Nature’s guillotine has decapitated LK-99’s superconductivity

The big news about the LK-99 is Dan Garisto’s story in the magazine nature which cuts its head superconductivity. It’s an echo of an article in arXiv that I already told you about (German article in LCMF, August 14, 2023) where high-purity lead crystals are made_{8.8 (3)}cu_{1.2 (3)}s₆also₂₅. The image of its translucent purple crystals is stunning (image not included in arXiv). Obviously, a transparent material cannot be a superconductor (or a magnetic material). the main author of the work, Pascal Popal, of the Max Planck Institute for Solid State Research in Stuttgart, Germany, specializes in crystal growth. Puphal claims that his new single-crystal synthesis method (which differs from the one patented by the Koreans) was what was needed to close the case: his single crystals show that LK-99 is a semiconductor, beyond any doubt. Furthermore, it indicates that the effects of superconductivity observed in LK-99 are due to copper impurities.₂Yes, it is absent in monocrystalline. On social networks, the few who still had hope were completely lost. Nature’s guillotine decapitated the surrounding superconductivity of LK-99.

But as I already told you, the summer snake is still alive and well. The reason is that powder X-ray diffraction (PXRD) of a single crystal of LK-99 shows that copper doping is a combination of two possibilities. Remember that copper ions can substitute for lead ions in the Wyckoff 4f or Pb (1) doping position, and the 6h or Pb (2) doping position. A mixture of both types of doping is observed in the synthesized purple single crystal. Can single crystals be superconductors? The Koreans claimed that their substance contains phase 4f, so could the (potential) secret of the Korean composition guarantee this steroids? Nobody knows the answer, though you already know my opinion. Neither dope apart, like their mixture, leads to a superconductor at room temperature. But this did not appear in the work led by Puphal. Remember that many snakes can survive (for a short time) decapitation, while maintaining some involuntary muscle reflexes. guillotine nature He cut off the head of the summer series, which can no longer bite, but is not dead yet.

I recommend you read the news with a bit of skepticism, Dan Garisto, “LK-99 is not a superconductor – how scientific investigators managed to solve the mystery. Multiples pieced together the puzzle as to why matter exhibits superconducting-like behaviors,” News, Nature, Aug. 16, 2023. What I like best is its ending: “The detective work done in gathering the evidence from the original note is remarkable and comparatively rare”. Without a doubt, the most interesting thing about the series is that it shows us science in action more quickly than usual; Reproducibility of all results is essential, and scientific consensus based on accumulated evidence is the hallmark of the scientific method. Although, do not forget that hastily done science, like anything else, ends with unreliable results.

Incidentally, three DFT-based theoretical papers have also been published on arXiv today. I don’t think any of them will interest you, but just in case. A critique of Griffin’s work with DFT has been published, and his conclusions about the existence of two half-full flat bars may be incorrect; According to the new DFT results, his conclusions are biased by the criteria he used (remember I said that at the time, LCMF, Aug 01, 2023, his criteria did not convince me after comparing them to other DFT results published the same day, and since). According to new DFT simulations, the LK-99 studied by Griffin is a semiconductor, with no possibility of it being a superconductor (as she suggested between the lines, although she later denied this on Twitter due to the criticism she received). Article by Michael W Swift, John L. [cond-mat.supr-con] (August 15, 2023), doi: https://doi.org/10.48550/arXiv.2308.08458.

Despite said comment, there is another article with DFT that supports Griffin’s findings; Copper doping of lead ions 4f (like Griffin) and 6h (which Griffin herself has shown to be more energetically favorable) have been studied. It is suggested that the synthesis of LK-99 results in a mixture of phases 4f (doped with Pb(1), called Wyckoff position 4f) and 6h (doped with Pb(2), Wyckoff position 6h), in different ratios., which explains the diversity of the published results. in experiments. In the 4f phase, copper doping presents a transition between a semiconductor state and a semimetallic state with two half-full flat bands. In the 6 h phase, copper doping does not show the said transition, the doping materials are semiconductors. The article is by Ran Liu, Ting Guo…and Tianxing Ma, “Different phase leads to different transfer behavior in Pb9Cu(PO4)6O compounds”, arXiv:2308.08454 [cond-mat.supr-con] (August 15, 2023), doi: https://doi.org/10.48550/arXiv.2308.08454.

A third article performs a thermodynamic analysis of the LK-99 synthesis reactions, concluding that it preferentially leads to Pb₈cu₂(s₄)₆with copper doping of two lead Pb(1) and without additional oxygen, instead of Pb₉quota₄)₆or (what Griffin and most DFT theorists use), or Pb₉quota₄)₆(oh)₂ (What is considered in the so-called Princeton article and others). This compound (with x = 2 in the original LK-99 formula) is also a semiconductor, with no trace of superconductivity. But the authors suggest that it would be interesting to synthesize them in the laboratory. The new element is lead phosphate phase stabilizer lead apatite_{10 − s}cu_x(s₄)₆O, Pb_{10 − s}cu_x(s₄)₆(oh)₂and Pb₈cu₂(s₄)₆arXiv: 2308.07941 [cond-mat.mtrl-sci] (Aug 14, 2023), doi: https://doi.org/10.48550/arXiv.2308.07941.

In summary, three articles with DFT have the usual problems of these articles; Their conclusions should be taken with extreme caution (regarding the possible superconductivity of the studied material). The most relevant today is the news of Dan Jaristo, who has been heavily criticized on Chinese and Korean social networks. But outside the Asian universe, most trust German science and the prestige of nature. But don’t be fooled, until a scientific consensus is reached, skepticism should be your banner.