Quantization, Magnetic Flux

a macroscopic quantum phenomenon whereby a magnetic flux through a superconductor ring carrying a current can only assume discrete values. The minimum value of the flux (the flux quantum) is Φ₀ = ch/2e ⋍ 2 × 10⁻⁷ grams force • cm², where c is the velocity of light, h is the Planck constant, and e is the charge of an electron. The magnetic flux in a superconductor may be equal only to an integral number of flux quanta. Magnetic flux quantization was theoretically predicted by F. London (1950), who obtained the value ch/e for the flux quantum. Experiments (in 1961) provided half this value for the flux quantum. This was splendid confirmation of the microscopic theory of superconductivity that had been developed by that time and according to which a superconducting current is due to the movement of pairsof electrons.