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Suppose a superconductor which is in a normal state (i.e. $T>Tc$) is subjected to a magnetic field. As soon as magnetic field switched from 0 to some value, eddy currents will develop on the surface and they will die away because of finite resistance. Now if I decrease the temperature below critical temperature, normal material will become superconductor and it will expel the magnetic field immediately, cf. the Meissner effect. I want to know the reason what causes the superconductor to push away magnetic fields.

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    $\begingroup$ Have you read en.wikipedia.org/wiki/London_equations ? $\endgroup$ – PM 2Ring Sep 8 '18 at 9:54
  • $\begingroup$ Yes I did. I have gone through London's original paper. However, I think it do not explain why magnetic filed push out from inside. It will you how magnetic filed will penetrate a superconductor and proves that magnetic filed could not live inside a superconductor mathematically. But why.. the physical reason remained un-explained. I would be happy if you explain it to me $\endgroup$ – Nilabja Kanti Sarkar Sep 8 '18 at 10:15
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I want to know the reason what causes the superconductor to push away magnetic fields.

The underlying assumption for London equations, describing Meissner effect, is that the transition to the superconducting state is associated with "setting up electric currents near its surface".

So, the magnetic field is pushed out of a superconductor by the currents flowing near its surface. Not sure if there exists a consensus on how exactly these currents are generated, though.

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  • $\begingroup$ I think there is. Supposedly the BCS theory contains the reason. $\endgroup$ – thermomagnetic condensed boson Sep 8 '18 at 17:57
  • $\begingroup$ @coniferous_smellerULPBG-W8ZgjR There are some papers (like this: pdfs.semanticscholar.org/ec22/…) that specifically question whether BCS correctly explains Meissner effect. I have no idea how credible they are, but thought to mention it. $\endgroup$ – V.F. Sep 8 '18 at 18:57

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