Scientists have found a key process required for superconductivity occur 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 as low as minus 190 degrees Fahrenheit (minus 123 degrees Celsius)—one of the secret ingredients to the nearly lossless flow of electricity in extremely cold superconductivity. materials.
Until now, physicists are puzzled as to 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.
“Electron pairs are telling us that they are ready to be superconductors, but something is holding them back,” the co-author said. Ke-Jun Xua graduate student in applied physics at Stanford University, said in a statement. “If we can find a new method to synchronize the pairs, we can apply it to building higher-temperature superconductors.”
Superconductivity arises from the ripples left in the electron waves as they move through a material. At low enough temperatures, these ripples attract atomic nuclei to each other, in turn causing a slight shift in charge that attracts a second electron to the first.
Normally, two negative charges should repel each other. But instead, something strange happens: the electrons bind together in a “Cooper pair”.
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Copper pairs follow different quantum mechanics rules than those of single electrons. Instead of accumulating externally in energy shells, they act as 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 along a material, it becomes a superfluid, flowing without any loss of energy due to electrical resistance.
The first superconductors, discovered by the Dutch physicist Heike Kamerlingh Onnes in 1911, went into this state of zero electrical resistance at unimaginably cold temperatures – close to absolute zero (minus 459.67 F, or minus 273.15 C). However, in 1986, physicists found a copper-based material called cuprate, which becomes a superconductor at a much warmer (but still very cold) minus 211 F (minus 135 C).
Physicists hoped that this discovery would lead to room-temperature superconductors. However, insights into what makes cuprates exhibit their unusual behavior slowed and, last year, viral claims of viable room-temperature superconductors ended in accusations of falsification of data AND disappointment.
To investigate further, the scientists behind the new research turned to a cuprate known as neodymium cerium copper oxide. The maximum superconducting temperature of this material is relatively low at minus 414.67 F (minus 248 C), so scientists haven’t bothered to study it much. But when the study’s researchers shone ultraviolet light on its surface, they observed something strange.
Typically, when packets of light, or photons, strike a cuprate carrying unpaired electrons, the photons give the electrons enough energy to be ejected from the material, causing it to lose a lot of energy. But electrons in Cooper pairs can resist their photon expulsion, causing the material to lose only a little energy.
Despite its zero-resistance state occurring only at very low temperatures, the researchers found that the energy gap persisted in the new material up to 150 K and that the pairing was, surprisingly, the strongest in most samples to resist flow of electricity. current.
This means that, although cuprate is unlikely to achieve room-temperature superconductivity, it may hold some hints for finding a material that can.
“Our findings open a potentially rich new path forward. We plan to study this pairing gap in the future to help engineer superconductors using new methods,” senior author Zhi-Xun Shena physics professor at Stanford, said in the statement. “On the one hand, we plan to use similar experimental approaches to gain further insight into this incoherent pairing state. On the other hand, we want to find ways to manipulate these materials to force these incoherent pairs into synchronization. “