Superconducting coherence length

In superconductivity, the superconducting coherence length, usually denoted as ${\displaystyle \xi }$ (Greek lowercase xi), is the characteristic exponent of the variations of the density of superconducting component.

In some special limiting cases, for example in the weak-coupling BCS theory it is related to characteristic Cooper pair size.

The superconducting coherence length is one of two parameters in the Ginzburg-Landau theory of superconductivity. It is given by:

while in BCS theory:

where ${\displaystyle \hbar }$ is the reduced Planck constant, ${\displaystyle m}$ is the mass of a Cooper pair (twice the electron mass), ${\displaystyle v_{f}}$ is the Fermi velocity, and ${\displaystyle \Delta }$ is the superconducting energy gap.

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