Superconducting is not absolutely without resistance, but very small, which is why it tends to zero infinitely: the resistance is too small to be measured, and it is not an absolutely zero metal smelting technology, so it is impossible to obtain an absolutely pure single metal, so superconducting alloy materials will contain very few other high-resistivity substances, resulting in the actual resistance is not zero, rather than a theoretical zero-resistance superconductor. The resistivity of various materials will change with the change of temperature. The resistivity of some materials decreases with the decrease of temperature. When the temperature drops to near absolute zero (-273℃), the resistivity suddenly drops to zero. This phenomenon is called superconductivity. A conductor in a superconducting state (that is, a conductor with no resistance at all) is called a superconductor, and the temperature at which a conductor transforms into a superconductor is called a transition temperature or a critical temperature. 19 1 1 year, Dutch physicists first discovered the superconductivity of mercury. Up to now, more than 100 superconductors have been discovered. Many metals, such as indium, tin, aluminum and zinc, as well as alloys and compounds, can become superconductors. Superconductors are widely used. For example, the superconducting coil made by using the property of zero superconductor resistance can greatly reduce power loss and improve power. At present, superconductors have been gradually applied to generators, cables, transportation equipment and so on. Due to the extremely low temperature required by superconductors, the technology and equipment needed to achieve low temperature are complex, which limits the application of superconductors. Therefore, developing high-temperature superconductors and simplifying low-temperature technology and equipment are important research topics in modern physics. Superconductors and gas liquefaction are one of the hot topics in physics in the19th century. 19 1 1 year, Agnes found that the resistance of mercury dropped sharply at a low temperature of about 42K, so that it disappeared completely (that is, the resistance was zero). 19 13 He used the word "superconductivity" to express this phenomenon for the first time in a paper. Agnes won the 19 13 Nobel Prize in Physics for her achievements in studying the properties of matter and liquefied helium at low temperature. It was not until 50 years later that people made a breakthrough. BCS theory marks the beginning of the modern stage of superconducting theory. BCS theory was first put forward by American physicists Badin, Cooper and schrieffer in 1957, and was named after the first capital letters of the three scientists. The core of this theory is to calculate the existence of * * vibration dynamics in superconductors, that is, the existence of "electron pairs". From 65438 to 0962, Josephson, a graduate student at Cambridge University in England, predicted according to BCS theory that there would be a current between two superconducting materials separated by a thin insulating layer, that is, an "electron pair" could pass through the thin insulating layer (tunneling effect); At the same time, there are some special phenomena, such as the current passing through the thin insulation layer without applying voltage. If a voltage is applied, the current will stop and generate high-frequency oscillation. This superconducting physical phenomenon is called "Josephson effect". This effect has been confirmed in bell laboratory. Josephson effect strongly supports BCS theory. Therefore, Badin, Coopa and schrieffer won the 1972 Nobel Prize in Physics. Josephson won the 1973 Nobel Prize in Physics. German physicist Bernoz and Swiss physicist Miao Lei began to concentrate on the superconductivity of rare earth oxides from 1983. 1986, they finally found an oxide material whose superconducting transition temperature was 12 degrees higher than that of previous superconducting materials. This discovery led to a major breakthrough in superconducting research. Scientists in the United States, China, Japan and other countries devoted themselves to research, and soon found ceramic materials with superconductivity in the temperature range of liquid nitrogen (below-196C), and then found superconducting materials with high critical temperature. This provides conditions for the application of superconductivity. Panoz and Miao Lei also won the 1987 Nobel Prize in Physics.