Multiple reversals! The issue of room temperature superconductivity in South Korea is getting more and more "exciting"...

In the past two weeks, people, whether they understand physics or not, have seen the words "room-temperature superconductivity" on different social platforms and in the news. The two camps supporting and opposing the research results have also been arguing fiercely. Today we will sort out the ins and outs of "superconductivity" and this "room-temperature superconductivity" according to the timeline.

Background introduction-What is superconductivity?

In 1908, after long efforts, Dutch physicist Heike Kamerlingh Onnes finally completed the preparation of liquid helium, providing a powerful tool for extremely low temperature physics experiments.

The origin of the concept of superconductivity

Superconductor, literally "superconductor", refers to a conductor with zero resistance at a certain temperature. In 1911, Onnes found that the resistance of mercury completely disappeared when he cooled mercury to 4.2 Kelvin (K) with liquid helium. He then found that other metals also became superconductors at extremely low temperatures, for which he won the 1913 Nobel Prize in Physics.

Meissner effect

The Meissner effect refers to the fact that a superconductor will strongly repel the external magnetic field in a magnetic field, resulting in complete diamagnetism, that is, a magnetic field is generated inside the body that completely cancels out the external magnetic field, resulting in zero magnetic induction intensity inside the body.

This diamagnetism can be partially destroyed by an external magnetic field in many superconductors, but the magnetic flux lines that enter the body will be firmly locked by the superconducting electrons. Therefore, the superconductor has both a strong repulsive force and a strong attractive force on the external magnetic field. This special interaction force can overcome the gravity effect, allowing the superconductor to float above the magnet and hang stably below the magnet, achieving extremely stable magnetic levitation. Note 1: Conversion relationship between Kelvin and Celsius: 0 K = -273.15 ℃, that is, 20 ℃ is 293.15 K. Note 2: The strength of the external magnetic field will also affect whether the superconducting material is in a superconducting state. Here it refers to the range of magnetic field strength that allows the material to maintain a zero-resistance superconducting state.

In summary, zero resistance and the Meissner effect have become two direct bases for determining superconductors .

Imagine if superconductors can be widely popularized, people's lives will be greatly changed. However, the current superconducting environment is somewhat too harsh for human survival, so a large number of scientists have invested a lot of energy in the development of room-temperature superconducting materials.

History of superconductivity

The following figure briefly summarizes the current history of superconductivity. We also use text to interpret this figure for you:

Image source: Luo Huiqian

Between 1911 and 1932, people discovered that lead, tin, niobium and other metals also have superconducting states at low temperatures. Among them, niobium has the highest superconducting critical temperature, reaching 9.2K.

On this basis, a series of alloys and metal nitrides were prepared, such as niobium germanium alloy (Nb3Ge), with a critical temperature of 23.2K.

Before 1980, the superconductors prepared by people could not maintain superconducting properties at temperatures above 40K.

In 1986, Johannes Bednorz and Karl Muller discovered the lanthanum-barium-copper-oxide (La-Ba-Cu-O) material, which has a critical temperature of 35K, opening a new chapter in the exploration of superconducting materials (the green part in the middle of the picture). The two scientists were also awarded the Nobel Prize in Physics in 1987. Note: The interval between awards was only 10 months, the second fastest in the history of the Nobel Prize.

In 1987, Chinese physicist Zhao Zhongxian and Chinese physicist Zhu Jingwu discovered the yttrium barium copper oxide (Y-Ba-Cu-O) material, which raised the superconducting temperature to above 90K, entering the temperature range of liquid nitrogen.

Later, scientists discovered materials such as bismuth strontium calcium copper oxide (Bi-Sr-Ca-Cu-O), thallium barium calcium copper oxide (Tl-Ba-Ca-Cu-O), and mercury barium calcium copper oxide (Hg-Ba-Ca-Cu-O), which gradually raised the superconducting critical temperature to around 130K. Among them, the gas pressure and temperature of mercury barium calcium copper oxide (Hg-Ba-Ca-Cu-O) can reach 134K at normal pressure.

After the 21st century, in 2001, the Japanese Akimitsu team discovered the MgB2 material, which has a critical temperature of 39K, the highest among binary metal compounds. Since the critical temperature is within the range of liquid hydrogen and the raw material source is abundant, many companies at home and abroad have put it into actual production.

In 2008, Japan's Hosono team discovered iron-based superconducting materials for the first time, ushering in the "Iron Age" of superconductivity research (the yellow text in the lower right corner of the picture).

Another way to approach room-temperature superconductivity is to apply pressure. For example, using diamond anvil cells to apply pressure, there are indeed papers that have achieved room-temperature superconductivity, but because the environment is too harsh, it is only of theoretical value at present (the red part in the upper right corner of the picture).

The latest breakthrough?

2020

The famous scientific journal Nature published a paper by Ranga Dias, which claimed that a new material composed of carbon, hydrogen and sulfur elements can achieve room-temperature superconductivity (15°C, 267GPa, about 2.67 million atmospheres), but it was subsequently withdrawn due to numerous doubts.

March 2023

This Dias brought even more significant results, again room-temperature superconductivity, and again in Nature. This time it was nitrogen-hydrogen-lutetium material, and this time the conditions were a critical temperature of 21°C and 1GPa. Later, it was also questioned because it could not be replicated.

July 25, 2023

A South Korean team posted two papers on the preprint website arXiv, claiming to have discovered the room-temperature superconducting material LK-99, whose critical temperature can exceed 400K (126.85℃) at normal pressure, triggering a new round of fanatical pursuit and beautiful imagination of room-temperature superconductivity.

Not only are the results of superconducting materials very attractive, but the preparation process is also extremely simple and can be prepared under most laboratory conditions. This has also triggered a wave of results reproduction among domestic and foreign peers and related enthusiasts, and they live broadcast or serialize their own experimental progress on social platforms.

July 28, 2023

Young-Wan Kwon, one of the authors of the paper, announced the results of the room-temperature superconductivity research at an international seminar in Seoul, South Korea, but no samples were displayed on site.

Professor Wen Haihu of Nanjing University told Pengpai Technology: "Based on our experience, (the data currently published in the paper) is not enough to prove that it is a superconductor." It is worth mentioning that this professor had just used data to refute Dias' room-temperature superconductivity paper.

July 30, 2023

Cailianshe reported that Hong Zhiyong, an expert in superconducting application research and director of the Shanghai Superconducting Materials and Systems Engineering Research Center, said that based on our experience, (the data published in the current paper) is not enough to prove that it is a superconductor.

July 31, 2023

Researchers from Beihang University submitted a paper on arXiv, stating that the samples they prepared were consistent with those of the Korean team, but that they were unable to detect giant diamagnetism and magnetic levitation phenomena, and that zero resistance did not exist.

Another collaborative article by Beihang University and the Shenyang National Laboratory for Materials Science of the Chinese Academy of Sciences theoretically analyzed the possibility of achieving superconductivity in this material.

On the same day, a theoretical research paper from the Lawrence Berkeley National Laboratory (LBNL) in the United States showed that density functional theory planning for LK-99 showed that the material has a special structure with the potential to achieve superconductivity. [11~12]

A collaborative article between Beihang University and Shenyang National Laboratory for Materials Science, Chinese Academy of Sciences

Lawrence Berkeley National Laboratory

August 1, 2023

The bilibili user "Guanshankou Male Technician" uploaded a related video. The video shows that Wu Hao, a postdoctoral fellow at the School of Materials Science and Engineering of Huazhong University of Science and Technology, and Yang Li, a doctoral student, successfully prepared the LK-99 sample under the guidance of Professor Chang Haixin, and successfully reproduced the antimagnetic characteristics of the sample for the first time. The angle of the sample suspension in the video is larger than that in the original author's paper. However, only the Meissner effect has been verified so far, and the sample is too small to complete the zero resistance measurement.

Zhihu user "Semiconductors and Physics" updated the progress and uploaded a video, also stating that it has the anti-magnetism shown in the paper.

Russian scientist Iris Alexandra successfully prepared LK-99 crystals with room-temperature diamagnetism, which is one of the hallmarks of superconducting crystals. The results were published on Twitter.

With the emergence of the reproduction results, superconductor-related concept stocks at home and abroad have soared. Shanghai's "First Financial Daily" reported that US superconductor concept stocks soared before the market opened on August 1, and once rose by nearly 150% before the market opened, and then the increase fell back. Superconductor concept stocks in the Chinese stock market also suddenly exploded on the same day, and Farsens rose straight and quickly hit the daily limit. Many concept stocks followed suit, with Guolan Testing rising by 20%, and many stocks such as Jingda Shares, Zhongfu Industry, Innovation New Materials, and Baili Electric hitting the daily limit.

August 3, 2023

Bilibili user "Science Investigation Bureau", Sun Yue, a professor at the School of Physics of Southeast University, uploaded a video. After successfully preparing the sample, the "zero resistance" phenomenon was observed at a temperature below 110K. Although it met the superconductivity requirements, the temperature difference was very large. The author also stated that the measurement was affected by the accuracy of the instrument.

Liu Xiaobing, a professor at Qufu Normal University, said that the test results found that LK-99 still has a large resistance value in the range of room temperature to 50K, and there was no sharp drop in resistance or zero resistance during the test, which is far from the expected zero resistance characteristic of "room temperature superconductivity".

Yonhap News Agency reported that an expert verification committee composed of the Korean Society of Low-Temperature Superconductors stated that LK-99 is not a room-temperature superconductor.

In terms of financial information, superconducting concept stocks opened sharply lower in the morning trading that day, and Zhongfu Industrial, Jingda Co., Ltd., Innovation New Materials, and Jinhui Co., Ltd. all hit the daily limit. As of the close of August 3, among the three stocks that had hit the daily limit the day before, Zhongfu Industrial, Farsen, and Baili Electric, Zhongfu Industrial and Farsen both hit the daily limit, while Baili Electric rose slightly by 0.42%. Many companies publicly stated that their businesses had nothing to do with superconducting materials. In the United States, American Superconductor, which had soared 60% the day before, fell nearly 30%.

August 4, 2023

HuynTak Kim, a professor at the University of William and Mary in the United States and one of the authors of the original paper, provided a second video showing the suspension properties of LK-99 to a New York Times reporter. The suspension morphology was similar to that in the previous paper, but no other data measurements were mentioned. [20]

An article in Time Weekly stated: “Searching for authors and teams that published LK-99-related papers after July 22 on the preprint website arXiv, a reporter called nine domestic teams involved in theoretical deduction and experimental verification, including the three teams mentioned above, but received no response by phone or email, or their interview requests were politely declined.

August 5, 2023

Douyin blogger "Alchemist Axiang" released a video, which not only stated that the anti-magnetism of LK-99 can be reproduced, but even complete suspension can be achieved. However, the video mentioned that some other compounds were added. At present, the authenticity of the result and the true identity of the author are still unclear.

Related speculation

Viewpoint 1: This material has excellent diamagnetism or weak ferromagnetism, but it has nothing to do with achieving room-temperature superconductivity .

Viewpoint 2: The material does have room-temperature superconducting properties, but the target product accounts for a very low proportion in the final product and is unevenly distributed, making it impossible to completely suspend it and measure the zero resistance phenomenon .

Viewpoint three: This material may not be the perfect room-temperature superconducting material in people’s minds, but like a door-knocker in the history of superconducting materials, it provides a good reference value for subsequent research .

References

[1] University Physics, edited by Zhang Sanhui, Tsinghua University Press

[2] "Room temperature superconductivity" concept stocks "cool down" as scientists encounter obstacles in reproducing experiments | South Korea | Fasten | superconductors | superconducting materials_NetEase Subscription (163.com)

[3] Video: Mu Gang from the Chinese Academy of Sciences: LK-99 has not been fully proven and room temperature and normal pressure superconductivity is still at the conceptual stage - 21 Finance (21jingji.com)

(To facilitate review, this article's citations, footnotes, etc. have been modified)

Author: Heartson Materials Engineer PhD in Materials Science, Zhejiang University

Reviewer: Luo Huiqian, Researcher, Institute of Physics, Chinese Academy of Sciences