Flux quantization

Flux quantization is a quantum phenomenon in which the magnetic field is quantized in the unit of $h/2e$, also known variously as flux quanta, fluxoids, vortices or fluxons.

History

Flux quantization occurs in Type II superconductors subjected to a magnetic field. Below a critical field H_c1, 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, H_c2, 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.

How it works

This quantization of the magnetic flux is observed in superconductors. Superconductivity is theorized to be due to a special correlation between pairs of electrons that extends over the whole body of the superconductor.

Type I

When a Type I superconductor is placed in a magnetic field and cooled below its critical temperature, it excludes all magnetic flux from its interior. This is called the Meissner effect. If there is a "hole" in the superconductor, then flux can be trapped in this hole. The flux trapped in the hole must be quantized. It has been experimentally verified that the trapped flux is quantized in units of thus verifying that the charge carriers in superconductors are indeed correlated electron pairs of charge 2e.

A possible solution is A=eM(1-cosq)/(rsinq) in the f-direction. But A is singular on the negative z-axis at q=p. If we consider A just a device for obtaining B, then we can construct a pair of vector potentials

See also

• Flux pinning
• Magnetic flux quantum