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Which type two s-wave superconductor has the smallest London penetration depth? What is l_lamda ?

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Is this a trick question? Normally I associate the London penetration depth with the distance that magnetic fields penetrate the superconductor. With a type-2 superconductor, there's no Meissner effect. So what does London penetration depth mean in that context? –  Anonymous Coward Apr 2 '11 at 0:47
    
@AC - you are correct about the London penetration depth, but there is definitely meissner effect in all SC - it is one hallmark of superconductivity. In type II SC, there are distinct regions where the magnetic flux is supported (ie, not fully expelled) in quantized fluxons, and regions where magnetic flux is fully expelled. –  Jen Aug 5 '11 at 13:32
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In element superconductors like Pb, Tl, or In the penetration depth is of the order of several µm. In the Cuprate superconductors about 100 nm scitation.aip.org. I am not sure if the new iron arsenide superconductors have a smaller penetration depth but probably not much smaller than the cuprates.

The penetration depth can be nicely visualized with magnetic force microscopy. The vortices of a type 2 superconductor in field decay over the London penetration depth.

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