Explanation

The Meissner effect describes the repulsion of the external magnetic field by the superconductor in the superconducting state. This effect was discovered by German physicists W. Meissner and R. Ochsenfdd in 1933 when they measured the external magnetic field distribution of metal tin and lead samples in the superconducting state. The experimental results of Meisner et al. show that for the first type of superconductor, whether it is cooling before applying a magnetic field or cooling after applying a magnetic field, the magnetic flux inside the sample always ends up zero in the superconducting state, achieving complete magnetic flux repulsion. The Meissner effect shows that superconductors are completely diamagnetic in addition to ideal conductors. The discovery of the Meissner effect directly led to the birth of the phenomenological theory of superconductors. The reason for the Meissner effect can be simply explained as follows: in the magnetic field environment, a lossless induced current will be generated on the surface of the superconductor in the superconducting state. The magnetic field generated by this induced current is exactly the same size and opposite direction as the external magnetic field, resulting in a total zero magnetic field intensity inside the superconductor. Therefore, the Meissner effect is a phenomenon that occurs at a certain thickness of the superconductor surface, which is called the magnetic field penetration thickness. The zero resisitivity effect and the Meissner effect are two independent and interrelated basic attributes of superconductors in the superconducting state. The Meissner effect is often used as an important basis for judging whether a substance has superconductivity.

Classification