- London penetration depth
In
superconductivity , London penetration depth (usually denoted as lambda, or lambda_L,) characterizes the typical distance to which a weakmagnetic field penetrates into a superconductor.Typical values of lambda_L, are between 50 and 500 nm. 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 B_0, applied along z-direction in the empty space x<0,, then inside the superconductor the magnetic field is given by :B(x)=B_0expleft(-frac{x}{lambda_L} ight),i.e. lambda_L, is the distance across which magnetic field becomese, times weaker. The above expression follows from the solution of the
London equation with proper boundary conditions.Further reading
*
Charles Kittel , "Introduction to Solid State Physics", 8-th edition, John Wiley & Sons, (2004), ISBN 978-0471415268, pages 262 (Meissner Effect) and 273 (London equations).ee also
London equations
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