenon.

The case of Kamerlingh Onnes’ observations (and superconductivity seen in other extremely cold metals) was finally cracked in 1957. John Bardeen, Leon Cooper, and John Robert Schrieffer figured out that at low temperatures, a material’s jittery atomic lattice quiets down, so more delicate effects come through. Electrons gently tug on protons in the lattice, drawing them inward to create an excess of positive charge. That deformation, known as a phonon, can then draw in a second electron, forming a “Cooper pair.” Cooper pairs can all come together into a coherent quantum entity in a way that lone elections can’t. The resulting quantum soup slips frictionlessly in between the material’s atoms, which normally impede electric flow.

Bardeen, Cooper, and Schrieffer’s theory of phonon-based superconductivity earned them the physics Nobel Prize in 1972. But it 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.

Heike Kamerlingh Onnes (left) stumbled upon superconductivity in 1911. An explanation for it eluded Albert Einstein and other luminaries until the 1950s, when John Bardeen, Leon Cooper, and John Robert Schrieffer (right photo, left to right) determined that atomic vibrations known as phonons were at work.

The higher-temperature superconductors seemed to have atoms arranged in a way that slows electrons down. And when electrons get the chance to mingle in a leisurely fashion, they collectively generate an ornate electric field that can make them do novel things, like form pairs rather than repel. Physicists now suspect that in cuprates, specifically, electrons hop between atoms in a particular way that favors pairing. But other “unconventional” superconductors are still quite mysterious.

Pablo Jarillo-Herrero, a physicist at the Massachusetts Institute of Technology, found that if you took a sheet of carbon atoms arranged in a honeycomb lattice—a 2D crystal called graphene—twisted it at precisely 1.1 degrees, and stacked it on top of another graphene sheet, the two layers could superconduct.

Researchers had already been dabbling with 2D materials and finding diverse behaviors. By applying electric fields, they could add electrons to the sheet or make the electrons feel almost as if the atomic grid were contracting. Twiddling these settings in a single 2D device could reproduce the behavior of thousands to millions of potential materials. Among those heaps of possibilities, Jarillo-Herrero had shown, was a new superconductor: “magic angle” graphene.

Then, a couple of years later, a group in California removed the magic angle, finding that three-layer, twist-free graphene devices could also superconduct.

Researchers are still discussing why electrons stick together in these cases. Phonons fit the data in some ways, but something new also seems responsible.

But what really thrilled physicists was the promise of a fresh way to investigate superconductivity in general. The customizable 2D devices had freed them from the drudgery of designing, growing, and testing new crystals one by one. Researchers would now be able to quickly re-create the effects of many different atomic lattices in a single device and find out exactly what electrons are capable of.

The research strategy is now paying off. This year, physicists found the first instances of superconductivity in 2D materials other than graphene, along with a completely novel form of superconductivity in a new graphene system. The discoveries have established that the earlier graphene superconductors mark just the outskirts of a wild new jungle.

In 2020, the physicist Cory Dean and his team at Columbia University tried stacking sheets of a different 2D crystal—this one, a honeycomb arrangement of two types of atoms, called a transition metal dichalcogenide (TMD). When they twisted the sheets at 5 degrees, the resistance plunged toward zero but didn’t stay there. It was an inconclusive hint of superconductivity.

The tentative nature of the detection didn’t stop Liang Fu of MIT and Constantin Schrade of Louisiana State University from trying to explain it. They suspected that phonons weren’t the answer. Twisted materials are powerful because the twist changes what the electrons experience, imbuing the material with a kaleidoscopic “moiré” pattern. The moiré features large hexagonal cells that act like artificial atoms, hosting electrons. In this new environment, electrons move slowly enough for their collective electrical interactions to guide their behavior.

But how were the electrons conspiring to form pairs? The Columbia group funneled electrons into the moiré. They observed that when there was one electron for each of the large cells in the moiré material, these electrons assumed an “antiferromagnetic” arrangement; their intrinsic magnetic fields tended to alternate between pointing up and down. Adding extra electrons to the moiré made the resistance drop to zero—Cooper pairs had formed. Fu and Schrade argued that the same electron-on-electron action was making both the antiferromagnetic state and the superconducting state possible. At one electron per cell, each electron can have a preferred location and magnetic orientation. But when additional electrons pile in, the magnetic arrangement becomes unstable, and the whole population starts to flow freely.

Cory Dean and his group at Columbia University spotted a flicker of superconductivity in a two-dimensional TMD material in 2020. This year, they confirmed the discovery.