Superconductivity is the phenomenon where the resistance to current flow in a material drops to zero. This means that there will be no loss of energy due to heat generation when current flows through the superconductor. Since resistive heat losses are one of the main limitations associated with any current-generated devices, superconductors open up enormous possibilities for technology that could revolutionize our lives. Unfortunately this phenomenon, first discovered by Heike Kamerlingh Onnes in 1911, only seemed to work at extremely low temperatures close to absolute zero that required cooling with liquid helium, making it impractical for everyday use.

Creating materials that would be superconducting at room temperatures became the Holy Grail of this area of research and a big breakthrough came in 1986 when materials were found that were superconducting at around 90K (-183C) which could be reached using liquid nitrogen. Even higher temperature superconducting materials at about 203K (-77C) have been found but that required enormous pressures, of about 10⁶ times atmospheric pressure.

Recent papers by a research team headed by Ranga Dias and Ahskan Salamat at the University of Rochester have claimed that they have found materials that are superconducting at temperature of 294K (17C) and at a pressure of 10 kbar or ten thousand times the atmospheric pressure. This is big news.

This article explains what was found.

The only superconducting materials previously discovered require extreme conditions to function, which makes them impractical for many real-world applications. The first known superconductors had to be cooled with liquid helium to temperatures only a few degrees above absolute zero. In the 1980s researchers found superconductivity in a category of materials called cuprates, which work at higher temperatures yet still require cooling with liquid nitrogen. Since 2015 scientists have measured room-temperature superconductive behavior in hydrogen-rich materials called hydrides. but they have to be pressed in a sophisticated viselike instrument called a diamond anvil cell until they reach a pressure of about a quarter to half of that found near the center of Earth.

The new material, called nitrogen-doped lutetium hydride, is a blend of hydrogen, the rare-earth metal lutetium and nitrogen. Although this material also relies on a diamond anvil cell, the study found that it begins exhibiting superconductive behavior at a pressure of about 10,000 atmospheres—roughly 100 times lower than the pressures that other hydrides require. The new material is “much closer to ambient pressure than previous materials,” says David Ceperley, a condensed matter physicist at University of Illinois at Urbana-Champaign, who was not involved in the new study. He also notes that the material remains stable when stored at a room pressure of one atmosphere. “Previous stuff was only stable at a million atmospheres, so you couldn’t really take it out of the diamond anvil” cell, he says. “The fact that it’s stable at one atmosphere of pressure, that also means that it’d be easier to manufacture.”

Understanding superconductivity theoretically has always been difficult. The article goes on to describe a possible process that might explain this new finding.

But there has been controversy, with other researchers casting doubt on the methodology, the data, and results and claiming that previous work by this group undermined their credibility that had resulted in the journal Nature in 2022 retracting an earlier 2020 paper.

The controversy drove Nature to retract the 2020 paper in 2022, a decision to which all its authors objected. Dias and Salamat say they stand by their results, and two investigations by the University of Rochester, where Dias works, found no wrongdoing. The authors also say they have rerun the original experiments at two different Department of Energy labs with outside observers present and that this effort verified the original results. “Time is a great peer-review process,” Salamat says. Dias says the researchers have updated their original paper as a preprint and resubmitted it to Nature. Other labs, however, have not been able to replicate the original results independently. But it can take a long time for a lab to reproduce and then test a specific material. The drawn out conflict has involved the release of multiple preprints, with neither side accepting the other’s arguments. And it eventually became so acrimonious that administrators of the preprint server arXiv.org removed papers from both parties and put Hirsch under a temporary publishing ban, which he objected to. “My papers analyzed the data and pointed out inconsistencies,” he says.

Another paper that was published in Physical Review Letters by this same research group has also come under scrutiny.

Hamlin went on to analyze a paper that Dias and Salamat published in Physical Review Letters (PRL) in 2021 in which they and their colleagues measured another hydride called manganese sulfide. Hamlin noted similarities between the electrical resistance data in the 2021 paper and those in Dias’s 2013 Ph.D. thesis, which had involved a completely different superconducting material. He shared these concerns with the journal and the paper’s authors. Salamat has since responded, suggesting that even though the two data sets may appear similar, the resemblance is not indicative of copied data. “We’ve shown that if you just overlay other people’s data qualitatively, a lot of things look the same,” he says. “This is a very unfair approach.”

This did not satisfy at least one of Salamat’s co-authors on the PRL paper: Simon A. J. Kimber, a former researcher, was disturbed to hear about the potential problem with the data and agrees with Hamlin’s conclusions. “I’ve been at this game for a long time, and I couldn’t think of a single reasonable explanation as to why those data sets should overlap like that,” he says. “I replied to everybody, to PRL’s editors, and said, ‘I think this should be retracted. I can’t think of any logical reason why this should be—retract, retract, retract.’” According to Jessica Thomas, executive editor at the journal’s publisher, the American Physical Society, editors are currently investigating these claims. “We take allegations of data fabrication very seriously,” she says. “At the same time, professional reputations are at stake, and we have to gather information thoughtfully and accurately. We also strive to ensure that the exchanges remain professional and respectful.”

The ultimate test in science as to whether results are showing a real effect and are not artifacts due to some local cause is if they can be replicated by others. Such efforts are now underway but so far have not borne fruit. But replication at the frontiers of science is not easy and so one has to suspend judgment until more work is done by many other groups.

Even if the results hold up, there is still a long way to go before these materials find widespread commercial applications. This is because carrying electricity in devices is easier if the conductor can be made into long, thin, flexible wires. Metals have this desirable property but high-temperature superconducting materials are ceramic-like which are brittle.

The current situation reminds me of cold fusion, another potentially revolutionary discovery that caused great excitement back in 1989 when it was suggested that fusion reactions could be made to occur at room temperature, and not at temperatures near that of the Sun. The controversy raged for some years until a consensus slowly emerged that the copious amounts of heat generated in the reactions were due to causes other than fusion. But, as with many scientific theories, true believers are still around.

I expect the controversy around this claim of room-temperature superconductivity to also drag out for some time because, as with cold fusion, the rewards for the phenomenon turning out to be real are so high that people will not want to relinquish that possibility easily.