Nature has retracted a controversial paper claiming the discovery of a superconductor — a material that carries electrical currents with zero resistance — capable of operating at room temperature and relatively low pressure.
The text of the retraction notice states that it was requested by eight co-authors. “They have expressed the view as researchers who contributed to the work that the published paper does not accurately reflect the provenance of the investigated materials, the experimental measurements undertaken and the data-processing protocols applied,” it says, adding that these co-authors “have concluded that these issues undermine the integrity of the published paper.” (The Nature news team is independent from its journals team.)
It is the third high-profile retraction of a paper by the two lead authors, physicists Ranga Dias at the University of Rochester in New York and Ashkan Salamat at the University of Nevada, Las Vegas (UNLV). Nature withdrew a separate paper last year and Physical Review Letters retracted one this August. It spells more trouble in particular for Dias, whom some researchers allege plagiarized portions of his PhD thesis. Dias has objected to the first two retractions and not responded regarding the latest. Salamat approved the two this year.
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“It is at this point hardly surprising that the team of Dias and Salamat has a third high-profile paper being retracted,” says Paul Canfield, a physicist at Iowa State University in Ames and at Ames National Laboratory. Many physicists had seen the Nature retraction as inevitable after the other two — and especially since The Wall Street Journal and Science reported in September that 8 of the 11 authors of the paper — including Salamat — had requested it in a letter to the journal.
Dias and Salamat did not respond to a request for comment by Nature’s news team. The retraction states that he and two other co-authors — Nugzari Khalvashi-Sutter and Sasanka Munasinghe, both at Rochester — "have not stated whether they agree or disagree with this retraction."
Early skepticism
This year’s report by Dias and Salamat is the second significant claim of superconductivity to crash and burn in 2023. In July, a separate team at a start-up company in Seoul described a crystalline purple material dubbed LK-99 — made of copper, lead, phosphorus and oxygen — that they said showed superconductivity at normal pressures and at temperatures up to at least 127 °C (400 kelvin). There was much online excitement and many attempts to reproduce the results, but researchers quickly reached a consensus that the material was not a superconductor at all.
Superconductors are important in many applications, from magnetic resonance imaging machines to particle colliders, but their use has been limited by the need to keep them at extremely low temperatures. For decades, researchers have been developing new materials with the dream of finding one that exhibits superconductivity without any refrigeration.
Specialists in the field have been sceptical since this year’s Dias and Salamat paper was published, says Lilia Boeri, a physicist at the Sapienza University of Rome. This, she says, is in part because of controversies swirling around the team and in part because the latest paper was not written to what she considers a high standard.
“Virtually every serious condensed-matter physicist I know saw right away that there were serious problems with the work,” says Peter Armitage, an experimental physicist at Johns Hopkins University in Baltimore, Maryland. In particular, members of the community took issue with measurements of the material’s electrical resistance, saying it was not clear whether the property truly dropped to zero, or whether Dias and Salamat had subtracted a background signal from a key plot of resistance to create the appearance that it did. Critics say that it should not be necessary to remove background from this type of measurement. In today's text, the journal stated, "An investigation by the journal and post-publication review have concluded that these concerns are credible, substantial and remain unresolved."
Armitage adds that the publication of the paper also raises questions about the editorial review process at Nature, and why reviewers didn’t catch the issues.
“The highly qualified expert reviewers we selected raised a number of questions about the original submission, which were largely resolved in later revisions,“ says Karl Ziemelis, chief physical sciences editor at Nature. “What the peer-review process cannot detect is whether the paper as written accurately reflects the research as it was undertaken.”
“Decisions about what to accept for publication are not always easy to make,” Ziemelis continues. “And there may be conflicts, but we strive to take an unbiased position and to ensure the interests of the community always drive our deliberations.”
Audible clamor
Nature published the now-retracted paper on 8 March. That week, Dias himself presented the results to a standing-room-only audience at a meeting of the American Physical Society in Las Vegas. Over the audible clamour of the crowd assembled outside the room’s doors — where conference staff limited entry to avoid violating fire regulations — Dias briefly described a compound made of hydrogen, lutetium and small amounts of nitrogen that was a superconductor at temperatures up to 21 °C (294 kelvin) when kept at a pressure of around 1 gigapascal (10,000 times atmospheric pressure).
Many teams had already created and experimented with similar hydrogen-rich materials, called hydrides, after a milestone discovery in 2015. A group led by physicist Mikhail Eremets at the Max Planck Institute for Chemistry in Mainz, Germany, reported superconductivity in a hydrogen–sulfur compound at −70 °C (203 kelvin); at the time, this was a record-high operating temperature for a superconductor. But Eremets’s material required a much higher pressure of 145 gigapascals (1.4 million times atmospheric pressure) — comparable to the crushing conditions at the centre of Earth.
Since then, researchers have made hydride superconductors that push closer and closer to operating at room temperature, but all of them work only under extreme pressures. When Dias and Salamat published their paper in Nature in March, they seemed to have made a significant step towards a material that could find practical applications.
But some specialists were already wary because of the first Nature retraction. And some say they immediately found the fresh claims to be improbable. For instance, the material described in the paper was supposed to have around three hydrogen atoms for every lutetium atom. But if so, the lutetium would tend to donate an electron to each hydrogen, resulting in a kind of salt, says Artem Oganov, a materials scientist at the Skolkovo Institute of Science and Technology in Moscow. “You get either an insulator or an extremely poor metal,” he says — not a superconductor.
One lab says it has partially reproduced Dias and Salamat’s results using a sample provided by the Rochester team. But many others, which tried creating their own samples and running tests, could not. And in the meantime, other causes for concern have arisen. An investigation launched by Physical Review Letters before it retracted its paper by Dias and Salamat found “apparent data fabrication,” as Nature’s news team reported in July. And an investigation launched by Nature’s journals team after it received an anonymous critique of data in this year’s paper found that “the credibility of the published results are in question,” according to September’s news story in Science.
Credibility concerns
Armitage does not think that Dias and Salamat will be able to keep doing research, pointing to the investigation findings and allegations of plagiarism in Dias’s PhD thesis. The University of Rochester has confirmed to Nature that it has launched an investigation into the integrity of Dias’s work, which is being conducted now by external experts. The university’s spokesperson did not answer questions about whether the institution has yet disciplined Dias. UNLV did not answer Nature’s queries about whether Salamat is being investigated, saying that “UNLV does not publicly discuss personnel matters,” but that it “is committed to maintaining the highest standards for research integrity campus wide.”
Canfield says that the Dias–Salamat collaboration has spread a “foul vapour” over the field, which “is scaring young researchers and funding agencies away.”
“I have some colleagues who simply are afraid that this case of Dias puts a shadow of doubt on the credibility of our field in general,” Eremets says.
Ho-Kwang Mao, director of the Center for High Pressure Science and Technology Advanced Research in Beijing, is more sanguine. “I do not think it will affect the funding for superconductivity research other than more careful reviews, which is not necessarily bad,” he says.
Hai-Hu Wen, director of the Center for Superconducting Physics and Materials at Nanjing University in China, agrees. “Actually, it seems more easy to get funding for the research of superconductivity since some government officials seem to be influenced by the expectation of a room-temperature superconductor,” he says.
But Boeri says she has heard researchers complain that the controversies — the allegations of PhD thesis plagiarism and the findings of apparent data fabrication — have made it harder to recruit students to work on superconductors. “We face a serious communication problem, to make people understand that the field is healthy — that although there may be some bad apples, the community’s standards are much higher,” she says.
“Serious people continue to do amazing and interesting work,” Armitage says. “Sure, they can be disheartened by this nonsense, but it won’t stop the science.”
Additional reporting by Lauren Wolf.
This article is reproduced with permission and was first published on November 7, 2023.