London penetration depth

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In superconductivity, London penetration depth (usually denoted as λ or λ_L) characterizes the typical distance on which weak magnetic field penetrates into a superconductor.

Typical values of λ_L are between 50 and 500nm. Deep inside a superconductor the magnetic field is zero (Meissner effect). For example, if one considers a superconducting semi-space at x > 0, and weak external magnetic field B₀ applied along z-direction in the empty space x < 0, then inside the superconductor the magnetic field is given by

i.e. λ_L is the distance across which magnetic field becomes e times weaker. The above expression follows from the solution of the London equation with proper boundary conditions.

[edit] see also

• London equations