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Scientists have discovered a key process required for superconductivity occurring at higher temperatures than previously thought. This could be a small but significant step in the search for one of physics' “holy grails” – a room-temperature superconductor.
A discovery made inside an unusual electrical insulator material shows electrons Bonding at temperatures as low as minus 190 degrees Fahrenheit (minus 123 degrees Celsius) is one of the secret ingredients to virtually lossless electrical flow in extremely cold superconducting materials.
Physicists can't yet figure out why this happens. But understanding it could help them find room-temperature superconductors. The researchers published their findings Aug. 15 in the journal Science.
“Electron pairs tell us they are ready to become superconducting, but something is stopping them,” says co-author Ke-Jun XuPhD student in the Department of Applied Physics at Stanford University, the statement says“If we can find a new method for pair synchronization, we could apply it to potentially create higher temperature superconductors.”
Superconductivity arises from waves left by electrons as they move through a material. At low enough temperatures, these waves attract atomic nuclei to each other, in turn causing a small shift in charge that attracts the second electron to the first.
Normally, two negative charges should repel each other. But instead, something strange happens: the electrons bind together into a “Cooper pair.”
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Cooper pairs follow different quantum mechanical rules than single electrons. Instead of lining up outward in energy shells, they act like particles of light, an infinite number of which can occupy the same point in space at the same time. If enough of these Cooper pairs are created in a material, they become a superfluid, flowing without losing energy due to electrical resistance.
The first superconductors, discovered by the Dutch physicist Heike Kamerlingh Onnes in 1911, entered a state of zero electrical resistance at unimaginably low temperatures—about absolute zero (minus 459.67 F or minus 273.15 C). However, in 1986, physicists discovered a copper-based material called cuprate that becomes a superconductor at a much higher (but still very cold) temperature of -211 F (minus 135 C).
Physicists had hoped that the discovery would lead them to room-temperature superconductors. However, understanding what makes cuprates exhibit their unusual behavior has slowed, and last year the viral claims of viable room-temperature superconductors ended accusations of falsification of data And disappointment.
To investigate further, the scientists behind the new study turned to a cuprate known as neodymium cerium copper oxide. This material has a relatively low maximum superconductivity temperature of minus 414.67 F (minus 248 C), so the scientists didn’t study it in detail. But when the researchers shone ultraviolet light on its surface, they noticed something odd.
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Normally, when packets of light, or photons, hit a cuprate that carries unpaired electrons, the photons give the electrons enough energy to fly out of the material, causing it to lose a lot of energy. But the electrons in Cooper pairs can resist their photonic expulsion, causing the material to lose only a little energy.
Although the zero-resistance state is only observed at very low temperatures, the researchers found that the energy gap persists in the new material up to 150 K, and that the pairing is, surprisingly, strongest in most of the samples that best resist the passage of electric current.
This means that while cuprate is unlikely to achieve room-temperature superconductivity, it may hold some clues toward finding a material that can.
“Our results open up a potentially rich new path forward. We plan to study this gap in pairwise interactions in the future to help design superconductors using new methods,” senior author Zhi-Xun Shen, a professor of physics at Stanford, said in a statement. “On the one hand, we plan to use similar experimental approaches to gain deeper insight into this incoherent pair state. On the other hand, we want to find ways to manipulate these materials to perhaps force these incoherent pairs to synchronize.”