Just add a bit Mr malawi gleen explanation,,,
1. Superconductor is a perfect dia-magnetic. When you apply an external magnetic field it will create a magnetic field that oppose the external one so it's repel the magnet. The magnetic field still remain since the free electron continues moving...
You have to look at the properties of diamond. It's SP3 hybrid bond, thus it make a non-polar molecule. We can see that it has no free electron moving inside the lattice and by calculate the total energy inside the 3 dimensional crystal with it's own Madelug constant, we found it's a good heat...