Meissner effect

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun The effect whereby magnetic fields are excluded from a superconductor's interior if the superconductor is below a critical temperature, since introducing a magnetic field immediately creates electric currents in the superconductor that cancel the magnetic field. The Meissner effect is responsible for the diamagnetic properties of superconductors.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun physics The total expulsion of magnetic flux from the interior of a superconducting metal when it is cooled in a magnetic field below a critical temperature, near absolute zero, at which the transition to superconductivity takes place.