Scientists have discovered a key process that is required for Superconductivity at higher temperatures than previously thought. It could be a small but important step in the search for one of the “holy grails” of physics, a superconductor that works at room temperature.
The discovery, made inside the unusual material of an electrical insulator, shows that electrons pair up at temperatures as low as minus 190 degrees Fahrenheit (minus 123 degrees Celsius) – one of the secret ingredients for the almost lossless flow of electricity in extremely cold superconducting materials.
So far, physicists are puzzled as to why this happens. But understanding it could help them find superconductors at room temperature. The researchers published their results on August 15 in the journal Science.
“The electron pairs tell us that they are ready to become superconducting, but something is stopping them,” said co-author Ke-Jun Xua PhD student in applied physics at Stanford University, said in a statement“If we find a new method to synchronize the pairs, we could potentially use it to build higher temperature superconductors.”
Superconductivity is caused by the waves left by electrons as they move through a material. At sufficiently low temperatures, these waves attract atomic nuclei together, which in turn causes a slight difference in charge that draws a second electron toward the first.
Normally, two negative charges should repel each other. But instead, something strange happens: the electrons are combined to form a “Cooper pair.”
Related: Superconductors at room temperature: The facts behind the “Holy Grail” of physics
Cooper pairs follow different quantum mechanical rules than those of individual electrons. Instead of piling up in energy shells facing outwards, they behave like light particles, an infinite number of which can occupy the same point in space at the same time. When enough of these Cooper pairs are created in a material, it becomes a superfluid, flowing through electrical resistance without losing energy.
The first superconductors, discovered in 1911 by the Dutch physicist Heike Kamerlingh Onnes, entered this state of zero electrical resistance at unimaginably low temperatures – at about absolute zero (minus 459.67 F or minus 273.15 C). But in 1986, physicists discovered a copper-based material called cuprate that becomes a superconductor at much warmer (but still very cold) temperatures of minus 211 F (minus 135 C).
Physicists hoped that this discovery would lead them to room-temperature superconductors. But knowledge of what causes the unusual properties of cuprates dwindled, and last year viral claims of viable room-temperature superconductors ended in Allegations of data falsification And disappointment.
To investigate this 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 haven’t studied it in detail. But when the researchers shone ultraviolet light on the surface, they observed something strange.
When packets of light, or photons, strike a cuprate carrying unpaired electrons, the photons typically give the electrons enough energy to eject them from the material, causing a lot of energy to be lost. However, electrons in Cooper pairs can resist their photonic ejection, causing the material to lose little energy.
Although the zero-resistance state only occurs at very low temperatures, the researchers found that the energy gap in the new material persisted up to 150 K and that, oddly enough, the pairing was strongest in most samples and best withstood the flow of electric current.
This means that although the cuprate is unlikely to achieve superconductivity at room temperature, it may still contain clues for the search for a material capable of doing so.
“Our results open up a potentially lucrative new path forward. We plan to investigate this pairing gap in the future to develop superconductors using new methods,” said the lead 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 potentially force these incoherent pairs into synchronization.”
