Motion of cooper pairs in superconductor

[CN495]

I have learned that as temperature decreases, the motion of particles in a lattice decreases.Then how can a cooper pair move so swiftly across the lattice when temperature is considerably low?Can anyone please explain?

 

[vkroom]

all electrons in a lattice cannot have their momenta go to zero due to Pauli exclusion principle. the lowest energy electrons are actually the one that are most easily excited. ironically they have a very large velocity called Fermi velocity. For most metals its around 10^6 m/s. Cooper pairing occurs for electrons that have velocity close to Fermi velocity.