Tag: lutetium hydride

The journal’s part in a retraction

This is another Ranga Dias and superconductivity post, so please avert your gaze if you’re tired of it already.

According to a September 27 report in Science, the journal Nature plans to retract the latest Dias et al. paper, published in March 2023, claiming to have found evidence of near-room-temperature superconductivity in an unusual material, nitrogen-doped lutetium hydride (N-LuH). The heart of the matter seems to be, per Science, a plot showing a drop in N-LuH’s electric resistance below a particular temperature – a famous sign of superconductivity.

Dias (University of Rochester) and Ashkan Salamat (University of Nevada, Las Vegas), the other lead investigator in the study, measured the resistance in a noisy setting and then subtracted the noise – or what they claimed to be the noise. The problem is apparently that the subtracted plot in the published paper and the plot put together using raw data submitted by Dias and Salamat to Nature are different; the latter doesn’t show the resistance dropping to zero. Meaning that together with the noise, the paper’s authors subtracted some other information as well, and whatever was left behind suggested N-LuH had become superconducting.

A little more than a month ago, Physical Review Letters officially retracted another paper of a study led by Dias and Salamat after publishing it last year – and notably after a similar dispute (and on both occasions Dias was opposed to having the papers retracted). But the narrative was more dramatic then, with Physical Review Letters accusing Salamat of obstructing its investigation by supplying some other data as the raw data for its independent probe.

Then again, even before Science‘s report, other scientists in the same field had said that they weren’t bothering with replicating the data in the N-LuH paper because they had already wasted time trying to replicate Dias’s previous work, in vain.

Now, in the last year alone, three of Dias’s superconductivity-related papers have been retracted. But as on previous occasions, the new report also raises questions about Nature‘s pre-publication peer-review process. To quote Science:

In response to [James Hamlin and Brad Ramshaw’s critique of the subtracted plot], Nature initiated a post-publication review process, soliciting feedback from four independent experts. In documents obtained by Science, all four referees expressed strong concerns about the credibility of the data. ‘I fail to understand why the authors … are not willing or able to provide clear and timely responses,’ wrote one of the anonymous referees. ‘Without such responses the credibility of the published results are in question.’ A second referee went further, writing: ‘I strongly recommend that the article by R. Dias and A. Salamat be retracted.’

What was the difference between this review process and the one that happened before the paper was published, in which Nature‘s editors would have written to independent experts asking them for their opinions on the submitted manuscript? Why didn’t they catch the problem with the electrical resistance plot?

One possible explanation is the sampling problem: when writing an article as a science journalist, the views expressed in the article will be a function of the scientists that I have sampled from within the scientific community. In order to obtain the consensus view, I need to sample a sufficiently large number of scientists (or a small number of representative scientists, such as those who I know are in touch with the pulse of the community). Otherwise, there’s a nontrivial risk of some view in my article being over- or under-represented.

Similarly, during its pre-publication peer-review process, did Nature not sample the right set of reviewers? I’m unable to think of other explanations because the sampling problem accounts for many alternatives. Hamlin and Ramshaw also didn’t necessarily have access to more data than Dias et al. submitted to Nature because their criticism emerged in May 2023 itself, and was based on the published paper. Nature also hasn’t disclosed the pre-publication reviewers’ reports nor explained if there were any differences between its sampling process in the pre- and post-publication phases.

So short of there being a good explanation, as much as we have a scientist who’s seemingly been crying wolf about room-temperature superconductivity, we also have a journal whose peer-review process produced, on two separate occasions, two different results. Unless it can clarify why this isn’t so, Nature is also to blame for the paper’s fate.

Is Dias bringing the bus back?

So Physical Review Letters formally retracted that paper about manganese sulphide, in the limelight for having been coauthored by Ranga P. Dias, yesterday. The retraction notice states: “Of the authors on the original paper, R. Dias stands by the data in Fig. 1(b) and does not agree to retract the Letter.” Figure 1(b) is reproduced below.

The problem with the second plot is that its curves reportedly resemble some in Dias’s doctoral thesis from 2013, in which he had examined the same properties of germanium tetraselenide, a different kind of material. Curves can look the same to the extent that they can have the same overall shape; it’s a problem when they also reproduce the little variations that are a result of the specific material synthesised for a particular experiment and the measurements made on that day.

That Dias is the only person objecting to the retraction is interesting because it means one of his coaouthors, Ashkan Salamat, agreed to it. Salamat heads a lab in the University of Nevada, Las Vegas, that’s been implicated in the present controversy. Earlier this year, well after Physical Review Letters said it was looking into the allegations against the manganese sulphide paper, Scientific American reported:

Salamat has since responded, suggesting that even though the two data sets may appear similar, the resemblance is not indicative of copied data. “We’ve shown that if you just overlay other people’s data qualitatively, a lot of things look the same,” he says. “This is a very unfair approach.”

Physical Review Letters also accused Salamat of attempting to obstruct its investigation after it found that the raw data he claimed to have submitted of the group’s experiments wasn’t in fact the raw data. Since then, Salamat may well have changed his mind to avoid more hassle or in deference to the majority opinion, but I’m still curious if he could have changed his mind because he no longer thought the criticisms to be unfair.

Anyway, Dias is in the news because he’s made some claims in the past about having found room-temperature superconductors. A previous paper was retracted in September 2022, two years after it was published and independent researchers found some problems in the data. He had another paper published in March this year, reporting room-temperature but high-pressure superconductivity in nitrogen-doped lutetium hydride. This paper courted controversy because Dias et al. refused to share samples of the material so independent scientists could double-check the team’s claim.

Following the retraction, The New York Times asked Dias what he had to say, and his reply seems to bring back the bus under which principal investigators (PIs) have liked to throw their junior colleagues at signs of trouble in the past:

[He] has maintained that the paper accurately portrays the research findings. However, he said on Tuesday that his collaborators, working in the laboratory of Ashkan Salamat, a professor of physics at the University of Nevada, Las Vegas, introduced errors when producing charts of the data using Adobe Illustrator, software not typically used to make scientific charts.

“Any differences in the figure resulting from the use of Adobe Illustrator software were unintentional and not part of any effort to mislead or obstruct the peer review process,” Dr. Dias said in response to questions about the retraction. He acknowledged that the resistance measurements in question were performed at his laboratory in Rochester.

He’s saying that his lab made the measurements at the University of Rochester and sent the data to Salamat’s lab at the University of Nevada, where someone else (or elses) introduced errors using Adobe Illustrator – presumably while visualising the data, but even then Illustrator is a peculiar choice – and these errors caused the resulting plot to resemble one in Dias’s doctoral thesis. Hmm.

The New York Times also reported that after refusing in the past to investigate Dias’s work following allegations of misconduct, the University of Rochester has now launched an investigation “by outside experts”. The university doesn’t plan to release their report of the findings, however.

But even if the “outside experts” conclude that Dias didn’t really err and that, honestly, Salamat’s lab in Las Vegas was able to introduce very specific kinds of errors in what became figure 1(b), Dias must be held accountable for being one of the PIs of the study – a role whose responsibilities arguably include not letting tough situations devolve into finger-pointing.