Meissner effect: a standalone construct

Walther Meissner and Robert Ochsenfeld first reported the effect in 1933, showing that when certain metals are cooled below a characteristic critical temperature and become superconducting, they push essentially all magnetic field out of their interior rather than merely letting their electrical resistance fall to zero. Fritz London and Heinz London gave the effect its enduring theoretical description in 1935, with a pair of equations showing that a superconductor screens an applied field within a thin surface layer, the penetration depth, so the bulk interior stays free of field. The behaviour is not what a hypothetical perfect conductor would do, because a perfect conductor would simply trap whatever field was present when its resistance vanished, whereas a superconductor actively drives out field that was already inside it. This active expulsion marks superconductivity as a distinct thermodynamic phase of matter rather than just a state of zero resistance, and it is the property most commonly used to confirm that a material has genuinely entered the superconducting state, including in the visible levitation of a magnet above a cooled superconductor.[1][2][3]

Unit

A physical phenomenon of the superconducting state: the near-complete expulsion of magnetic flux from the bulk of the material below its critical temperature

Recovery means

Not applicable

Measured by

Detected by measuring magnetic flux or magnetic susceptibility as a sample is cooled through its critical temperature, revealing near-perfect diamagnetism, and shown directly by stable magnetic levitation