Meiss·ner effect 
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n
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n. 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.
[After Fritz Walther Meissner (1882-1974), German physicist who discovered it in collaboration with Robert Ochsenfeld (1901-1993), German physicist.]