Understanding the Meissner Effect: Causes and Explanation

[pleasehelpmeno]

I am trying to understand WHY the Meissner effect occurs NOT WHAT the Meissner effect is.

Does it occur because below Tc eddy currents are created in the surface of the material and these oppose and cancel any internal B field. Then above Tc these do not occur and it behaves like a normal material? I don't however know why these eddy currents would create themselves at low T

 

[mfb]

Then above Tc these do not occur and it behaves like a normal material?

More precise: Above Tc then cannot exist permanently, as there is a resistance in the material.

I don't however know why these eddy currents would create themselves at low T

You always have electrons with non-zero momentum in the material. In the presence of a magnetic field, they will "move in circles" (careful: classical picture), so the magnetic field is cancelled.

 

[pleasehelpmeno]

Sorry, just to confirm above Tc there is resistance so eddy currents can't form, hence no B expulsion?

 

[mfb]

Right.