What is the name of the superconducting effect in which a material expels magnetic fields?

The Meissner effect is the expulsion of magnetic fields from a superconducting material as it enters its superconducting state.

Below its critical temperature, an ideal superconductor does more than conduct electricity with zero direct-current resistance. It actively excludes magnetic flux from its interior, except for a thin surface region. This magnetic behavior distinguishes superconductivity from merely perfect conductivity.

Walther Meissner and Robert Ochsenfeld discovered the effect in 1933 while studying superconducting samples. Their observation showed that superconductivity is a thermodynamic state with its own magnetic properties. It helped establish that magnetic-field history matters differently in superconductors than in hypothetical perfect conductors.

The effect produces magnetic levitation when a suitable magnet and superconductor are arranged correctly. Type-II superconductors can admit magnetic flux in quantized vortices between lower and upper critical fields, so the simple statement of complete expulsion has important limits.