The most contentious scientific topic this week has been the “Possible superconductivity at 294 K and 1 GPa in a nitrogen-doped lutetium hydride” (LCMF, 14 Mar 2023). The first attempt to replicate the result has failed: nitrogen-doped lutetium hydride (LuH2±xNy) is not superconducting above 10 K at pressures between 1 GPa and 6 GPa; in fact, it doesn’t even show any color change (from blue to red to pink). Such a color change is observed in lutetium hydride (LuH2), its blue color changes to pink at ~2.2 GPa and then to red at ~4 GPa; but this material is not a superconductor at pressures up to 7.7 GPa above 1.5 K. Furthermore, a superhydride of lutetium (Lu4H23) is superconducting at 71 K at pressures of 218 GPa (at 65 K at 181 GPa), not superconducting at ~1 GPa. As expected, the article by the Dias group in Nature it is not replicable.
Obviously, Dias and his group will say that their nitrogen-doped lutetium hydride is LuH3−xNy (92 %) con LuN1−xHy (7%) instead of LuH2±xNy; however, the X-ray diffraction (XRD) spectrum of the latter (see figure) is almost identical (right graph) to that published by Dias in en Nature. These new papers (and those to be published next week) leave no doubt that nitrogen-doped lutetium hydride is not a high-temperature superconductor at pressure as low as 1 GPa; and, furthermore, it is very far from reaching ambient temperatures (~300 K) even at pressures greater than 200 GPa. Dias’s fiasco not only discredits his group, but also the journal Nature and the entire scientific community that investigates high-pressure superconducting hydrides.
We all remember the aphorism popularized by Carl Sagan: affirmations extraordinary require evidence extraordinary. Los nuevos artículos son Xue Ming, Ying-Jie Zhang, …, Hai-Hu Wen, «Absence of near-ambient superconductivity in LuH2±xNy,» arXiv:2303.08759 [cond-mat.supr-con] (15 Mar 2023), doi: https://doi.org/10.48550/arXiv.2303.08759 (this article, due to its format, has been sent to Nature o Nature Physics); Pengfei Shan, Ningning Wang, …, Jingguang Cheng, «Pressure-induced color change in the lutetium dihydride LuH2,» Chinese Physics Letters 40: 046101 (15 Mar 2023), doi: https://doi.org/10.1088/0256-307X/40/4/046101, arXiv:2303.06718 [cond-mat.supr-con] (12 Mar 2023); y Zhiwen Li, Xin He, …, Changqing Jin, «Superconductivity above 70 K experimentally discovered in lutetium polyhydride,» arXiv:2303.05117 [cond-mat.supr-con] (09 Mar 2023), doi: https://doi.org/10.48550/arXiv.2303.05117.
A priori, the synthesis at high pressures of a nitrogen-doped lutetium hydride is not difficult (perhaps for this reason it is omitted by Dias and his group in Nature). In fact, the XRD spectrum of Ming et al. which is almost identical to that of Dias has the advantage that it is cleaner and has fewer impurities (no traces of Lu are observed).2O3, 0.46 % in the Dias sample). Unfortunately, the LuH2±xNy it does not show any color change between 1 GPa and 5.2 GPa (suggesting that Dias might be observing something else).
Nitrogen-doped lutetium hydride shows a resistance versus temperature curve characteristic of a metal, being linear between 40 K and 300 K, and quadratic below 40 K. There is no indication of superconductivity (only a small slope change at 315 K which could be a systematic error of the measuring instrument). As this figure shows, for pressures between 1.3 and 6.28 GPa, there is also no indication of superconductivity for temperatures between 10 and 350 K. Nothing in these curves points to what Dias and his group claim to observe after applying their (peculiar) subtraction technique. From the bottom.
The magnetic moment vs. temperature curves at 1 GPa and 2.1 GPa also show no indication of diamagnetism due to the Meissner effect (when Dias results in Nature they were textbook curves). The results of Ming et al. leave no doubt about the absence of superconductivity in the LuH2±xNy at pressures of the order of 1 GPa (a result in good agreement with previous studies on lutetium hydrides).
The color change observed by Dias in Naturefrom blue to red through pink in the superconducting phase, points to lutetium hydride (LuH2). Its X-ray spectrum differs from that published in Nature, but the color change has been observed by Ming et al. and by Shan et al. By the way, Shan et al. they acquired lutetium powder from Aladdin, which turned out to be a mixture of LuH2 (70%), blue in color, and Lu2O3 (27%), white; they had to separate the first one to study its color changes. As Dias reported in his sample Lu2O3 (0.46 %), it may be that oxygen impurities are responsible for the pressures at which the color changes reported in Nature are observed to be different from those of LuH2.
Unfortunately, the resistance versus temperature curve of lutetium hydride (LuH2) does not show any type of superconductivity signal for temperatures between 1.5 and 300 K at pressures between 0.5 and 6.7 GPa. The observed behavior is metallic, although it presents an irreversibility (very apparent at low pressures), which points to the need for future studies; although there is nothing to suggest that these studies are going to observe superconducting behavior.
Finally, the superconductivity with a critical temperature of 71 K (65 K) of a lutetium polyhydride (Lu4H23) at a high pressure of 218 GPa (181 GPa). An interesting material because it supports a critical magnetic field of ~36 T (teslas).
Lutetium polyhydride has structural characteristics that point to superconductivity at high pressures according to Ashcroft’s (1968) theory for metallic hydrogen. Of course, it is very far from room temperature. Future studies will have to confirm its properties, but for what interests us here, everything points to the fact that Dias’ article in Nature will end up being withdrawn (retracted) like his 2020 article. How can the editor of Nature (Magdalena Skipper) allow your magazine to accept articles like the new one by Dias? The increase in the impact index of this journal in recent years is being accompanied by a growing loss of prestige. Needs Nature a rudder blow?