Meissner effect

The Meissner effect is the expulsion of magnetic flux from a material as it enters the superconducting state, producing near-zero magnetic fields inside it. It distinguishes superconductivity from perfect electrical conductivity alone.

London equations: Equations describing how electric currents and electromagnetic fields behave in superconductors. They predict magnetic-field screening and the characteristic depth over which fields penetrate.
Superconductivity: A state of matter with zero electrical resistance and distinctive electromagnetic behavior below a critical temperature. The Meissner effect is one of the defining properties of this state.
Walther Meissner: German physicist who co-discovered magnetic-field expulsion in superconductors in 1933. His measurements with Robert Ochsenfeld revealed the effect that bears his name.
Magnetic levitation: Suspension of an object without direct support by forces that counteract gravity. Flux exclusion and pinning can stabilize levitation above a superconductor.
Flux trapping: The retention of magnetic flux within a material after changes in its magnetic or superconducting state. Trapped flux contrasts with complete expulsion and commonly occurs when vortices are pinned.
London penetration depth: The distance over which a magnetic field decays inside a superconductor. The Meissner effect excludes flux over this finite length, rather than at an infinitely sharp boundary.
Perfect conductor: An idealized material with zero electrical resistance and perfectly conserved magnetic flux. A perfect conductor can retain preexisting flux, unlike a superconductor entering the Meissner state.
Robert Ochsenfeld: German physicist who co-discovered magnetic-field expulsion in superconductors in 1933. His work with Walther Meissner established that superconductors actively exclude magnetic fields.
Flux pinning: The immobilization of magnetic vortices by defects or other pinning sites in a type-II superconductor. Pinning can lock a levitated magnet's position after flux enters the superconductor.
Type-I superconductor: A superconductor that excludes magnetic flux below a single critical field and becomes normal above it. Its nearly complete Meissner state contrasts with the vortex-bearing mixed state of type-II materials.

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