Cooper Effect

the combining of conduction electrons in a metal into pairs (Cooper pairs), giving rise to superconductivity; predicted in 1956 by L. Cooper.

The Cooper effect serves as the basis for the modern theory of superconductivity. If the Cooper effect is not taken into account in the ground state of a metal (at 0°K) the electrons fill a volume in momentum space which is bounded by the Fermi surface—the so-called Fermi sphere. According to Cooper, the electrons found near the Fermi surface and having oppositely directed momenta and spins can combine into pairs owing to the existence of weak mutual attraction because of the crystal lattice. Cooper pairs have integral (zero) spin, that is, they are Bose particles (bosons) and therefore possess a super fluidity, which for charged particles is manifested as superconductivity.

The low binding energy of electron pairs is why superconductivity exists only at low temperatures (approximately up to 20°K). It has been proposed that in some substances superconductivity can exist at higher temperatures (up to room temperature).