This is the story of American physicists who on March 8th published in the most prestigious scientific journal in the world experimental results revealing the existence of an exotic phenomenon, never before observed at room temperature, that of superconductivity, in a material of their invention . Such a discovery would normally evoke a chorus of praise, but this time it prompted a symphony of doubts instead. Just two weeks after this publication, the first results contradict the controversial scientific claim.
To understand where we are going with this story, we must first understand where we are coming from. Discovered in 1911 in mercury cooled to -269 °C, superconductivity is a state of matter that allows electric currents to flow without resistance. The possibilities offered by this wonder of nature immediately had physicists dreaming, who would receive no fewer than five Nobel prizes for advances in this niche in the decades that followed. The main challenge was to find materials that are superconducting at warmer temperatures.
A breakthrough came in the 1980s with the development of “high-temperature” superconducting ceramics whose magic lasts even beyond -196°C. Some superconductors have found their way into special applications where helium or liquid nitrogen is used to keep them cold. They are therefore now at the heart of most magnetic resonance tomographs in hospitals. Magnetic levitation trains also benefit from this, 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 proportion of hydrogen. These prove to be superconducting at temperatures as low as -13°C, but at gigantic pressures (150-200 gigapascals), on the order of those found halfway to the center of the Earth. Only a few laboratories in the world manage to achieve such pressures with “diamond anvils”. The temperature problem may have been going away, but a new constraint, that of pressure, replaced it.
Then, on March 7, at the American Physical Society’s annual meeting in Las Vegas, Ranga Dias, a University of Rochester professor, presented to a packed room new findings that were due to be published the following day in Nature magazine. His research group has created a material, a nitrogen-doped lutetium hydride, that is superconducting at temperatures of up to 21 °C and pressures of around 1 gigapascal. This pressure may seem high – it is ten times that of the deepest oceanic chasms – but in the world of advanced materials it is considered 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 that turns pink under moderate pressure while also becoming superconducting, according to the reported results. “Do you know the movie Back to the Future? Mr. Dias asked the audience during the presentation regarding this film work in which a character moves on a flying skateboard. “Things like that could now be possible,” he said, according to the trade press.
Not the first time
To be too good to be true ? ” Very fast [après avoir lu la publication dans Nature], I came to the conclusion that I didn’t believe it at all. Incidentally, most of the experts in the field that I talk to about this are of the same opinion,” replies Louis Taillefer, a professor at the University of Sherbrooke and an internationally renowned experimenter in the field of superconductors. Mr. Taillefer bases his opinion on the analysis of the experimental data, which he believes has serious flaws – a background signal in the resistance curve would be unduly subtracted – but also on the story of Mr. Dias, who does not inspire confidence.
Because this isn’t the first time this researcher has claimed to have found the holy grail of high-temperature superconductivity. In October 2020, he and his collaborators claimed such a feat with a hydrogen, carbon, and sulfur-based material, 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 for an “atypical” treatment of the data that the authors had not explained. Other physicists, after analyzing the raw data, claimed it was downright fabricated. Simultaneously, allegations of plagiarism regarding Mr. Dias’ doctoral thesis have surfaced.
In interviews given this month, Mr Dias firmly denied the allegation of data falsification. He also claimed to have performed new experiments that were verified by other scientists and submitted a new paper to the publisher confirming his 2020 findings. Regarding the accusations about his thesis, he declared that they were “a mistake”. Neither Mr Dias nor his university responded to interview requests from Le Devoir.
see clearer
After initial skepticism, the scientific community is now busy trying to understand or reproduce the latest discovery from the Dias lab. “I think everyone is working on it,” says Lilia Boeri, a professor at Rome’s La Sapienza University and a theorist of high-temperature superconductivity. She is one of the unbelievers who test if they can explain the inexplicable.
Ms. Boeri has just specialized in hydrogen-rich superconductors, such as the lutetium compound that is being talked about so much now. “I’ve studied these systems a lot,” she told Le Devoir. If the results [de M. Dias] are true, then it is very unlikely that it is a superconductor as we have predicted. Until recently, the theory brilliantly explained the laboratory-measured properties of superconducting hydrides. The physicist, who finds it difficult to believe in the new results, nevertheless acknowledges that “it is the essence of great discoveries to find something unexpected”.
In fact, the ball is usually in the camp of the experimenters. Already two groups of Chinese researchers have published results online that have not yet been peer-reviewed and 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 create their own crystal, which changes from blue to pink. And if they don’t find superconductivity there, critics can still claim they baked the wrong cake.
Here the story takes an incredible new turn: Mr. Dias and Ashkan Salamat, another author of the recent publication, are co-founders of a technology start-up, Unearthly Materials, which intends to “propel the century of superconductivity forward”. They just filed a patent application for their lutetium hydride. In an interview with The New York Times, Mr Dias said he would be happy to share the recipe for the material with independent researchers who could test it or send them samples, but that intellectual property issues had to be considered first decided. The researcher and entrepreneur previously said that Unearthly Materials raised $20 million from Spotify and OpenAI-related investors; One of Mr Dias’ representatives later denied the allegation.
The commercial ramifications of the case therefore risk slowing down the process of uncovering the truth. “One message we must try to get across is that there can be fraud in our field; I don’t think physicists are virtuous by default, but we’re fortunate to have the experience, the comparison with nature that’s the final judgement,” notes Michel Côté, a physics professor at the University of Montreal who researches superconductor modeling. “The truth is discovered when consensus is formed in the community, and not with a single article,” adds the one who also belongs to the “skeptic” camp.