Ward's identity and the suppression of spin fluctuation superconductivity

Abstract

Of crucial importance in superconductors is the vanishing of certain coherence factors, such as pkq = ukuk+q - vkvk+q for bare fermion energies {epsilon}k = {epsilon}k+q. This result leads to the abrupt drop of the acoustic attenuation rate below T{sub c} in conventional superconductors. Similarly the interference of {phi}k and {phi}k+Q for the statically distorted normal crystal leads to gkQ {yields} O, corresponding to a deformation potential theorem for the zone boundary phonon.