Little Parks Effect

In superconducting materials, the Little Parks effect describes a periodic oscillation of the transition temperature under the influence of an external magnetic field.

It was first discovered in 1962 in experiments with a superconducting, thin-walled hollow cylinder that was exposed to a parallel, slowly rising, external magnetic field. The researchers William A. Little and Roland D. Parks recognized that the electrical resistance of the cylinder had a period of

${\displaystyle {\frac {h}{2e}}=2,07e^{-15}\mathrm {Tm^{2}} }$

oscillated. Here h is Planck's quantum of action and e is the elementary charge . Since this period corresponds to a flux quantum , the smallest unit of the magnetic flux, the total flux through the cylinder is increased by a flux quantum with each period.

The periodic oscillation of the electrical resistance is caused by the oscillation of the critical temperature. If the external magnetic field is increased, the kinetic energy of the electrons in the cylinder increases to the same extent . At the same time, however, flux tubes form in the superconductor, in which magnetic field lines are guided through the superconductor, which reduces the kinetic energy of the electrons in the cylinder. If these two effects are combined, there is a periodic oscillation of the kinetic energy, which under the simplified assumption

${\displaystyle E_{kin}=kT}$

with the Boltzmann constant k , is directly proportional to the transition temperature.

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• WA Little, RD Parks: Physical Review Letters . tape 9. , 1962, pp. 9 .