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Scientists have discovered a key process required for superconductivity that occurs at higher temperatures than previously thought. It could be a small but significant step in the search for one of the “holy grails” of physics, a superconductor that operates at room temperature.
The discovery, made inside the unlikely material of an electrical insulator, reveals electrons pairing up at temperatures of up to minus 190 degrees Fahrenheit (minus 123 degrees Celsius) – one of the secret ingredients for the almost lossless flow of electricity in very cold superconductivity . materials.
Until now, the physicists are concerned about why this is happening. But understanding it could help them find room temperature superconductors. The researchers published their findings on August 15 in the journal Science.
“The electron pairs are telling us that they are ready to be superconducting, but something is stopping them,” co-author Ke-Jun Xu, a graduate student in applied physics at Stanford University, said in a statement. “If we can find a new way to synchronize the pairs, we could apply that to building higher temperature superconductors.”
Superconductivity results from the leakages left in electron wakes as they move through a material. At low enough temperatures, these ripples attract atomic nuclei to each other, causing a slight offset in charge that attracts the second electron to the first.
Normally, there should be two negative charges rising from each other. But instead, something strange happens: the electrons are bound together in a Cooper pair.
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Cooperating pairs follow quantum mechanical rules rather than individual electron rules. Instead of stacking out in energy shells, they act like particles of light, and an infinite number can occupy the same point in space at the same time. If enough of these Cooper pairs are formed throughout a material, it becomes a superfluid, flowing without any loss of energy due to electrical resistance.
The first superconductors, discovered by Dutch physicist Heike Kamerlingh Onnes in 1911, transitioned into this state of zero electrical resistance at unimaginably cold temperatures — close to absolute zero (minus 459.67 F, or minus 273.15 C). But, in 1986, physicists discovered a copper-based material, called cuprate, which becomes a superconductor at a much warmer (but still very cold) temperature of minus 211 F (minus 135 C).
The physicists hoped that this discovery would lead to superconductors at room temperature. But insights into what causes cuprates to exhibit their unusual behavior have slowed and, last year, viral claims about viable room-temperature superconductors ended in allegations of data falsification and disappointment.
To investigate further, the scientists behind the new research turned to a cuprate called neodymium cerium copper oxide. The maximum superconducting temperature of this material is relatively low at minus 414.67 F (minus 248 C), so scientists have had no trouble studying it. But when the researchers of the study shone ultraviolet light on its surface they saw something strange.
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Normally, when packets of light, or photons, hit cuprate carrying unpaired electrons, the photons give the electrons enough energy to eject them from the material, causing it to lose a lot of energy. But electrons in Cooper pairs can resist their photonic ejection, causing the material to lose only a small amount of energy.
Despite the fact that its zero resistance state only occurs at very low temperatures, the researchers found that the energy gap remained in the new material up to 150 K, and that the pairing was, curiously, the strongest in the best samples resisting the electric flow. current.
This means that although the cuprate is unlikely to reach superconductivity at room temperature, there may be some clues to finding material that can.
“Our results open a potentially rich new path. We plan to study this pairing gap in the future to help engineer superconductors using new methods,” said senior author Zhi- Xun Shen, professor of physics at Stanford, in the statement. “On the one hand, we plan to use similar experimental approaches to gain further insight into this incoherent pair situation. On the other hand, we want to find ways to manipulate these materials to possibly make the pairs pushing these incoherent into synchronization.”
