Scientists have discovered a key process necessary for superconductivity This is a superconductor that works at higher temperatures than previously thought. It could be a small but significant step in the quest for one of the “holy grails” of physics: a superconductor that works at room temperature.
The discovery, made inside the unlikely material of an electrical insulator, reveals electrons pairing at temperatures as low as minus 190 degrees Fahrenheit (minus 123 degrees Celsius), one of the secret ingredients for the nearly lossless flow of electricity in extremely cold superconducting materials.
So far, physicists don't understand why this happens, 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 superconductors, but something is stopping them,” said co-author Ke Jun Xugraduate student in applied physics at Stanford University, said in a statement“If we can find a new method to synchronize the pairs, we could apply it to the possible construction of higher-temperature superconductors.”
Superconductivity arises from the ripples left by electrons as they move through a material. At low enough temperatures, these ripples attract atomic nuclei to each other, which in turn causes 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 stick together and form a “Cooper pair.”
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Cooper pairs remain different quantum mechanics The rules are more different than those of solitary electrons. Instead of stacking 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 Cooper pairs are created in a material, they become a superfluid, flowing without any loss of energy due to electrical resistance.
The first superconductors, discovered by Dutch physicist Heike Kamerlingh Onnes in 1911, switched to this state of zero electrical resistivity at unimaginably cold temperatures, near absolute zero (minus 459.67 F, or minus 273.15 C). However, in 1986, physicists found a copper-based material, called cuprate, that becomes a superconductor at a much warmer (but still very cold) temperature of minus 211 F (minus 135 C).
Physicists had hoped that this discovery would lead to the creation of room-temperature superconductors. However, understanding of why cuprates exhibit their unusual behavior slowed, and last year, viral claims of 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 known as neodymium cerium copper oxide. The material's maximum superconducting temperature is relatively low, at -248 degrees Celsius (-414.67 degrees Fahrenheit), so scientists haven't bothered to study it much. But when the study's researchers shined ultraviolet light on its surface, they noticed something strange.
Typically, when packets of light, or photons, collide with 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 photonic ejection, causing the material to lose only a little energy.
Even though its zero-resistance state only occurs 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, oddly, strongest in the majority of samples that best resisted the flow of electric current.
This means that while cuprate is unlikely to achieve superconductivity at room temperature, it could hold some clues to finding a material that can do so.
“Our findings open a new and potentially enriching path. We plan to study this pairing gap in the future to help design superconductors using new methods,” senior author Zhi-Xun Shen, a professor of physics at Stanford, said in the statement. “On the one hand, we plan to use similar experimental approaches to gain more insight into this incoherent pairing state. On the other hand, we want to find ways to manipulate these materials to perhaps force these incoherent pairs to synchronize.”
