189 1 year, Louis Garrett successfully liquefied a small amount of "permanent gases"-nitrogen, air and hydrogen in France and Raoul Pictet, Switzerland. Russian Urobo levski asked Glasko to carry out experiments and successfully obtained a certain amount of liquid air. He found that the relationship between the resistivity of pure metal and temperature was a little strange: it seemed that its resistance would disappear completely near the absolute temperature of zero. This wonderful possibility has led to many theories that can predict the low temperature performance from zero resistance to infinite resistance.
The following year, james dewar invented a vacuum heat-insulating silver-plated glass container, which was named after him. Using this container, he obtained the amount of liquid hydrogen that can be used in the experiment and further reduced the temperature. At this temperature, he found that the resistance of metal did not disappear, but the resistance did not change with temperature.
Finally, less than 20 years after william ramsey discovered helium on the earth, that is, 1908, Kamelin Annis successfully liquefied it again. Liquid helium reduces the temperature of laboratory experiments by an order of magnitude. Three years later, Kamelin Annis and his student holst found that when mercury was cooled in liquid helium, the resistance of the sample suddenly disappeared at the critical temperature. There is still no obvious attenuation of the continuous current generated by induction in the future.
After Anis, 1933, Mesner Superconducting Laboratory in Berlin made another important discovery, namely the so-called Mesner effect. Messner and his colleague Osenfeld found that superconductors have amazing magnetism in their experiments. If the superconductor encounters a magnetic field, it will form a shielding current on the surface of the superconductor to resist the external magnetic field, so that the magnetic field cannot penetrate the inside of the superconductor, but the inside remains zero. The reverse test is also the same result, that is, a material is first placed in a magnetic field, and then cooled to a superconducting state, which also produces shielding current and repels the magnetic field. This phenomenon is therefore called the Mesner effect, that is, the magnetic induction inside the superconductor is zero, and the current flows on the surface. This effect can be proved by an experiment: a permanent magnet can suspend superconductors immersed in liquid nitrogen.
Mesner effect only appears when the magnetic field is small. If the magnetic field is too large, it will penetrate into the metal, and the metal will lose its superconductivity.