Abstract

In addition to the magnetic penetration depth λ discussed in Chapter A2.4, there is another important length scale: the superconducting coherence length ξ₀ first introduced by Pippard [1]. The length ξ₀ is a measure of the spatial extent of the wave function describing Cooper pairs and is therefore the minimum distance over which the density n _s of superconducting electrons can change significantly. It indicates the spatial rigidity of the superconducting wave function. An estimate based on the Heisenberg uncertainty principle yields A2.5.1 ξ o ≈ ℏ v F Δ ≈ ℏ v F k B T c