Superconductivity ‘damaged’ as researchers look to move on from retractions – Physics World

“I’m going to introduce a new material for the first time.” So said the condensed-matter physicist Ranga Dias to a packed conference room at the March meeting of the American Physical Society in Las Vegas earlier this year. The material in question was nitrogen-doped lutetium hydride, or Lu-N-H, and Dias went on to describe measurements claiming to have seen evidence for superconductivity at a remarkable 294 K (a balmy 20 °C) under a pressure of 1 GPa (10 kbar).

Based at the University of Rochester in the US, Dias claimed to have observed many signatures of superconductivity such as the electrical resistance dropping to zero at a particular transition temperature and the material expelling magnetic field lines. He and his colleagues also measured the sample’s specific heat, which showed a characteristic response at the transition temperature.

Their finding appeared to mark the culmination of a century-long quest in condensed-matter physics: the search for materials that superconduct under ambient conditions. Yet following the talk no-one spoke a word and there was no wild celebration. Dias simply finished his talk and passed the microphone over to the next speaker.

A member of the audience asked if there would be questions. “We don’t have time,” responded session chair Minta Akin from the Lawrence Livermore National Laboratory, her reply greeted with an audible groan from the room.

The atmosphere seemed very different from a previous APS March meeting in 1987 – the famous “Woodstock of physics” in New York City that took place just after the first high-temperature superconductors had been discovered.

Back then the physicists Georg Bednorz and Alex Müller had set the world of condensed-matter physics alight after discovering the year before that a material containing copper oxide, lanthanum and barium became superconducting at around 35 K. This was some 50% higher than the previous record of 23 K that had been achieved more than a decade earlier in niobium-germanium (Nb₃Ge).

The new “cuprate” materials caused such a buzz because they were not metals but insulators and they offered the possibility of finding new stoichiometries and compounds that could potentially reach even higher transition temperatures.

A room-temperature superconductor was the holy grail, holding out the hope for a wide-range of applications from ultra-efficient energy grids to medical applications that require powerful magnets.

Bednorz and Müller later won the 1987 Nobel Prize for Physics for the discovery and in the decades that followed researchers created new cuprate-based compounds that reached transition temperatures of 133 K at ambient pressure and 166 K at a pressure of around 30 GPa.

From cuprates to hydrides

While the cuprates had been the de facto superconducting kings for the past couple of decades, that all began to change in the mid-2010s. In 2015 Mikhail Eremets and colleagues at the Max Planck Institute for Chemistry and the Johannes Gutenberg University Mainz, both in Germany, observed superconductivity at 203 K in a sample of hydrogen sulphide.

Although the material needed to be squeezed to 150 GPa (Nature 525 73), in 2018 a group led by Russell Hemley, then at George Washington University in the US, reported superconductivity at 260 K in lanthanum superhydride, albeit still under pressures of over 180 GPa, work that was published in 2019 (Phys. Rev. Lett. 122 027001).

That same year Eremets’ team reported superconductivity at temperatures up to 250 K  in lanthanum hydride at 170 GPa (Nature 569 528).

Work on these so-called binary hydrides – compounds that contain hydrogen and one other element such as hydrogen sulphide – sparked a “gold rush” in the search for high-temperature superconductors.

But what was most exciting is that they were predicted entirely from first-principles calculations, with theory agreeing almost perfectly with experiment.

Dias’ inconsiderate behaviour has harmed the reputation of the field and it may take a few years to repair the damage

Lilia Boeri

“The hydrides have probably been the single most exciting discovery in superconductivity after the cuprates, and an amazing success story of the interplay between theory and experiment,” says theoretical physicist Lilia Boeri from the University of Rome La Sapienza.

Dias and colleagues entered the high-temperature superconductivity game in 2020. Using his experience squeezing hydrogen to high pressure (see box below), Dias’s group published a paper on carbonaceous sulphur hydride that claimed to show superconductivity at 288 K under a pressure of about 260 GPa (Nature 586 373).

Around the same time Dias co-founded a company — Unearthly Materials — to commercialize room-temperature superconductors and that year the work was awarded a 2020 Physics World Breakthrough of the Year.

In 2021 Dias was even named as a TIME100 Next innovator for his work. “Let’s be clear: hoverboards, magnetic levitation trains and resistance-free power lines are not coming this year or next,” noted Time magazine. “But thanks to Ranga Dias, they’re closer than they ever were.”  

But not everything was as it seemed. In 2021 concerns were raised by researchers about some of the data processing in the paper, in particular the manner in which a background had been subtracted from the resistance measurements to show the sample falling to zero resistance after the transition temperature.

Temperature’s rising

Then, in September 2022, the group’s Nature paper was retracted. “We have now established that some key data processing steps – namely, the background subtractions applied to the raw data used to generate the magnetic susceptibility plots – used a non-standard, user-defined procedure,” noted an editorial update written by the authors of the original paper.

All nine authors on the paper disagreed with the decision by Nature to retract, although the University of Rochester began three internal inquiries, two of which were completed in May 2022, and another after the retraction. Rochester announced that the investigations had found no evidence of misconduct but have not released full details of the inquiries.

Dias was undeterred and, after giving his talk at the APS meeting this year, his team’s work on Lu-N-H was published, again in Nature (615 244).

In April, a patent listing Dias as the inventor was published (although filed in April 2022) for a lutetium hydride material that can superconduct at room temperature. No details of the material’s exact stoichiometry were, however, given. But just as with the 2020 Nature paper, questions were raised around the background subtraction in the new study.

There were also concerns that the stated success rate of measuring superconductivity at high temperatures in Lu-N-H samples was only about 35%, when one would hope that all samples made to a certain recipe would be superconducting to aid reproducibility.

I still feel that hydride superconductivity has a good chance of eventually providing a superconductor at ambient conditions

David Ceperley

And when other researchers tried to reproduce the findings, they failed. Di Peng from the Institute of Solid State Physics in Hefei, China, and colleagues, for example, found some signs of a transition at about 240 K, but suggest they are not indicative of superconductivity (arXiv:2307.00201).

Theorists who tried to explain the high-temperature superconductivity found themselves struggling too. Boeri and colleagues recently showed that not only could they not identify a single compound in the Lu-N-H phase diagram that could explain Dias’ extraordinary claims, but also that Lu-N-H hydrides are intrinsically low-temperature superconductors (Nature Commun. 14 5367). “There is no single theoretical paper that finds a plausible explanation for Dias’ results,” she says.

Support for Dias’s work, however, came from Hemley, who is now at the University of Illinois Chicago. Having been given material prepared by Dias’ team, Hemley and colleagues measured the electrical resistance of the samples under various pressures, finding evidence for superconductivity as high as 276 K at 15 kbar (arXiv:2306.06301).

“Our measurements are in excellent agreement with what’s reported in the Nature paper,” Hemley told Physics World. “Moreover, the magnitude of the drop is even larger than that of the earlier data.”

Hemley says that theoretical analysis he and colleagues have carried out show that the electronic structure of Lu-N-H is ”remarkable” (arXiv: 2305.18196).

“With these continued discoveries, the pursuit of superconductors that function at or even above room temperature, together with the quest for stabilizing these materials near ambient pressure, remains very exciting,” he adds.

Science will suffer if we fail to preserve academic integrity

But there was further bad news in store for Dias. On 1 September 2023 Nature published an editor’s note alerting readers that Dias’ Lu-N-H paper is being investigated.

“The reliability of data presented in this manuscript is currently in question,” Nature said. “Appropriate editorial action will be taken once this matter is resolved.”

According to a report in the Wall Street Journal in late September, eight of the 11 authors of the Lu-N-H paper had written to Tobias Rödel, a senior editor at Nature, requesting that the paper be retracted, claiming that Dias “has not acted in good faith in regard to the preparation and submission of the manuscript”.

Apparently, Rödel replied to them within a few days noting: “We are in absolute agreement with your request that the paper be retracted.” So far, the only researchers to stick to their findings are Dias and two of his current PhD students.

David Ceperley from the University of Illinois, who penned a News & Views article for Nature about the Lu-N-H results, says he is “disappointed” that Nature did not do a better job of reviewing the paper in the first place.

“We were only provided with the accepted manuscript and not the data files or referee comments,” he says. “It was only after the paper came out that we learned of some the problems that could have been found earlier.”

Moving on

What will happen regarding Dias’ group is unknown. In August the University of Rochester announced it is investigating Dias’ work again, although when that investigation will be complete is unknown. “Unfortunately, Dias’ inconsiderate behaviour has harmed the reputation of the field and it may take a few years to repair the damage,” says Boeri.

That view is backed by condensed-matter physicist James Hamlin from the University of Florida, who examined some of Dias’ group’s work. “I do think the whole saga is damaging to science in general, and superconductivity research more so and more broadly it’s fuel for anti-science types,” he told Physics World. “It could have an impact on funding for high pressure research and that would be unfortunate given that it’s been such a fruitful area with so many exciting recent developments.”

Hamlin also thinks that scientific research journals should broaden their communications to include all authors of the paper rather than just the corresponding author when potential research misconduct is raised. “All authors are subject to potential reputational harm from a misconduct allegation, so all authors should be privy to the relevant communications from editors from the very beginning,” he adds.

Despite these issues, work on the hydrides is progressing. In July Guangtao Liu of Jilin University, China, and colleagues found superconductivity up to 110 K at a pressure of 80 GPa in the ternary hydride LaBeH₈ (Phys. Rev. Lett. 130 266001).

Room-temperature superconductor arrives at last, a dark-matter detector mystery

Although this temperature is not that high, these ternary compounds are exciting because they have a wider potential variety of structures than their binary cousins, which could expand the materials available for high-temperature superconductivity. “The field [of hydride research] is healthy and has the potential to yield many more ground-breaking results in future,” adds Boeri.

Ceperley agrees. “I still feel that hydride superconductivity has a good chance of eventually providing a superconductor at ambient conditions, which would have vast technological applications,” he notes. “The space of possible compounds and fabrication methods is so vast it may take some time to find them.”

As for Dias, he declined to comment for this article although in previous media comments he said he stood by his results.

In July Physics World even offered to publish an interview with Dias and sent a set of written questions to him via 30 Point, a US-based PR agency acting on Dias’s behalf. Despite having agreed to answer the questions, Dias later pulled out of the interview.

Physics World has since learned that 30 Point no longer works with Dias.

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• Source: https://physicsworld.com/a/superconductivity-damaged-as-researchers-look-to-move-on-from-retractions/