Diagram of the Meissner effect. Magnetic field lines, represented as arrows, are excluded from a superconductor when it is below its critical temperature.

The Meissner effect (or Meissner-Ochsenfeld effect) is the total exclusion of any magnetic flux from the interior of a superconductor. It is often referred to as perfect diamagnetism. It was discovered by Walter Meissner and Robert Ochsenfeld in 1933.

In the effect, there is an exclusion of magnetic flux brought about by electrical "screening currents" that flow at the surface of the superconducting metal and which generate a magnetic field that exactly cancels the externally applied field inside the superconductor. The Meissner effect is one of the defining features of superconductivity, and its discovery served to establish that the onset of superconductivity is a phase transition. Superconducting magnetic levitation is due to the Meissner effect (which repels a permanent magnet) and flux pinning, which stops the magnet from sliding away.

Note that there is a difference from a Perfect Diamagnet and a Superconductor.

See also

• Superdiamagnetism
• Superfluidity