Archive for superconductivity

Not the First Room-Temperature Superconductor?

Posted in The Universe and Stuff with tags , , , , , on August 13, 2023 by telescoper

A few weeks ago I reported on a paper on arXiv entitled The First Room-Temperature Ambient-Pressure Superconductor. It presented a material now known as LK-99. The quest for high temperature superconductivity has been very active for many years so this claim generated a lot of interest and LK-99 now has a very active Wikipedia page. Not entirely surprisingly, the claim of superconductivity has been met with some resistance. Geddit?

To summarise, a number of groups seem to have managed to synthesize LK-99, but none have managed to recreate the claimed superconductivity.

This paper on arXiv by scientists at the CSIR National Physical Laboratory in India states:

The report of synthesis of modified Lead apatite (LK-99) with evidence of superconductivity at more than boiling water temperature has steered the whole scientific community. There have been several failures to reproduce superconductivity in LK-99 including partial successes. Here, we have continued our efforts to synthesize phase pure LK-99 with improved precursors. The process has been followed as suggested by Sukbae Lee et. al., [1,2]. The phase purity of each precursor is evidenced by Powder X-ray diffraction (PXRD) and well fitted by Rietveld refinement. The PXRD confirms the synthesis of phase pure polycrystalline LK-99 with apatite structure. The freshly synthesized sample does not show any signature of superconductivity levitation on a magnet (diamagnetism). The magnetization measurements on SQUID also show that LK-99 is diamagnetic at 280 K, there is no sign of superconductivity in LK-99 at room temperature. Moreover, we have also performed first principle calculations to investigate the electronic band structure of the LK-99 near Fermi level. Our study verifies that the Cu doped lead apatite (LK-99) has bands crossing at Fermi level, indicating generation of strong correlation in the system.

arXiv:2308.03544

There is also this paper submitted to arXiv on the same day (7th August) by scientists from the University of Manchester:

Recently, two arXiv preprints (arXiv:2307.12008, arXiv:2307.12037) reported signatures of superconductivity above room temperature and at ambient pressure, striking worldwide experimental research efforts to replicate the results3-7, as well as theoretical attempts to explain the purported superconductivity8-12. The material of interest has chemical formula Pb10−xCux(PO4)6O, where x≈1, and was named by the authors as LK-99. It belongs to lead apatite family, and was synthesized from two precursors, lanarkite (PbSO4⋅PbO) and copper phosphide (Cu3P). Here we performed a systematic study on LK-99, starting from solid-state synthesis, followed by characterisation and transport measurements. We did not observe any signatures of superconductivity in our samples of LK-99.

arXiv:2308.03823

While other studies suggest that LK-99 may have some interesting magnetic properties, it’s not looking good for this as a room-temperature superconductor, or indeed any kind of superconductor at all. I would like to see a few more results published before deciding firmly that the matter is closed, but I don’t think I’ll be buying shares in LK-99.

P.S. Nobody should get too overwrought if the claim is refuted: it’s an example of a thing called the scientific method.

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The First Room-Temperature Superconductor?

Posted in The Universe and Stuff with tags , , , on July 25, 2023 by telescoper

This is outside my usual areas, but there’s a new paper on arXiv which, if verified, could be extremely important. It’s called The First Room-Temperature Ambient-Pressure Superconductor and it is written by three scientists based in Korea. High temperature superconductivity has been, er, a hot topic for some years. One must be cautious because (as far as I am aware) the article has not yet been refereed, but is this a breakthrough?

Here is the abstract:

It seems to me that 400K is a bit hot for a room, but the point is that the material behaves as a superconductor (i.e. zero resistivity) for T < Tc so cooler rooms would do! The current definition of “high temperature” is Tc > 77K which is much lower than the Tc = 400 K stated here.

Here’s part of a figure from the paper showing (right) the material LK-99 and its structure (left):

I’m not an expert, but it looks like the material involved is neither particularly expensive nor particularly complicated so it should be relatively easy to determine whether these results are reproducible.

Comments from experts are welcome!

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From the Inventor of the H-index

Posted in Biographical, The Universe and Stuff with tags , , , , on March 5, 2020 by telescoper

My third-year students are busily engaged with a Computational Physics class test so I thought I’d occupy myself for a few minutes by sharing an interesting little paper that appeared on the arXiv a few weeks ago. The paper is by Jorge Hirsch, the inventor of the (in)famous H-index.

Here is the abstract:

A magnetic field H is expelled from the interior of a metal becoming superconducting. Everybody thinks the phenomenon is perfectly well understood, particularly scientists with the highest H-index think that. I don’t. I will explain why I believe that without Holes, conceptualized by Heisenberg in 1931 fifty years after Hall had first detected them in some metals, neither magnetic field expulsion nor anything else about superconductivity can be understood. I have been a Heretic in the field of superconductivity for over 30 years, and believe that Hans’ little story about the emperor perfectly captures the essence of the situation. Here is (a highly condensed version of) the wHole story.

You will see that, despite the liberal sprinkling of letters H, the paper isn’t ostensibly about the H-index, but it does contain some interesting comments thereon, including:

I proposed the H-index hoping it would be an objective measure of scientific achievement. By and large, I think this is believed to be the case. But I have now come to believe that it can also fail spectacularly and have severe unintended negative consequences. I can understand how the sorcerer’s apprentice must have felt.

I think the opinion of a scientist about the value of the H-index roughly speaking divides according to whether a said scientist has a big one or a small one. Those lucky enough to have a high H-index probably think it is fine, while those who have a low value can probably find a reason why it is flawed. My own H-index (42 according to Google Scholar) is mediocre, which I reckon is a fair reflection of my status.

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