Is London depth in superconductors analogous to skin depth?

In summary, the London penetration depth and skin depth have similar equations but are not physically equivalent. The skin depth is due to dissipation while the penetration depth is related to the effective photon mass in a superconductor. They are somewhat similar in practical applications, but cannot be used interchangeably in calculating electromagnetic properties. At low frequencies, superconductors behave like perfect conductors with the main difference being the presence of a significant kinetic inductance in type II superconductors.
  • #1
iVenky
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London penetration depth that's defined for superconductors has a similar equation to skin depth in conductors derived from maxwell's equations. Are they equivalent?
 
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  • #3
Yes, from a practical point of view they are somewhat similar.
However, there are not "the same thing"; you can for example not replace the skin depth by the penetration depth when e.g. calculating EM properties.
The EM properties of superconductors at low frequencies (frequencies much lower than the energy of the gap) behave pretty much like perfect conductors from a EM point of view. The main difference (for type II superconductors) is actually presence of a fairly significant kinetic inductance, rather than the penetration depth.
 
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1. What is London depth in superconductors?

The London depth, also known as the penetration depth, is a characteristic length scale that describes how far magnetic fields can penetrate into a superconductor. It is a measure of the superconductor's ability to expel magnetic fields.

2. How is London depth related to skin depth?

London depth and skin depth are both measures of how far electromagnetic fields can penetrate into a material. However, they are calculated using different properties of the material. London depth is based on the superconductor's ability to expel magnetic fields, while skin depth is based on the material's electrical conductivity.

3. What factors affect London depth in superconductors?

London depth is affected by the superconductor's material properties, such as its critical temperature, critical magnetic field, and coherence length. It is also influenced by the presence of impurities or defects in the material.

4. Is London depth the same for all superconductors?

No, London depth can vary depending on the type of superconductor. For example, type I superconductors have a smaller London depth compared to type II superconductors, which have a larger London depth and can support higher magnetic fields.

5. How is London depth measured in superconductors?

London depth can be measured using various techniques, such as microwave measurements or magnetic field penetration experiments. These methods involve applying a magnetic field to the superconductor and measuring the changes in its electrical properties, which can then be used to calculate the London depth.

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