Only 1 week Chinese team falsifies 'room temperature superconductivity'
At the March 2023 APS meeting in Las Vegas, Ranga Dias and his team at the University of Rochester in New York described their claimed achievement as the culmination of a more than century-long quest for the condensed "holy grail": a material capable of conducting electrons with zero resistance at ambient temperature. Knowing that such a breakthrough would mark an important step toward a future in which room-temperature superconductors transform electrical grids, computer processors and medical diagnostic tools, the team's discovery could rank among the greatest scientific advances of the 21st century if it is true.
The audience reaction to such disruptive research was muted or hesitant.
Part of the audience was cautious because - they had encountered this before, and in fact, in 2020, Dias' team announced in a paper in Nature that they had created a material, carbonaceous sulfur hydride, that was superconducting at 287 K and 267 GPa, and researchers and the news media praised the discovery, but two years later the paper was retracted after outside researchers found oddities in the results.
Another reason is that the findings themselves are highly suspect, with the samples studied in the latest findings ranging from 70 to 100 μm in diameter and 10 to 20 μm in thickness.
Unfortunately, the chemical composition (stoichiometry) of the new material made at very high pressure is unknown (surprisingly the article does not specify the details of the synthesis method): X-ray diffraction points to H3-δNε ( 92.25 %) containing LuN1-δHε (7.29 %) and Lu2O3 (0.46 % ); future studies will have to clarify it.
The problem is that it is impossible to explain the observed superconductivity with this composition (the distance between hydrogens is too large); the current-voltage (IV) curve is perfectly linear (pointing to unconventional superconductivity); the magnetization rate curve (Meissner effect) shows strange (or unexpected) behavior, and it is unclear why the reviewers did not ask for a detailed discussion.
Physicists believe that Dias' paper does not present a detailed approach to replication, which makes replication difficult and makes this research less feasible.
(a) The current-voltage (IV) curve is perfectly linear
(b) These curves are very similar to those criticized by Jorge Hirsch (University of California, San Diego) in his retracted article
(c) This graph shows the original data in the paper (left) and the graph that appears in the article (right). The data show a resistance between 2 and 9 mΩ (milliohms), adjusted by five polynomials that should produce the curve that appears on the right. Subtracting the polynomial (to eliminate the observed "residual resistance") shows almost zero between 125 and 225 K, with a sharp shift between 225 and 275 K.
Due to the sensational nature of the study and the multiple doubts, several groups have already studied the high pressure superconductivity of Lu-H compounds, but none of them have been able to reproduce the results of the room temperature superconductivity experiments of Dias' team.
l Wen Haihu's team at Nanjing University
"This conclusion is definitely overturned, without any doubt." Wen Haihu, director of the Center for Superconductivity Physics and Materials Research at Nanjing University, spoke this statement to Science China in a firm enough tone.
Haihu Wen Photo credit: Nanjing University
On March 15, Wen Haihu's team submitted a 16-page research paper including nine authors to the preprint site arXiv that bluntly dismissed Dias' findings. The paper concludes, "Our experiments clearly show that superconductivity does not exist in the lutetium nitrogen-hydrogen material LuH2±xNy from ambient pressures down to 6.3 GPa and temperatures down to 10 K (about -263 degrees Celsius)."
The main point of the analysis, based on the team's submitted paper Absence of near-ambient superconductivity in LuH2±x Ny, is as follows: a priori, it is not difficult to synthesize nitrogen-doped lutetium hydride at high pressures (perhaps for this reason, Dias and his team in Nature omitted it).
In fact, the XRD spectra of Ming et al. is almost identical to that of Dias, with the advantage of being cleaner and with fewer impurities (no traces of Lu2O3 were observed, 0.46% in Dias' sample). Unfortunately, LuH 2±x N y does not show any color change between 1 GPa and 5.2 GPa (suggesting that Dias may be observing something else).
The nitrogen-doped lutetium hydride shows the resistance versus temperature curve properties of the metal, linear between 40 K and 300 K, and quadratic below 40 K. There is no sign of superconductivity (only a small slope change at 315 K, which could be a systematic error of the measurement instrument). As shown above, for pressures between 1.3 and 6.28 GPa, there is also no sign of superconductivity at temperatures between 10 and 350 K.
The magnetic moment curves as a function of temperature at 1 GPa and 2.1 GPa also show no sign of antimagnetism due to the Meissner effect (when the results given by Dias are textbook curves). The results given by Haihu Wen's team are that there is no superconductivity at pressures of the order of LuH 2±x N and 1 GPa (the results are in good agreement with previous studies on lutetium hydrogenation).
l Jinguang Cheng's team at Institute of Physics
The pressure-induced color change of LuH2 was investigated by Cheng's group, and the related paper was published in China Physics Letters. This pressure-induced color change is very similar to the phenomenon observed in N-doped LuH3-δ by Dias et al.
However, the results of variable temperature resistance tests at high pressure showed that LuH2 did not show superconductivity below 7.7 GPa and above 1.5 K.
The color presented by LuH2 at different pressures. It is dark blue at ambient pressure, turns pink at about 2.2 GPa, and changes to bright red at about 4 GPa, and this pressure-induced color change is reversible.
This experimental work confirms that LuH2 undergoes a significant color change at high pressure, which is similar to the phenomenon observed by Dias et al. in N-doped lutetium hydrogenation, although LuH2 does not appear superconducting at high and low temperatures. The results are of reference value to further resolve the structure and possible superconductivity of the Lu-H-N system.
l Changqing Jin's team at Institute of Physics
The team found that lutetium polyhydrides with fully filled f-shells are high-temperature superconductors. The lutetium polyhydride was successfully synthesized by a diamond anvil device combined with in situ high pressure laser heating technique under high pressure and high temperature conditions. Resistance measurements with temperature were carried out at the same synthesis pressure to study the transition to superconductivity (SC).
In the experiments, the superconductivity transition was observed at a maximum onset temperature (Tc) of 71 K at a maximum pressure of 218 GPa. When the pressure was released to 181 GPa, Tc dropped to 65 K. The study of the SC evolution under an applied magnetic field led to an upper critical field u0Hc2(0) of ~36 Tesla at zero temperature.
In situ high-pressure X-ray diffraction experiments indicate that the high-Tc SC should come from the Pm3-n of the Lu4H23 phase, which forms a new type of hydrogen-cage framework, different from the previously reported rare-earth polyhydride superconductors.
Although it is not yet possible to say with certainty that the research results of Dias's team are definitely faked, based on these replica experiments, it is probable that this paper will not be able to escape the fate of retraction.
In response to Dias' dubious research results, some sources pointed out that he had founded a company and was looking for $20 million in financing, which inevitably aroused suspicion: Dias was trying to obtain financing through subversive research results, and Dias had actually been accused of academic misconduct several times.
Image credit: Ranga Dias, University of Rochester
l CSH greenhouse superconductivity accused of data falsification
In 2020 Dias' team proposed greenhouse superconductivity, claiming that by adding a little carbon to the precursor used to make H 3 S, a known hydride superconductor, they were able to create carbon-sulfur hydride (CSH) materials that pushed the superconducting temperature up to 287 K (nearly 15°C) , the temperature of a cooler room. The results were published in the October 14, 2020 issue of Nature and received worldwide acclaim. Several scientists have tried to replicate or extend this finding with little success, and scientist Hirsch also found that some of the CSH AC magnetization data looked very similar to other now questionable data from a 2009 Physical Review Letters paper on europium superconductivity at high pressures, after which Hirsch emailed a request for the original data to Dias, but Dias refused to provide the relevant data. Hirsch therefore began to question the CSH findings] as a result of data manipulation and alteration.
The CSH paper was withdrawn on September 26, 2022, after several scientists and associates reviewed the findings.
l Accused of plagiarism
As Hamlin delved into the CSH data, he came across some familiar-looking sentences in his paper presenting the original CSH data - sentences he recalled from his 2007 doctoral dissertation. On a hunch, he extracted Dias' 2013 thesis and entered both his paper and Dias' into a plagiarism checker. His computer screen lit up; the two documents contained many of the same passages.
Physics Magazine independently compared the two papers and found dozens of word-for-word matching passages and two graphs with striking similarities.
In response to allegations that he plagiarized Hamlin's paper, Dias said he did nothing wrong: "I had proper citations." Washington State University, which awarded Dias his doctorate, declined to comment on whether they had conducted a misconduct investigation. A statement from the University of Rochester said, "Dr., Dias takes responsibility for these errors and has worked with his dissertation advisor ...... to revise the dissertation."
Hamlin found a match between the resistivity diagram for germanium selenide (GeSe4 ) in Dias' paper and the resistivity diagram for manganese sulfide (MnS2 ) in the 2021 PRL paper, respectively. Simon Kimber, co-author of the PRL paper, said that when he received the email, he "couldn't think of a chemical or physical explanation for the similarity." Kimber emailed PRL requesting a retraction, and PRL has launched an investigation into the paper.
The paragraphs on pages 64 and 66 of Hamlin's paper on magnetization measurements (left) contain the same text as page 6 of Dias and Salamat's 2021 arXiv paper, in which the two share the original CSH data (right). Image credit: D. Garisto/APS
Mounting allegations and various paper retractions have led Dias' condensed matter colleagues to be wary of his scientific claims. "I don't want to believe the allegations, though, because it's too serious," says Eremets, who would prefer that the field simply forget about the irreproducible CSH results and move on. Others, however, are less forgiving. "I think these various issues need to be addressed before the community accepts any further claims," Hamlin said.
Reference links：
[1]https://francis.naukas.com/2023/03/14/posible-superconductividad-a-294-k-y-1-gpa-en-un-hidruro-de-lutecio-dopado-con-nitrogeno/
[2]https://doi.org/10.48550/arXiv.2303.08759
[3]https://doi.org/10.1088/0256-307X/40/4/046101
[4]https://doi.org/10.48550/arXiv.2303.05117
[5]https://physics.aps.org/articles/v16/40[6]https://www.zhihu.com/question/590708129
