Flux quantization
Flux quantization is a quantum phenomenon in which the magnetic field is quantized in the unit of , also known variously as flux quanta, fluxoids, vortices or fluxons.
Flux quantization occurs in Type II superconductors subjected to a magnetic field. Below a critical field Hc1, all magnetic flux is expulsed according to the Meissner effect and perfect diamagnetism is observed, exactly as in a Type I superconductor. Up to a second critical field value, Hc2, flux penetrates in discrete units while the bulk of the material remains superconducting. Both critical fields are temperature dependent, and tabulated values are the zero-temperature extrapolation unless otherwise noted.