A material called red matter, after the colour change it undergoes when subjected to pressure, was hailed as a potential room temperature superconductor, but now other researchers are finding they can't replicate the results.
Red matter, a material that researchers last week claimed showed evidence of being a room-temperature superconductor with the promise of revolutionising electronics, might not be so super after all, after another group has struggled to replicate the results.
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| Attempts to recreate red matter under various pressures failed to replicate the material’s changing colour Nanjing University |
Last week, Ranga Dias at the University of Rochester in New York and his colleagues said they had created a superconducting material – one that allows electricity to flow with zero resistance – that they called red matter to reflect its colour change under pressure. All other known superconductors require low temperatures and high pressures, making them impractical, but the team said that red matter works at just 21°C (69°F) and a pressure of 1 gigapascal.
Now, Hai-Hu Wen at Nanjing University in China and his colleagues say they have used the same ingredients of hydrogen, nitrogen and lutetium to create a sample with the same structure, but it lacks any superconducting properties.
“We measured the two basic properties for characterising a superconductor, which is the resistivity and the magnetisation,” says Wen. “Under the same pressure [as Dias’s group used] and different pressures, we found that, actually, no trace of superconductivity can be found.”
In terms of the raw data, the two samples showed very similar readings, says Wen, so the different conclusions come down to how you interpret that data. Wen says that Dias’s group unnecessarily subtracted background noise from the raw data to discover superconductivity, a point also made by other critics of the work.
“We find it difficult to assume this group accurately recreated our material,” says Dias, noting that Wen’s material doesn’t show the distinctive colour change under pressure that gives red matter its name. “This is conclusive evidence that they are not testing our sample.”
Questions around red matter are heightened because of previous accusations of unconventional data techniques levelled at Dias and his colleagues. In 2022, Natureretracted a 2020 paper from Dias that claimed room-temperature superconductivity in a different compound. The authors all disagreed with the retraction, saying their data supported the paper’s claims. Physical Review Letters has also announced it is reviewing one of Dias’s papers due to claims of plagiarism. Dias denies the allegations.
“Thousands of researchers have looked for room temperature superconductivity for 112 years and haven’t found any. Ranga Dias has claimed to find room temperature superconductivity in four different compounds in recent years,” says Jorge Hirsch at the University of California, San Diego.
Because of this, the publication of the red matter paper was greeted cautiously, with researchers hoping it would be replicated soon. But when Wen and his team tried to follow the recipe set out by Dias’s team, they found it impossible to react lutetium with hydrogen and nitrogen gas at the suggested temperature of -208.15°C. Instead, they used their own method, mixing lutetium with calcium hydride and ammonia at 300°C, which gave off the required nitrogen and hydrogen to mix with the lutetium.
To check they had produced red matter, Wen and his team used X-ray diffraction to determine its crystal structure. “The structure is exactly the same, the only unknown thing is the concentration of nitrogen,” says Wen. “Maybe their sample is lower, ours is a bit higher.”
However, Dias’s sample seems to contain a mixture of different structures of material and X-ray diffraction can’t always tell the difference between similar structures, says Lilia Boeri at the University of Rome in Italy.
The difference in colour change under pressure also might indicate that the two materials don’t have identical compositions, says Tim Strobel at the Carnegie Institution for Science in Washington DC. Strobel and his team are currently trying to reproduce the work of both groups to validate the findings, and say they will have results soon.
Ultimately, we need more data, says James Hamlin at the University of Florida, but the fact that the raw data looks similar is encouraging, and would fit with the suggestion that some people have made for Dias’s work, which is that the raw data is revealing structural changes in red matter as it is pressurised, and not superconductivity. “I don’t think it’s gonna settle it once and for all, but I think it’s another data point,” says Hamlin.
Dias says replication will take time and cannot be achieved in the week that has elapsed since his team’s publication. “This work can’t be done easily or quickly by anyone, it takes specialised technique, advanced lab work and incredible patience,” he says. “Any group working to replicate our results should expect to be challenged, and multiple failed experiments are also likely, if our experience is any guide.”
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