SPIN HOLSTEIN EFFECT

The Holstein effect arising from the s- and d-wave couplings of electr ons to spin fluctuation modes is discussed. In a singlet superconducto r the s-wave coupling suppresses the order parameter and weakens the s trong-coupling effects of phonons in the gap function and in the densi ty of states, but enhances the effect in the infrared conductivity. Th e d-wave attractive coupling gives the same effect as phonons but the resulting d-wave character of the energy gap makes the typical gap thr eshold in the conductivity smeared out and makes the spectrum rather m ore dependent on the impurity scattering rate.