This is the story of American physicists who published, on March 8, in the most prestigious scientific journal in the world, experimental results revealing the existence of an exotic phenomenon and hitherto never observed at room temperature. , that of superconductivity, in a material of their invention. Such a discovery would normally elicit a chorus of praise, but it instead raised, this time around, a symphony of doubts. Two weeks after this publication, first results already contradict the controversial scientific claim.
To understand where we are going with this story, we must first understand where we come from. Superconductivity, discovered in mercury cooled to -269°C in 1911, is a state of matter that allows electric currents to flow without resistance. The possibilities engendered by this wonder of nature immediately made physicists dream, who, over the following decades, would be awarded no less than five Nobel Prizes for advances in this niche. The main challenge was to find materials that would superconduct at warmer temperatures.
In the 1980s, a breakthrough came with the creation of “high temperature” superconducting ceramics, the magic of which persists even beyond -196°C. A few superconductors have found their way into specialized applications, where helium or liquid nitrogen are used to keep them cold. They are thus found today at the heart of most magnetic resonance imaging machines in hospitals. Magnetic suspension trains also benefit from it, as do some underground cables.
At the same time, research continues. Since 2015, new temperature records have been set with “hydrides”, i.e. compounds with a high hydrogen content. These turn out to be superconducting at temperatures as high as -13°C, but at gigantic pressures (150-200 gigapascals), of the order of those found halfway to the center of the Earth. Only rare laboratories in the world manage to obtain such pressures with “diamond anvils”. The problem of temperature was perhaps in the process of being settled, but a new constraint, that of pressure, replaced it.
Then, on March 7, at the annual meeting of the American Physical Society in Las Vegas, Ranga Dias, a professor from the University of Rochester, presented to a crowded room new results, which were to be published the following day in the review Nature. His research group has created a material, a nitrogen-doped lutetium hydride, which is found to be superconducting at temperatures as high as 21°C and pressures of around 1 gigapascal. This pressure may seem high – it is ten times higher than that of the deepest oceanic abysses – but, in the world of advanced materials, it is considered to be close to ambient conditions.
The material in question is obtained by crushing lutetium, one of the rarest rare earths, for several hours, and injecting it with nitrogen and hydrogen. The result is a blue crystal which, when subjected to moderate pressure, turns pink, and at the same time becomes, according to the reported results, superconducting. “Do you know the movie Back to the future ? Mr. Dias asked the audience during the presentation, in reference to this cinematographic work where a character moves on a skateboard flying. “Such things may now be possible,” he said, according to the trade press.
Not the first time
Too good to be true ? ” Very quickly [après avoir lu la publication dans Nature], I came to the conclusion that I did not believe it at all. Most of the experts in the field to whom I speak about it are moreover of the same opinion”, replies Louis Taillefer, professor at the University of Sherbrooke and experimenter of international reputation in the field of superconductors. Mr. Taillefer bases his opinion on the analysis of the experimental data, which according to him has serious flaws — a background signal in the resistivity curve would be unduly subtracted —, but also on the history of Mr. Dias, who does not does not inspire confidence.
Because this is not the first time that this researcher claims to have found the Holy Grail of very high temperature superconductivity. In October 2020, he and his collaborators claimed such an accomplishment with a material based on hydrogen, carbon and sulfur, again in the journal Nature. This paper, which had quickly raised doubts in the scientific community, was then withdrawn by the publisher in September 2022 due to an “atypical” treatment of the data that the authors had not explained. Other physicists, after analyzing the raw data, claimed that it was downright fabricated. At the same time, accusations of plagiarism have surfaced regarding Mr. Dias’ doctoral thesis.
In interviews given this month, Mr. Dias strongly denied the data fabrication allegation. He also claimed to have carried out new experiments, verified by other scientists, and submitted a new article to the publisher confirming his 2020 results. As for the accusations on his thesis, he explained that they are ‘a mistake “. Neither Mr. Dias nor his university responded to interview requests from the Duty.
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After the initial skepticism, the scientific community is now busy trying to understand or reproduce the latest discovery from the Dias laboratory. “I think everyone is working on this,” says Lilia Boeri, a professor at La Sapienza University in Rome and a high-temperature superconductivity theorist. She is one of the unbelievers checking to see if they can explain the unexplainable.
Mme Boeri specializes precisely in hydrogen-rich superconductors, such as the lutetium compound that is now so much talked about. “I’ve studied these systems a lot,” she told the Duty. If the results [de M. Dias] are true, then it is very unlikely that it is a superconductor of the kind we have predicted to exist. Until recently, the theory brilliantly explained the properties of superconducting hydrides measured in the laboratory. The physicist, who finds it hard to believe in the new results, recognizes all the same that “it is the essence of great discoveries to find something unexpected”.
In fact, the ball is mostly in the camp of the experimenters. Already, two groups of Chinese researchers have published results online, not yet peer-reviewed, that contradict those of the University of Rochester. Before measuring the electrical resistance of a sample of nitrogen-doped lutetium hydride, competing laboratories must synthesize this material, the exact recipe of which remains secret for the time being. They are therefore forced to grope to produce their own crystal changing from blue to pink. And if they don’t detect superconductivity there, critics can always claim they baked the wrong cake.
Here is where the story takes an incredible new turn: Mr. Dias and Ashkan Salamat, another author of the recent publication, are co-founders of a technological start-up, Unearthly Materials, which intends to “fuel the century of superconductivity “. They have just filed a patent application for their lutetium hydride. In interview at New York TimesDias said he would like to pass the recipe for the material to independent researchers, who could test it, or even ship samples to them, but there were intellectual property issues that needed to be resolved first. The researcher-entrepreneur previously said that Unearthly Materials raised $20 million from Spotify and OpenAI-related investors; one of Mr. Dias’ representatives later denied the claim.
The commercial ramifications of the case therefore risk slowing down the process towards the truth. “A message that we must try to convey is that fraud can exist in our field; I don’t think physicists are virtuous by default, but we are lucky to have the experience, the comparison with nature, which is the final judge”, observes Michel Côté, a professor of physics at the University of Montreal, which studies superconductors through modelling. “The truth is discovered when a consensus is formed in the community, and not with a single article”, adds the one who also ranks in the camp of “skeptics”.