TypISupraleiter

Typ I-Supraleiter, or Type I superconductor, denotes a class of superconducting materials characterized by a single critical magnetic field Hc and by the complete expulsion of magnetic flux from the interior below that field (the Meissner-Ochsenfeld effect). The superconducting state occurs below a critical temperature Tc and below Hc. The Ginzburg-Landau parameter κ = λ/ξ is smaller than 1/√2, which differentiates Type I from Type II superconductors.

In applied magnetic fields, Type I superconductors exhibit complete flux exclusion up to Hc. Above Hc, superconductivity is destroyed and the material becomes a normal conductor. In bulk samples there can be an intermediate state near Hc in which normal and superconducting regions coexist, a pattern shaped by demagnetization effects.

Typical Type I superconductors are pure elemental metals, including lead (Pb), mercury (Hg), tin (Sn), indium (In) and aluminum (Al). They generally have relatively low critical fields and require high purity to remain Type I; introducing impurities or alloying tends to raise κ and push the material toward Type II behavior.

Because of their low Hc and limited performance in high magnetic fields, Type I superconductors are not used for high-field magnets. They are, however, important for fundamental studies of superconductivity, and they find use in certain low-field shielding applications and historical research contexts. In contrast, most practical superconductors for magnets are Type II.