What is superconductivity? And what is 'LK-99' that realizes superconductivity at normal temperature and pressure & summary of the results of the reproduction experiment
In July 2023, a South Korean research team
LK-99: The Live Online Race for a Room-Temperature Superconductor (Summary) – Eiri Sanada
https://eirifu.wordpress.com/2023/07/30/lk-99-superconductor-summary/
◆What is superconductivity?
To put it simply, superconductivity is a state in which electrical resistance becomes zero when a substance is cooled to a low temperature, and substances that cause this state are called superconductors. In the world of technology, it is sometimes written as 'superconductivity', and the Japanese Industrial Standards (JIS) uses the notation 'superconductivity', but in the academic world it is written as 'superconductivity', so this notation is used in this article. is used.
Superconductivity was discovered in 1911 by the Dutch physicist Kamarin Onnes . In 1908, Onnes was the first to liquefy helium. From this, human beings are now able to study physical properties at absolute zero.
In general, the electrical resistance of metals increases when heated and decreases when cooled. From this, Onnes thought, ``If you cool the metal to the limit, the electrical resistance will be zero. It turns out that the resistance suddenly becomes zero. This was the moment when superconductivity was confirmed for the first time in the world.
◆Why does superconductivity occur?
More than 100 years after its discovery, the principle of superconductivity is still not well understood. However, the theory that explains why superconductivity occurs was proposed by John Bardeen, Leon Cooper, and John Shrieffer in 1957, and this theory is based on the initials of the three names. It is called '
Metals are conductive substances that conduct electricity, and the electrons of metal atoms become ``free electrons'' and move around, giving them conductivity. However, when the negatively charged free electrons move between the crystal lattices of metal atoms, they are attracted to the positively charged crystal lattice. Since the crystal lattice of metal atoms restricts the behavior of free electrons, metals have some electrical resistance.
BCS theory showed the idea that electrons form pairs called 'Cooper pairs', and the electrical resistance becomes zero due to the interaction between electrons. In this model, even if one electron is attracted to the crystal lattice and loses energy, the other electron takes energy from the crystal lattice. From the Cooper pair, the energy that the electron loses to the crystal lattice becomes zero plus or minus, so the electrical resistance becomes zero. In other words, superconductivity can be said to be 'a state in which electrons in a metal form Cooper pairs'.
Using the BCS theory, I was able to explain that superconductivity occurs at 30 to 40K (-243°C to -203°C). Furthermore, the BCS theory has made it possible to theoretically calculate the temperature at which a material transitions to superconductivity (critical temperature) and the specific heat. For this achievement, Bardeen, Cooper, and Schrieffer were awarded the Nobel Prize in Physics in 1972. However, it was discovered in 1987 that copper oxide becomes superconducting at a relatively high temperature of 93K (approximately -180°C). rice field.
◆What are the characteristics of superconductivity?
In addition to 'zero electrical resistance', a major feature of superconductors is the 'Meissner effect', which prevents magnetic fields from penetrating into superconductors. Superconductors eliminate magnetic fields due to the Meissner effect, so when a magnet approaches them, they repel and try to move away. Then, when a magnetic field with a strength above a certain level is applied, it ceases to be in a superconducting state and the magnetic field penetrates.
When a magnetic field exceeding the limit is applied, a material that suddenly loses its superconductivity due to a sudden magnetic field penetration is called a first-class superconductor. I call. When this second-class superconductor is placed on a strong magnet, it basically eliminates the magnetic field, but it partially penetrates the magnetic field. This phenomenon is called the 'pinning effect' because it becomes a state in which several skewers of magnetic lines of force are stuck in the superconductor, so to speak, and it is fixed in the magnetic field and cannot move.
Due to the pinning effect, the positional relationship between the superconductor and the magnet is fixed and they always levitate at the same height, so they do not come off the top of the magnet. An application of this can be seen from the following movie in the experiment of a linear motor car with a superconductor.
◆What can we do when superconductivity becomes possible?
Superconductivity itself has already been put into practical use, and MRI used for medical examinations in hospitals is one of them. Superconductors have zero electrical resistance, so once a current has flowed it will continue to flow forever without loss. In MRI, a coil made of an alloy called niobium titanium is cooled by liquefied helium, and it continues to be a powerful electromagnet even when the power is turned off.
Also, since the electrical resistance becomes zero, the loss can be greatly reduced if the power transmission cable is made of superconductors. In addition, superconductivity can also be applied to quantum computers, and in fact, quantum computers using superconductivity are being actively developed in Japan.
AIST: Launch of 'Quantum Computing Cloud Service' that allows the use of quantum computers Minus Release of the first domestic superconducting quantum computer
https://www.aist.go.jp/aist_j/news/pr20230324.html
However, in any system, it is necessary to maintain a cryogenic environment in order to maintain superconductivity, and for that purpose liquefied helium or liquefied hydrogen must be used, so the cost is ridiculously high. .
◆ What is 'LK-99'?
LK-99 was first synthesized in 1999 and named after its discoverers and first preprint presenters, Sukbae Lee and Jihoon Kim.
Superconductivity is when the electrical resistance becomes 0 due to the phase transition of substances caused by lowering the temperature. LK-99 has become a hot topic because it has been reported that it undergoes a phase transition to superconductivity at a much higher temperature and normal pressure than before. Basically, the superconducting transition temperature under normal pressure is extremely low, and under normal pressure, it is a kind of copper oxide and the highest value is 133 K (minus about 140 ° C). Above that temperature, the superconducting transition has been confirmed only in experiments under high pressure.
However, a paper originally published on the preprint server arXiv claimed that LK-99 achieved a superconducting transition at 400 K (approximately 127 °C), above the boiling point of water. LK-99 can be synthesized by finely pulverizing and mixing lanalkite (Pb 2 (SO 4 )O) and copper phosphide (Cu 3 P) and firing it in a vacuum chamber at 925°C for one day. That's what I'm talking about. The fact that it is easy to synthesize at home as long as the materials are available is another point that has attracted public attention.
Room temperature normal pressure superconductivity can clear the high cost condition of 'maintaining an extremely low temperature environment', so it is very beneficial for human beings and will definitely be a big breakthrough for civilization. However, it has never been confirmed until now, and although there have been a number of published papers, they have all been retracted due to errors or falsified data. For this reason, researchers around the world are conducting supplementary tests on LK-99 based on the contents of preprints.
You can see the place where LK-99 in superconducting state is placed on the permanent magnet in the following movie. However, LK-99 in the movie is not completely floating on the magnet, but part of it is sunk, so the Meissner effect that repels the magnet cannot be confirmed. This is why some experts have raised doubts about it.
Movie [LK-99]-YouTube
At the time of writing the article, the status of supplementary tests and surveys by universities and research organizations is as follows.
| group | Country | status | result | overview | papers, etc. |
| Quantum Energy Research Center (Korea) ICT Fundamental Laboratory, Institute of Electronics and Communication Research (Korea) Department of Physics, University of William and Mary (USA) Hanyang University (Korea) | South Korea/USA | none | none | first published paper | arXiv |
| Argonne National Laboratory | America | - | - | ``They don't have much knowledge about superconductivity, and the way some data is presented is questionable,'' he said, skeptical. | Science |
| Department of Physics, Nanjing University | China | - | - | A summary of the flow immediately after the announcement. | ScienceNet.cn |
| Huazhong University of Science and Technology | China | Supplementary exam | partially successful → successful | The source is only a WeChat screenshot, and the video is also uploaded to Bilibili. | |
| Science and Industry Research Council National Physical Laboratory of India | India | Supplementary exam | 1st time: failure 2nd time: failure | Dr. VPS Awana of the National Institute of Physics of India posted the results on Facebook. | Facebook (1st time) Facebook (2nd time) |
| Department of Materials Science and Engineering, Peking University | China | Results announced | Failure | Although LK-99 functioned like a semiconductor, it did not become superconducting and did not levitate due to the Meissner effect. | Arxiv |
| Lawrence Berkeley National Laboratory | America | simulation | - | It simulates how lead and copper interact to become superconducting. | arXiv |
| Sungkyunkwan University Korea University Seoul National University | Korea | Supplementary exam? | - | A special verification committee is set up by the Korean Superconducting and Cryogenic Society. Professor Kim Chang-yong of Seoul National University is in charge, and supplementary examinations have started at each of the three universities. | press release |
| Southeast University Superconducting Materials Laboratory | China | Failure | 1st time: Paper and X-ray data match, but no sign of superconductivity was found. 2nd time: Although there was a drop in resistance that was thought to be due to superconductivity, the electrical resistance did not reach zero. 3rd time: Superconductivity was observed at 110K (approximately -163°C). | Bilibili (1st time) Bilibili (2nd time) Arxiv (3rd time) |
Here's what I've personally tested.
| individual | Country | Career | situation | result | overview | Papers, result reports, etc. |
| Andrew McCalip | America | engineer | LK-99 during firing | not yet | Follow our progress on Twitter and live stream on Twitch as we use the furnace to fire LK-99. However, in the United States, individuals cannot newly obtain red phosphorus, so they are waiting for acquaintances to synthesize copper phosphide. | |
| semi-conductor giving physics | China | ? | Supplementary exam | success? | Regularly post LK-99 synthesis procedures. He reported that he was able to confirm particles with unusual properties. | |
| red bean | China | Unknown, it's highly likely that they didn't actually do a follow-up test. | During the synthesis of copper phosphide | Failure | Regularly post the synthesis procedure of LK-99 with images. | |
| Seki Yamaguchi Men's Technician | China | Confirmed to belong to Huazhong University of Science and Technology | Supplementary exam finished | Failure | ||
| Iris Alexandra | Russia | Junior Researcher, Institute of Gene Biology, Russian Academy of Sciences | Supplementary exam | partially successful | He criticizes preprint compositing methods and advocates faster compositing methods. It reportedly 'produced particles of matter with floating properties.' | |
| scientific research farming | China | ? | not clear | success? | Reported ``success in refining a substance with anomalous properties'' | Bilibili |
| zoubair | France | Collège de France, Institute for Solid State Chemistry and Energy, Ph.D. | Supplementary exam | Failure | It seems that he is working as a member of the laboratory, but it is not an official research. Both the first and second attempts failed. However, in the second time, X-ray data showed some abnormalities. | Twitter (1st time) Twitter (2nd time) |
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