How did it become clear that LK-99, which caused a whirlwind in the scientific world as a ``superconductor at normal temperature and pressure'', is not a superconductor?
LK-99 isn't a superconductor — how science sleuths solved the mystery
https://www.nature.com/articles/d41586-023-02585-7
The beginning of the matter was announced by a group of researchers working at the Quantum Energy Research Center, a startup in Seoul, South Korea, ``LK-99 is a superconductor at temperatures up to at least 127 degrees''. in the thesis. Until now, it was thought that it was necessary to cool the substance to a cryogenic state in order to create a superconductor, but the research team claims that LK-99 becomes a superconductor state at `` normal temperature and pressure ''. I was.
A paper and movie stating that ``a substance that becomes superconducting at room temperature and normal pressure'' has been developed will be released-GIGAZINE
This research paper attracted great interest in the scientific community, and many researchers conducted experiments to reproduce LK-99. And from the results of repeated reproduction experiments, many researchers are confidently saying that LK-99 is not a superconductor at normal temperature and pressure.
According to the latest research, LK-99, which is a compound of copper, lead, phosphorus, and oxygen, has a 'rapid drop in electrical resistivity' and 'partial floating on a magnet' due to the impurity copper sulfide it contains. has been shown to cause
Inna Visic, a condensed matter experimentalist at the University of California, Davis, said of the conclusion that LK-99 is not a superconductor, ``I think it's pretty decisive at this point.''
The research team at the Quantum Energy Research Center, which announced LK-99 as a superconductor at normal temperature and normal pressure, has two characteristics of LK-99, ``floating on a magnet'' and ``sudden decrease in electrical resistivity''. On the basis, they claimed that this is a superconductor.
However, several research institutes, including Peking University and the Chinese Academy of Sciences, have explained these two phenomena as ``the phenomenon caused by copper sulfide'' as mentioned above. Another study by American and European researchers combined experimental and theoretical evidence to demonstrate that LK-99 is an impractical superconductor. In addition, another research group synthesized samples of LK-99 and proved that the material is an insulator rather than a superconductor.
The most impressive evidence supporting the claim that LK-99 is a superconductor is the following video taken by a Korean research team, ``How LK-99 floats up''.
Movie [LK-99]-YouTube
The research team explained that LK-99 floats due to the Meissner effect . After that, unverified videos of LK-99 floating will be circulated on multiple SNS. However, none of the researchers who have tried to reproduce LK-99 have succeeded in reproducing this levitation.
Derrick van Gennep, a former condensed matter physicist at Harvard University, noted that in the video, the edges of LK-99 appear to stick together like magnets. On the other hand, a real superconductor floating on a magnet can be twirled in the air and even held upside down. Therefore, Mr. Genep said, ``The behavior that can be seen in the original superconductor movie is not seen in the LK-99 movie.''
Therefore, Mr. Genep seems to have come to think that ``the characteristics of LK-99 are likely to be the result of ferromagnetism''. Therefore, Mr. Genep created pellets by bonding iron powder to compressed graphite shavings. Although this pellet is not a superconductor, it seems to behave very similar to LK-99 because it is a ferromagnetic material. In fact, a research team at Peking University also points out that LK-99 is semi-floating due to ferromagnetism.
Below is a video of a ``pellet that is a ferromagnetic material instead of a superconductor'' created by Mr. Genep and semi-floated with a magnet.
I was able to closely mimic the “levitation” behavior of LK-99 with a ferromagnetic sample.
—Derrick VanGennep (@VanGennepD) August 6, 2023
For comparison, see the original LK-99 video in the tweet below.pic.twitter.com/bKmf3cOoS2
The reaction to synthesize LK-99 produces a large number of copper and sulfur as well as copper-doped lead phosphate crystals that are pure LK-99. Anything other than pure LK-99 is an impurity, which appears to be copper sulfide that reproduces two properties of superconductors.
A group of researchers at the Quantum Energy Research Center claimed that there is a temperature at which the electrical resistivity of LK-99 drops sharply from '0.02 ohm cm' to '0.002 ohm cm'. ``This is the temperature at which CuS (cuprous sulfide) undergoes a phase transition,'' points out chemist Prashant Jain of the University of Illinois at Urbana-Champaign, an expert on copper sulfide. Below this temperature, the electrical resistivity of Cu2S in contact with air drops sharply, but the research group overlooked this fact.
In addition, according to the reproduction experiment of the Chinese Academy of Sciences, the Cu2S content rate is 5% when LK-99 is synthesized in a vacuum, while the Cu2S content rate is 70% when synthesized in air. is. In the case of LK-99 with a Cu2S content of 5%, the electrical resistivity changes relatively smoothly with temperature changes, but in the case of LK-99 with a Cu2S content of 70%, the electrical resistivity changes sharply around 112°C. has been confirmed to decrease to
Research is also being conducted to remove impurities from LK-99, but it has become clear that LK-99 from which impurities have been removed is not a superconductor but an insulator with a resistance value of several million ohms. I'm here. Pure LK-99 with impurities removed shows slight ferromagnetism and diamagnetism, but it seems that it is not enough to reproduce partial levitation.
Based on these, the two characteristics of LK-99 as a superconductor, ``sudden decrease in electrical resistivity'' and ``partial suspension on the magnet,'' are likely due to the impurities contained in the product. It is thought that it is caused by Cu2S.
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