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# London penetration depth

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

Typical values of λL 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
$B(x)=B_0\exp\left(-\frac{x}{\lambda_L}\right),$

### Additional recommended knowledge

i.e. λL 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.

## see also

This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "London_penetration_depth". A list of authors is available in Wikipedia.
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