When superconductors are cooled below their critical temperature, they repel magnetic fields and do not allow magnetic fields to penetrate.This peculiarity in superconductors is known as the Meissner Impact. This peculiarity was found by German physicists “Walther Meissner” and “Robert Ochsenfeld” in 1933. During one experiment, they measured the magnetic field outside samples of superconducting tin and lead. They observed that when the sample is cooled below the transition (critical) temperature in the presence of an external magnetic field, the value of the magnetic field outside the sample increases. This increase in the magnetic field outside the sample represents the emission of the magnetic field from the interior of the sample. The phenomenon demonstrated that in the superconducting state, the sample repels the external magnetic field.
This Meissner state is broken when the magnetic field (either external or produced by the current-flowing superconductor itself) increases beyond a certain value and the sample begins to behave like a normal conductor.
Application of Meissner Effect:
This effect of superconductivity is used in magnetic levitation, which is the basis of modern high-speed bullet trains. In the superconducting state (phase), due to the emission of an external magnetic field, a sample of superconducting material levitates over or against the magnet.Present day rapid projectile trains utilize the peculiarity of attractive levitation.