Scientists clarify how the best-known superconductor works

Cooper pair diffusion process on the magnetic impurity (Nd) in the lanthanum superhydride structure LaH10. Credit: Dmitrii Semenok (Skoltech)

In a series of experiments on lanthanum superhydride with impurities, researchers from Skoltech, Lebedev Physical Institute of RAS and their colleagues from the United States, Germany and Japan established the mechanism behind superconductivity at highest temperature in polyhydrides observed to date. Posted in Advanced materials, the finding paves the way for future studies of electrically conductive materials with zero resistance at or near room temperature. These would be useful for superconducting electronics and quantum computers, maglev trains, MRI machines, particle accelerators and maybe even nuclear fission reactors and lossless power lines, if you like that kind of things.

While not the holy grail of materials science, near room temperature superconductors are certainly among the most sought-after materials with technological applications. If discovered, such material would enable monster electromagnets that could be used in fundamental research instruments, such as ultra-precise magnetic sensors and particle accelerators that would render the Large Hadron Collider puny, as well as in medical technology ( best MRI scanners), magnetic levitation trains, miniature motors and generators, and gadgets with extended battery life. Among the most futuristic applications are long-distance power transmission lines that would provide electricity with almost no losses.

Theoretically, pure hydrogen should be the best high-temperature superconductor, provided you can squeeze it hard enough to turn it into metal. But it’s quite a challenge, to say the least. Instead, scientists are exploring compounds that contain additional elements, in addition to lots of hydrogen. In this way, they sacrifice some temperature to bring the pressures needed to stabilize the superconducting material down and into the range of what is technologically possible.

“Currently, lanthanum superhydride LaHten is the top contender in this superconductor race, with a critical temperature of minus 23 degrees Celsius,” commented the study’s lead researcher, Skoltech Professor Artem R. Oganov. “It’s very impressive, but to go even higher, we first had to understand how superconductivity works in this material. Now we do.”

There are several mechanisms that can allow electrical conductivity with zero resistance. The best understood is called conventional phonon-mediated superconductivity. It occurs by virtue of electronic interactions with oscillations of the crystal lattice. The well-established theory of conventional superconductivity can be used to improve lanthanum superhydride, perhaps by introducing a crucial third element to create a new compound of hydrogen and two other well-chosen elements.

“The problem was, until now, that no model of ternary superconducting systems existed to know to what extent we can improve the superconducting properties of polyhydrides – temperature superconductivity. We have paved the way by eliminating this uncertainty” , Oganov said.

His team established the behavior of superconductivity in lanthanum superhydride based on the widely accepted Anderson’s theorem. It indicates that conventional superconductors – and only them – retain their properties when a non-magnetic impurity is introduced, but experience a decrease in the critical temperature of superconductivity when doped with magnetic impurities.

“Having confirmed in an earlier paper that the addition of yttrium, which is non-magnetic, does not affect the critical superconductivity temperature in LaHten, we instead doped this material with magnetic neodymium. And of course, the more neodymium atoms were added, the more that superconductivity was removed, eventually destroying it to around 15-20 atomic percent Nd,” said Dmitrii Semenok, PhD student at Skoltech and lead author of the study. . .

According to the researchers, we now have a better understanding of how impurities will affect superconductivity in hydrides and we can predict the properties of many ternary hydride systems. The team will build on the findings to predict, synthesize, and test new three-element hydrogen-rich compounds, hoping to improve lanthanum superhydride by raising its critical temperature, lowering the synthesis pressure, or both.

Research on anomalous hydride compounds has done much to deepen our understanding and dispel misconceptions about superconductivity. Much of this research has used USPEX, a computer program developed by Oganov to predict largely counterintuitive compounds that exist at very high pressures.


New ternary hydrides of lanthanum and yttrium join the ranks of high-temperature superconductors


More information:
Dmitrii V. Semenok et al, Effect of magnetic impurities on superconductivity in LaH 10, Advanced materials (2022). DOI: 10.1002/adma.202204038

Provided by Skolkovo Institute of Science and Technology

Quote: Scientists clarify how the best known superconductor works (August 15, 2022) Retrieved August 15, 2022 from https://phys.org/news/2022-08-scientists-superconductor.html

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