EFFECT OF FERROMAGNETIC SPIN CORRELATIONS ON SUPERCONDUCTIVITY

Abstract:

If the superconducting transition temperatures of the transition metals are fit by the BCS relation¹

where ϴ_D is the Debye temperature and N(0) is the density of states at the Fermi surface, then the pairing interaction V_BCS is found to be roughly constant, except for metals at the beginning and end of each series, where it rapidly decreases.² Traditionally, one writes where V_ph represents the phonon interaction and V_C* is the Coulomb pseudopotential.³ While at present one cannot rule out the possibility that V_ph-V_C* is small or negative for metals near the ends of these series, the fact that their paramagnetic susceptibility is anomalously large⁴ suggests that there are strong ferromagnetic exchange forces which enhance the spin susceptibility and presumably also suppress superconductivity for singlet spin pairing, as first discussed by Doniach⁵ on the basis of a phenomenological exchange interaction…