Type-I superconductor

A superconductor that expels magnetic flux below a single critical magnetic field and becomes normal when that field is exceeded.

Meissner effect: The expulsion of magnetic flux from a material as it enters the superconducting state. It is the defining magnetic response of a type-I superconductor below its critical field.
Superconductivity: A state of matter with zero direct-current electrical resistance and distinctive magnetic behavior. Type-I behavior is one form of this broader state.
Type-II superconductor: A superconductor with two critical magnetic fields and a mixed state containing quantized magnetic vortices. Unlike type I, it can remain superconducting while magnetic flux penetrates its interior.
Mercury (element): A chemical element that is liquid at room temperature and becomes superconducting below about 4.2 kelvin. It was the first material in which superconductivity was discovered and is type I.
London equations: Equations describing how electric and magnetic fields behave in a superconductor. They explain magnetic-field screening and the finite penetration depth beneath the surface.
Magnetic penetration depth: The characteristic distance over which an applied magnetic field decays inside a superconductor. It sets how deeply flux penetrates the surface before Meissner screening suppresses it.
Abrikosov vortex: A quantized tube of magnetic flux surrounded by circulating supercurrents in a type-II superconductor. Such stable flux tubes characterize type-II materials, not the Meissner state of type-I materials.
Lead (element): A dense metallic element that becomes superconducting below about 7.2 kelvin. Lead is a familiar elemental type-I superconductor with a higher transition temperature than mercury.
Critical magnetic field: The magnetic-field strength at which a material changes its physical state or behavior. A type-I superconductor has one such field, above which superconductivity disappears.
Superconducting coherence length: The characteristic distance over which the superconducting order parameter varies. Compared with penetration depth, it determines whether a material is type I or type II.

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SuperconductorBroader topic: Its single critical field contrasts with the mixed-state behavior of type-II materials.