Superconductivity fact file (part 2)

• Transition between normal and superconducting state is thermodynamically reversible.
• London's equation is j=-CA/4π(λ_L)² , where λ_L is constant with dimensions of length and A is the vector potential.
• London equation accounts for Meissner effect . In a pure SC state the only field allowed is exponentially damped as we go from an external surface  B(x)=B(0)exp(-x/λ_L)  where λ_Lis the London penetration depth and is the measure of penetration of magnetic field.
• An applied magnetic field will penetrate a thin film fairly uniformly if the thickness is much less than λ_L. Thus in a thin film Meissner effect is not complete.
• Coherence length ξ is the measure of the distance within which SC electronic concentration can not change drastically in spatially varying magnetic field.
• Coherence length is a measure of the range over which we should average A to obtain j.
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