Question

cooper paif (iv) (a) In the context of superconductivity, what is meant by a Cooper Pair? By what mechanism is it proposed that they form? How, qualitatively, does this lead to zero resistance? 15

Answer 1

The cooper pairs are pairs coupling over a range of 100 nanometers, three order of lattice spacing in a superconductor. These coupled electrons can take the character of boson and condense into the ground state.

Cooper pairs are formed by electron-phonon interactions. The cations within the lattice are oscillating about their positions. The resulting propagating lattice vibrations are called phonons. The electrons are indirectly attracted to each other and form a cooper pair.

Cooper pair can break up in scattering events. However, they will combine again to form a cooper pair. The phonons and electrons come to lower energy state and all the electrons on the Fermi surface have opposite spin. The scattering on the lattice atoms is eliminated hence causing a zero resistance. The BCS theory explains the phenomenon of the cooper pair and superconductivity.