Superconductor, as the name suggests, is a conductor with no energy dissipation after an electric current.) It is the result of a large number of paired electrons condensing into a coherent state that is "synchronized" and its motion is not scattered by the lattice.) Since the Dutch scientist O00es discovered the superconductivity of mercury in 1911, people have been looking forward to finding a room-temperature superconductor. This is a long-held dream) people in the following 70 years, only the transition temperature increased to 23K (about minus 250 degrees Celsius). At the end of 1986, Swiss researchers first found a superconductor with a transition temperature of more than 30K in the original unexpected oxide, which set off a pursuit of high-temperature superconductivity in the world. Soon after, Chinese scientists independently discovered superconductors above the temperature of liquid nitrogen (77.3K). At present, the transition temperature of oxide superconductors has reached more than 130 K (up to 160K under high pressure), and the application of oxide superconductors has been emerging in some aspects. In addition, the superconducting mechanism of oxide superconductors is also one of the most meaningful and challenging topics in front of condensed matter physicists. Understanding the mechanism of HTS may lead to an understanding of the physical nature of a large class of materials known as electron strong correlations, as well as a scientific and technological leap forward!

        Due to its own characteristics, the application of oxide superconductors in many aspects is limited! These features include very small coherence length leading to small cohesion energy and magnetic flux pinning energy, layered structure leading to magnetic flux system easy to become two-dimensional and produce motion, ceramic characteristics making materials easy to crack, raw material prices are relatively expensive making the application cost very high and so on! So people need to find new superconductors! In early March 2001, Japanese scientists reported that the binary material magnesium diboride showed superconducting properties at about 39K. The discovery quickly sparked a worldwide research frenzy! In the study of oxide high-temperature superconductors for more than ten years, people have accumulated rich experience and established advanced means, so the research on the properties of magnesium diboride superconductors has progressed very rapidly! Chinese scientists have also carried out research at a very fast pace and obtained some important results! Since this new discovery was only reported in early March 2001, this important discovery and the resulting work could only be presented in a special session at the American Physics Annual Meeting (Seattle, USA) at the end of March 2001! More than 60 reports from around the world continue from 8pm until after 1am! Scientists from the Chinese Academy of Sciences were invited to give two presentations at this special session!

        The research on the mechanism of magnesium diboride superconductor has experienced a three-fold process! Since the superconducting transition temperature of magnesium diboride is close to the upper limit of traditional electroacoustic coupling, the superconductivity that many people believed in at first may not come from traditional electroacoustic coupling, but from other reasons! Later, the experiment on the isotopic effect of boron atoms in magnesium diboride demonstrated that the superconducting transition temperature is obviously dependent on the atomic mass, so people gradually believed that the electroacoustic coupling is very important for the formation of superconductivity! Further, it was found that any form of doping in this system will only reduce the superconducting temperature, so people increasingly believe that magnesium diboride superconductor may be just a "fish in the net" among many binary alloy superconductors, and people will completely attribute its superconductivity to the traditional superconductor BCS mechanism! However, there is always some gap between human imagination and the objective facts of nature, which is also the motivation for scientists to constantly update and improve their cognition! Later theoretical calculation shows that there is more than one band across the Fermi surface in the magnesium diboride, and the instability of the Fermi surface caused by electroacoustic coupling may completely produce a energy gap at the Fermi surface of the two bands! This is completely different from all traditional superconductors! Images of the two bandgaps were later widely confirmed by experiments on specific heat, nuclear magnetic resonance, electron tunneling spectroscopy, and angle-differential photoelectron spectroscopy! How the two energy gaps are formed and how it affects the superconducting properties is a hot topic in the research of magnesium diboride superconductors.

        The application opportunities of magnesium diboride superconductors are far more exciting than their physical understanding! Soon after its discovery, many of its macroscopic electrical, magnetic, and thermal properties were measured, including a great deal of excellent work by Chinese scientists. First, they found that this superconductor can carry a large superconducting current at a temperature of about 20K and 80,000 times that of the Earth's magnetic field, and the energy consumption is very low! Since the temperature of 20K can be easily obtained using small chillers, it is thought that the superconducting magnets of nuclear magnetic imaging instruments used in hospitals of the future will no longer need to run on expensive liquid helium, but just need to be plugged in! In addition, the price of magnesium diboride material is very low, and it is far easier to process than the oxide high-temperature superconductor with ceramic characteristics, so soon after the discovery, the United States 23 456 laboratory was able to pull out tens of meters of wire and strip!

        In addition, the superconducting coherent length of magnesium diboride superconductor is long, and it is easy to prepare superconducting quantum interference devices for the detection of weak electromagnetic signals, which has a promising application in earth prospecting, medical instruments, environment and military.

        Chinese scientists have shown considerable competitiveness in the research of magnesium diboride superconductors! In less than a week after learning the news, the State Key Laboratory of Superconductivity of the Institute of Physics of the Chinese Academy of Sciences prepared high-quality samples, and then did a lot of excellent research work! For example, they quickly realized that there was a huge difference between the upper critical magnetic field and the flux melting magnetic field of the magnesium diboride superconductor, and proposed reasonable images to explain this gap. For example, they and Norwegian scientists used different methods to independently discover the existence of small and dense magnetic flux jump in the superconducting magnesium diboride film, and Chinese scientists clearly defined the scope of this magnetic flux jump, which played a positive role in overcoming difficulties in weak current applications in the future! In addition, the work of Chinese scientists on the doping and electron microscope observation of magnesium diboride superconductors has attracted wide attention in the world! In terms of application, Chinese scientists have been able to successfully prepare tens of meters of wire, laying a solid foundation for the next preparation of superconducting magnets! It can be predicted that in the next three years, superconducting magnets made of magnesium diboride wire will be born in the hands of Chinese scientists!