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The London equations relate the current to electromagnetic fields in and around a superconductor. Their purpose is to describe the magnetic field exclusion that is characteristic of a superconductor, and known as the Meissner effect.
Additional recommended knowledge
The first London equation relates the superconducting current to the electric field:
where ns is the density of Cooper pairs, and es and m are the charge and mass of a Cooper pair, respectively, which is simply twice the charge and mass of an electron.
The second London equation relates the supercurrent to the magnetic field:
Writing the magnetic field in terms of the vector potential , we find that the current is simply,
where φ is an arbitrary phase. Substituting this equation into the fourth of Maxwell's equations, , and making use of Maxwell's third equation, , we have
is the London penetration depth.
|This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "London_equations". A list of authors is available in Wikipedia.|