Russian scientists working with high-pressure room-temperature superconductors have had an anomalous result that hints at another mechanism for the effect beyond established models.
Leading an international team, Artem Oganov (Skoltech and MISIS) and Ivan Troyan (Russian Academy of Sciences) performed theoretical and experimental research on the high-temperature superconductor yttrium hydride (YH6).
Over the last few years, extreme pressures have be found to raise the operational temperatures of some superconductors to around room temperature.
According to Skoltech (the Skolkovo Institute of Science and Technology), yttrium hydrides rank amongst the best highest-temperature superconductors discovered so far: “The leader among the three is a material with an unknown S-C-H composition and superconductivity at 288K, which is followed by the lanthanum hydride LaH10, superconducting at temperatures up to 259K and the yttrium hydrides YH6 and YH9, with maximum superconductivity temperatures of 224K and 243K respectively.” – Superconductivity of YH6 was predicted by Chinese scientists in 2015.
“Right now, the whole point is to attain room-temperature superconductivity at lower pressures,” said Skoltech researcher Dmitry Semenok.
These materials were initially theoretically predicted, and then created for experiment.
“First, we look at the bigger picture and study a multitude of different materials on the computer,” said lead researcher Oganov. “This makes things much faster. The initial screening is followed by more detailed calculations. Sorting through fifty or a hundred materials takes about a year, while an experiment with a single material of particular interest may last a year or two.”
Typically, critical superconductivity temperatures are predicted by theory with an error of ~10-15%, and similar accuracy is achieved in critical magnetic field predictions, said Skoltech.
However, this has been found not work for YH6 where, for example, the critical magnetic field observed in experiment is 2 to 2.5x greater than theory predicts.
“This is the first time scientists encounter such discrepancy which is yet to be explained, said Skoltech. “Perhaps, there are some additional physical effects which contribute to superconductivity of this material and were not accounted for in theoretical calculations.”
Several Russian institutions collaborated with partners in the US, Spain, France, China and Japan. The full list can be found at the top of the Advanced Materials’ paper which describes the work: ‘Anomalous high‐temperature superconductivity in YH6.
According to that paper: “The results of superconducting density functional theory and anharmonic calculations, together with anomalously high critical magnetic field, suggest notable departures of the superconducting properties from the conventional Migdal–Eliashberg and Bardeen–Cooper–Schrieffer theories, and presence of an additional mechanism of superconductivity.”
source: .electronicsweekly
