Applied Electromagnetics Using QuickField and MATLAB

Section 8.2 - Superconductivity: London Theory and the Meissner Effect

The Meissner effect refers to the expulsion of magnetic flux from the interior of a superconductor, or perfect diamagnetism. In a normal metal with conductivity σ, Ohm's law describes the current density, where the current density is proportional to electric field.

To explain the Meissner effect, London's theory proposes, in part due to the assumed rigidity of the wave function, that the current density in a superconductor is proportional to the vector potential

whereis the London penetration depth

Becauseaccording to equation (8.1) the electric field is then proportional to the time derivative of the supercurrent density

London's first equation also obtained from Newton's second lawis proportional to the curl of

From the Maxwell relations

and substituting the London equations (8.5) and (8.6) we obtain

For time-harmonic fields that vary asthe above equations become

These equations reduce to

for static applied magnetic fields. For static electric fields

For a uniform magnetic field with flux densitytangential to a super-conducting half-space located at , the magnetic field, vector potential, and current density attenuate in the superconductor according to

so that these field components fall off exponentially inside the superconductor.

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Category: Superconductors and Superconducting Materials
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