News Analysis： Breakthrough or Oolong —— The room temperature superconductivity of LK-99 material needs to be verified.

　　Xinhua News Agency, Beijing, August 9th 　News Analysis: Breakthrough or Oolong — — Room temperature superconductivity of "LK-99" material needs to be verified.

　　Xinhua news agency reporter

　　Recently, a big news that caused a sensation in the scientific community was that the Korean research team claimed to have synthesized a room temperature superconducting material called "LK-99".

　　On July 22nd, researchers from Korea Institute of Quantum Energy and other institutions published a paper on the pre-printed website arXiv, saying that the "LK-99" material they synthesized has superconductivity, the critical temperature of superconductivity is about 127 degrees Celsius, and it has superconductivity under normal pressure. LK-99 is a modified lead apatite crystal structure. The Korean research team mixed several powdered compounds containing lead, oxygen, sulfur and phosphorus, and then heated them at high temperature for several hours. After the powder reacted chemically, a copper-doped lead apatite crystal was obtained.

　　While the achievements claimed by the Korean team have aroused great concern in the scientific community, they have also been questioned by many scholars.

　　The goal pursued by the scientific community

　　All kinds of materials have a certain resistance at room temperature. When electrons flow from one end of the material to the other, they constantly collide and slow down, similar to the deceleration of air when the wind blows through leaves. In 1911, Dutch physicist Heck Kamelin Agnes found that the resistance of mercury dropped sharply at about 4 Kelvin (4 degrees Celsius above absolute zero, that is, about 269 degrees Celsius below zero), and entered a new state where the resistance was too small to be measured in practice. He called this new state of mercury superconducting. Agnes also won the Nobel Prize in Physics in 1913 for his discovery of superconductivity.

　　Superconductors can only show zero resistance at a specific temperature, and their two key characteristics are zero resistance and complete diamagnetism, that is, Messner effect. The temperature at which the superconductor resistance turns to zero is called the critical temperature. According to the critical temperature, superconducting materials can be divided into low temperature superconductors and high temperature superconductors.

　　Up to now, dozens of metal elements — — Lead, mercury, niobium, tin and their alloys will become superconductors when cooled to near absolute zero. However, the superconducting conditions of these materials are harsh. Even the so-called "high-temperature superconductors" usually have a critical temperature of MINUS 100 degrees Celsius or lower. They need liquid helium or liquid nitrogen for refrigeration and high pressure, which is difficult and costly, and almost impossible to use. At present, the confirmed world record is that researchers in the United States and Germany use lanthanum hydride materials to achieve superconductivity at 250 Kelvin (about MINUS 23 degrees Celsius) and an extremely high pressure of about 1 million times atmospheric pressure.

　　If a material can achieve superconductivity at near room temperature and normal pressure, it will certainly bring a revolutionary breakthrough to the world. For example, computer chips can run faster and consume less energy, the power grid can be close to lossless transmission, and high-speed maglev trains may soon be put into practical use … … Therefore, in recent decades, researchers all over the world have invested great energy in this field.

　　"LK-99" also attracts attention because Korean researchers claim that its critical temperature is close to normal temperature, and its composition and synthesis method are unexpectedly simple and cheap. In the past, the scientific community often sought a breakthrough in the direction of rare metal elements. Once it is verified and its mechanism is understood, it may soon be close to practical use.

　　Whether the breakthrough needs to be verified.

　　However, "LK-99" is not the first material that claims to realize room temperature superconductivity. In the past, some researchers have announced "major breakthroughs", but so far it has not been verified and reproduced successfully.

　　American researcher Ranga Diaz and others reported in the British journal Nature in 2020 that a compound containing carbon, sulfur and hydrogen showed superconductivity at 15 degrees Celsius and became a superconductor with zero resistance, but the paper was withdrawn last year. On March 8 this year, another paper by Diaz team was published on the website of Nature, which claimed that a material containing lutetium, hydrogen and nitrogen was developed, and it showed superconductivity at a room temperature of about 20.6 degrees Celsius and a pressure of 10 kilobar (about 10,000 times atmospheric pressure). So far, several teams have reported that their results cannot be reproduced.

　　What about "LK-99"? Because its preparation and verification are relatively simple, many international scientific research teams, including China, are trying to reproduce it.

　　Sinead Griffin of Lawrence Berkeley National Laboratory in the United States published a paper on the pre-printed website arXiv on the properties of LK-99, saying that superconductivity can explain the characteristics of LK-99, but a large number of other phenomena, such as metal-insulator transition and charge density wave, can also be explained. According to some media reports, her computer simulation "supports ‘ LK-99’ The superconductivity of "LK-99", Griffin stressed on social media that his paper did not provide evidence that "LK-99" has superconductivity.

　　The website of Nature magazine reported on the 4th that "LK-99" was synthesized by two independent experiments conducted by the Indian National Physics Laboratory and Beijing, China University of Aeronautics and Astronautics, but no signs of superconductivity were observed. The experiment conducted by the researchers of Southeast University in China found no Messner effect, but the resistance of "LK-99" was close to zero at minus 163 degrees Celsius, which was far below room temperature, but it was very high for superconductors. The article points out that the uncertainty of "LK-99" structure limits the researchers to draw conclusions from theoretical calculation.

　　The LK-99 Verification Committee of Korea Superconducting and Cryogenic Society said that the characteristics of this material shown in the images and papers related to LK-99 did not conform to the Messner effect, which was not enough to prove that LK-99 was a room temperature superconductor.

　　Edwin Forton, an associate professor in the Department of Materials Science and Engineering at Rensselaer Institute of Technology in the United States, said that to realize room temperature superconductivity, it is necessary to make breakthroughs in understanding the basic principles behind superconductivity, inventing new materials or finding new ways to increase the critical temperature. Whether "LK-99" is a breakthrough or an "oolong" requires researchers to reproduce it first. At present, it may take some time for significant progress to be made in the field of room temperature superconductivity.